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Hefty black hole weighs in at 33 Suns
Researchers have confirmed that a black hole lurking in the dwarf galaxy IC 10, and dubbed IC 10 X-1, weighs in at up to 33 Suns, double the previous record for a "single star" black hole held by M33 X-7 which tips the scales at 16 Suns. IC 10 X-1, lying 1.8 million light years from Earth, was first spotted back in 2007 by the …
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Friday 22nd February 2008 15:32 GMT Pete Mallam
Why do they call them "Black Holes"???
The sun is a big thing made up of stuff that is hot and gives out light. It's like a big fireball. When the stuff that burns runs out, the flame goes out and all the other stuff that's left is left.
The sun is high in gravity, a thing that pulls things to it. This is cos of the stuff thats in it that would either burn or is the ash left over when the thing is done burning.
If the sun isnt burning, it sits there not burning. Not giving heat out as it cools it pulls stuff towards it, being bigger and getting higher in that gravity thing. Thngs that would normally burn out if they got too close or are pushed away by the heat or the "vapour" of the flames on the sun are no longer affected this way. They hit the sun and make the sun bigger and more gravitied.
Cos the sun isnt on fire any more, the sun isnt bright.
Cos the sun isn't bright, it's difficult to see from the distance we are from it.
Cos we can't see it... We call it a hole?
Why?
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Friday 22nd February 2008 17:20 GMT Hans Mustermann
@Pete Mallam
You got it all wrong, sorry.
First of all, technically, when the sun cools down, it'll still give off a bit of light (gradually going towards infra-red as opposed to visible light) for hundreds of billions of years, because anything that size takes a freaking huge time to cool down. And because it's an asymptotic curve, it'll likely never reach truly zero Kelvin. So technically it'll never be "black".
Second, even if it cooled to zero K, it still wouldn't qualify as a black hole. The simplest explanation I can think of is: if you pointed a flashlight at it, you could still see it. You know, "oh, there's this big freakin' blob of frozen helium." It would still reflect and refract light.
Basically light can still get out of there. You shine some light in, it comes out in one direction or another. It's not a black hole then.
To qualify as a black hole, it has to have enough gravity that past a point even light can't get out any more. f you point a flashlight at it, well, ok, you'd have funky beam curving. But at an oversimplified level, any light that hits that spherical limit ("event horizon") can't come out any more, because of sheer gravity.
That's why it's called a "hole", basically. Because anything that falls in, stays in. It's not even theoretically possible to get out of there, no matter with what engines.
And "black", because, well, it's the ultimate black. It actually absorbs all light that crosses that event horizon. Not a bit grey, not a bit shiny around the edges in the right light, etc. It's the ultimate black. So black, it would look like a 2D hole. Exactly 100% of the light hitting it, isn't coming back out again.
So how do we detect them? Via the stuff that hasn't crossed the event horizon yet. Your typical black hole has a bunch of matter spiralling into it, much like water spirals down the drain in your sink. And being accelerated to insane velocities, so it starts emitting X rays.
So although the hole itself is perfectly black, it will have a "halo" of matter around it, that emits X-Ray.
Third, our Sun doesn't have enough mass to form a black hole.
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Friday 22nd February 2008 17:20 GMT Shadowthrone
@ Pete Mallam
I think we still refer to them as black holes due to the perspective of the original observers. When first discovered it appeared to be literally a black hole in space into which everything was sucked. Early thoughts were that a black hole behaved a like a worm hole spitting out the matter it pulls in at an indeterminable location. Later science and discovery have obviously led to our current understanding of black holes but the naming has stayed the same.
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Friday 22nd February 2008 17:20 GMT Ian
@ Pete Mallam
A black hole isn't just a star that has run out of fuel.
If the star has little mass you end up with a brown dwarf, which is close to
what you describe.
If the star has enough mass that it's gravity is stronger than what keeps electrons
around the atoms, then you end up with a neutron star. This is a ball made
from atomic nuclei, all the electrons are stripped away.
If the gravity is stronger than the forces that repel nuclei, then the star collapses
into a blackhole, no normal matter is left at all. Everything is compressed into
a single point and the resulting gravity is strong enough to prevent even light
escaping. Hence 'black hole'.
<insert favorite search engine> it, there are quite a few good sites around about
it.
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Monday 3rd March 2008 16:24 GMT Peter Mellor
Re: Why do they call them "Black Holes"??? (By Pete Mallam)
Because it was once thought that they would be "black", i.e., give out no radiation at all.
In fact, when it was first realised that (theoretically, none having been observed) an object above a certain mass, without enough radiation pressure from within, must collapse into a singularity, such hypothetical objects were referred to as "frozen stars", for the following reasons:
- As the body shrank towards the "event horizon", defined by the Shwartzschild radius, time at the surface of the body would slow down (according to Einstein's theory of general relativity) until it stopped as the surface of the body reached the horizon. An observer on the surface of the body (and he or she would need to be pretty tough!) would observe the entire life of the universe pass before their eyes before they hit the horizon.
- The wavelength of any light emitted from the surface would become progressively longer until it reached infinity as the surface reached the event horizon. If our stout observer were sending out regular "beeps" on a signalling device, those receiving the signal from outside the horizon would see these signals getting progressively weaker, longer in wavelength, and at longer intervals. A signal sent from the event horizon would never reach them.
An intrepid traveller plunging into the event horizon of an already-formed frozen star would be hit by a blast of radiation consisting of all of the emissions from the star from the point at which it passed the horizon until infinity. The photons would be stuck on the surface at the event horizon and frozen in time like flies on fly-paper. (I'm guessing here: I've never seen this confirmed by a cosmologist.)
What happens inside the event horizon leaves my intuition rudderless. I have heard that "space becomes time and time becomes space". An observer must move inexorably (in space) to the singularity at the centre (just as time moves inexorably forward in the outside universe) but time is negotiable, and the observer could move around in it, just as we can move around in space.
Steven Hawking eventually realised that black holes are not really "black", since in a vacuum, particle/antiparticle pairs continually separate and rejoin to mutually annihilate each other, according to quantum uncertainty (Heisenberg). If the birth of the particle/antiparticle pair occurs close to the even horizon of a black hole, one of the pair might get sucked into the horizon and lose contact with the observable universe. Its partner would shoot off, and we would observe such particles as a steady glow of radiation (Hawking radiation) from the supposedly "black" surface. This would (from our external viewpoint) cause the black hole to gradually lose mass and shrink over "our" time.
However, time is an illusion: it all depends on how heavy you are and how fast you're moving. If you're a photon, time doesn't exist, as Einstein realised when he was just a kid.
Hope this helps.
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