Spinning black hole pushes the speed limit

HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS NEWS RELEASE via Spaceflight Now ^ | November 20, 2006 | HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS

[Excuse_My_Bellicosity]

The existence of black holes is perhaps the most fascinating prediction of Einstein's Theory of General Relativity. When any mass, such as a star, becomes more compact than a certain limit, its own gravity becomes so strong that the object collapses to a singular point, a black hole. In the popular mind, this immense gravity well is a place where strange things happen. And now, a Center for Astrophysics-led team has measured a black hole spinning so rapidly - turning more than 950 times per second - that it pushes the predicted speed limit for rotation.

"I would say that this regime of gravity is as far from direct experience and knowing as the subatomic world itself," says CfA astronomer Jeffrey McClintock.

Applying a technique to measure spin developed jointly by McClintock and CfA astrophysicist Ramesh Narayan, the team used NASA's Rossi X-ray Timing Explorer satellite data to provide the most direct determination yet of black hole spin.

McClintock and Narayan led an international group consisting of Rebecca Shafee, Harvard University Physics Department; Ronald Remillard, Kavli Center for Astrophysics and Space Research, MIT; Shane Davis, University of California, Santa Barbara, and Li-Xin Li, Max-Planck Institute for Astrophysics, Germany, in this research. The results are published in today's issue of the Astrophysical Journal.

"We now have accurate values for the spin rates of three black holes," says McClintock. "The most exciting is our result for the microquasar GRS1915+105, which has a spin that is between 82% and 100% of the theoretical maximum value."

"This result has major implications for explaining how black holes emit jets, for modeling possible sources of gamma-ray bursts, and for the detection of gravitational waves," says theorist Narayan.

Why do astronomers care about spin?

"In astronomy, a black hole is completely described by just two numbers that specify its mass and how rapidly it is rotating," says McClintock. "We know of nothing else this simple except for a fundamental particle like an electron or a quark."

Although astronomers have been successful at measuring black hole mass, they have found it much more difficult to measure the second fundamental parameter of a black hole, its spin.

"Indeed, until this year, there was no credible estimate of spin for any black hole," says Narayan.

A black hole's gravity is so strong that, as the black hole spins, it drags the surrounding space along. The edge of this spinning hole is called the event horizon. Any material crossing the event horizon is pulled into the black hole.

"The black hole spin frequency we measured is the rate at which space-time is spinning, or is being dragged, right at the black hole's event horizon," says Narayan.

The high-speed black hole, GRS 1915, is the most massive of the 20 X-ray binary black holes for which masses are presently known, weighing about 14 times as much as the Sun. It is well known for unique properties such as ejecting jets of matter at nearly the speed of light and rapid variations in its X-ray emission.

Over the last few decades, dozens of black holes have been discovered in X-ray binary systems. An X-ray binary is a system in which two objects orbit around each other, with gas from one - a normal star like the Sun - being transferred steadily to the other - in this case, a black hole. The gas spirals onto the black hole by a process called accretion. As it spirals in, it heats up to millions of degrees and radiates X-rays. The team used the X-ray spectrum of the black hole's accretion disk to determine its spin.

The technique is based on a key prediction of relativity theory: gas that accretes onto a black hole radiates only down to a certain radius that lies outside the black hole - outside its event horizon. Inside this radius, the gas falls into the hole too quickly to produce much radiation. The critical radius depends on the black hole spin, so measuring this radius provides a direct estimate of the spin. The smaller the radius is, the hotter the X-rays which are emitted from the disk. The temperature of the X-rays, coupled with the X-ray brightness, gives the radius which, in turn, gives the black hole's spin rate.

"It is really cool to be able to measure something this fundamental," says Rebecca Shafee, who is a graduate student in the Physics Department at Harvard University. "Our method is very simple in concept and easy to understand. We are really lucky to have powerful X-ray observatories such as the Rossi X-ray Timing Explorer in space and telescopes on Earth to carry out the measurements we need."

The search for the cause of gamma-ray bursts, which can be, for a moment, the brightest flash in the universe, may be helped by the team's results. Theoretical astrophysicist Stan Woosley of the University of California, Santa Cruz, has modeled gamma-ray bursts based on the collapse of a massive star. These models, however, depend on the existence of black holes with very high spin, which until now had never been confirmed.

"This is extremely important," Woosley says. "I had no idea such measurements could be made."

The paper concludes that GRS 1915 and two other black holes studied by the team were born with their high spins. That is, the collapsing core of the original massive star poured its angular momentum down into the black hole.

"Ever since the community figured out many years ago how to measure black hole mass, measuring spin has been the holy grail in this field," says McClintock. "The technique we used on GRS 1915 can be applied to a number of other black hole X-ray binaries. We cannot wait to see what we find!"

"One of our fond hopes is that the black hole systems that we are studying will also be studied by other groups using their favorite methods of measuring spin," says Narayan. "Once these other methods are developed further and become more reliable, cross-comparison of results from the different methods would be most interesting."

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

[Excuse_My_Bellicosity]

This illustration shows a swirling disk of accreting gas orbiting a fast-spinning black hole, with the bulk of the X-rays pouring out of the inner, white-shaded region of the disk. Credit: David A. Aguilar (CfA)

This illustration shows a swirling disk of accreting gas orbiting a black hole, with the bulk of the X-rays pouring out of the inner, white-shaded region of the disk. For the non-spinning black hole shown at left, this inner radius is large, which leaves a big dark hole cut out of the center of the hot disk of gas. Credit: NASA/CXC/M.Weiss

[Deaf Smith]

I noted that the illustrations show that they spin clockwise.

Is there a point in the universe that gives a division such as a "equator" where those on the other end spin counter clockwise?

[gcruse]

It looks CW when viewed from the 'top.' Viewed from the 'bottom' they rotate CCW.

[Deaf Smith]

Ah yes, the China Syndrome

[OSHA]

Original photo before the photoshp.

[patton]

Darn interesting question, that.

[Deaf Smith]

If we're going to try to latter send space craft across the universe via worm holes, gotta know which way the toilet's gonna flush.

[patton]

YOU try it, I will wait for further evidence. LOL.

[Andrew Byler]

We need a picture with Tourist Guy in it.

[dangerdoc]

Uhh, look at it from the other side?

[wastedyears]

Call me ignorant or stupid, but all of this is still theoretical.

[RightWhale]

Is there a point in the universe that gives a division such as a "equator" where those on the other end spin counter clockwise?

No. Rotation in the visible universe, the Hubble sphere. has been measured and is as close to zero overall as it might matter. Goedel spent considerable time measuring galactic rotation and found no net rotation in the pre-Hubble visible universe which forced him to eliminate one of his universe models.

[RightWhale]

all of this is still theoretical

And now, still.

New Theory: all of this will always be theoretical, so don't wait up.

[gb63]

"Viewed from the 'bottom' they rotate CCW."
This implies that you have perhaps crawled under a black hole at some time? Just asking....

[timer]

The mistake they make is believing Einstein is the LAST WORD on gravity waves. Gravity waves don't travel at C, they are flux-linking MATTER WAVES that travel by the formula U = c^2/v DeBroglie's equation for the speed of a matter wavecrest. If you care to go LOOK, the earth's response to the sun's gravitational pull is NOT 8 minutes c-retarded, it is instantaneous : 149,000,000 km/9 x 10^16 km/sec = about a billionth of a second. Thus "gravity" is fermions bose-bonded/flux-linked by matter waves in a capacitance well, much like cooper pair electrons in superconductivity.

[Tanniker Smith]

And just outside of the black hole is an impossible planet, which strangely enough, has a blue British police box call on it.

[SmartAZ]

It's not just theoretical, it's impossible.

X-rays are electromagnetic. Gravity is neither electro nor magnetic. Gravity can't make X-rays.

To make a black hole you need to squeeze an electron into a proton. Gravity is attractive. All the gravity in a proton won't attract an electron into it. Not enough energy. All the gravity in any number of protons won't attract the same number of electrons into themselves. Still not enough energy. The black hole is a mathematical invention, not a physical fact.

Astronomy is based entirely on looking at stuff, that is, no direct measurements are possible. Astronomers might think they see a black hole, but they are seeing faces in clouds.

[annie laurie]

Ping

[gb63]

So you're saying there are no black holes, therefore we don't have to worry about one coming along in a billion years and gobbling us up. Whew. That's a relief....

[bondserv]

If you care to go LOOK, the earth's response to the sun's gravitational pull is NOT 8 minutes c-retarded, it is instantaneous : 149,000,000 km/9 x 10^16 km/sec = about a billionth of a second.

So it takes a second if you are a billion miles away? Then the walkie talkie on the space ship would only be usable to a certain distance.

I read somewhere that manipulating the protons of a divided atom causes instantaneous reations at any distance.

Projective Capitalism at it's best.