Evidence For Rotating Black Holes

Ambush_Bug writes: "Tod Strohmayer of NASA's Goddard Spaceflight Center has announced the first real observational evidence for a rotating black hole. The Washington Post covers the article here. There's a really awesome real video artists rendition of a black hole accreting mass from a nearby blue giant star... check it out!" And how many science writers get to use the words "a specimen about 10,000 light-years from Earth appears to be whipping matter around itself at 27,000 revolutions per minute, flashing X-rays in unsteady spasms and twisting the fabric of space-time"?

Geeez...Stop wasting the Physics Majors...

[big_groo]

"We don't know what's beyond that [event] horizon," Trimble said. "Every grad student we've sent in to study this has never come back."

Might I suggest using the Liberal Arts students? There seems to be an abundance of them. ;P

g

Singularity w/ spin -> macroscopic effect?

[HorsePunchKid]

This is really fascinating. The original start that formed the black hole was spinning. It had an easily observable property of rotation. Then it collapsed into a singularity which inherited that angular momentum. But once it's a singularity, the angular momentum (if I understand correctly) is only expressible as a quantum state of spin, which (from my one semester of quantum physics) doesn't really have any macroscopic meaning. (How can a point be rotating?) That's curious enough in itself to me. It's even more fascinating that now we've observed that indeed that spin does then cause a macroscopic effect, such that the matter falling into it tends to spin around it faster. The Rossi instrument also observed frame dragging [nasa.gov] a few years ago.

I dunno... Sounds kinda racy to me...

[Bonker]

Hmmm....

Breathily, the blue giant star leaned over the black hole, his eyes locked upon her event horizon. She stared lovingly into his corona as he began to caress her singularity with strong, hot tendrils of superheated gas and waves of intense gravity. With a grin of pleasure, he reached back and whipped her with his accreting mass.

"Please," the black hole whispered, letting the supergiant know she was ready for his super-dense mass and fusion-powered passion.

They began slowly, but quickly worked up to almost 27,000 revolutions per minute. After just a short while, she began to flash her x-rays in unsteady spasms of delight and joy. She twisted the fabric of space-time beneath her in ecstacy...

Suddenly, she realized that the blue supergiant had gone.

"Hello?" she cried out. "Where did you go? Damn it! I lose more stars that way..."

Gravity and time

[Dancin_Santa]

Wouldn't the intense gravity of the black hole cause a change in the progression of time within the black hole? Could it be possible that the black hole is actually spinning at a much different rate than we are able to observe considering that our rate of time may be different?

Dancin Santa

Re:Gravity and time

[bph]

Wouldn't the intense gravity of the black hole cause a change in the progression of time within the black hole? Could it be possible that the black hole is actually spinning at a much different rate than we are able to observe considering that our rate of time may be different?

The short answer is, yes and yes. Time will be different near the event horizon than where we are, and that the apparent rotation rate measured at the event horizon will be very different than the one we measure. This is why whenever you make a theoretical prediction, you always compute what you will observe infinitely far away.

Re:Gravity and time

[Dancin_Santa]

This is why whenever you make a theoretical prediction, you always compute what you will observe infinitely far away.

Could you explain this? I'm having trouble following it.

Dancin Santa

Geez, if you had taken it in for service earlier..

[xixax]

"Now you know you should rotate your black holes every 5 billion years. I'm afraid it's all out of balance now and I'll have to do an entropy balance to get your event horizons right again..."

Xix.

Not the 1st spinning black hole

[Caid Raspa]

I suppose GRO1655-40 is the 1st rotating black hole detected by Americans. Science is made also outside USA, and sometimes USA is not the first.

XTE J1748-288 is another system with a rotating black hole. Also GRS1915+105 and SS433 could be, but I am not sure of this. (All the four sources are microquasars, and rotating black holes should be in all of them) These sources are all in our galaxy.

I am not that interested in extragalactic stuff, but I think there are also several active galaxies with known spinning central black holes.

A good resource for checking 'First ever' astronomy discoveries: ADS abstract service [harvard.edu]

Re:Singularity w/ spin -> macroscopic effect?

[Caid Raspa]

Who the * modded this 'overrated'?
'Interesting' would be better.

DISCLAIMER: I am not an expert, but I have studied some astrophysics.

The event horizon of a black hole is the surface with an escape velocity equal to the light speed. We see this as the 'surface' of the black hole. Rotating black holes have a distorted, non-spherical event horizon that produces the observed effects (This is called Kerr metrics). The dimensions of the event horizon are a few kilometers, so I can not see how quantum mechanics would be relevant at these distances.

The singularity itself is hidden by the event horizon, so we can not see quantum gravitation effects.

Re:Singularity w/ spin -> macroscopic effect?

[HorsePunchKid]

There are still some interesting (if not necessarily productive) thought experiments that you can do though. For example, imagine moving into the black hole. If you found a large enough black hole (and certainly they're out there... ones equivalent to billions of solar masses), the tidal forces at the event horizon would be small enough that you could pass it without harm. (In other words, since the radius of the event horizon (in the Schwarzschild metric sense) is so large, the gravitational force is essentially constant, like on the surface of the earth.) Of course you still couldn't see anything coming from a gravitational potential lower than yours. So what would that be like? Then there are other metrics that turn the event horizon into something you can only asymptotically approach, but the singularity itself is flattened out (don't remember the name of the metric). Passing through the singularity, the space coordinates become imaginary, and time becomes real (!), but there's no discontinuity at the origin (where the singularity is in the Schwarzschild metric). The sci.physics black hole FAQ [harvard.edu] has some more interesting info.

Re:Geeez...Stop wasting the Physics Majors...

[pubudu]

You have to read the next line, too:

We think they may have gone to industry.

Really now, do you want to send all the Liberal Arts folk into industry? English majors designing your seatbelts? Classicists deciding whether to use rebar or not?

I think we all feel a lot safer with us Liberal Arts folks locked up in our ivory tower, where we belong.

Re:Geez, if you had taken it in for service earlie

[Dancin_Santa]

How much is that going to cost?

Dancin Santa

Re:Geez, if you had taken it in for service earlie

[Anonymous Coward]

How much ya got?

Re:Not the 1st spinning black hole

[stixman]

(sarcasm)Yes, but I'm sure you'll agree that it's much more meaningful when the Americans finally accomplish the same thing.(/sarcasm)