SEEING STARS: The motions of stars at the center of the Milky Way reveal the nature of the black hole suspected to reside there.
Image: ESO/S. Gillessen et al.
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A pair of new long-term studies tracking the orbits of stars at the center of the Milky Way Galaxy further refine the evidence that a supermassive black hole lurks there. The two teams of researchers used data going back to 1992 and were even able to track a full revolution of one star, known as S2, around the theorized black hole, known as Sagittarius A*, some four million times the mass of the sun.
Both papers provide new, closely related estimates for the mass of the suspected black hole and the distance between our sun and the galactic center, roughly 26,000 light-years away. These two figures "are fundamental parameters for the Milky Way," says astrophysicist Stefan Gillessen of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, lead author of one of the studies.
The other study's first author, Andrea Ghez, a professor of astronomy at the University of California, Los Angeles, agrees. "Much of our knowledge of the structure of the Milky Way is tied to...the distance between the sun and the center of our galaxy," she says. To sharpen that knowledge as much as possible, she adds, "you'd really like that number nailed down very precisely."
The study by Ghez and her team appears in the current issue of The Astrophysical Journal; Gillessen and his colleagues are set to publish their findings in an upcoming issue of the same journal.
Direct study of a black hole such as the one widely suspected to exist at the center of our galaxy is tricky, as black holes swallow up nearby light, rendering themselves virtually invisible. But researchers can infer properties of a black hole from its hearty gravitational influence on nearby stars.
Ghez says that tracking the orbits of stars is the most direct way to study the black hole's properties. "The physics is simplest if you can just look at the motions of stars," she says. "Anything else requires much more theory, so you're basically building up a larger house of cards. The beauty of this experiment is that it has very few assumptions."
To limit inherent systematic uncertainties, Ghez's group accounted for overlapping light sources when one star passes in front of another or near the black hole itself, where infalling material emits radiation. The team also had to account for any drift by the bodies in the absence of a fixed reference point, a process that Ghez describes as "more subtle than I could have ever imagined." Gillessen's group took similar steps to identify potential sources of error, refining their coordinate system and examining the effects of image distortion and light-source confusion on the estimates.
In earlier approaches, Ghez says, "we had sort of the teenage view of things. We were very excited, we were very emphatic about what we could do, but a little naive." The new papers, she says, try to adopt a more sophisticated view. "What we learned is that we were less knowledgeable than we thought we were," she says. "So our measurements are better, but we understand that there are systematics, and once you account for them, the measurement of the black hole's properties are, in fact, less precise than we used to think they were."
Ghez's team focused on S2, a relatively bright star with a short orbit around the black hole, whereas Gillessen's group determined the orbits of 28 stars, including S2. "It really is amazing to see that we can describe the motions of that many stars" by assuming one massive central anchor, Gillessen says. "The stars fly around wildly, in all directions, at different radii. But all that governs that is simply Newton's law."
The motion of S2, Gillessen says, gives an outer boundary to the central object, which, combined with its inferred mass, helps prove that it is a black hole. "Having four million solar masses sitting there, not shining...and being confined by [the orbit of] the star S2 is really a convincing case," he says. In 2002, Gillessen says, S2 passed within 16 light-hours of the black hole's event horizon, or point of no return; two years earlier, another star passed even closer, around 11 light-hours.
Sheperd Doeleman, an astrophysicist at the Massachusetts Institute of Technology's Haystack Observatory in Westford, Mass., says that pinning down the black hole's parameters is important work and notes that both groups analyzed mounds of data "with particular attention paid to careful error analysis." At the same time, he says, the studies refine rather than redefine prior understanding of the nature of the galactic center.
With more advanced telescopes and optical techniques, Ghez says, these estimates will continue to evolve. A more finely honed picture of the center of the galaxy could even provide a test bed for the fundamental assumptions of Einsteinian physics.
"In principle, these stars could test general relativity, because they get into a very strong gravitational field at the central black hole," Ghez says. "And if the measurements are precise enough, you should be able to see the impacts on the orbit."
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16 Comments
Add CommentIf a black hole is in our galaxy and black holes act like a vacuum to close neighboring planets, then can we expect our entire milky way to be swallowed up and be disintegrated ? If so, an empirical estimate?
Reply | Report Abuse | Link to thisWhile black holes do a "act like a vacuum to close neighboring planets" the majority of the galaxy is not close enough to the center.
Reply | Report Abuse | Link to thisThink of it like this, the sun could easily consume Jupiter however Jupiter is in a stable orbit and will remain there until after the sun burns out.
Also the mass of the galaxy is 100,000 times larger than the black hole. So basically the black hole has eaten out the middle of the galaxy and the galaxy is revolving around itself.
I assume that when a star is consumed in the galactic center, it will be big news all around the world. What are the odds that it will happen in the forseeable future?
Reply | Report Abuse | Link to thisHow will we know when our sun is ready to burn out? We keep talking about thousands of light years and Sagittarius (S2) being four million times the mass of our sun! These thing have been going on infinitely and are mind boggling! How then can we be sure that tomorrow our sun will not burn out? A lot of these things have been scientifically proven, however, there appears to be a lot of conjecture and postulation added.
Reply | Report Abuse | Link to thisWhy do the stars have to rotate into a black hole "like a toilet bowl', why would,nt they sucked straight in without rotating???
Reply | Report Abuse | Link to thisjo, It appears that from what I read and hear, EVERYTHING in the universe is in a huge rotation. (thank goodness, when I flush I don't get sucked in) It appears that everything in the entire universe eventually burns out, gets sucked in, (black holes) out again, (worm holes) blows it out again (white holes, no pun intended), and starts all over again!
Reply | Report Abuse | Link to thisOk, basically, the reason they rotate, rather than being sucked straight in, is that they have motion when they first enter the field, and as they move across, the gravity from the planet pulls them towards it, but because it is moving, it becomes a circular direction as the angle changes. The reason they do not simply fly into the planet, is that their own velocity gives them radial acceleration (the interaction formerly known as centrifugal force) which fights the gravity and pulls it away. As the object comes closer to the sun/black hole/planet, the radius decreases, which means that the object moves faster, and has more outward facing radial acceleration. This keeps planets, stars, and other objects in a fairly stable motion.
Reply | Report Abuse | Link to thisAnd if they were not moving when they entered the gravitational field, they would have been sucked straight in long ago, and thus we do not see those objects anymore.
Indeed, it doesn't seem any individual of the human race will have sufficient time to be swallowed by the supermassive balck hole at the center of the Milky Way. It needs a long time for the Milky Way, located in a quiet place in one of the Spiral Galaxy's arms, to get that close to the center. Why? Simply because long before that, 5 billion years from now -due to astrologists- the Sun will run out of Hydrogene and while trying to fuse Helium and eventually getting bigger and hotter than it can withstand, it will go on a destructive explosion that makes all life die. Before that, it has already swallowed Mercury and Venus, hopefully not our home, teh Earth. Thank goodness Sun is not a very massive star to turn into a Black Hole after its death and it rather will become a white dwarf.
Reply | Report Abuse | Link to thisSoory guys, there was a mistake. It needs a long time for the SOLAR SYSTEM, located in the .... Sorry for the mistake.
Reply | Report Abuse | Link to thisBlack hole and Big bang.
Reply | Report Abuse | Link to this1.
A black hole is a theoretical region of space in which the
gravitational field is so powerful that nothing can escape.
2.
Hawking Radiation theorizes that black holes do not,
in fact, absorb all matter absolutely; they give off some
return matter.
3.
Once upon a time, 20 billions of years ago, all matter
(all elementary particles and all quarks and their
girlfriends- antiparticles and antiquarks, all kinds of
waves: electromagnetic, gravitational, muons…
gluons field ….. etc.) – was assembled in a “single point”
The reason of this unity is gravitational force.
4.
How does this “single point” created if the matter
can escape from any strong gravitational force?
==========..
Best wishes.
Israel Sadovnik. / Socratus.
http://www.socratus.com
http://www.wbabin.net
http://www.wbabin.net/comments/sadovnik.htm
http://www.wbabin.net/physics/sadovnik.pdf
Science has not succeeded to explain neither how that single point came in to existance, nor what made the explosion. Still, the theory of the Big Bang is not the most perfect explanation of the beginning of the universe. In some cases the Steady Universe theory wins, like if there was a Big Bang then temperatures of the univers couldn't be the same in all directions. But it is and only the second theory can explain such fact.
Reply | Report Abuse | Link to thisAt the beginning there was not just a strong gravitational force in a singularity. There scientists suppose were a combination of the 4 forces which now are considered separately: G, EM, SN and WN. This all might have kept it together and then all of a sudden due to rise of temperature of the point of escape of gravity or whatever reason science is still unable to explain a huge eplosion caused the beginning of our current universe.
Science has not succeeded to explain neither how that single point came in to existance, nor what made the explosion. Still, the theory of the Big Bang is not the most perfect explanation of the beginning of the universe. In some cases the Steady Universe theory wins, like if there was a Big Bang then temperatures of the univers couldn't be the same in all directions. But it is and only the second theory can explain such fact.
Reply | Report Abuse | Link to thisAt the beginning there was not just a strong gravitational force in a singularity. There scientists suppose were a combination of the 4 forces which now are considered separately: G, EM, SN and WN. This all might have kept it together and then all of a sudden due to rise of temperature of the point of escape of gravity or whatever reason science is still unable to explain a huge eplosion caused the beginning of our current universe.
Its amazing that some physicists still doubt the existence of black holes. It is not difficult to realise that black hole physics will shape the theories of our physical world in the next 100 years or so. These black bodies that are still largely mysterious will become very common language in physics, and soon too. The universe rests on an intricate balance; on one end there is positive energy and space, on the other negative energy and space. what makes real sense is the existence of black holes, they maintain this balance. What should come next is visualising and studying them. there are yet many secrets nature has kept from us and some of them have to do with the forces that operate within and around black holes.
Reply | Report Abuse | Link to thisMichael S.O.
The existance of Black Holes is proved by a method called Gravitational Lensing. It's when stars or other celestial objects move from behind a Black Hole and their light emitted toward us is distorted. Furhtermore, the strong gravitational force that attracts matter toward itself is another proof for their existance. But there is something strange about them. Some Black Holes eject beams of light, perhaps jets of some matter they can't/don't swallow out. Although there are theories about this mystery, but this makes even the theories underlying Black Holes to be a little uncertain. If nothing can escape from a Black Hole's gravity, then how come those jets of matter could be spitted out. Do they move faster than light, so that can escape? It's not possible due to Einstein! And science is still unable to explain what really happens inside a Black Hole. Will we really die if we are swallowed by one? Who knows?
Reply | Report Abuse | Link to thisYou guys are very smart.
Reply | Report Abuse | Link to thisHas science proved that single point was ever in existance?
Reply | Report Abuse | Link to this