Simulations uncover 'flashy' secrets of merging black holes (w/ Video)

Sep 27, 2012 by Francis Reddy
Frame from a imulation of the merger of two black holes and the resulting emission of gravitational radiation (colored fields). The outer red sheets correspond directly to the outgoing gravitational radiation that one day may be detected by gravitational-wave observatories. Credit: NASA/C. Henze

(Phys.org)—According to Einstein, whenever massive objects interact, they produce gravitational waves—distortions in the very fabric of space and time—that ripple outward across the universe at the speed of light. While astronomers have found indirect evidence of these disturbances, the waves have so far eluded direct detection. Ground-based observatories designed to find them are on the verge of achieving greater sensitivities, and many scientists think that this discovery is just a few years away.

Catching from some of the strongest sources—colliding black holes with millions of times the sun's mass—will take a little longer. These waves undulate so slowly that they won't be detectable by ground-based facilities. Instead, scientists will need much larger space-based instruments, such as the proposed , which was endorsed as a high-priority future project by the .

A team that includes astrophysicists at NASA's Goddard Space Flight Center in Greenbelt, Md., is looking forward to that day by using computational models to explore the mergers of supersized black holes. Their most recent work investigates what kind of "flash" might be seen by telescopes when astronomers ultimately find gravitational signals from such an event.

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Supercomputer models of merging black holes reveal properties that are crucial to understanding future detections of gravitational waves. This movie follows two orbiting black holes and their accretion disk during their final three orbits and ultimate merger. Redder colors correspond to higher gas densities. Credit: NASA's Goddard Space Flight Center; P. Cowperthwaite, University of Maryland

Studying gravitational waves will give astrophysicists an unprecedented opportunity to witness the universe's most extreme phenomena, leading to new insights into the fundamental , the death of stars, the birth of black holes and, perhaps, the earliest moments of the universe.

A black hole is an object so massive that nothing, not even light, can escape its gravitational grip. Most big galaxies, including our own Milky Way, contain a central black hole weighing millions of times the sun's mass, and when two galaxies collide, their monster black holes settle into a close .

"The black holes orbit each other and lose orbital energy by emitting strong gravitational waves, and this causes their orbits to shrink. The black holes spiral toward each other and eventually merge," said Goddard astrophysicist John Baker.

Close to these titanic, rapidly moving masses, space and time become repeatedly flexed and warped. Just as a disturbance forms ripples on the surface of a pond, drives seismic waves through Earth, or puts the jiggle in a bowl of Jell-O, the cyclic flexing of space-time near binary black holes produces waves of distortion that race across the universe.

While gravitational waves promise to tell astronomers many things about the bodies that created them, they cannot provide one crucial piece of information—the precise position of the source. So to really understand a merger event, researchers need an accompanying electromagnetic signal—a flash of light, ranging from radio waves to X-rays—that will allow telescopes to pinpoint the merger's host galaxy.

Understanding the electromagnetic counterparts that may accompany a merger involves the daunting task of tracking the complex interactions between the black holes, which can be moving at more than half the speed of light in the last few orbits, and the disks of hot, magnetized gas that surround them. Since 2010, numerous studies using simplifying assumptions have found that mergers could produce a burst of light, but no one knew how commonly this occurred or whether the emission would be strong enough to be detectable from Earth.

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To explore the problem in greater detail, a team led by Bruno Giacomazzo at the University of Colorado, Boulder, and including Baker developed computer simulations that for the first time show what happens in the magnetized gas (also called a plasma) in the last stages of a black hole merger. Their study was published in the June 10 edition of The Astrophysical Journal Letters.

The simulations follow the complex electrical and magnetic interactions in the ionized gas—known as magnetohydrodynamics—within the extreme gravitational environment determined by the equations of Einstein's general relativity, a task requiring the use of advanced numerical codes and fast supercomputers.

Both of the simulations reported in the study were run on the Pleiades supercomputer at NASA's Ames Research Center in Moffett Field, Calif. They follow the black holes over their last three orbits and subsequent merger using models both with and without a magnetic field in the gas disk.

Additional simulations were run on the Ranger and Discover supercomputers, respectively located at the University of Texas, Austin, and the NASA Center for Climate Simulation at Goddard, in order to investigate the effects of different initial conditions, fewer orbits and other variations.

"What's striking in the magnetic simulation is that the disk's initial magnetic field is rapidly intensified by about 100 times, and the merged black hole is surrounded by a hotter, denser, thinner accretion disk than in the unmagnetized case," Giacomazzo explained.

In the turbulent environment near the merging , the magnetic field intensifies as it becomes twisted and compressed. The team suggests that running the simulation for additional orbits would result in even greater amplification.

The most interesting outcome of the magnetic simulation is the development of a funnel-like structure—a cleared-out zone that extends up out of the accretion disk near the merged black hole. "This is exactly the type of structure needed to drive the particle jets we see from the centers of black-hole-powered active galaxies," Giacomazzo said.

The most important aspect of the study is the brightness of the merger's flash. The team finds that the magnetic model produces beamed emission that is some 10,000 times brighter than those seen in previous studies, which took the simplifying step of ignoring plasma effects in the merging disks.

"We need gravitational waves to confirm that a black hole merger has occurred, but if we can understand the electromagnetic signatures from mergers well enough, perhaps we can search for candidate events even before we have a space-based gravitational wave observatory," Baker said.

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LagomorphZero
3 / 5 (5) Sep 27, 2012
Article: "The simulations follow the complex electrical and magnetic interactions in the ionized gas—known as magnetohydrodynamics"

I don't think hydro(meaning water) is correct the root word to use here, magneto-plasma-dynamics possibly?
Silverhill
5 / 5 (5) Sep 27, 2012
The 'hydro' part means, more generally, 'liquid' or 'fluid'. From the Wikipedia article:
Magnetohydrodynamics (MHD) (magneto fluid dynamics or hydromagnetics) is an academic discipline which studies the dynamics of electrically conducting fluids. Examples of such fluids include plasmas, liquid metals, and salt water or electrolytes.


(from the article)
A black hole is an object so massive that nothing, not even light, can escape its gravitational grip.
More properly, it is an object so *dense* that its escape speed exceeds c. Black holes can be low-mass as well as high-mass.

show what happens in the magnetized gas (also called a plasma)
A plasma is not necessarily magnetized, but it *is* ionized (and therefore easily magnetizable).
LagomorphZero
5 / 5 (4) Sep 27, 2012
@silverhill - Thank you for the correction and additional information, I can see why it's used in this way.
cantdrive85
1 / 5 (5) Sep 28, 2012
"There are no known solutions to the field equations for two or more black holes and there is no existence theorem by which it can even be asserted that the field equations contain latent solutions for two or more black holes." Schmidt

http://www.thunde...there-2/
Silverhill
4 / 5 (3) Sep 28, 2012
In that article, the author shows an odd lack of comprehension.
Scientists frequently assert that the escape velocity of a black hole is that of light in vacuum and that nothing, not even light, can escape from the black hole. In fact, according to the same scientists, nothing, including light, can even leave the black hole. But there is already a serious problem with these claims. If the escape velocity of a black hole is that of light in vacuum, then light, on the one hand, can escape.
The escape speed is c only at the distance of the event horizon; inside, it is > c, effectively transfinite.
On the other hand, light is allegedly not able to even leave the black hole; so the black hole has no escape velocity.
No. See above.
...if the black hole has an escape velocity then material bodies can in fact leave the black hole and eventually stop and fall back to the black hole
They can move away from the singularity, but still not past the horizon.
ValeriaT
1 / 5 (3) Sep 29, 2012
Magnetohydrodynamics (MHD) models are nice and all, but they're based on many approximations. As such they cannot explain, why the black hole are formed at all. They're semiclassical models, which don't work well, when the general relativity effects are taken into account. For example, in relativistic models the black holes don't merge spontaneously at all - they do behave like the mercury droplets, which refuse to coalesce due their surface tension. I presume, when the general relativity improved with dark matter models would be taken into account, this situation would become even more pronounced. This deceleration would indeed limit the intensity of magnetic fields predicted with magnetohydrodynamical models and it could limit the probability of black hole merging as such.
Fleetfoot
5 / 5 (6) Sep 29, 2012
.. thunderbolts.info ..


There's no point quoting crank pseudo-science sites.
Fleetfoot
5 / 5 (5) Sep 29, 2012
In that article, the author shows an odd lack of comprehension.


It's an "electric universe" propaganda site.

They can move away from the singularity, but still not past the horizon.


Actually, nothing can even move away from the centre as it would have to exceed c to do so (given meaningful coordinates of course).

vidyunmaya
1 / 5 (5) Sep 29, 2012
Sub: Need to catch-up- Origins-Cosmology Vedas
The Cosmology groups before the simulations must understand cosmic Function of the Universe.All Electromagnetic phenomena cannot be clubbed under gravitation waves- perceptions must change to Space Vision..Space Time Energy concepts must take into account dimensional knowledge - request prmote Cosmology Chairs -East West Interaction .Vidyardhi nanduri
Fleetfoot
5 / 5 (3) Sep 30, 2012
Sub: Need to catch-up- Origins-Cosmology Vedas
The Cosmology groups before the simulations must understand cosmic Function of the Universe.


Trying to merge religious beliefs into science seldom adds new ideas, only bias.
gwrede
4 / 5 (4) Sep 30, 2012
.. thunderbolts.info ..
There's no point quoting crank pseudo-science sites.
There's no point in commenting on that, since up to half of the writers here have no ability to recognize whether a site is pseudo or real science. And some don't even understand there is such a concept.
Fleetfoot
5 / 5 (2) Oct 01, 2012
.. thunderbolts.info ..
There's no point quoting crank pseudo-science sites.
There's no point in commenting on that, since up to half of the writers here have no ability to recognize whether a site is pseudo or real science. And some don't even understand there is such a concept.


Too true, but that's precisely why I did comment :-)
antialias_physorg
3 / 5 (2) Oct 01, 2012
Actually, nothing can even move away from the centre as it would have to exceed c to do so (given meaningful coordinates of course).

Yep. What goes for the event horizon goes even more so for any (arbitrary) surface enclsong the singularity inside the event horizon.
william_f_hagen
1 / 5 (2) Oct 11, 2012
We will never be able to detect gravitational waves because as the waves distort both time and space, they also distort by exactly the same amount any electromagnetic waves or physical matter in that space-time by exactly the same amount, thus rendering any detectors useless.
antialias_physorg
3.7 / 5 (3) Oct 11, 2012
We will never be able to detect gravitational waves

You might want to look up the math/physics behind that before making such statements (or just head on over to the LIGO website)

Scientists are pretty inventive when it comes to figuring out how to measure stuff. Certainly much moreso than the (below) average poster on the internet. So: you 'pronouncement' that we will never be able to measure something is just silly.

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