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

orbit?

[HermanAB]

Actually, I don't understand it at all. Why would the matter spiral in. Why won't it stay in orbit? What is slowing the matter down to make the orbit decay?

Re:orbit?

[Gaccm]

Hmmm - So friction in the revolving gas could will cause it to heat up and possibly glow, while slowing down its rotation, causing it to cross the event horizon and fall in?

Yes. The only way something can fall into a black hole is by losing energy to fall it. If it doesn't lose any energy it will keep revolving around the black hole. Same thing with Earth, if Earth was in the middle of a cloud of gas that could eat away at very large amounts of the Earth's momentum, then the Earth could spiral into the Sun. Since that gas isn't there our Earth keeps revolving around the Sun, which is good for us.

Big distance but useless figures

[Red Flayer]

310316400000000 km is the last leg of the journey?

FYI, that's 2,074,335.22 Astronomical Units, or 32.8 Lightyears, or about the distance from Sol to the Cepheids. Dang.

Too bad they don't specify how far out (radially) from the event horizon the last leg starts. Or even loosely define what 'last leg' means in this case.

Re:Facts

[Shimmer]

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.

Not true. The speed of light is a constant, even near a black hole.

As I understand it, what actually happens to the light emitted by an object approaching an event horizon is that it gets increasingly red-shifted. So an observer at a safe distance would see the object "fade" into infrared and then into ever-longer radio waves until it crosses the horizon.

Re:Facts

[Black Parrot]

> The Singularity is the true point of destruction, the actual hole part of the black hole

No, the event horizon is the methaphorical "hole in space".

Lots of physicists doubt that singularities even exist. Singularity essentially means "the math broke", a result of applying GR at scales where QM effects almost certainly dominate. If we ever get a theory that unifies GR and QM, we might discern what actually happens at the center of a black hole.

Reuters was only off by 99.99%

[xmark]

"The one-way journey from the heart of a galaxy into the oblivion of a black hole probably takes about 200,000 years..."

"...scientists figured that material moving at 177 000km an hour would still take eons to cross into a black hole."

Eons are the largest division of geologic time. There have been just four of them since the formation of the Earth. In rough terms, that's a billion years each.

Maybe the reporter can get a job working on unit conversion for the next Mars probe. (*cough*)

Re:Reuters was only off by 99.99%

[Phanatic1a]

From our frame of reference, matter moving at 177,000km an hour would still take eons to cross into a black hole. In fact, we'd never observe it doing so, by the time it crosses the event horizon any radiation from it will be redshifted to infinity.

From the frame of reference of that matter, entry into the black hole will take but an instant.

This is relativity. Always specify your FOR.

What they don't mention

[merlin_jim]

Is the scientific reason that gas can take 200,000 years to be pulled in by the most gravitationally massive type of object possible in the universe.

It is for two reasons; first off, gravitational time dilation - time gets slower the closer you get. The gas is orbitting the black hole, which also adds relativistic time dilation.

The gas, in fact, probably orbits at just under escape velocity - thanks to a fun little effect called (IANAA) relativistic frame dragging - basically the black hole drags the fabric of spacetime around itself - and objects within about 1.5 radii of the event horizon start feeling the effect - effectively locking them into a particular path. One way to look at this is to say that time is swallowed by the black hole same as mass - and therefore objects in the vicinity of the black hole fall in because their time arrow points to its dark, dark heart.

This frame dragging should happen at speeds approaching the speed of light - and require comparable amounts of energy to change your frame. There's even some theory that infalling matter will follow gravitational field lines, like you get around a magnet - but I'm not sure how much I believe that...