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# Using Supercomputers To Predict Signs of Black Holes Swallowing Stars

#### samzenpus posted about 3 months ago | from the hungry-hungry-black-holes dept.

31

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."

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disruptionsin

### Re:disruptionsin (0)

#### Anonymous Coward | about 3 months ago | (#46749031)

Do you have a piont?

### Re:disruptionsin (0)

#### Anonymous Coward | about 3 months ago | (#46758551)

I think a "point" is entirely counter to the goal of disrupting - or preventing - useful discussion via trolling.

### Re:disruptionsin (0)

#### Anonymous Coward | about 3 months ago | (#46749087)

it's the super-plural of "disruptions"

### Black Holes Swallowing Stars (0)

#### Anonymous Coward | about 3 months ago | (#46749189)

So, like Kim Kardashian giving Kris Humphries a blowjob?

### Re:Black Holes Swallowing Stars (1, Funny)

#### Jeremiah Cornelius (137) | about 3 months ago | (#46749251)

So, like Kim Kardashian giving Kris Humphries a blowjob?

This is SO WRONG!

It's more like Hugh Grant and Divine Brown. [mugshots.org]

### Re:Black Holes Swallowing Stars (-1)

#### Anonymous Coward | about 3 months ago | (#46750525)

You, like always, sound intellectually deficient. Thanks for another moment of what it's like living a life of a commoner with an IQ just under average.

### Re:Black Holes Swallowing Stars (0)

#### Impy the Impiuos Imp (442658) | about 3 months ago | (#46749843)

She had her apparently black hole bleached.

### FTL space travel (0)

#### bluefoxlucid (723572) | about 3 months ago | (#46749197)

Wait until we can FTL to other star systems and check them out ourselves. The universe gets really weird when it looks completely different depending on where you're stopping for a burger today, and never looks like what the maps say. I mean seriously, people get in arguments with me and I point and go, "I'M LOOKING RIGHT AT IT, YOU MORON!" And this is a situation where what you're looking right at is wholly wrong.

### Re (0)

#### Anonymous Coward | about 3 months ago | (#46755373)

Unfortunately, it's extremely unlikely that FTL will ever be possible.

### Impossible (1)

#### Squidlips (1206004) | about 3 months ago | (#46749219)

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 (2)

#### Suki I (1546431) | about 3 months ago | (#46749259)

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 (-1)

#### Anonymous Coward | about 3 months ago | (#46749271)

Its well explained here [bit.ly]

### Re:Impossible DON'T CLICK (-1)

#### Anonymous Coward | about 3 months ago | (#46749413)

Goatse link. Mod parent and me down.

### Re:Impossible (0)

#### Anonymous Coward | about 3 months ago | (#46749313)

I wouldn't be too sure it always swallows the star after sucking it in.

I would think that sometimes it spits....

### Re:Impossible (1)

#### mysidia (191772) | about 3 months ago | (#46749315)

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 (2)

#### wonkey_monkey (2592601) | about 3 months ago | (#46749499)

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 (2)

#### Neil Boekend (1854906) | about 3 months ago | (#46754217)

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:Impossible (0)

#### Anonymous Coward | about 3 months ago | (#46755799)

If you have an observer in free fall into a black hole, they (or their constituent particles...) will reach the singularity in a finite time in their frame assuming the GR solution extends to inside the black hole without some new physics. There isn't some sort of infinite time dilation or blue shift, because as they are in free fall they are accelerating and that effectively cancels out some of the dilation effects. In other words, the light from the rest of the universe still has to catch up to them, instead of piling up all at once. If you are not in free fall, that is a different story. Someone using an extreme amount of energy to hover a short distance above the event horizon will experience a huge amount of time dilation, approaching infinity the closer they get, but also approaching an infinite amount of thrust and energy needed to hover without falling in.

### Re:Impossible (0)

#### Anonymous Coward | about 3 months ago | (#46749397)

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

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.).

For the perspective of the black hole, we have no idea. Relativity clearly breaks once you get to something like that. Trying to solve the relative speed of time formula just results in nasty collisions of infinities, zeros, and negatives applied to units that we don't want to consider having a negative possibility.
The exact point at which relativity stops being useful is unknown, so physicists assume that it remains a valid model until it starts putting out strange answers like 'infinite mass, negative volume, no time' when you try to calculate off of an apparent gravitic influence.

### Re:Impossible (1)

#### mikael (484) | about 3 months ago | (#46749541)

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 (1)

#### Anonymous Coward | about 3 months ago | (#46749745)

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 (1, Informative)

#### mmell (832646) | about 3 months ago | (#46749405)

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 (4, Informative)

#### wonkey_monkey (2592601) | about 3 months ago | (#46749417)

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 (0)

#### Anonymous Coward | about 3 months ago | (#46753003)

If the black hole is big enough, the star wouldn't be in the least perturbed by the experience

The "no drama" conjecture does not quite result in what you wrote, assuming the star (or some GR thinker comoving near it) calculates the future world lines of its radiation and the gravitational blueshift of objects near the black hole.

That is, "no drama" does not dispense with the EEP and anyone inside a black hole event horizon -- no matter how big R_Sch is and how small the tidal force is (ca. 10^-6 m/s^2 at the galactic centre) -- will see things as if she or he is being significantly accelerated. At R=R_Sch for a typical stellar black hole, that becomes *enormously* accelerated (ca. 10^7 m/s^2).

Several proposed resolutions to the "firewalls" debate (and more generally to non-exact solutions based on educated guesses about the equation of state of the interior of collapsars in the generic sense) suggest interesting things about what an infalling person would calculate is the location of the event horizon, and about the relativity of simultaneity between an observer at a great distance at rest with respect to the collapsar and the infaller that *should* scale to all Schwarzchild radiuses. (That a handful of such proposals clearly do not scale to arbitrary black hole masses suggests that those proposals are shaky enough that they should not be considered to be saying anything useful about the validity of semiclassical gravity as an EFT outside the horizon).

An infalling person will know he or she is doomed because "no drama" is a statement about observations of *local* physics and not observations of distant objects. Just because one does not expect to be fried by Planck energy radiation at or very near the event horizon does not mean that observations of distant quasars, or even necessarily telemetry from a probe launched locally and sent to sub-astronomical distances will look much like they would outside the horizon.

### Re:Impossible (0)

#### Anonymous Coward | about 3 months ago | (#46753135)

I don't think anyone (or at least anyone I've seen in a long time) has implied that no-drama implies it is impossible to know when you cross the event horizon. Instead, if no firewall, it comes down to not noticing the exact moment you cross the event horizon without careful measurement. Both the moments leading up to and after the crossing will involve a blue shifted tunnel vision of distant objects and the effects of being accelerated.

### Re:Impossible (0)

#### Anonymous Coward | about 3 months ago | (#46756091)

I don't think anyone (or at least anyone I've seen in a long time) has implied that no-drama implies it is impossible to know when you cross the event horizon

That the location of the event horizon is observer-dependent is non-controversial. The smoothness of the event horizon might be as well. The usual approach (even now, rather than just "a long time" ago) is to deal with a circular orbit at 2 R_Sch and to chase the instabilities.

without careful measurement

... which might not be physically possible given a sufficiently massive black hole and a windowless lab.

Both the moments leading up to and after the crossing will involve a blue shifted tunnel vision of distant objects and the effects of being accelerated

You're right that for an isolated Swarzchild black hole, optical effects (for an observer at rest with respect to the black hole) depend only on R/R_Sch only. It's generally hard to be certain one is at rest with respect to any black hole, particularly considering de Sitter effects. For Kerr black holes, it's more complicated, and it's more complicated still for extremals, since frame-dragging is non-negligible (i.e., you have to know where you are relative to the static limit). Any view might be made hard to analyse by the presence of accretion and Unruh material. It therefore isn't especially controversial to argue that a journey into a realistic black hole hides information about the precise location of the event horizon from any infaller; that's not to say that at sufficient distance from the event horizon an infaller cannot determine on which side of the event horizon he or she is.

The salient point, GR-wise, with a typical black hole metric is the switch of meaning of the radial coordinate or its equivalent to a timelike coordinate (i.e., at the event horizon you will inevitably (and quite quickly) reach the singularity). That is *real* and not observer-dependent. However, as physical black holes are neither eternal nor unchanging, it is not just possible but almost unavoidable to grind out exact solutions which demand a quantum gravity theory to precisely fix whether one is in (in Kerr terms) region I or II, i.e., what the +/- sign is in r = M \pm \sqrt(M^2 - a^2) when |r| is small.

### Re:Impossible (0)

#### Anonymous Coward | about 3 months ago | (#46752057)

Slashdot has the ability to draw out the worst possible answers from the least qualified people at the speed of internetz.
And in quantity.
even morgan freeman thinks your a dumbass.

### Look for the obvious (1)

#### Tablizer (95088) | about 3 months ago | (#46749425)

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

### Ah! Now it makes sense. (4, Interesting)

#### 140Mandak262Jamuna (970587) | about 3 months ago | (#46749463)

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.

### Re:Ah! Now it makes sense. (0)

#### Anonymous Coward | about 3 months ago | (#46750463)

Although in this case they are talking about a hydrodynamic simulation showing how most of the hydrogen can be stripped from a star before it spirals into the black hole, in response to spectral data from an event that showed luminosity as expected for a star spiraling into a black hole buy missing hydrogen spectral lines. In general, the codes used for simulations of black holes and things like accretion disks tend to be separate (or rarely long ago forked) from normal codes for solving such problems because of the non-Euclidean geometry involved, among other possible every day assumptions made by engineering software that no longer apply. Although most of it is work on plasma, hydrodynamic, and numeric relativity simulations, which can be nastily non-linear compared to EM FEM software. I'm not sure if something like HFSS can even come close to simulating what is needed unless there is a lot more access to the back end solver.
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