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"."

Don't confuse the x-ray radiation (emitted outside of a black hole) with Hawking radiation, which is the true cause for black hole evaporation.

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:Facts

[tgrigsby]

To clarify:

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

The time taken to do this for any appreciably large black hole is on the order of trillions of years. Theoretically speaking, of course. Black hole evaporation only really makes sense in high energy particle collisions.

* 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 "hole" is a mathematical construct. There is no actual hole, just a point beyond which information cannot escape, including information contained in light.

Re:orbit at greater than c

[Anonymous Coward]

In fact, circular motion around a black hole would require v>c if the radius of the orbit is less than 1.5 R, where R is the black hole radius, and such motion is unstable at distances below 3.0 R.

And, of course, don't forget that an object travelling around the black hole emits gravitation waves and loses energy (but that applies to our Solar system too).

Re:Big distance but useless figures

[Hobbex]

You think so three dimensionally.

(Consider relativity...)

Wikipeding?

[bubulubugoth]

So, if there is a "googling" action, also is there a wikipedin action?
The Wikipedia entry about Event Horizon has an interesting "faq" about, orbitig the event horizon and sticking you hand into the event...
Also the wikipedia companion, talks about Stephen Hawking saying that no "event horizon" can be formed at a black hole... This article needs edition... :)
Good reading before a good sleep...
Btw, there is a neat animation about a neutron star X-ray burst


enough of karma whoring...

Re:It was never in orbit

[MillionthMonkey]

What makes you think it is in orbit in the first place? It's just basic gravity. Things fall down.

You're drawing a distinction where there is none. That's what an orbit is.

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.

Re:orbit?

[Cyberax]

Because of some obscure effects of general relativity, and not because of gravity waves as some people think. I can write you differential equations of, but I'm not going to write them here in ASCII art.

These effects are extremely weak in our Solar System, but they can be observed in perihellion precession of planets ( http://en.wikipedia.org/wiki/Precession#Precession _of_planetary_orbits ). Right now Gravity Probe B ( http://einstein.stanford.edu/ ) is in the final stage of experiment which aims to check the gravitomagnetic effect which is another manifestation of GR (and is partially responsible for decay of black hole orbits).

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?

[DiamondGeezer]

Because there's a critical distance away from the black hole below which matter cannot orbit because the orbital speed would be greater than the speed of light. So anything orbiting that reaches the critical orbital radius (which depends on the black hole's mass) will be sucked in.

In that sense, it shows how differently General Relativity is compared to Newtonian Mechanics.

See this site for a visual demonstration and an explanation.

By the way, I've no idea where "the 200,000 years to hit the event horizon" comes from. According to GR, from our frame of reference it would take an infinite amount of time to hit the event horizon.

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.

Re:Big distance but useless figures

[Phanatic1a]

They're referring to the effects of relativity as an infalling object approaches the event horizon. The object is accelerating towards c, so as it approaches the event horizon (from our external frame of reference), its clock is moving slower and slower, and it takes longer to travel a given distance.

More to an orbit

[snowwrestler]

An orbit is not just things falling down, it also requires a tangential velocity within a specific range. Gas spiraling into a black hole does have a tangential velocity, but it's not within the range create a orbit. In other words, yes, it was never in orbit.

Re:What I found intersting

[twifosp]

Even if we could travel at say, .75c, anything "near" a black hole any living thing would be hosed. The g forces of orbit insertion would likely tear our fragile bodies and crafts apart. Additionally the Xrays, gamma particles, and other nasty radiation would cook and fry everything.

Achieving neccesary velocity to not fall into a black hole would be easiest part. Even if we got into some kind of orbit, at near C speeds, you'd never leave. You'd need even closer to C speeds, and if you were near the event horizon, you'd need to actually achieve C to escape, should you ever want to extend your orbit beyond the black holes sphere of influence. IE come home. Which would require infinite energy.

SO in short, I suggest we just stay the hell away from black holes :D