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..."

Comments

Not necessarily spiralling into it

[1984]

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.

density of a black hole is infinite.

[moller]

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

Re:density of a black hole is infinite.

[Dyolf Knip]

the only real requirement for a black hole is to have zero volume, anything could become a black hole if compressed enough

Indeed. Problem is, the smaller a black hole, the faster it evaporates due to Hawking radiation*. So while you could theoretically turn my cat into a black hole, neither he nor it will last very long (provided you do it somewhere far away from some mass is can eat up). And you'd owe me a new cat.

* Hawking radiation: he hypothesized that all the time all over the universe, pairs of virtual particles pop up. They are anti-particles to each other, so they annihilate each other as soon as they appear and nobody is the wiser. But, should a pair appear right on the event horizon, one particle gets sucked in and the other goes free and to balance the energy books, the black hole loses a very, very small amount of energy. Needless to say, it takes a while. This big monster of a hole will probably evaporate around 10^100 A.D.