Vanishing matter points to black hole in Milky Way

[n2doc]

29 April 2009 by David Shiga

MATTER and energy are vanishing without a trace at the centre of the Milky Way, providing the best evidence so far that a black hole is lurking there.

Falling into a black hole is aone-way trip - once matter or light crosses a threshold called the event horizon, it can never escape. While astronomers have identified many dark, dense objects they strongly suspect are black holes, it is difficult to prove that they possess event horizons, the defining feature of such objects. Among the proposed alternatives are dense balls of exotic matter called boson stars, which don't have event horizons.

Now Avery Broderick of the Canadian Institute of Theoretical Astrophysics and his colleagues have analysed previous infrared and radio observations of the galactic centre and put forward the strongest evidence yet that an object at our galaxy's centre does indeed have an event horizon.

The team reasoned that if the object were not a black hole, it should glow in the infrared. This is because the kinetic energy of matter hitting the object would be converted into heat. Given the rate that matter appears to be falling onto the central object, it should have a temperature of at least a few hundred Kelvin, they calculate. The resulting infrared glow would be 250 times as bright as the actual glow coming from the region containing the massive object and its disc of matter, when previously measured during quieter moments when the disc is not flaring up.

http://www.newscientist.com/article/mg20227064.400-vanishing-matter-points-to-black-hole-in-milky-way.html



The centre of the Milky Way, as seen from NASA's Chandra X-ray Observatory. New evidence strongly suggests that there is a black hole lurking in there (Image: Q D Wang et al / UMass Amherst / CXC / NASA)

[On the Road]

1. I Thought It Was Commonly Accepted

that the Milky Way, and most galaxies for that matter, have a supermassive black hole at the center. Is this just scientific confirmation?

[DrDan]

4. I also thought that was the case

[IDFbunny]

2. I thought that was already established.

That super massive blackholes are at the center of every galaxy. Super massive black holes account for the missing matter in space, that is there is no dark matter.

[Towlie]

5. But if the matter drawn inside still exerts gravity then it's not "vanishing without a trace."

So the article is wrong.

[Jackpine Radical]

3. Oh, good. Now we have a place to put our trash--

things like nuclear waste, used Pampers and Rush Limbaugh.

[TechBear_Seattle]

6. I cannot believe that New Scientist would engage in such sloppy reporting on science

First off, falling into a black hole is NOT a one-way trip. Black holes "evaporate," giving off what is called Hawking radiation, named for Stephen Hawking who provided the basis for its existence in 1974.

[FiveGoodMen]

7. If I remember right, that effect was related to the curvature of the event horizon

so that very small black holes could evaporate more quickly than large ones.

Super-massive black holes would have very flat (locally speaking) surfaces.

One would think that they'd take virtually forever to disappear even if new matter weren't falling into them all the time.

[TechBear_Seattle]

8. By the ratio of surface area to volume, I think

As I understand it, the surface area "covered" by the event horizon should give off Hawking radiation at a predictable, consistant rate (I say "should" because there is as yet no direct experimental proof that Hawking radiation exists.) As you decrease the volume of a sphere, the ratio of surface area to volume increases; with a black hole, that would increase the "evaporation" rate. The result is that, as a black hole gets smaller and smaller, its "evaporation" rate increases. Smallish black holes, with event horizons the size of a molecule, would dissolve into a cloud of energy almost immediately; gigantic black holes, such as the ones in the middle of a galaxy, could last for longer than the universe has existed.

Of course, this assumes that there is no matter/energy going into the hole. If there is enough material able to get past the event horizon, it should be possible for even a tiny black hole to last indefinitely.

[FiveGoodMen]

9. The way I had heard it explained

was that the radiation was produced when phantom pairs of matter/anti-matter popped up near the event horizon and were quickly pulled apart by tidal forces -- one falling into the black hole, one staying out -- before they could annihilate each other.

[TechBear_Seattle]

11. That is the source of the radiation, yes

It takes a lot of energy for virtual particle/anti-particle pairs to form, which is "borrowed" from the universe at large. Normally, these pairs exist for such a tiny slice of time that they vanish before payment comes due. When they do not annihilate one another, the energy loan must be paid. According to the equations, the particle that remains outside of the event horizon is "kicked" away from the black hole, basically stealing energy from it. That results in a net loss of energy from the black hole and, therefore, a net loss of the hole's mass. And again, the smaller the event horizon is, the more mass gets lost until the hole collapses back into normal space.

Scientific American had an article about two years ago on this very subject. If you can find it, I highly recommend it.

[Raspberry]

10. I wonder

how many socks are in there?