Clocking the rotation rate of a supermassive black hole
The rotational rate of one of the most massive black holes in the universe has been accurately measured by an international team of astronomers, using several optical telescopes and NASA's SWIFT X-ray telescope. The rotational rate of this massive black hole is one third of the maximum spin rate allowed in General Relativity. This 18 billion solar mass heavy black hole powers a quasar OJ287 which lies about 3.5 billion light years away from Earth.
A recent observational campaign involving more than two dozen optical telescopes and NASA's space based SWIFT X-ray telescope allowed a team of astronomers to measure very accurately the rotational rate of one of the most massive black holes in the universe. The rotational rate of this massive black hole is one third of the maximum spin rate allowed in General Relativity. This 18 billion solar mass heavy black hole powers a quasar called OJ287 which lies about 3.5 billion light years away from Earth. Quasi-stellar radio sources or `quasars' for short, are the very bright centers of distant galaxies which emit huge amounts of electro-magnetic radiation due to the infall of matter into their massive black holes.
This quasar lies very close to the apparent path of the Sun's motion on the celestial sphere as seen from Earth, where most searches for asteroids and comets are conducted. Therefore, its optical photometric measurements already cover more than 100 years. A careful analysis of these observations show that OJ 287 has produced quasi-periodic optical outbursts at intervals of approximately 12 years dating back to around 1891. Additionally, a close inspection of newer data sets reveals the presence of double-peaks in these outbursts.
These deductions prompted Prof. Mauri Valtonen of University of Turku, Finland and his collaborators to develop a model that requires the quasar OJ287 to harbour two unequal mass black holes. Their model involves a massive black hole with an accretion disk (a disk of interstellar material formed by matter falling into objects like black holes) while the comparatively smaller black hole revolves around it. The quasar OJ287 is visible due to the slow accretion of matter, present in the accretion disk, onto the largest black hole. Additionally, the small black hole passes through the accretion disk during its orbit which causes the disk material to heat up to very high temperatures. This heated material flows out from both sides of the accretion disk and radiates strongly for weeks. This causes peaks in the brightness, and the double peaks arise due to the ellipticity of the orbit, as shown in the figure.
The binary black hole model for OJ287 implies that the smaller black hole's orbit should rotate, and this changes where and when the smaller hole impacts the accretion disk. This effect arises from Einstein's General Theory of Relativity and its precessional rate depends mainly on the two black hole masses and the rotation rate of the more massive black hole. In 2010, Valtonen and collaborators used eight well timed bright outbursts of OJ287 to accurately measure the precession rate of the smaller hole's orbit. This analysis revealed for the first time the rotation rate of the massive black hole along with accurate estimates for the masses of the two black holes. This was possible since the smaller black hole's orbit precess at an incredible 39 degrees per individual orbit. The General Relativistic model for OJ287 also predicted that the next outburst could occur around the time of GR Centenary, 25 November 2015, which marks the 100th anniversary of Einstein's General Theory of Relativity.
An observational campaign was therefore launched to catch this predicted outburst. The predicted optical flare began around November 18, 2015 and reached its maximum brightness on December 4, 2015. It is the timing of this bright outburst that allowed Valtonen and his co-workers to directly measure the rotation rate of the more massive black hole to be one third of the maximum spin rate allowed in General Relativity. In other words, its Kerr parameter is accurately measured to be 0.31 and its maximum allowed value in General Relativity is one. In comparison, the Kerr parameter of the final black hole associated with the first ever direct detection of gravitational waves is only estimated to be below 0.7.
The observations leading to accurate spin measurement have been made due to the collaboration of a number of optical telescopes in Japan, South Korea, India, Turkey, Greece, Finland, Poland, Germany, UK, Spain, USA and Mexico. The effort, led by Staszek Zola of Poland, involved close to 100 astronomers from these countries. Interestingly, a number of key participants were amateur astronomers who operate their own telescopes. Valtonen's team that developed and contributed to the spinning binary black hole model include theoretical astrophysicist A. Gopakumar from TIFR, India, and Italian X-Ray astronomer Stefano Ciprini who obtained and analyzed the X-ray data.
The occurrence of the predicted optical outburst of OJ287 also allowed the team to confirm the loss of orbital energy to gravitational waves within two percent of General Relativity's prediction. This provides the first indirect evidence for the existence of a massive spinning black hole binary emitting gravitational waves. This is encouraging news for the Pulsar Timing Array efforts that will directly detect gravitational waves from such systems in the near future. Therefore, the present optical outburst of OJ287 makes a fitting contribution to the centenary celebrations of General Relativity and adds to the excitement of the first direct observation of a transient gravitational wave signal by LIGO.
This quasar lies very close to the apparent path of the Sun's motion on the celestial sphere as seen from Earth, where most searches for asteroids and comets are conducted. Therefore, its optical photometric measurements already cover more than 100 years. A careful analysis of these observations show that OJ 287 has produced quasi-periodic optical outbursts at intervals of approximately 12 years dating back to around 1891. Additionally, a close inspection of newer data sets reveals the presence of double-peaks in these outbursts.
These deductions prompted Prof. Mauri Valtonen of University of Turku, Finland and his collaborators to develop a model that requires the quasar OJ287 to harbour two unequal mass black holes. Their model involves a massive black hole with an accretion disk (a disk of interstellar material formed by matter falling into objects like black holes) while the comparatively smaller black hole revolves around it. The quasar OJ287 is visible due to the slow accretion of matter, present in the accretion disk, onto the largest black hole. Additionally, the small black hole passes through the accretion disk during its orbit which causes the disk material to heat up to very high temperatures. This heated material flows out from both sides of the accretion disk and radiates strongly for weeks. This causes peaks in the brightness, and the double peaks arise due to the ellipticity of the orbit, as shown in the figure.
The binary black hole model for OJ287 implies that the smaller black hole's orbit should rotate, and this changes where and when the smaller hole impacts the accretion disk. This effect arises from Einstein's General Theory of Relativity and its precessional rate depends mainly on the two black hole masses and the rotation rate of the more massive black hole. In 2010, Valtonen and collaborators used eight well timed bright outbursts of OJ287 to accurately measure the precession rate of the smaller hole's orbit. This analysis revealed for the first time the rotation rate of the massive black hole along with accurate estimates for the masses of the two black holes. This was possible since the smaller black hole's orbit precess at an incredible 39 degrees per individual orbit. The General Relativistic model for OJ287 also predicted that the next outburst could occur around the time of GR Centenary, 25 November 2015, which marks the 100th anniversary of Einstein's General Theory of Relativity.
An observational campaign was therefore launched to catch this predicted outburst. The predicted optical flare began around November 18, 2015 and reached its maximum brightness on December 4, 2015. It is the timing of this bright outburst that allowed Valtonen and his co-workers to directly measure the rotation rate of the more massive black hole to be one third of the maximum spin rate allowed in General Relativity. In other words, its Kerr parameter is accurately measured to be 0.31 and its maximum allowed value in General Relativity is one. In comparison, the Kerr parameter of the final black hole associated with the first ever direct detection of gravitational waves is only estimated to be below 0.7.
The observations leading to accurate spin measurement have been made due to the collaboration of a number of optical telescopes in Japan, South Korea, India, Turkey, Greece, Finland, Poland, Germany, UK, Spain, USA and Mexico. The effort, led by Staszek Zola of Poland, involved close to 100 astronomers from these countries. Interestingly, a number of key participants were amateur astronomers who operate their own telescopes. Valtonen's team that developed and contributed to the spinning binary black hole model include theoretical astrophysicist A. Gopakumar from TIFR, India, and Italian X-Ray astronomer Stefano Ciprini who obtained and analyzed the X-ray data.
The occurrence of the predicted optical outburst of OJ287 also allowed the team to confirm the loss of orbital energy to gravitational waves within two percent of General Relativity's prediction. This provides the first indirect evidence for the existence of a massive spinning black hole binary emitting gravitational waves. This is encouraging news for the Pulsar Timing Array efforts that will directly detect gravitational waves from such systems in the near future. Therefore, the present optical outburst of OJ287 makes a fitting contribution to the centenary celebrations of General Relativity and adds to the excitement of the first direct observation of a transient gravitational wave signal by LIGO.
Young sun-like star shows a magnetic field was critical for life on the early Earth
Nearly four billion years ago, life arose on Earth. Life appeared because our planet had a rocky surface, liquid water, and a blanketing atmosphere. But life thrived thanks to another necessary ingredient: the presence of a protective magnetic field. A new study of the young, Sun-like star Kappa Ceti shows that a magnetic field plays a key role in making a planet conducive to life.
Nearly four billion years ago, life arose on Earth. Life appeared because our planet had a rocky surface, liquid water, and a blanketing atmosphere. But life thrived thanks to another necessary ingredient: the presence of a protective magnetic field. A new study of the young, Sun-like star Kappa Ceti shows that a magnetic field plays a key role in making a planet conducive to life.
"To be habitable, a planet needs warmth, water, and it needs to be sheltered from a young, violent Sun," says lead author Jose-Dias Do Nascimento of the Harvard-Smithsonian Center for Astrophysics (CfA) and University of Rio G. do Norte (UFRN), Brazil.
Kappa Ceti, located 30 light-years away in the constellation Cetus, the Whale, is remarkably similar to our Sun but younger. The team calculates an age of only 400-600 million years old, which agrees with the age estimated from its rotation period (a technique pioneered by CfA astronomer Soren Meibom). This age roughly corresponds to the time when life first appeared on Earth. As a result, studying Kappa Ceti can give us insights into the early history of our solar system.
Like other stars its age, Kappa Ceti is very magnetically active. Its surface is blotched with many giant starspots, like sunspots but larger and more numerous. It also propels a steady stream of plasma, or ionized gases, out into space. The research team found that this stellar wind is 50 times stronger than our Sun's solar wind.
Such a fierce stellar wind would batter the atmosphere of any planet in the habitable zone, unless that planet was shielded by a magnetic field. At the extreme, a planet without a magnetic field could lose most of its atmosphere. In our solar system, the planet Mars suffered this fate and turned from a world warm enough for briny oceans to a cold, dry desert.
The team modeled the strong stellar wind of Kappa Ceti and its effect on a young Earth. The early Earth's magnetic field is expected to have been about as strong as it is today, or slightly weaker. Depending on the assumed strength, the researchers found that the resulting protected region, or magnetosphere, of Earth would be about one-third to one-half as large as it is today.
"The early Earth didn't have as much protection as it does now, but it had enough," says Do Nascimento.
Kappa Ceti also shows evidence of "superflares" -- enormous eruptions that release 10 to 100 million times more energy than the largest flares ever observed on our Sun. Flares that energetic can strip a planet's atmosphere. By studying Kappa Ceti, researchers hope to learn how frequently it produces superflares, and therefore how often our Sun might have erupted in its youth.
Nearly four billion years ago, life arose on Earth. Life appeared because our planet had a rocky surface, liquid water, and a blanketing atmosphere. But life thrived thanks to another necessary ingredient: the presence of a protective magnetic field. A new study of the young, Sun-like star Kappa Ceti shows that a magnetic field plays a key role in making a planet conducive to life.
"To be habitable, a planet needs warmth, water, and it needs to be sheltered from a young, violent Sun," says lead author Jose-Dias Do Nascimento of the Harvard-Smithsonian Center for Astrophysics (CfA) and University of Rio G. do Norte (UFRN), Brazil.
Kappa Ceti, located 30 light-years away in the constellation Cetus, the Whale, is remarkably similar to our Sun but younger. The team calculates an age of only 400-600 million years old, which agrees with the age estimated from its rotation period (a technique pioneered by CfA astronomer Soren Meibom). This age roughly corresponds to the time when life first appeared on Earth. As a result, studying Kappa Ceti can give us insights into the early history of our solar system.
Like other stars its age, Kappa Ceti is very magnetically active. Its surface is blotched with many giant starspots, like sunspots but larger and more numerous. It also propels a steady stream of plasma, or ionized gases, out into space. The research team found that this stellar wind is 50 times stronger than our Sun's solar wind.
Such a fierce stellar wind would batter the atmosphere of any planet in the habitable zone, unless that planet was shielded by a magnetic field. At the extreme, a planet without a magnetic field could lose most of its atmosphere. In our solar system, the planet Mars suffered this fate and turned from a world warm enough for briny oceans to a cold, dry desert.
The team modeled the strong stellar wind of Kappa Ceti and its effect on a young Earth. The early Earth's magnetic field is expected to have been about as strong as it is today, or slightly weaker. Depending on the assumed strength, the researchers found that the resulting protected region, or magnetosphere, of Earth would be about one-third to one-half as large as it is today.
"The early Earth didn't have as much protection as it does now, but it had enough," says Do Nascimento.
Kappa Ceti also shows evidence of "superflares" -- enormous eruptions that release 10 to 100 million times more energy than the largest flares ever observed on our Sun. Flares that energetic can strip a planet's atmosphere. By studying Kappa Ceti, researchers hope to learn how frequently it produces superflares, and therefore how often our Sun might have erupted in its youth.
NASA's IBEX observations pin down interstellar magnetic field
A new study uses IBEX data and simulations of the interstellar boundary -- which lies at the very edge of the giant magnetic bubble surrounding our solar system called the heliosphere - to better describe space in our galactic neighborhood.
 |
| (Artist concept) Far beyond the orbit of Neptune, the solar wind and the interstellar medium interact to create a region known as the inner heliosheath, bounded on the inside by the termination shock, and on the outside by the heliopause. Immediately after its 2008 launch, NASA's Interstellar Boundary Explorer, or IBEX, spotted a curiosity in a thin slice of space: More particles streamed in through a long, skinny swath in the sky than anywhere else. The origin of the so-called IBEX ribbon was unknown -- but its very existence opened doors to observing what lies outside our solar system, the way drops of rain on a window tell you more about the weather outside.
Now, a new study uses IBEX data and simulations of the interstellar boundary -- which lies at the very edge of the giant magnetic bubble surrounding our solar system called the heliosphere -- to better describe space in our galactic neighborhood. The paper, published Feb. 8, 2016, in Astrophysical Journal Letters, precisely determines the strength and direction of the magnetic field outside the heliosphere. Such information gives us a peek into the magnetic forces that dominate the galaxy beyond, teaching us more about our home in space.
The new paper is based on one particular theory of the origin of the IBEX ribbon, in which the particles streaming in from the ribbon are actually solar material reflected back at us after a long journey to the edges of the sun's magnetic boundaries. A giant bubble, known as the heliosphere, exists around the sun and is filled with what's called solar wind, the sun's constant outflow of ionized gas, known as plasma. When these particles reach the edges of the heliosphere, their motion becomes more complicated.
"The theory says that some solar wind protons are sent flying back towards the sun as neutral atoms after a complex series of charge exchanges, creating the IBEX ribbon," said Eric Zirnstein, a space scientist at the Southwest Research Institute in San Antonio, Texas, and lead author on the study. "Simulations and IBEX observations pinpoint this process -- which takes anywhere from three to six years on average -- as the most likely origin of the IBEX ribbon."
Outside the heliosphere lies the interstellar medium, with plasma that has different speed, density, and temperature than solar wind plasma, as well as neutral gases. These materials interact at the heliosphere's edge to create a region known as the inner heliosheath, bounded on the inside by the termination shock -- which is more than twice as far from us as the orbit of Pluto -- and on the outside by the heliopause, the boundary between the solar wind and the comparatively dense interstellar medium.
Some solar wind protons that flow out from the sun to this boundary region will gain an electron, making them neutral and allowing them to cross the heliopause. Once in the interstellar medium, they can lose that electron again, making them gyrate around the interstellar magnetic field. If those particles pick up another electron at the right place and time, they can be fired back into the heliosphere, travel all the way back toward Earth, and collide with IBEX's detector. The particles carry information about all that interaction with the interstellar magnetic field, and as they hit the detector they can give us unprecedented insight into the characteristics of that region of space.
"Only Voyager 1 has ever made direct observations of the interstellar magnetic field, and those are close to the heliopause, where it's distorted," said Zirnstein. "But this analysis provides a nice determination of its strength and direction farther out."
The directions of different ribbon particles shooting back toward Earth are determined by the characteristics of the interstellar magnetic field. For instance, simulations show that the most energetic particles come from a different region of space than the least energetic particles, which gives clues as to how the interstellar magnetic field interacts with the heliosphere.
For the recent study, such observations were used to seed simulations of the ribbon's origin. Not only do these simulations correctly predict the locations of neutral ribbon particles at different energies, but the deduced interstellar magnetic field agrees with Voyager 1 measurements, the deflection of interstellar neutral gases, and observations of distant polarized starlight.
However, some early simulations of the interstellar magnetic field don't quite line up. Those pre-IBEX estimates were based largely on two data points -- the distances at which Voyagers 1 and 2 crossed the termination shock.
"Voyager 1 crossed the termination shock at 94 astronomical units, or AU, from the sun, and Voyager 2 at 84 AU," said Zirnstein. One AU is equal to about 93 million miles, the average distance between Earth and the sun. "That difference of almost 930 million miles was mostly explained by a strong, very tilted interstellar magnetic field pushing on the heliosphere."
But that difference may be accounted for by considering a stronger influence from the solar cycle, which can lead to changes in the strength of the solar wind and thus change the distance to the termination shock in the directions of Voyager 1 and 2. The two Voyager spacecraft made their measurements almost three years apart, giving plenty of time for the variable solar wind to change the distance of the termination shock.
"Scientists in the field are developing more sophisticated models of the time-dependent solar wind," said Zirnstein.
The simulations generally jibe well with the Voyager data.
"The new findings can be used to better understand how our space environment interacts with the interstellar environment beyond the heliopause," said Eric Christian, IBEX program scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in this study. "In turn, understanding that interaction could help explain the mystery of what causes the IBEX ribbon once and for all."
|
ALMA spots baby star’s growing blanket
Researchers using the Atacama Large Millimeter/submillimeter Array (ALMA) have made the first direct observations delineating the gas disk around a baby star from the infalling gas envelope. This finding fills an important missing piece in our understanding of the early phases of stellar evolution. A research team observed the baby star named TMC-1A located 450 light years away from us, in the constellation Taurus (the Bull). TMC-1A is a protostar, a star still in the process of forming. Large amounts of gas still surround TMC-1A.
Stars form in dense gas clouds. Baby stars grow by taking in the surrounding gas, like a fetus receiving nutrition from the mother's placenta. In this process, gas cannot flow directly into the star. Instead it first accumulates and forms a disk around the star, and then the disk feeds into the star. However, it is still unknown when in the process of star formation this disk appears and how it evolves. Lack of sensitivity and resolution in radio observations has made it difficult to observe these phenomena.
"The disks around young stars are the places where planets will be formed," said Aso, the lead author of the paper that appeared in the Astrophysical Journal. "To understand the formation mechanism of a disk, we need to differentiate the disk from the outer envelope precisely and pinpoint the location of its boundary."
Using ALMA, the team directly observed the boundary between the inner rotating disk and the outer infalling envelope with high accuracy for the first time. Since gas from the outer envelope is continuously falling into the disk, it had been difficult to identify the transition region in previous studies. In particular, the tenuous but high speed gas in rotating disks is not easy to see. But ALMA has enough sensitivity to highlight such a component and illustrate the speed and distribution of gas in the disk very precisely. This enabled the team to distinguish the disk from the infalling envelope.
The team found that the boundary between the disk and envelope is located 90 astronomical units from the central baby star. This distance is three times longer than the orbit of Neptune, the outermost planet in the Solar System. The observed disk obeys Keplerian rotation: the material orbiting closer to the central star revolves faster than material further out.The high-sensitivity observations provided other important information about the object. From detailed measurement of the rotation speed, the research team could calculate that the mass of the baby star is 0.68 times the mass of the Sun. The team also determined the gas infall rate to be a millionth of the mass of the Sun per year, with a speed of 1 km per second. Gravity causes gas to fall towards the central baby star, but the measured speed is much less than the free-fall speed. Something must be slowing the gas down. The researchers suspect that a magnetic field around the baby star might be what is slowing the gas.
"We expect that as the baby star grows, the boundary between the disk and the infall region moves outward," said Aso. "We are sure that future ALMA observations will reveal such evolution."
These observational results were published as Aso et al. "ALMA Observations of the Transition from Infall Motion to Keplerian Rotation around the Late-phase Protostar TMC-1A " in the Astrophysical Journal, issued in October 2015.
NASA THINKS THERE’S A WAY TO GET TO MARS IN 3 DAYS
We’ve achieved amazing things by using chemical rockets to place satellites in orbit, land people on the Moon, and place rovers on the surface of Mars. We’ve even used ion drives to reach destinations further afield in our Solar System. But reaching other stars, or reducing our travel time to Mars or other planets, will require another method of travel. One that can approach relativistic speeds.
We can execute missions to Mars, but it takes several months for a vehicle to reach the Red Planet. Even then, those missions have to be launched during the most optimal launch windows, which only occur every 2 years. But the minds at NASA never stop thinking about this problem, and now Dr. Philip Lubin, Physics Professor at the University of California, Santa Barbara, may have come up with something: photonic propulsion, which he thinks could reduce the travel time from Earth to Mars to just 3 days, for a 100 kg craft.
The system is called DEEP IN, or Directed Propulsion for Interstellar Exploration. The general idea is that we have achieved relativistic speeds in the laboratory, but haven’t taken that technology—which is electromagnetic in nature, rather than chemical—and used it outside of the laboratory. In short, we can propel individual particles to near light speed inside particle accelerators, but haven’t expanded that technology to the macro level.
Directed Energy Propulsion differs from rocket technology in a fundamental way: the propulsion system stays at home, and the craft doesn’t carry any fuel or propellant. Instead, the craft would carry a system of reflectors, which would be struck with an aimed stream of photons, propelling the craft forward. And the whole system is modular and scalable.
If that’s not tantalizing enough, the system can also be used to deflect hazardous space debris, and to detect other technological civilizations. As talked about in this paper, detecting these types of systems in use by other civilizations may be our best hope for discovering those civilizations.
There’s a roadmap for using this system, and it starts small. At first, DEEP IN would be used to launch small cube satellites. The feedback from this phase would then inform the next step, which would be to test a unit for defending the ISS from space debris. From then, the systems would meet goals of increasing complexity, from launching satellites to LEO (Low-Earth Orbit) and GEO (Geostationary Orbit), all the way up to asteroid deflection and planetary defense. After that, relativistic drives capable of interstellar travel is the goal.
There are lots of questions still to be answered of course, like what happens when a vehicle at near light-speed hits a tiny meteorite. But those questions will be asked and answered as the system is developed and its capabilities grow.
Obviously, DEEP IN has the potential to bring other stars into reach. This system could deliver probes to some of the more promising exo-planets, and give humanity its first detailed look at other solar systems. If DEEP IN can be successfully scaled up, as Lubin says, then it will be a transformational technology.
WE HAVE UNDERESTIMATED OUR SUN’S DESTRUCTIVE REACH
The Sun has enormous destructive power. Any objects that collide with the Sun, such as comets and asteroids, are immediately destroyed.
But now we’re finding that the Sun has the ability to reach out and touch asteroids at a far greater distance than previously thought. The proof of this came when a team at the University of Hawaii Institute of Astronomy was looking at Near-Earth Objects (NEOs) catalogued by the Catalina Sky Survey, and trying to understand what asteroids might be missing from that survey.
An asteroid is classified as an NEO when, at its closest point to the Sun, it is less than 1.3 times the distance from the Earth to the Sun. We need to know where these objects are, how many of them there are, and how big they are. They’re a potential threat to spacecraft, and to Earth itself.
The Catalina Sky Survey (CSS) detected over 9,000 NEOs in eight years. But asteroids are notoriously difficult to detect. They are tiny points of light, and they’re moving. The team knew that there was no way the CSS could have detected all NEOs, so Dr. Robert Jedicke, a team member from the University of Hawaii Institute of Astronomy, developed software that would tell them what CSS had missed in its survey of NEOs.
This took an enormous amount of work—and computing power—and when it was completed, they noticed a discrepancy: according to their work, there should be over ten times as many objects within ten solar diameters of the Sun as they found. The team had a puzzle on their hands.
The team spent a year verifying their work before concluding that the problem did not lay in their analysis, but in our understanding of how the Solar System works. University of Helsinki scientist Mikael Granvik, lead author of the Nature article that reported these results, hypothesized that their model of the NEO population would better suit their results if asteroids were destroyed at a much greater distance from the sun than previously thought.
They tested this idea, and found that it agreed with their model and with the observed population of NEOs, once asteroids that spent too much time within 10 solar diameters of the Sun were eliminated. “The discovery that asteroids must be breaking up when they approach too close to the Sun was surprising and that’s why we spent so much time verifying our calculations,” commented Dr. Jedicke.
There are other discrepancies in our Solar System between what is observed and what is predicted when it comes to the distribution of small objects. Meteors are small pieces of dust that come from asteroids, and when they enter our atmosphere they burn up and make star-gazing all the more eventful. Meteors exist in streams that come from their parent objects. The problems is, most of the time the streams can’t be matched with their parent object. This study shows that the parent objects must have been destroyed when they got too close to the Sun, leaving behind a stream of meteors, but no apparent source.
There was another surprise in store for the team. Darker asteroids are destroyed at a greater distance from the Sun than lighter ones are. This explains an earlier discovery, which showed that brighter NEOs travel closer to the Sun than darker ones do. If darker asteroids are destroyed at a greater distance from the Sun than their lighter counterparts, then the two must have differing compositions and internal structure.
“Perhaps the most intriguing outcome of this study is that it is now possible to test models of asteroid interiors simply by keeping track of their orbits and sizes. This is truly remarkable and was completely unexpected when we first started constructing the new NEO model,” says Granvik.
Five-dimensional black hole could 'break' general relativity
Scientists have successfully simulated a black hole shaped like a very thin ring, which gives rise to a series of 'bulges' connected by strings that become thinner over time. These strings eventually become so thin that they pinch off into a series of miniature black holes, similar to how a thin stream of water from a tap breaks up into droplets.Researchers have successfully simulated how a ring-shaped black hole could cause general relativity to break down: assuming the universe contains at least five dimensions, that is.The researchers, from the University of Cambridge and Queen Mary University of London, have successfully simulated a black hole shaped like a very thin ring, which gives rise to a series of 'bulges' connected by strings that become thinner over time. These strings eventually become so thin that they pinch off into a series of miniature black holes, similar to how a thin stream of water from a tap breaks up into droplets.
Ring-shaped black holes were 'discovered' by theoretical physicists in 2002, but this is the first time that their dynamics have been successfully simulated using supercomputers. Should this type of black hole form, it would lead to the appearance of a 'naked singularity', which would cause the equations behind general relativity to break down. The results are published in the journal Physical Review Letters.
General relativity underpins our current understanding of gravity: everything from the estimation of the age of the stars in the universe, to the GPS signals we rely on to help us navigate, is based on Einstein's equations. In part, the theory tells us that matter warps its surrounding spacetime, and what we call gravity is the effect of that warp. In the 100 years since it was published, general relativity has passed every test that has been thrown at it, but one of its limitations is the existence of singularities.
A singularity is a point where gravity is so intense that space, time, and the laws of physics, break down. General relativity predicts that singularities exist at the centre of black holes, and that they are surrounded by an event horizon -- the 'point of no return', where the gravitational pull becomes so strong that escape is impossible, meaning that they cannot be observed from the outside.
"As long as singularities stay hidden behind an event horizon, they do not cause trouble and general relativity holds -- the 'cosmic censorship conjecture' says that this is always the case," said study co-author Markus Kunesch, a PhD student at Cambridge's Department of Applied Mathematics and Theoretical Physics (DAMTP). "As long as the cosmic censorship conjecture is valid, we can safely predict the future outside of black holes. Because ultimately, what we're trying to do in physics is to predict the future given knowledge about the state of the universe now."
But what if a singularity existed outside of an event horizon? If it did, not only would it be visible from the outside, but it would represent an object that has collapsed to an infinite density, a state which causes the laws of physics to break down. Theoretical physicists have hypothesised that such a thing, called a naked singularity, might exist in higher dimensions.
"If naked singularities exist, general relativity breaks down," said co-author Saran Tunyasuvunakool, also a PhD student from DAMTP. "And if general relativity breaks down, it would throw everything upside down, because it would no longer have any predictive power -- it could no longer be considered as a standalone theory to explain the universe."
We think of the universe as existing in three dimensions, plus the fourth dimension of time, which together are referred to as spacetime. But, in branches of theoretical physics such as string theory, the universe could be made up of as many as 11 dimensions. Additional dimensions could be large and expansive, or they could be curled up, tiny, and hard to detect. Since humans can only directly perceive three dimensions, the existence of extra dimensions can only be inferred through very high energy experiments, such as those conducted at the Large Hadron Collider.
Einstein's theory itself does not state how many dimensions there are in the universe, so theoretical physicists have been studying general relativity in higher dimensions to see if cosmic censorship still holds. The discovery of ring-shaped black holes in five dimensions led researchers to hypothesise that they could break up and give rise to a naked singularity.
What the Cambridge researchers, along with their co-author Pau Figueras from Queen Mary University of London, have found is that if the ring is thin enough, it can lead to the formation of naked singularities.
Using the COSMOS supercomputer, the researchers were able to perform a full simulation of Einstein's complete theory in higher dimensions, allowing them to not only confirm that these 'black rings' are unstable, but to also identify their eventual fate. Most of the time, a black ring collapses back into a sphere, so that the singularity would stay contained within the event horizon. Only a very thin black ring becomes sufficiently unstable as to form bulges connected by thinner and thinner strings, eventually breaking off and forming a naked singularity. New simulation techniques and computer code were required to handle these extreme shapes.
"The better we get at simulating Einstein's theory of gravity in higher dimensions, the easier it will be for us to help with advancing new computational techniques -- we're pushing the limits of what you can do on a computer when it comes to Einstein's theory," said Tunyasuvunakool. "But if cosmic censorship doesn't hold in higher dimensions, then maybe we need to look at what's so special about a four-dimensional universe that means it does hold."
The cosmic censorship conjecture is widely expected to be true in our four-dimensional universe, but should it be disproved, an alternative way of explaining the universe would then need to be identified. One possibility is quantum gravity, which approximates Einstein's equations far away from a singularity, but also provides a description of new physics close to the singularity
the COSMOS supercomputer at the University of Cambridge is part of the Science and Technology Facilities Council (STFC) DiRAC HPC Facility.
|
| Scientists have successfully simulated a black hole shaped like a very thin ring, which gives rise to a series of 'bulges' connected by strings that become thinner over time. These strings eventually become so thin that they pinch off into a series of miniature black holes, similar to how a thin stream of water from a tap breaks up into droplets.Researchers have successfully simulated how a ring-shaped black hole could cause general relativity to break down: assuming the universe contains at least five dimensions, that is.The researchers, from the University of Cambridge and Queen Mary University of London, have successfully simulated a black hole shaped like a very thin ring, which gives rise to a series of 'bulges' connected by strings that become thinner over time. These strings eventually become so thin that they pinch off into a series of miniature black holes, similar to how a thin stream of water from a tap breaks up into droplets.
Ring-shaped black holes were 'discovered' by theoretical physicists in 2002, but this is the first time that their dynamics have been successfully simulated using supercomputers. Should this type of black hole form, it would lead to the appearance of a 'naked singularity', which would cause the equations behind general relativity to break down. The results are published in the journal Physical Review Letters.
General relativity underpins our current understanding of gravity: everything from the estimation of the age of the stars in the universe, to the GPS signals we rely on to help us navigate, is based on Einstein's equations. In part, the theory tells us that matter warps its surrounding spacetime, and what we call gravity is the effect of that warp. In the 100 years since it was published, general relativity has passed every test that has been thrown at it, but one of its limitations is the existence of singularities.
A singularity is a point where gravity is so intense that space, time, and the laws of physics, break down. General relativity predicts that singularities exist at the centre of black holes, and that they are surrounded by an event horizon -- the 'point of no return', where the gravitational pull becomes so strong that escape is impossible, meaning that they cannot be observed from the outside.
"As long as singularities stay hidden behind an event horizon, they do not cause trouble and general relativity holds -- the 'cosmic censorship conjecture' says that this is always the case," said study co-author Markus Kunesch, a PhD student at Cambridge's Department of Applied Mathematics and Theoretical Physics (DAMTP). "As long as the cosmic censorship conjecture is valid, we can safely predict the future outside of black holes. Because ultimately, what we're trying to do in physics is to predict the future given knowledge about the state of the universe now."
But what if a singularity existed outside of an event horizon? If it did, not only would it be visible from the outside, but it would represent an object that has collapsed to an infinite density, a state which causes the laws of physics to break down. Theoretical physicists have hypothesised that such a thing, called a naked singularity, might exist in higher dimensions.
"If naked singularities exist, general relativity breaks down," said co-author Saran Tunyasuvunakool, also a PhD student from DAMTP. "And if general relativity breaks down, it would throw everything upside down, because it would no longer have any predictive power -- it could no longer be considered as a standalone theory to explain the universe."
We think of the universe as existing in three dimensions, plus the fourth dimension of time, which together are referred to as spacetime. But, in branches of theoretical physics such as string theory, the universe could be made up of as many as 11 dimensions. Additional dimensions could be large and expansive, or they could be curled up, tiny, and hard to detect. Since humans can only directly perceive three dimensions, the existence of extra dimensions can only be inferred through very high energy experiments, such as those conducted at the Large Hadron Collider.
Einstein's theory itself does not state how many dimensions there are in the universe, so theoretical physicists have been studying general relativity in higher dimensions to see if cosmic censorship still holds. The discovery of ring-shaped black holes in five dimensions led researchers to hypothesise that they could break up and give rise to a naked singularity.
What the Cambridge researchers, along with their co-author Pau Figueras from Queen Mary University of London, have found is that if the ring is thin enough, it can lead to the formation of naked singularities.
Using the COSMOS supercomputer, the researchers were able to perform a full simulation of Einstein's complete theory in higher dimensions, allowing them to not only confirm that these 'black rings' are unstable, but to also identify their eventual fate. Most of the time, a black ring collapses back into a sphere, so that the singularity would stay contained within the event horizon. Only a very thin black ring becomes sufficiently unstable as to form bulges connected by thinner and thinner strings, eventually breaking off and forming a naked singularity. New simulation techniques and computer code were required to handle these extreme shapes.
"The better we get at simulating Einstein's theory of gravity in higher dimensions, the easier it will be for us to help with advancing new computational techniques -- we're pushing the limits of what you can do on a computer when it comes to Einstein's theory," said Tunyasuvunakool. "But if cosmic censorship doesn't hold in higher dimensions, then maybe we need to look at what's so special about a four-dimensional universe that means it does hold."
The cosmic censorship conjecture is widely expected to be true in our four-dimensional universe, but should it be disproved, an alternative way of explaining the universe would then need to be identified. One possibility is quantum gravity, which approximates Einstein's equations far away from a singularity, but also provides a description of new physics close to the singularity
the COSMOS supercomputer at the University of Cambridge is part of the Science and Technology Facilities Council (STFC) DiRAC HPC Facility.
|
ATLASGAL survey of Milky Way completed
A spectacular image of the Milky Way has been released to mark the completion of the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). The APEX telescope has mapped the full area of the Galactic Plane visible from the southern hemisphere for the first time at submillimeter wavelengths and in finer detail than space-based surveys. The APEX telescope allows the study of the cold universe, a few tens of degrees above absolute zero.
 |
| This part image of the Milky Way has been released to mark the completion of the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). The new ATLASGAL maps cover an area of sky 140 degrees long and 3 degrees wide, more than four times larger than the first ATLASGAL release [3]. The new maps are also of higher quality, as some areas were re-observed to obtain a more uniform data quality over the whole survey area. |
The ATLASGAL survey is the single most successful APEX large programme with nearly 70 associated science papers already published, and its legacy will expand much further with all the reduced data products now available to the full astronomical community [4].
At the heart of APEX are its sensitive instruments. One of these, LABOCA (the LArge BOlometer Camera) was used for the ATLASGAL survey. LABOCA measures incoming radiation by registering the tiny rise in temperature it causes on its detectors and can detect emission from the cold dark dust bands obscuring the stellar light.
The new release of ATLASGAL complements observations from ESA's Planck satellite [5]. The combination of the Planck and APEX data allowed astronomers to detect emission spread over a larger area of sky and to estimate from it the fraction of dense gas in the inner Galaxy. The ATLASGAL data were also used to create a complete census of cold and massive clouds where new generations of stars are forming.
"ATLASGAL provides exciting insights into where the next generationof high-mass stars and clusters form. By combining these with observations from Planck, we can now obtain a link to the large-scale structures of giant molecular clouds," remarks Timea Csengeri from the Max Planck Institute for Radio Astronomy (MPIfR), Bonn, Germany, who led the work of combining the APEX and Planck data.
The APEX telescope recently celebrated ten years of successful research on the cold Universe. It plays an important role not only as pathfinder, but also as a complementary facility to ALMA, the Atacama Large Millimeter/submillimeter Array, which is also located on the Chajnantor Plateau. APEX is based on a prototype antenna constructed for the ALMA project, and it has found many targets that ALMA can study in great detail.
Leonardo Testi from ESO, who is a member of the ATLASGAL team and the European Project Scientist for the ALMA project, concludes: "ATLASGAL has allowed us to have a new and transformational look at the dense interstellar medium of our own galaxy, the Milky Way. The new release of the full survey opens up the possibility to mine this marvellous dataset for new discoveries. Many teams of scientists are already using the ATLASGAL data to plan for detailed ALMA follow-up."
Notes
[1] The map was constructed from individual APEX observations of radiation with a wavelength of 870 µm (0.87 millimetres).
[2] The northern part of the Milky Way had already been mapped by the James Clerk Maxwell Telescope and other telescopes, but the southern sky is particularly important as it includes the Galactic Centre, and because it is accessible for detailed follow-up observations with ALMA.
[3] The first data release covered an area of approximately 95 square degrees, a very long and narrow strip along the Galactic Plane two degrees wide and over 40 degrees long. The final maps now cover 420 square degrees, more than four times larger.
[4] The data products are available through the ESO archive.
[5] The Planck data coverhe full sky, but with poor spatial resolution. ATLASGAL covers only the Galactic plane, but with high angular resolution. Combining both provides excellent spatial dynamic range.
Signs of second largest black hole in the Milky Way
Astronomers using the Nobeyama 45-m Radio Telescope have detected signs of an invisible black hole with a mass of 100 thousand times the mass of the Sun around the center of the Milky Way. The team assumes that this possible 'intermediate mass' black hole is a key to understanding the birth of the supermassive black holes located in the centers of galaxies.
A team of astronomers led by Tomoharu Oka, a professor at Keio University in Japan, has found an enigmatic gas cloud, called CO-0.40-0.22, only 200 light years away from the center of the Milky Way. What makes CO-0.40-0.22 unusual is its surprisingly wide velocity dispersion: the cloud contains gas with a very wide range of speeds. The team found this mysterious feature with two radio telescopes, the Nobeyama 45-m Telescope in Japan and the ASTE Telescope in Chile, both operated by the National Astronomical Observatory of Japan.
To investigate the detailed structure, the team observed CO-0.40-0.22 with the Nobeyama 45-m Telescope again to obtain 21 emission lines from 18 molecules. The results show that the cloud has an elliptical shape and consists of two components: a compact but low density component with a very wide velocity dispersion of 100 km/s, and a dense component extending 10 light years with a narrow velocity dispersion.
What makes this velocity dispersion so wide? There are no holes inside of the cloud. Also, X-ray and infrared observations did not find any compact objects. These features indicate that the velocity dispersion is not caused by a local energy input, such as supernova explosions.
The team performed a simple simulation of gas clouds flung by a strong gravity source. In the simulation, the gas clouds are first attracted by the source and their speeds increase as they approach it, reaching maximum at the closest point to the object. After that the clouds continue past the object and their speeds decrease. The team found that a model using a gravity source with 100 thousand times the mass of the Sun inside an area with a radius of 0.3 light years provided the best fit to the observed data. “Considering the fact that no compact objects are seen in X-ray or infrared observations,” Oka, the lead author of the paper that appeared in the Astrophysical Journal Letters, explains “as far as we know, the best candidate for the compact massive object is a black hole.”
If that is the case, this is the first detection of an intermediate mass black hole. Astronomers already know about two sizes of black holes: stellar-mass black holes, formed after the gigantic explosions of very massive stars; and supermassive black holes (SMBH) often found at the centers of galaxies. The mass of SMBH ranges from several million to billions of times the mass of the Sun. A number of SMBHs have been found, but no one knows how the SMBHs are formed. One idea is that they are formed from mergers of many intermediate mass black holes. But this raises a problem because so far no firm observational evidence for intermediate mass black holes has been found. If the cloud CO-0.40-0.22, located only 200 light years away from Sgr A* (the 400 million solar mass SMBH at the center of the Milky Way), contains an intermediate mass black hole, it might support the intermediate mass black hole merger scenario of SMBH evolution.
These results open a new way to search for black holes with radio telescopes. Recent observations have revealed that there are a number of wide-velocity-dispersion compact clouds similar to CO-0.40-0.22. The team proposes that some of those clouds might contain black holes. A study suggested that there are 100 million black holes in the Milky Way Galaxy, but X-ray observations have only found dozens so far. Most of the black holes may be “dark” and very difficult to see directly at any wavelength. “Investigations of gas motion with radio telescopes may provide a complementary way to search for dark black holes” said Oka. “The on-going wide area survey observations of the Milky Way with the Nobeyama 45-m Telescope and high-resolution observations of nearby galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA) have the potential to increase the number of black hole candidates dramatically.”
Astronomers using the Nobeyama 45-m Radio Telescope have detected signs of an invisible black hole with a mass of 100 thousand times the mass of the Sun around the center of the Milky Way. The team assumes that this possible 'intermediate mass' black hole is a key to understanding the birth of the supermassive black holes located in the centers of galaxies.
A team of astronomers led by Tomoharu Oka, a professor at Keio University in Japan, has found an enigmatic gas cloud, called CO-0.40-0.22, only 200 light years away from the center of the Milky Way. What makes CO-0.40-0.22 unusual is its surprisingly wide velocity dispersion: the cloud contains gas with a very wide range of speeds. The team found this mysterious feature with two radio telescopes, the Nobeyama 45-m Telescope in Japan and the ASTE Telescope in Chile, both operated by the National Astronomical Observatory of Japan.
To investigate the detailed structure, the team observed CO-0.40-0.22 with the Nobeyama 45-m Telescope again to obtain 21 emission lines from 18 molecules. The results show that the cloud has an elliptical shape and consists of two components: a compact but low density component with a very wide velocity dispersion of 100 km/s, and a dense component extending 10 light years with a narrow velocity dispersion.
What makes this velocity dispersion so wide? There are no holes inside of the cloud. Also, X-ray and infrared observations did not find any compact objects. These features indicate that the velocity dispersion is not caused by a local energy input, such as supernova explosions.
The team performed a simple simulation of gas clouds flung by a strong gravity source. In the simulation, the gas clouds are first attracted by the source and their speeds increase as they approach it, reaching maximum at the closest point to the object. After that the clouds continue past the object and their speeds decrease. The team found that a model using a gravity source with 100 thousand times the mass of the Sun inside an area with a radius of 0.3 light years provided the best fit to the observed data. “Considering the fact that no compact objects are seen in X-ray or infrared observations,” Oka, the lead author of the paper that appeared in the Astrophysical Journal Letters, explains “as far as we know, the best candidate for the compact massive object is a black hole.”
If that is the case, this is the first detection of an intermediate mass black hole. Astronomers already know about two sizes of black holes: stellar-mass black holes, formed after the gigantic explosions of very massive stars; and supermassive black holes (SMBH) often found at the centers of galaxies. The mass of SMBH ranges from several million to billions of times the mass of the Sun. A number of SMBHs have been found, but no one knows how the SMBHs are formed. One idea is that they are formed from mergers of many intermediate mass black holes. But this raises a problem because so far no firm observational evidence for intermediate mass black holes has been found. If the cloud CO-0.40-0.22, located only 200 light years away from Sgr A* (the 400 million solar mass SMBH at the center of the Milky Way), contains an intermediate mass black hole, it might support the intermediate mass black hole merger scenario of SMBH evolution.
These results open a new way to search for black holes with radio telescopes. Recent observations have revealed that there are a number of wide-velocity-dispersion compact clouds similar to CO-0.40-0.22. The team proposes that some of those clouds might contain black holes. A study suggested that there are 100 million black holes in the Milky Way Galaxy, but X-ray observations have only found dozens so far. Most of the black holes may be “dark” and very difficult to see directly at any wavelength. “Investigations of gas motion with radio telescopes may provide a complementary way to search for dark black holes” said Oka. “The on-going wide area survey observations of the Milky Way with the Nobeyama 45-m Telescope and high-resolution observations of nearby galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA) have the potential to increase the number of black hole candidates dramatically.”
'Music' Heard by Apollo 10 Astronauts at the Moon Not from Aliens
NASA recently released evidence buried for decades showing that astronauts on the Apollo 10 lunar mission in 1969 heard strange "space music" that seemingly defies explanation – or did it ... and does it? Many news services have picked up on the story and claim that the "space music" incident is only now being made public, but NASA disagrees. According to the space agency, the audio and transcripts from the mission have been available in the National Archives since 1973 and the explanation of the event is quite down to Earth.
The Science Channel's speculative program NASA's Unexplained Files recently aired a story claiming that when the Apollo mission was on the far side of the Moon and out of radio contact with Earth, the crew heard weird electronic sounds that were described by Lunar Module Pilot Eugene Cernan as "outer-space-type music." The narration of the segment puts a lot of emphasis on the "out of contact" angle – hinting that "something" exciting and exotic might have been behind the strange sound. Aliens, perhaps?
The segment then goes on to claim that the information was only released in 2008, implying that the evidence of the incident was suppressed by the US government for decades, and that the astronauts themselves feared to talk about the incident. These assertions were subsequently picked up and repeated by many major news services.However, NASA disagrees with the Science Channel's account and in a statement released today says that though the tape recordings and transcripts of astronaut conversations were marked Classified in 1969 as a matter of standard security, the audioand transcripts were made public in 1973 and deposited in the National Archives. The agency also says that, though the incident was well known in radio and space circles, the only new releases regarding the "space music" incident have been digital files that can be streamed over the internet.
In addition, astronaut Cernan said on Monday that the crew didn't regard the incident as at all significant."I don't remember that incident exciting me enough to take it seriously. It was probably just radio interference," said Cernan. "Had we thought it was something other than that we would have briefed everyone after the flight. We never gave it another thought."
The transcript from Apollo 10 record the conversation of the astronauts regarding whooing and whooping sounds coming from the radio equipment while the crew carried out various tasks. Below are the relevant segments with time stamps in mission day, hour, minute, and second, and the speakers identified as Commander Thomas Stafford (CDR), Command Module Pilot John Young (CMP), and Lunar Module Pilot Eugene Cernan (LMP).
- 04 06 13 02 LMP That music even sounds outer-spacey, doesn't it? You hear that? That whistling sound?
- 04 06 13 06 CDR Yes.
- 04 06 13 07 LMP Whooooooo. Say your –
- 04 06 13 12 CMP Did you hear that whistling sound, too?
- 04 06 13 14 LMP Yes. Sounds like – you know, outer-space-type music.
- 04 06 13 18 CMP I wonder what it is.
- ...
- 04 06 17 58 LMP Boy, that sure is weird music.
- 04 06 18 01 CMP We're going to have to find out about that. Nobody will believe us.
- 04 06 18 07 LMP Yes. It's a whistling, you know, like an outerspace-type thing.
- 04 06 18 10 CMP Yes... VHF-A ...
- 04 06 18 16 LMP Yes. I wouldn't believe there's anyone out there.
VHF-A refers to a radio system aboard the spacecraft and points to the cause of the odd sounds. Writing in Air and Space, Paul D. Spudis of the Lunar and Planetary Institute in Houston, Texas, says that Apollo carried many radio links for voice, telemetry, navigation, biomedical data, and other information.
NASA recently released evidence buried for decades showing that astronauts on the Apollo 10 lunar mission in 1969 heard strange "space music" that seemingly defies explanation – or did it ... and does it? Many news services have picked up on the story and claim that the "space music" incident is only now being made public, but NASA disagrees. According to the space agency, the audio and transcripts from the mission have been available in the National Archives since 1973 and the explanation of the event is quite down to Earth.
The Science Channel's speculative program NASA's Unexplained Files recently aired a story claiming that when the Apollo mission was on the far side of the Moon and out of radio contact with Earth, the crew heard weird electronic sounds that were described by Lunar Module Pilot Eugene Cernan as "outer-space-type music." The narration of the segment puts a lot of emphasis on the "out of contact" angle – hinting that "something" exciting and exotic might have been behind the strange sound. Aliens, perhaps?
The segment then goes on to claim that the information was only released in 2008, implying that the evidence of the incident was suppressed by the US government for decades, and that the astronauts themselves feared to talk about the incident. These assertions were subsequently picked up and repeated by many major news services.However, NASA disagrees with the Science Channel's account and in a statement released today says that though the tape recordings and transcripts of astronaut conversations were marked Classified in 1969 as a matter of standard security, the audioand transcripts were made public in 1973 and deposited in the National Archives. The agency also says that, though the incident was well known in radio and space circles, the only new releases regarding the "space music" incident have been digital files that can be streamed over the internet.
In addition, astronaut Cernan said on Monday that the crew didn't regard the incident as at all significant."I don't remember that incident exciting me enough to take it seriously. It was probably just radio interference," said Cernan. "Had we thought it was something other than that we would have briefed everyone after the flight. We never gave it another thought."
The transcript from Apollo 10 record the conversation of the astronauts regarding whooing and whooping sounds coming from the radio equipment while the crew carried out various tasks. Below are the relevant segments with time stamps in mission day, hour, minute, and second, and the speakers identified as Commander Thomas Stafford (CDR), Command Module Pilot John Young (CMP), and Lunar Module Pilot Eugene Cernan (LMP).
VHF-A refers to a radio system aboard the spacecraft and points to the cause of the odd sounds. Writing in Air and Space, Paul D. Spudis of the Lunar and Planetary Institute in Houston, Texas, says that Apollo carried many radio links for voice, telemetry, navigation, biomedical data, and other information.
 |
How to find and study a black hole
Black holes sound too strange to be real. But they are actually pretty common in space. There are dozens known and probably millions more in the Milky Way and a billion times that lurking outside. The makings and dynamics of these monstrous warpings of spacetime have been confounding scientists for centuries.
Add caption
Imagine, somewhere in the galaxy, the corpse of a star so dense that it punctures the fabric of space and time. So dense that it devours any surrounding matter that gets too close, pulling it into a riptide of gravity that nothing, not even light, can escape.
And once matter crosses over the point of no return, the event horizon, it spirals helplessly toward an almost infinitely small point, a point where spacetime is so curved that all our theories break down: the singularity. No one gets out alive.
Black holes sound too strange to be real. But they are actually pretty common in space. There are dozens known and probably millions more in the Milky Way and a billion times that lurking outside. Scientists also believe there could be a supermassive black hole at the center of nearly every galaxy, including our own. The makings and dynamics of these monstrous warpings of spacetime have been confounding scientists for centuries.
A history of black holes
It all started in England in 1665, when an apple broke from the branch of a tree and fell to the ground. Watching from his garden at Woolsthorpe Manor, Isaac Newton began thinking about the apple's descent: a line of thought that, two decades later, ended with his conclusion that there must be some sort of universal force governing the motion of apples and cannonballs and even planetary bodies. He called it gravity.
Newton realized that any object with mass would have a gravitational pull. He found that as mass increases, gravity increases. To escape an object's gravity, you would need to reach its escape velocity. To escape the gravity of Earth, you would need to travel at a rate of roughly 11 kilometers per second.
It was Newton's discovery of the laws of gravity and motion that, 100 years later, led Reverend John Michell, a British polymath, to the conclusion that if there were a star much more massive or much more compressed than the sun, its escape velocity could surpass even the speed of light. He called these objects "dark stars." Twelve years later, French scientist and mathematician Pierre Simon de Laplace arrived at the same conclusion and offered mathematical proof for the existence of what we now know as black holes.
In 1915, Albert Einstein set forth the revolutionary theory of general relativity, which regarded space and time as a curved four-dimensional object. Rather than viewing gravity as a force, Einstein saw it as a warping of space and time itself. A massive object, such as the sun, would create a dent in spacetime, a gravitational well, causing any surrounding objects, such as the planets in our solar system, to follow a curved path around it.
A month after Einstein published this theory, German physicist Karl Schwarzschild discovered something fascinating in Einstein's equations. Schwarzschild found a solution that led scientists to the conclusion that a region of space could become so warped that it would create a gravitational well that no object could escape.
Up until 1967, these mysterious regions of spacetime had not been granted a universal title. Scientists tossed around terms like "collapsar" or "frozen star" when discussing the dark plots of inescapable gravity. At a conference in New York, physicist John Wheeler popularized the term "black hole."
How to find a black hole
During star formation, gravity compresses matter until it is stopped by the star's internal pressure. If the internal pressure does not stop the compression, it can result in the formation of a black hole.
Some black holes are formed when massive stars collapse. Others, scientists believe, were formed very early in the universe, a billion years after the big bang.
There is no limit to how immense a black hole can be, sometimes more than a billion times the mass of the sun. According to general relativity, there is also no limit to how small they can be (although quantum mechanics suggests otherwise). Black holes grow in mass as they continue to devour their surrounding matter. Smaller black holes accrete matter from a companion star while the larger ones feed off of any matter that gets too close.
Black holes contain an event horizon, beyond which not even light can escape. Because no light can get out, it is impossible to see beyond this surface of a black hole. But just because you can't see a black hole, doesn't mean you can't detect one.
Scientists can detect black holes by looking at the motion of stars and gas nearby as well as matter accreted from its surroundings. This matter spins around the black hole, creating a flat disk called an accretion disk. The whirling matter loses energy and gives off radiation in the form of X-rays and other electromagnetic radiation before it eventually passes the event horizon.
This is how astronomers identified Cygnus X-1 in 1971. Cygnus X-1 was found as part of a binary star system in which an extremely hot and bright star called a blue supergiant formed an accretion disk around an invisible object. The binary star system was emitting X-rays, which are not usually produced by blue supergiants. By calculating how far and fast the visible star was moving, astronomers were able to calculate the mass of the unseen object. Although it was compressed into a volume smaller than the Earth, the object's mass was more than six times as heavy as our sun.
Several different experiments study black holes. The Event Horizon Telescope will look at black holes in the nucleus of our galaxy and a nearby galaxy, M87. Its resolution is high enough to image flowing gas around the event horizon.
Scientists can also do reverberation mapping, which uses X-ray telescopes to look for time differences between emissions from various locations near the black hole to understand the orbits of gas and photons around the black hole.
The Laser Interferometer Gravitational-Wave Observatory, or LIGO, seeks to identify the merger of two black holes, which would emit gravitational radiation, or gravitational waves, as the two black holes merge.
In addition to accretion disks, black holes also have winds and incredibly bright jets erupting from them along their rotation axis, shooting out matter and radiation at nearly the speed of light. Scientists are still working to understand how these jets form.
What we don't know
Scientists have learned that black holes are not as black as they once thought them to be. Some information might escape them. In 1974, Stephen Hawking published results that showed that black holes should radiate energy, or Hawking radiation.
Matter-antimatter pairs are constantly being produced throughout the universe, even outside the event horizon of a black hole. Quantum theory predicts that one particle might be dragged in before the pair has a chance to annihilate, and the other might escape in the form of Hawking radiation. This contradicts the picture general relativity paints of a black hole from which nothing can escape.
But as a black hole radiates Hawking radiation, it slowly evaporates until it eventually vanishes. So what happens to all the information encoded on its horizon? Does it disappear, which would violate quantum mechanics? Or is it preserved, as quantum mechanics would predict? One theory is that the Hawking radiation contains all of that information. When the black hole evaporates and disappears, it has already preserved the information of everything that fell into it, radiating it out into the universe.
Black holes give scientists an opportunity to test general relativity in very extreme gravitational fields. They see black holes as an opportunity to answer one of the biggest questions in particle physics theory: Why can't we square quantum mechanics with general relativity?
Beyond the event horizon, black holes curve into one of the darkest mysteries in physics. Scientists can't explain what happens when objects cross the event horizon and spiral toward the singularity. General relativity and quantum mechanics collide and Einstein's equations explode into infinities. Black holes might even house gateways to other universes called wormholes and violent fountains of energy and matter called white holes, though it seems very unlikely that nature would allow these structures to exist.
Sometimes reality is stranger than fiction.
|
| Add caption |
Imagine, somewhere in the galaxy, the corpse of a star so dense that it punctures the fabric of space and time. So dense that it devours any surrounding matter that gets too close, pulling it into a riptide of gravity that nothing, not even light, can escape.
And once matter crosses over the point of no return, the event horizon, it spirals helplessly toward an almost infinitely small point, a point where spacetime is so curved that all our theories break down: the singularity. No one gets out alive.
Black holes sound too strange to be real. But they are actually pretty common in space. There are dozens known and probably millions more in the Milky Way and a billion times that lurking outside. Scientists also believe there could be a supermassive black hole at the center of nearly every galaxy, including our own. The makings and dynamics of these monstrous warpings of spacetime have been confounding scientists for centuries.
A history of black holes
It all started in England in 1665, when an apple broke from the branch of a tree and fell to the ground. Watching from his garden at Woolsthorpe Manor, Isaac Newton began thinking about the apple's descent: a line of thought that, two decades later, ended with his conclusion that there must be some sort of universal force governing the motion of apples and cannonballs and even planetary bodies. He called it gravity.
Newton realized that any object with mass would have a gravitational pull. He found that as mass increases, gravity increases. To escape an object's gravity, you would need to reach its escape velocity. To escape the gravity of Earth, you would need to travel at a rate of roughly 11 kilometers per second.
It was Newton's discovery of the laws of gravity and motion that, 100 years later, led Reverend John Michell, a British polymath, to the conclusion that if there were a star much more massive or much more compressed than the sun, its escape velocity could surpass even the speed of light. He called these objects "dark stars." Twelve years later, French scientist and mathematician Pierre Simon de Laplace arrived at the same conclusion and offered mathematical proof for the existence of what we now know as black holes.
In 1915, Albert Einstein set forth the revolutionary theory of general relativity, which regarded space and time as a curved four-dimensional object. Rather than viewing gravity as a force, Einstein saw it as a warping of space and time itself. A massive object, such as the sun, would create a dent in spacetime, a gravitational well, causing any surrounding objects, such as the planets in our solar system, to follow a curved path around it.
A month after Einstein published this theory, German physicist Karl Schwarzschild discovered something fascinating in Einstein's equations. Schwarzschild found a solution that led scientists to the conclusion that a region of space could become so warped that it would create a gravitational well that no object could escape.
Up until 1967, these mysterious regions of spacetime had not been granted a universal title. Scientists tossed around terms like "collapsar" or "frozen star" when discussing the dark plots of inescapable gravity. At a conference in New York, physicist John Wheeler popularized the term "black hole."
How to find a black hole
During star formation, gravity compresses matter until it is stopped by the star's internal pressure. If the internal pressure does not stop the compression, it can result in the formation of a black hole.
Some black holes are formed when massive stars collapse. Others, scientists believe, were formed very early in the universe, a billion years after the big bang.
There is no limit to how immense a black hole can be, sometimes more than a billion times the mass of the sun. According to general relativity, there is also no limit to how small they can be (although quantum mechanics suggests otherwise). Black holes grow in mass as they continue to devour their surrounding matter. Smaller black holes accrete matter from a companion star while the larger ones feed off of any matter that gets too close.
Black holes contain an event horizon, beyond which not even light can escape. Because no light can get out, it is impossible to see beyond this surface of a black hole. But just because you can't see a black hole, doesn't mean you can't detect one.
Scientists can detect black holes by looking at the motion of stars and gas nearby as well as matter accreted from its surroundings. This matter spins around the black hole, creating a flat disk called an accretion disk. The whirling matter loses energy and gives off radiation in the form of X-rays and other electromagnetic radiation before it eventually passes the event horizon.
This is how astronomers identified Cygnus X-1 in 1971. Cygnus X-1 was found as part of a binary star system in which an extremely hot and bright star called a blue supergiant formed an accretion disk around an invisible object. The binary star system was emitting X-rays, which are not usually produced by blue supergiants. By calculating how far and fast the visible star was moving, astronomers were able to calculate the mass of the unseen object. Although it was compressed into a volume smaller than the Earth, the object's mass was more than six times as heavy as our sun.
Several different experiments study black holes. The Event Horizon Telescope will look at black holes in the nucleus of our galaxy and a nearby galaxy, M87. Its resolution is high enough to image flowing gas around the event horizon.
Scientists can also do reverberation mapping, which uses X-ray telescopes to look for time differences between emissions from various locations near the black hole to understand the orbits of gas and photons around the black hole.
The Laser Interferometer Gravitational-Wave Observatory, or LIGO, seeks to identify the merger of two black holes, which would emit gravitational radiation, or gravitational waves, as the two black holes merge.
In addition to accretion disks, black holes also have winds and incredibly bright jets erupting from them along their rotation axis, shooting out matter and radiation at nearly the speed of light. Scientists are still working to understand how these jets form.
What we don't know
Scientists have learned that black holes are not as black as they once thought them to be. Some information might escape them. In 1974, Stephen Hawking published results that showed that black holes should radiate energy, or Hawking radiation.
Matter-antimatter pairs are constantly being produced throughout the universe, even outside the event horizon of a black hole. Quantum theory predicts that one particle might be dragged in before the pair has a chance to annihilate, and the other might escape in the form of Hawking radiation. This contradicts the picture general relativity paints of a black hole from which nothing can escape.
But as a black hole radiates Hawking radiation, it slowly evaporates until it eventually vanishes. So what happens to all the information encoded on its horizon? Does it disappear, which would violate quantum mechanics? Or is it preserved, as quantum mechanics would predict? One theory is that the Hawking radiation contains all of that information. When the black hole evaporates and disappears, it has already preserved the information of everything that fell into it, radiating it out into the universe.
Black holes give scientists an opportunity to test general relativity in very extreme gravitational fields. They see black holes as an opportunity to answer one of the biggest questions in particle physics theory: Why can't we square quantum mechanics with general relativity?
Beyond the event horizon, black holes curve into one of the darkest mysteries in physics. Scientists can't explain what happens when objects cross the event horizon and spiral toward the singularity. General relativity and quantum mechanics collide and Einstein's equations explode into infinities. Black holes might even house gateways to other universes called wormholes and violent fountains of energy and matter called white holes, though it seems very unlikely that nature would allow these structures to exist.
Sometimes reality is stranger than fiction.
OUR UNIVERSE MAY HAVE EMERGED FROM A BLACK HOLE IN A HIGHER DIMENSIONAL UNIVERSE
THE EVENT HORIZON OF A BLACK HOLE — THE POINT OF NO RETURN FOR ANYTHING THAT FALLS IN — IS A SPHERICAL SURFACE. IN A HIGHER-DIMENSIONAL UNIVERSE, A BLACK HOLE COULD HAVE A THREE-DIMENSIONAL EVENT HORIZON, WHICH COULD SPAWN A WHOLE NEW UNIVERSE AS IT FORMS.
New research from theoretical physicists at the Perimeter Institute proposes that our universe may have emerged from a black hole in a higher-dimensional universe.
The big bang poses a big question: if it was indeed the cataclysm that blasted our universe into existence 13.7 billion years ago, what sparked it?
Three Perimeter Institute researchers have a new idea about what might have come before the big bang. It’s a bit perplexing, but it is grounded in sound mathematics, testable, and enticing enough to earn the cover story in Scientific American, called “The Black Hole at the Beginning of Time.”
our known universe could be the three-dimensional “wrapping” around a four-dimensional black hole’s event horizon. In this scenario, our universe burst into being when a star in a four-dimensional universe collapsed into a black hole.
In our three-dimensional universe, black holes have two-dimensional event horizons – that is, they are surrounded by a two-dimensional boundary that marks the “point of no return.” In the case of a four-dimensional universe, a black hole would have a three-dimensional event horizon.
New research from theoretical physicists at the Perimeter Institute proposes that our universe may have emerged from a black hole in a higher-dimensional universe.
The big bang poses a big question: if it was indeed the cataclysm that blasted our universe into existence 13.7 billion years ago, what sparked it?
Three Perimeter Institute researchers have a new idea about what might have come before the big bang. It’s a bit perplexing, but it is grounded in sound mathematics, testable, and enticing enough to earn the cover story in Scientific American, called “The Black Hole at the Beginning of Time.”
our known universe could be the three-dimensional “wrapping” around a four-dimensional black hole’s event horizon. In this scenario, our universe burst into being when a star in a four-dimensional universe collapsed into a black hole.
In our three-dimensional universe, black holes have two-dimensional event horizons – that is, they are surrounded by a two-dimensional boundary that marks the “point of no return.” In the case of a four-dimensional universe, a black hole would have a three-dimensional event horizon.
No comments:
Post a Comment