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Black Hole Observed by X-Ray Satellite
eldavojohn writes "Scientists at JAXA and NASA used the Japanese Suzaku satellite to collect data and observations at a distance nearer to a black hole than we've ever been. From the article: 'The observations include clocking the speed of a black hole's spin rate and measuring the angle at which matter pours into the void, as well as evidence for a wall of X-ray light pulled back and flattened by gravity. The findings rely on a special feature in the light emitted close to the black hole, called the "broad iron K line," once doubted by some scientists because of poor resolution in earlier observations, now unambiguously revealed as a true measure of a black hole's crushing gravitational force.' Suzaku also has been providing images and data of super novas and their activities. It's always nice to see national space agencies working together, it almost gives me hope that the world might one day be united in space exploration."
"Nothing for you to see here. Move along."
The grass is always greener on the other side of the light cone.
An Indian-American Hindu committed to non-violent thought/speech/action alarmed by the global explosion of radical Islam
Good question. Short answer: we don't know.
Long answer: According to the General Theory of Relativity, black holes have all their mass contained in a geometric point called the "singularity". This singularity is surrounded by a finite-sized spherical boundary called the "event horizon" which is defined as the locus of points where not even light can escape the gravity of the singularity. Because nothing (that we know of) can travel fast than light, the event horizon is a seemingly impenetrable barrier to any investigation of the singularity itself.
So we're unlikely to view a singularity directly and measure its size. On the other hand, most physicists are convinced that the General Relativistic description of the singularity as a literal geometric point most be wrong. They believe this because very small objects are governed by quantum mechanics, and a new theory (which does not exist yet) called "Quantum Gravity" must take over at densities like those found in singularities.
I'm generally a fairly skeptical chap, and it took a long time to even convince me that event horizons exist. For the longest time, all "proofs" of black holes basically said "here is something that is more dense than a neutron star, and since the ONLY THING more dense than a neutron star is a black hole, this object must be a black hole." I was never really convinced that there weren't other objects denser than neutron stars that didn't actually have event horizons, so this argument never swayed me. These recent observations seem to conclusively prove that event horizons exist, but singularities are an entirely different matter. We'll have to wait for the final word on that subject...
PhysicsPhil has a pretty good explanation. Here's another way of phrasing it.
Electrons, neutrons, and so on don't really exist as volumes, but rather as forces. Think about a balloon filled with air; it takes up space, but the only reason it does is because of the pressure of the air inside pushes out on the surface.
Now, if you squeeze the balloon, it'll shrink. The more you squeeze, the smaller it gets. If you could squeeze as hard as you please, you can continue to shrink the balloon smaller and smaller.
Particles are like that. Gravity is unique in that it's a force that can get infinitely strong, so it can overcome any other force, and squeeze everything together down to an arbitrarily small point.
Interestingly, from the perspective of a star collapsing into a black hole, it never actually quite makes it, as time slows down as gravity becomes stronger. It's like Zeno's paradox: If you try to go from point A to point B, crossing half the distance each time, do you ever get there? Intuitively, you'd think no, but if you take an infinite number of steps, yes.
In other words, black holes, from the perspective of the black hole, take forever to collapse down to a singularity. However, from our perspective outside the black hole, the singularity forms essentially instanteously, as our subjective time speeds up relative to the black hole's subjective time.
(As a side note, we don't have a theory of quantum gravity, so we don't actually know what the absolute center of a black hole is like, but we do understand the physics up to and past the event horizon, all the way to the singularity, all of which is just subject to general relativity. All the effects with astronomical significance occur outside the event horizon, as information that goes past there is effectively meaningless.)
Because Hawking radiation scales inversely to the area of the event horizon, the Hawking radiation from anything but extremely small black holes (which we don't even know actually exist) is negligible and far below what we have the ability to detect. It is literally less than the background radiation of space.
For practical purposes, the grandparent is correct, if a little simplified.
You may find it interesting though, that if small black holes actually do exist (they would have to be incidental products of the Big Bang), we may be able to detect their last moments of evaporation by Hawking radiation as x-ray/gamma ray bursts. Some researchers are plan to look use data from one of NASA's upcoming x-ray observatories to look for such flashes that can not be attributed to other known sources.
it almost gives me hope that the world might one day be united in space exploration
I guess you missed yesterday's story documenting the US' clear intention to be the single entity with control over access to space; 'The policy calls upon the Secretary of Defense to "develop capabilities, plans, and options to ensure freedom of action in space, and, if directed, deny such freedom of action to adversaries."'
Interestingly, from the perspective of a star collapsing into a black hole, it never actually quite makes it, as time slows down as gravity becomes stronger.
No. Time flows normally from the perspective of the star. It's for the outside observer that time appears to slow down (it never really would appear to *stop* it would just approach infinitely slow.)
But for a hypothetical observer on the star, time would appear to proceed normally. Also, if I'm remembering right, for the star observer the *rest of the universe* would appear to slow down, as well, if there was some way to observe it. (I know that applies to high-percent of c velocities but can't remember if it applies to gravitational effects as well)
*snark*