## Scientists Discover Teeny Tiny Black Hole 277 277

AbsoluteXyro writes

*"According to a Space.com article, NASA scientists have discovered the smallest known black hole to date. The object is known as 'XTE J1650-500'. Weighing in at a scant 3.8 solar masses and measuring only 15 miles across, this finding sheds new light on the lower limit of black hole sizes and the critical threshold at which a star will become a black hole upon its death, rather than a neutron star. XTE J1650-500 beats out the previous record holder, GRO 1655-40, by about 2.5 solar masses."*
## Size vs Age (Score:5, Interesting)

## untrue statement (Score:5, Interesting)

## Re:We weren't the first (Score:3, Interesting)

## Re:15 miles across? (Score:3, Interesting)

## Re:The Earth in danger from microscopic black hole (Score:4, Interesting)

"If they were able to make a small blackhole, and it got "loose" and fell to the center of the Earth, the pressures at the Earths core would force material into it so fast that even a very small one would gobble us up very fast. I am not sure what the exact pressure is at the Earths core but it could force material through even a very small "hole" very quickly. I do agree that once it gobbled up the Earth, it would just continue to orbit the Sun, and the Moon would still orbit the blackhole as if it were the Earth..."

No, you should read this thread.

First of all, a black hole that falls to the center of the earth, wouldn't stop there, but would continue falling up on the other side, just to plunge in again, and on and on, because there's no "friction" on the black hole.

Second, there have been posted in this thread a lot of calculations of the speed at which it would gobble up matter.

Don't forget that the black hole we're talking about here IS MUCH MUCH SMALLER THAN A PROTON. As such, pressures on *atomic* level (such as in the center of the earth) matter little: the black hole travels most of the time in the empty space between nucleae.

A way to calculate the probability of hitting a nucleus (and somehow imagining that it would gobble up the entire nucleus, which is MUCH MUCH bigger than the black hole itself - which is a worst-case scenario) is done by calculating the "cross section" of the black hole and its probability to cross a nucleus on its voyages through the earth. We know its speed (just falling), and knowing the cross section and the density of nucleae, we can estimate how many nucleae it could eat per unit of time.

For a classical black hole, the calculation is done in the link provided by Pervect in this post:

http://www.physicsforums.com/showpos...4&postcount=12 [physicsforums.com]

for a MUCH LARGER black hole, about the size of a proton, weighting a billion tons (figure that! A black hole *the size of a proton* weights a billion tonnes ; we're talking here about black holes that weight 10 TeV or 10^(-24) kg - go figure how small it is !)

For more exotic calculations which are more severe, orion made some, and arrived at a time to eat the earth ~ 10^46 years.

All this in the following rather un-natural hypotheses:

- no Hawking radiation (which would make the black hole evaporate almost immediately)

- production of black hole EXACTLY IN THE CENTER OF GRAVITY of the collision (no remnant particles)

- very high production rate, producing billions of black holes per second.

I am not a physicist, but from what little physics I have had, and from reading threw the thread/flamewar, I dont think we have to worry about the LHC

## Re:Probably Something Stupid (Score:3, Interesting)

manywell-defined radii, depending on what you mean by the term (as you point out, this comes about because of the non-Euclidean nature of the geometry). The commonly quoted "Schwarzschild radius" r = 2GM/c^2 is obtained by taking the area of the horizon and figuring out which "r" you would have to plug into A = 4 pi r^2 [true for a flat space sphere] to get the right result. Taking the circumference and dividing by 2 pi would achieve the same result. However, it is quite possible to figure out the proper distance between the horizon and the singularity by measuring the distance an infalling observer would travel. This distance is finite.A problem can occur if you try and use constant time slices, using the "natural" time coordinate as defined by an observer far from the black hole. This gives silly results, but that is only because of badly behaved coordinates.

## Re:The Earth in danger from microscopic black hole (Score:3, Interesting)

## Re:Probably Something Stupid (Score:4, Interesting)

No, actually it doesn't. What is usually called the Schwartzschild "radius" is not actually a radius by the definition of the word, "distance to the center".

manywell-defined radii, depending on what you mean by the term (as you point out, this comes about because of the non-Euclidean nature of the geometry). The commonly quoted "Schwarzschild radius" r = 2GM/c^2 is obtained by taking the area of the horizon and figuring out which "r" you would have to plug into A = 4 pi r^2 [true for a flat space sphere] to get the right result.Exactly. You can calculate the area (which is well defined) and divide it by 4 pi, and you are free to call that the radius if you like. Or, equivalently, divide the circumference by two pi. But you can't measure the distance to the center.

Finite... and timelike. It would be a little like trying to define the radius of a circle if you're standing on the circumference, and the center is next Tuesday at noon.

Within the event horizon,

anychoice of coordinates is rather badly behaved, because there is no well-behaved stationary coordinate system.## Re:Probably Something Stupid (Score:3, Interesting)

it doesn't actually have a well-defined radius (since you can't measure across the middle!)Why do you need to measure *across* the middle to measure the radius?

Is there a (theoretical) problem with using some kind of high tech space calipers to measure the radius without going anywhere near the 'middle'?

I hope I'm not totally wrong about this... I'm working from an analog of special relativity, which I did study a little...

## Re:Probably Something Stupid (Score:3, Interesting)

## Re:Size vs Age (Score:2, Interesting)

So the CMBR at 2.7 Kelvin is about 165 million times warmer than this black hole.

Now as an academic aside, assuming the universe doesn't end in either a big rip or a big crunch, but rather a disappointing heat death, eventually the matter and energy in the universe would be so diffuse due to ordinary expansion that the temperature would drop below that 16.4 nano-Kelvin, and the hole would start losing mass. Over probably close to a googol years it would evaporate away. Because temperature is inversely related to mass, it would warm as it did so, and the evaporation would speed up.

Yet even as it reached the current mass of the earth, it would still be colder than liquid helium. However, the polynomially increasing temperature means the accelleration of the process becomes more rapidly apparent. The final 200 tons evaporate in a mere second, with all that matter converted into energy equivalent to the explosion of several million of our most powerful nuclear warheads.

It's more than a little mind boggling to imagine something smaller than an atom (but as heavy as a 747) exploding with the energy of millions of atomic bombs.

## Rotating black holes [Re:Probably Something S...] (Score:5, Interesting)

Well, maybe. Actually, rotating black holes radiate away angular momentum, and they also preferentially eat material that reduces their angular momentum, so it's an open question as to whether real black holes will be rotating. Probably, because the accretion disk is likely to be rotating, and it swallows up the accretion disk and gains the momentum from it, but I'm not sure you can necessarily say that

allnatural black holes will rotate.It was this tear that lead, if I recall, to the original conjectures of a white hole, and the Einstein-Rosen bridge.

Actually, the Einstein-Rosen bridge comes from the maximum analytical extension of the Flamm embedding, way predating the Kerr solution. (It's a very trivial embedding, z = sqrt(r). The extension is z = plus or minus sqrt(r).) Turns out that the extended Flamm embedding is misleading, and a Schwartzschild black hole isn't a wormhole after all. But that wasn't obvious.

## Re:Size vs Age (Score:2, Interesting)

The person riding on the object would see the Universe more and more blue-shifted, until, due to the extreme time dilation, the Universe ends before they ever fall in. So, without Hawking Radiation, the black hole will outlive the Universe, and nothing will ever fall in. Weird, huh?

With Hawking Radiation, it's harder to predict what will happen. Will the infalling matter see a vicious blast of Hawking Radiation before ever crossing the event horizon? How can anything fall into a black hole if the black hole dissolves, and the Universe ends before it can cross the event horizon?

## Re:That's nothing... (Score:3, Interesting)

## Re:Size vs Age (Score:3, Interesting)

## Re:Quantum Foam (Score:3, Interesting)

## Re:That's nothing... (Score:2, Interesting)