Black Hole at Center of Milky Way 165
kwertii writes: "The Washington Post reports new evidence that there is a black hole with the mass of 2.6 million suns at the center of our galaxy. The Chandra X-Ray Observatory happened to be looking at the presumed site of the hole at the moment it absorbed a comet, blasting x-rays off into space as a byproduct. The implication is that the Milky Way is slowly spiraling down into a giant galactic drain..."
Other links (Score:4, Informative)
Official website [harvard.edu]
Official press release [harvard.edu]
Story on CNN [cnn.com]
Re:No fear, the galaxy's safe. (Score:2, Informative)
The implication in this case is that the black hole provides a central gravity source large enough that the entire galaxy slowly circles it, in a gradually degrading orbit. In this aspect you are right - without such an object the Milky Way could not exist as it does now, as there would be nothing stronger than the attraction between solar systems to hold it together.
However, that does not mean that the black hole is incapable of "swallowing" the galaxy. The fact that the Milky Way is a spiral demonstrates that the orbit is degrading. As more objects are drawn in to the black hole, it can only serve to increase the size and mass and make an even more powerful gravity well.
Re:..Its not really suprising.. (Score:1, Informative)
This article from the BBC's web site is more informative: [bbc.co.uk]
http://news.bbc.co.uk/hi/english/sci/tech/newsi
Re:No fear, the galaxy's safe. (Score:3, Informative)
Steven Hawking explains this concept pretty well in his Brief History of Time
Re:No fear, the galaxy's safe. (Score:2, Informative)
Actually, it is impossible to for a black hole to ever swallow all of the matter orbiting it, unless some outside force (not gravity) starts literally pushing it in. This is a simple consequence of the conservation of energy.
For any object in a bound orbit in a gravitation field with a 1/r^2 force (true for a black hole except when you get extremely close), the average kinetic energy of the orbit <T> and the average potential energy <U> obey <U> = -2 <T>. This is due to the famous Virial Theorem. As a result, the average total energy is always negative and equal to half of the average potential energy.
Now, as the average radius of an orbit decreases, the potential energy will become more negative, and so will the total energy. If this were to happen to all of the matter orbiting the black hole, the total energy of the system would decrease--impossible!
What actually happens is that the particles in orbit constantly bounce off each other, some gaining energy and some losing. Those that lose enough, fall into the black hole. Those that gain enough, escape never to be seen again.
This is exactly what is observed to happen with the clouds of dust that collect to form stars. It all bounces around, and some of it ends up in the star while the rest of it flies off into the great beyond. Of course, some of the extra energy in the black hole case is lost from the X-rays originating from the extremely hot region just outside the horizon. That, however, can't explain how something the size of a galaxy could all end up that close to the horizon of the black hole to begin with. A very large fraction of the matter must escape long before then.
Re:Shouln't this exact moment not last for ever?? (Score:3, Informative)
You are correct ... and you are also wrong.
Let me explain :-)
To an observer outside the event horizon of the black hole, the object never appears to actually cross the horizon, just to approach it more and more slowly as time goes on. In other words, the clock of an infalling observer will appear to run slower than the clock of an observer that does not approach the horizon. More generally, to a distant observer a clock in a strong gravity field will run slower than a clock he carries around with him.
Meanwhile, for the poor observer entering the black hole, as he approaches the horizon, the clock HE carries appears to continue ticking away at its usual rate, while his view of the universe slowly gets distorted, so that it looks like he is travelling down a tunnel towards the hole's surface. In a finite amount of time, he crosses the event horizon, and the "tunnel vision" he has of the rest of the universe shrinks to zero size. He doesn't notice his clock slowing down, and he eventually will hit the "bottom" of the hole.
Interesting fact: if he tries to fight the hole to prolong the time before he hits the bottom, he'll actually hit the bottom sooner than if he didn't fight.... of course, when you've already been ripped apart by the tidal forces, you wouldn't notice, but let's consider just and "ideal observer" :-)
This "strange" (some would incorrectly say "paradoxical") behavior of the same set of events appearing differently to two observers is one of the hallmarks of the "Theory of Relativity" ... but results like this where two people disagree qualitatively on the outcome can only occur when the two can never again communicate with each other. Otherwise, they will only disagree quantitatively on the outcome of an "experiment".
A small piece of basic physics (Score:5, Informative)
Q: What would happen to the orbit of the earth if all the matter in the sun were suddenly compacted into a black hole?
A: Absolutely nothing. A black hole which contains the mass of the sun would still also have the same gravity as the sun. The earth would continue to orbit as it always has.
Q: The galaxies stars orbit around the black hole.
A: This isn't proven. Some galaxies don't have any evidence of a black hole, yet theirorbit around a center of mass. In any case, the black hole at the center of our galaxy is 2.6million solar masses. This is NOTHING compared to the billions of stars in the galaxy, so the effect of the black hole of the actual shape and orbit of the stars is not significant.
Q: Doesn't it sound like someone has pulled the stats on this black hole out of their arse?
A: Not really, the size of this black hole has been measured in several ways, including observing very high velocity stars near the black hole. The motion of these stars betrays the existence and size of the massive object at the galaxy's center.
Q: Aren't black holes required for the formation of galaxies?
A: We don't know for sure yet. There are galaxies without black holes, so it might not be required. Of course, we might just not be detecting the black holes that are in those galaxies.
Re:density of a black hole is infinite. (Score:3, Informative)
Hawking's contribution was thinking about how they might interact with black holes. Interestingly his theory was incomplete in that it rested on a major assumption that was not proved (it's math so "proved" is the right word) until quite recently. To be honest though we won't be certain about Hawking radiation till we have a good understanding of quantum gravity. Until then it's just a good hack trying to apply both quantum mechanics and general relativity to a problem, despite the fact that they are inherently incompatible theories.
As far as compressing things down, many physicists believe a black hole can't swallow anything whose de Broglie wavelength is greater than the diameter of the event horizion. De Broglie wavelength is a quantum mechanical property that in this context can roughly be thought of as a measure of something's intrinsic size. Once something gets pulled in, it would get compressed far smaller, but the black hole has to be able to catch it first. Electrons have a wavelength on the order of 10^-10 m, where as nuclear particles are about 10^-15 m. Schwarzschild radius is given by 2*G*M/c^2, which implies that a hole of 10^-15 m has about 6.7e11 kg of matter in it.
Thus you can't make a black hole out of a cat because a cat doesn't have enough mass to generate an event horizon that would encompass it's atoms. Besides we already wondering whether the cat is dead or alive, why subject him to anything else.
One final note, some of the plans for quantum gravity would replace the singularity with a highly compact structure of miniscule but non-zero volume. IIRC something with radius on the order of 10^-30 to 10^-34 m.
Our Destiny is Density? Computation & Black Ho (Score:2, Informative)
I write a monthly newsletter on accelerating change, Signs of the Singularity, available at my website:
http://www.SingularityWatch.com
If you've heard of the singularity, or ever thought carefully about accelerating change from a cosmological or developmental perspective, I'd suggest you check it out.
Major Speculation Warning:
As many of my readers know, I see black holes (the garden variety ones, not the rare and easily observable supermassives) as the most reasonable candidates for the transcension of complex civilizations. This scenario very nicely explains why we haven't been colonized by robotic Von Neumann probes from other clearly ubiquitous civilizations in our galaxy, even though the galactic core is many billions of years older than us, and we are a mere 30,000 light years away from it. If Eric Chaisson, Seth Lloyd, and others are right, the developmental computational destiny of all complex systems appears to be the exponential approximation of black hole density with our computational architecture (ie, macro, meso, micro, nano, femto, black hole computational substrates). It's a short leap from this to realize that the whole universal system may be built for accelerating computational transcension, with black holes as the most likely multi-local endpoints and portals. As I argue in my forthcoming book, Destiny of Species, we may be perhaps twenty or thirty years away from theoretically (and eventually, experimentally!) proving a black hole destiny for all complex systems in the universe, as they head off to some even more complex environment within the multiverse. Keep your eyes open. Whatever we find, it's guaranteed to be a fascinating story...