Using Supercomputers To Predict Signs of Black Holes Swallowing Stars

aarondubrow (1866212) writes "A 'tidal disruption' occurs when a star orbits too close to a black hole and gets sucked in. The phenomenon is accompanied by a bright flare with a unique signature that changes over time. Researchers at the Georgia Institute of Technology are using Stampede and other NSF-supported supercomputers to simulate tidal disruptions in order to better understand the dynamics of the process. Doing so helps astronomers find many more possible candidates of tidal disruptions in sky surveys and will reveal details of how stars and black holes interact."

Comments

Impossible

[Squidlips]

How can a black hole swallow a star if the star's clock slows to a stop as it approaches the event horizon?

Re:Impossible

[Suki I]

How can a black hole swallow a star if the star's clock slows to a stop as it approaches the event horizon?

Just be thankful that this breakthrough is coming just in the nick of time dilation.

Re:Impossible

[mysidia]

How can a black hole swallow a star if the star's clock slows to a stop as it approaches the event horizon?

It stops from the star's perspective, maybe. From the perspective of an outside observer: the star is absorbed into the blackhole and ceases to exist.

but according to Hawking, there is no event horizon as previously believed; just an apparent horizon.

Re:Impossible

[mmell]

Somebody mod this guy up "Hilarious". I'm relatively sure that's what he was going for . . . and I have to admit to having to reread that (perfectly reasonable and appropriate) question twice before forcing my brain to parse it out correctly.

"I'm not a fig plucker . . . "

Re:Impossible

[wonkey_monkey]

How can a black hole swallow a star if the star's clock slows to a stop as it approaches the event horizon?

Because it doesn't.

The star's clock may slow to a stop relative to ours, sitting safely outside, but as far as the star is concerned, its clock continues to tick happily away. If the black hole is big enough, the star wouldn't be in the least perturbed by the experience.

Re:Impossible

[wonkey_monkey]

I think you might have that the wrong way around. From the star's perspective - if the black hole is big enough - nothing untoward occurs. It certainly won't see its own clock slowing down. From an outside perspective, objects approaching an event horizon undergo time dilation and fade from view, but are never seen to cross the horizon.

Re:Impossible

[mikael]

So, traveling to the event horizon of a black hole is basically a short cut to the end of the universe. Of if you are lucky, the restaurant at the end of the universe.

Re:Impossible

[Anonymous Coward]

The leading edge that passes the event horizon first will perceive the rest of the universe aging at an accelerated rate, (depending on the density of the black hole) it might even perceive the rest of the star burning out of old age as it also falls inward. Yet from an outside perspective, the star is getting sucked in at whatever speed the classical mechanics indicate (pull of gravity vs. other velocities, affected by any high energy debris orbiting the black hole, etc.).

You have this backwards according to GR: from the outside perspective it falls in at a slower and slower rate, but is also red shifted quite quickly so it still disappears from view. From the perspective of the stuff falling in, the universe continues on roughly at its normal rate and it hits the singularity (or whatever point stress destroys such an observer) in a short, finite time.

Assuming all the relativities work out in practice when dealing with the absurd gravities that would tear quarks into foam, it's confusing.

The absurd gravity as far as GR is concerned doesn't happen until you get near the singularity, while the gravitational stresses at the event horizon are nothing particular special. Depending on the size of the black hole, whatever you consider "absurd" in terms of what it can rip apart can occur some point outside the event horizon, or well inside it.

Re:Impossible

[Neil Boekend]

Correct me if I am wrong, but my limited knowledge of what happens tells me this:
Probably, assuming the observer is infinitely strong and can survive the gravity shear and immense pressure of the black hole:
From the observers POV the universe speeds up, until the surroundings (except for the black hole itself) become a bright light, because time dilation causes the cosmic background radiation to appear like visible light.
Then the black hole evaporates due to Hawking radiation and the observer is free again. When checking an outside ("absolute") clock billions of years have passed but the observer only felt a relative short while. The observer never encountered anything that could be considered a black hole. Time dilation reached near infinite before it could get there. The observer did encounter a lot of mass, mass that was falling into the black hole, never reaching it because time dilation didn't allow it to reach anything.
This mass has unknown properties. It is far denser than neutronium. It is still falling towards the core, only slowed down by time dilation.
The star itself was torn apart way before the "visible cosmic background" part. It kept falling towards the black hole as part of that mass with unknown properties.

From the outside an object doesn't exactly fall into the event horizon. It falls towards it but slows down before it. The light reflected or emitted by the object gets redshifted to nothingness. The event horizon does grow to meet the object.
Assuming the event horizon doesn't grow extremely fast the object will be invisible due to extreme redshift. Whether it is torn apart by gravity shear before that depends on the mass of the black hole and the strength of the object.

Re:Black Holes Swallowing Stars

[Jeremiah Cornelius]

So, like Kim Kardashian giving Kris Humphries a blowjob?

This is SO WRONG!

It's more like Hugh Grant and Divine Brown.

   

Look for the obvious

[Tablizer]

The star system's population sending "Heelllppp!" is a good sign.

Ah! Now it makes sense.

[140Mandak262Jamuna]

There was a electromagnetic simulation software called Ansoft-HFSS. Most structures it dealt with were IC chips, packages, PCBs and antennae. Most of these were drawn in microns, or mils (milli inches, don't ask), mm or at the most in meters. But the drop down box for unit selection went all the way to light years. I thought must be some inside joke, some user must have complained some unit was not available and the developer, in a fit of indignation, must have added every damned length units he/she could find. Now it makes sense. You can use that software to simulate black holes gobbling up stars.