NASA telescope sees black hole gulping remote star

[Kain]

Sorry more probably random stuff from me

http://news.yahoo.com/s/nm/20061206/sc_nm/blackhole_dc

Kain

[richard42]

that is cool! and i thought i had an appetite

[The Warthog]

That's probably a young black hole, a teenager.

That artist's concept probably got it wrong, too. I don't think a black hole looks like a bowling ball in space.

[lunator]

I guess a bowling ball is a fair analogy.

The event horizon would be spherical but it would be very small.

AM maybe you can confirm the size of black-holes.

If I remember rightly the A* BH in the milky way is not much bigger than the Solar System. Although the accretion disk is much larger.

Cheers

Ian

[Kaptain Klevtsov]

Are we not part of the accretion disk? I suspect that as the orbits decay, everything in the milky way will get eaten eventually.

Captain Chaos

[The Warthog]

Why should the orbits decay? I suspect that when we finally collide with the Andromeda Galaxy, a lot of stars will get flung into intergalactic space, anyway. I'd like to be on one of those. Imagine a sky with nothing but DSOs!

I was thinking that the 'black hole' should be BRIGHT, according to Hawking, because of strange shenanigans going on at the event horizon, where some particles get sucked into the singularity, and some get flung out at high energy levels.

[lunator]

WH

You are talking about 'hawking radiation'

Where pairs of short-lived (nano-second) particles are created and one gets sucked into BH and the other escapes and in so doing the BH will slowly decay. I reckon this could take sometime to happen

[Astroman]

Ok, there's a lot of questions here, so hang on.

WARNING: Impending math ahead.

That's probably a young black hole, a teenager.

That artist's concept probably got it wrong, too. I don't think a black hole looks like a bowling ball in space.

Not sure about the age of the BH, or to which one you refer, WH. The BH in the galaxy is probably billions of years old, but the one in the drawing my be young? Regardless, you're right-the artist got it wrong. A BH is infinitessimally small by definition. Its "size" is determined by its influence, or "event horizon" as everyone knows. Here's the math. GM/c², where G is the gravitational constant, M is the mass of the BH and c is the speed of light. So, if the event horizon is said to be 5 km, it is measured from the center of the BH. But, since the BH is infinitely small, it may as well be the surface, too. Anyway, if you took the Sun down to a BH, with a mass of 2x10³⁰ kg, its event horizon would be ~3km. The event horizon of some say, 20 million solar masses would be proportionately larger, while the BH itself would remain infinitesimal. The best thing the artist got right is the visual distortion around the BH. Short answer, (I know, too late AM), you wouldn't see the BH at all, but you would see the event horizon, and it would be bright, especially after consuming a star.

I guess a bowling ball is a fair analogy.

The event horizon would be spherical but it would be very small.

AM maybe you can confirm the size of black-holes.

If I remember rightly the A* BH in the milky way is not much bigger than the Solar System. Although the accretion disk is much larger.

Cheers

Ian

According to the above Ian, the event horizon is about the size of the solar system. If you'd care to calculate it, the gravitational constant is ~6.7 x10^-11m³kg²s². Messy, very, very messy. Plus, it should read "SGR A* BH" but that's splitting hairs.

Are we not part of the accretion disk? I suspect that as the orbits decay, everything in the milky way will get eaten eventually.

Captain Chaos

Why should the orbits decay? I suspect that when we finally collide with the Andromeda Galaxy, a lot of stars will get flung into intergalactic space, anyway. I'd like to be on one of those. Imagine a sky with nothing but DSOs!

I was thinking that the 'black hole' should be BRIGHT, according to Hawking, because of strange shenanigans going on at the event horizon, where some particles get sucked into the singularity, and some get flung out at high energy levels.

CC: We're more part of the formation disk for the galaxy and while we're under the influence of the mass of the galaxy as a whole, the central BH's influence is very very tiny, due to its immense distance. From the inverse square law, if the distance between two objects increases by a factor of twn, the gravitational influence decreases by a factor of 100. Twenty-two thousand light years is a long way for the BH to reach. You're somewhat right, though, in that the stars and matter closer in will be consumed eventually, and WH is right about "the rest of us" being flung off into space when we collide with Andromeda.

WH

You are talking about 'hawking radiation'

Where pairs of short-lived (nano-second) particles are created and one gets sucked into BH and the other escapes and in so doing the BH will slowly decay. I reckon this could take sometime to happen

When matter falls into a BH it gives a last dying gasp of x-rays and in this case, UV rays. Its final trajectory is crucial. Hawking describes matter interactions at the event horizon as material falls within the influence of the BH. So, Ian is mostly right on this one. I saw an article in Science last year describing the process. I didn't understand most of it, but the jist was it'll take 120 to 300 billion years for all the black holes to dissipate inthis manner. Well before then, the universe will be a very cold, dark place.

HTH. I'm gonna take some aspirin now....