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Black Hole at Center of Milky Way
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..."
Official website
Official press release
Story on CNN
I saw a BBC "Horizon" about this the other day on a flight. They talked a lot about "feeding" of apparent suppermassive black holes that they think live in (probably all) galactic centres.
Apparently they stop "feeding" after a while because the mass of the surounding matter in the galaxy means it won't fall in. The attraction from the black hole is balanced, so the matter orbits the hole. Anything itinerant -- like a comet say -- that passed near the hole slowly or closely enough would still get swallowed, but most of the galaxy should stay intact.
Of course, that's iff nothing else intereferes. The Andromeda Galaxy is heading our way, so in some (distant) future time matter in it will become a significant gravitational influence on matter in our own Milky Way. That should upset the balance, and researchers are hypothesising the disruption setting off feeding of the black holes at the centre of both galaxies, which will go on to swallow up large portions of each galaxy.
Should be quite a show.
Or approximately infinite.
Density is defined as d = m/v (m is mass, v is volume.)
The volume of a singularity (the object at the center of a black hole) is effectively zero, so the density of the singularity is undefined (though commonly said to be infinite).
When the diameter of a black hole is referred to, they are most often talking about the Event Horizon, the boundary around the singularity from which nothing can escape, not even light.
Note that the distance of the event horizon from the singularity is determined by the mass of the black hole, not the density or volume (since density and volume for ALL singularities are effectively equal). Gravity is still dependent on mass, and the event horizon is simply the region of space where the escape velocity from the singularity's gravitational pull exceeds the speed of light.
(on a side note, since the only real requirement for a black hole is to have zero volume, anything could become a black hole if compressed enough.)
~Moller
I've noticed that some people have a bit of confusion here about exactly what the effects of a black hole are. Here's are examples:
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.
If tits were wings it'd be flying around.