Slowly Pulling Facts from Black Holes

lee1 writes "Astronomers have proven the existence of the event horizon, the 'point of no return' that surrounds black holes. An MIT and Harvard team said they showed its existence by looking for X-ray bursts from neutron stars and more compact objects thought to be black holes." Relatedly beuges writes "IOL is reporting that by tracking the death spiral of cosmic gas at the center of a galaxy called NGC1097, scientists figured that material moving at 177 000km an hour would still take eons to cross into a black hole. 'It would take 200 000 years for gas to travel the last leg of its one-way journey,' Kambiz Fathi of Rochester Institute of Technology told reporters at a meeting of the American Astronomical Society."

Comments

Re:orbit at greater than c

[Harmonious Botch]

You can't orbit a black hole inside the event horizon without going faster than the speed of light.

Facts

[Anonymous Coward]

A few interesting facts about black holes that some people aren't aware of:

• Black holes emit x-ray radiation and get smaller and smaller until they disappear, or "evaporate".

• Most black holes are formed from the death of large stars (larger than the sun) that run out of fuel and cannot sustain its nuclear reaction. The star loses the force pushing itself outward and is overcome by the force of its own gravity pulling inward. Eventually, the star has so much gravity and is so compacted that it "eats itself" until there is nothing left but a hole in the "fabric" of space-time, created by the gravity left over from the star.

• The gravity around the "hole" of a black hole is so strong that NOTHING can make its way back out after a critical distance.

• Even before crossing the event horizon, though possible to travel away from the black hole, it is not easy. Even light has a hard time getting out, so light being emitted from something almost at the Event Horizon but not yet inside the threshold takes a much longer time to escape and be seen by someone then it would in normal space going at 186,000 miles per second.

• The Singularity is the true point of destruction, the actual hole part of the black hole, although any object, especially a person, would be long dead before they reached the Singularity.

• Some black holes are spinning and have several event horizons called the "Ergosphere", "Outer Event Horizon", and "Inner Event Horizon".

Stephen Hawking's recent concession that black holes do not irretrievably eradicate information after all has garnered much attention. In my opinion, it is refreshing to see the public focused, if just for a moment, on an important conundrum that has fascinated theoretical physicists for three decades, and prompted much conceptual progress. The scientific issues, however, remain much less settled than Dr. Hawking's celebrated wager on the question. He most recently pronounced: "If you jump into a black hole, your mass energy will be returned to our universe, but in a mangled form, which contains information about what you were like but in an unrecognizable state." These ideas are profound and will have a lasting effect on our scientific theories as well as life as we know it.

Re:Facts

[Anonymous Coward]

> Black holes emit x-ray radiation and get smaller and smaller until they disappear, or "evaporate".

Not really. The black hole itself emits black body radiation and the temperature of a reasonably large hole will be very low, so it's emitting radio waves. As it gets smaller, the temperature goes up, so the emissions will pass through visible light, x-ray and so on. However most large black holes have gas streaming into them from their surroundings, which gets really hot while spiralling into the black hole and this is the part that usually emits x-rays.

> Most black holes are formed from the death of large stars.

Unknown. Unproven.

Re:Facts

[strider44]

I think you and the grandparent are getting a bit confused here on this issue (though it has been a few years since I studied Cosmology, and I may be wrong here, but I *do* try to keep abreast of the journals and recent discoveries when I have time).

A black hole itself has no temperature and emits no light. It literally can't. Hawking radiation comes from particles from before the event horizon. The actual amount of radiation is insignificant for astronomical black holes since they absorb more radiation from just the cosmic background microwave radiation than is let go through Hawking radiation. It's only really important for quantum black holes.

Stellar-mass black holes pretty much have been proven to come from the death of larger stars, more than about 3-4 stellar masses. Whether it's proven depends on how strict you are with the word "proof". Supermassive black holes *probably* started as stellar black holes, a long long time ago, maybe not. I'm not sure if anyone knows or has given proof, but if they have then I haven't heard about it. I'd like to though!

Re:Facts

[Wolfbone]

It doesn't actually matter what direction the light is emitted in - the "slowdown" of light occurs along radial paths too. It is, as you say, due to the badly bent spacetime that this effect is observed, but it's because of the metric structure of the spacetime itself, not the path of the light. In a "normal" (t,r,theta,phi) coordinate system - appropriate to a far away observer - where the Schwarzschild metric describes the spacetime structure surrounding a massive body at the origin, the radial coordinate speed of light (dr/dt) turns out to be (c - 2GM/rc). You get a better picture of what is happening near black holes with more suitable coordinate systems but at least here you can see that if we describe spacetime with a set of coordinates appropriate to "normal", speed of light = c conditions, "the speed of light" really is affected by the massive body.

Re:Facts

[Wolfbone]

"A black hole itself has no temperature"

Actually it is considered to have a temperature, though it's not the same thing as the temperature of ordinary matter. The analogy of black holes as thermodynamic systems (which I think arose from the study of rotating black holes and Penrose processes) is what motivated Bekenstein historically to suggest that a black hole /should/ emit black body radiation. Hawking set out to prove him wrong and - ironically - discovered that they do indeed.

Re:minor error

[DarkKnightRadick]

Light moves, generally, at c.

The problem is though, that light can be slowed down. According to several sources, light can be slowed down, although they all seem to agree that a photon travels at the speed of light no matter what, just the absorption/release/re-absorption process can slow down how quickly it crosses a given distance.

Re:What would happen..

[Gleng]

Or would they actually be destroyed by some force inside the hole itself?

Have a read about Spaghettification.

Scanning Tunneling Microscope

[Shashvat]

You can now take pictures of atoms with a scanning tunneling microscope.

Researchers at IBM even move individual atoms around to create artwork.

More here: http://www.almaden.ibm.com/vis/stm/corral.html

Re:orbit?

[Phanatic1a]

Relativity.

The closest stable orbit around a black hole is at a distance three times the Schwarzchild radius. Closer orbits exist, but they're unstable, the slightest perturbation in them will result in either an escape to infinity or an intersection with the event horizon. At 1.5 Schwarzchild radii, you have the photon sphere; at this distance, orbital velocity equals c, and it's unstable so nothing stays there. Anything closer than 1.5 radii, there are no orbits possible.