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Astronomers See Another Star Torn Apart By a Black Hole

samzenpus posted about 2 years ago | from the dr.-reinhardt-approved dept.

Space 127

The Bad Astronomer writes "A star in a galaxy 2.7 billion light years away wandered too close to a supermassive black hole and suffered the ultimate fate: it was literally torn apart by the black hole's gravity. The event was seen as a flash of ultraviolet light flaring 350 times brighter than the galaxy itself, slowly fading over time. Astronomers were able to determine that some of the star's material was eaten by the black hole, and some flung off into space. Although rare, this is the second time such a thing has been seen; the other was just last year."

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First Post for Junior Seau (-1)

Anonymous Coward | about 2 years ago | (#39873669)

RIP brother. Kept it real.

Re:First Post for Junior Seau (-1)

Anonymous Coward | about 2 years ago | (#39873733)

Stupid people shouldn't play with guns.

Will black hole devour dark matter, anti-matter? (4, Interesting)

Taco Cowboy (5327) | about 2 years ago | (#39873923)

We know that black holes can suck in matter - the gamma ray radiation emitted when matters are flatten to a disc before it's being sucked in are indication of black hole devouring matter.

But how about dark matter, or anti-matter?

Will black hole's gravity pull pulls in dark matter and/or anti-matter?

What effect would that have?

Re:Will black hole devour dark matter, anti-matter (3, Informative)

Beryllium Sphere(tm) (193358) | about 2 years ago | (#39874025)

Dark matter responds to gravity, and antimatter should as well. So they'd get pulled in and never seen again.

Re:Will black hole devour dark matter, anti-matter (4, Funny)

robot256 (1635039) | more than 2 years ago | (#39874967)

Dark matter responds to gravity, and antimatter should as well. So they'd get pulled in and never seen again.

Which really isn't saying much, since they were never seen before, either.

Re:Will black hole devour dark matter, anti-matter (5, Insightful)

FrootLoops (1817694) | more than 2 years ago | (#39875399)

Uh, antimatter is seen all the time. Heck, the "P" in "PET scan" stands for "positron", the electron's antiparticle. As for dark matter, it's "seen" in gravitational effects, which is admittedly indirect and somewhat inconclusive. Still, humans are rather biased. The matter you're made out of is mostly quarks and electrons. Quarks are affected by all four fundamental forces: (G)ravity, (E)lectromagnetism, (W)eak, and (S)trong. Electrons are only affected by GEW. Neutrinos have just GW and are therefore hard to detect. Maybe there's matter that's just affected by G; it would only show up on cosmological scales like dark matter seems to.

Quoting myself [slashdot.org] ,

Who knows? Maybe there's a whole segment of matter humans are unfamiliar with which interacts very little with the matter we know about but interacts with itself in complicated ways. Maybe there are dark matter solar systems populated by dark matter people who are just as confused as we are about the weird gravitational anomalies caused by our otherwise invisible existence. Communicating through gravity would certainly be an interesting challenge! I don't really believe this, but my point is basically the same as Hamlet's: "There are more things in heaven and earth than are dreamt of in your philosophy"--that is, it's arrogant to expect humans to be in a position to observe all the parts of the universe. Perhaps some things are just hidden.

Another recent post of mine in this vein is a summary of particle classifications [slashdot.org] .

Re:Will black hole devour dark matter, anti-matter (3, Insightful)

robot256 (1635039) | more than 2 years ago | (#39875603)

I'll grant you the antimatter issue, but I still like my tongue-in-cheek jab at the GGP for saying that dark matter wouldn't be "seen" after falling into a black hole. It is "dark" after all, meaning it cannot be seen in the human sense of the word, so the difference between it being in a black hole and not being in a black hole is visibly none.

Of course, the really interesting thing is that it's possible that the actual act of falling into a black hole is the only thing that would ever make dark matter visible. So it would never be seen before, or after, but possibly could be seen *during* its descent into the singularity.

Re:Will black hole devour dark matter, anti-matter (1)

Anonymous Coward | more than 2 years ago | (#39875923)

Maybe there are dark matter solar systems populated by dark matter people...

So far, the only force that we know dark matter responds to is gravity. If it's only influenced by gravity, then it's hard to see how it would build up the nice, complex chemistry that the electromagnetic force produces, which allows our form of life to exist.

Of course, it's possible that there are other forces that affect dark matter (and don't affect regular matter). There are ways we could detect this: for example, if two clumps of dark matter hit each other, then they should pass right through each other (if they only interact through gravity) or stop and clump together like regular matter (if there's another force by which they interact). Last I heard, though, no astronomers had seen any definite indications of this type of effect.

Re:Will black hole devour dark matter, anti-matter (3, Interesting)

Yew2 (1560829) | more than 2 years ago | (#39874393)

Does anyone ever wonder if antimatter is our representation of what exists as matter on the other side of any given (or perhaps all) black hole(s) inside another dimension/universe/whatever you wanna call it? Universe pairs? Hawking theorized that black holes have white hole pairs - maybe his math just indicated that there is no Lord Nibbler poo at the completion of a black hole (or the start of our universe) but rather another instance of er...space ie- how does a singularity occur w/ infinite mass (or so we would calculate) with the law of conservation of mass - lots of cosmologists must be trying to prove it goes somewhere so why not another dimension/universe/etc - and to consider attractive forces like that perhaps draw a theoretical parallel with polarity so that since our typical everyday matter is attracted to a black hole, perhaps that dimension/etc's typical everyday matter is as well (their own BH, WH to us) and perhaps the other side of any black hole is what would be our theoretical white hole counterpart to a black hole, our antimatter counterpart to our matter, etc etc?

Re:Will black hole devour dark matter, anti-matter (0)

Anonymous Coward | more than 2 years ago | (#39874439)

If you squint closely enough at a couple of graphs and turn them sideways, an anti-electron (positron) is just a regular electron going back in time. Close enough?

Re:Will black hole devour dark matter, anti-matter (5, Informative)

Trax3001BBS (2368736) | more than 2 years ago | (#39874905)

ie- how does a singularity occur w/ infinite mass (or so we would calculate) with the law of conservation of mass

"How the Universe Works: Black Holes", The Discovery channel, Netflix (and others I'm sure) is an excellent reference for your answers.
The entire series is very informative.

Re:Will black hole devour dark matter, anti-matter (2)

triclipse (702209) | more than 2 years ago | (#39875867)

I just finished Leonard Susskind's "The Black Hole War" - also very readable and informative.

Re:Will black hole devour dark matter, anti-matter (3, Informative)

Bengie (1121981) | more than 2 years ago | (#39875059)

I am not a physicist

The mass doesn't just go "somewhere". Blackholes slowly dissipate over time as they give off energy in the form of gravity. Eventually a blackhole will just disapear. poof

Mass and energy are interchangeable. You have to stop thinking of a blackhole as matter and think of it as a big ball of energy.

Blackholes don't have infinite mass, they have infinite density.

That being said, what Trax3001BBS posted is really good. Netflix "Universe". There is A LOT. Keep using your imagination :p

Re:Will black hole devour dark matter, anti-matter (4, Informative)

Neil Boekend (1854906) | more than 2 years ago | (#39876573)

IANAP either, but as far as I know gravity isn't energy. Black holes evaporate due to Hawking radiation [wikipedia.org] .

Re:Will black hole devour dark matter, anti-matter (1)

Anonymous Coward | more than 2 years ago | (#39876989)

"Blackholes slowly dissipate over time as they give off energy in the form of gravity."

That's not true. Gravity is not energy that is "given off".
However, it is theorized that black holes slowly dissipate over time as they give off energy in the form Hawking radiation.

Re:Will black hole devour dark matter, anti-matter (2)

drerwk (695572) | more than 2 years ago | (#39877461)

No. Black holes like the one being talked about do not loose much energy to gravitational waves. In order to dissipate energy via gravitational waves the mass must accelerate. So a pair of masses orbiting each other will shed gravitational energy, a galactic black hole sitting in the center of the galaxy does not move much and so does not emit gravity waves.
Regarding Hawing radiation dissipation, the temperature of the Hawking radiation is greater as the mass of the BH is smaller. In order to loose net mass, this temperature has to be larger than the CMB, which is only true for I think smaller than stellar size BHs.

Re:Will black hole devour dark matter, anti-matter (1)

FrootLoops (1817694) | more than 2 years ago | (#39875537)

Here are some relevant bits of physics you might not be aware of:
  * White holes are somewhat shaky. From their Wikipedia article,

However, this region does not exist for black holes that have formed through gravitational collapse, nor are there any known physical processes through which a white hole could be formed.

There are apparently solutions to the Einstein field equations giving black/white hole pairs, but black holes do not need white holes to exist.
  * There is an interpretation of antimatter in quantum field theory as matter traveling backwards through time (that phrase is very imprecise unfortunately). More details here [stackexchange.com] ; I'm not qualified to really discuss it as I'm just a mathematician with an interest in physics. Still, perhaps in vague terms your parallel universe dichotomy can be replaced with the two directions of time.
  * Black holes have infinite density, not infinite mass.
  * Hawking radiation [wikipedia.org] allows black holes to evaporate away if they don't eat up enough mass.

Re:Will black hole devour dark matter, anti-matter (1)

Yew2 (1560829) | more than 2 years ago | (#39876831)

I did mean to put that I am a total um "not a physics guy" just the armchair piece-together-what-i-can-repeat dreamer type. but heck yea thanks for the detail

Re:Will black hole devour dark matter, anti-matter (1, Informative)

Anonymous Coward | more than 2 years ago | (#39875755)

Black holes don't have infinite mass. Just many stars' worth of mass, squeezed into a very tiny area. Relativity tells us that the *density* is infinite, but quantum mechanics shows that even the singularity must have some volume. The mass doesn't go anywhere - in fact, things that fall into the black hole never actually make it to the center due to time dilation effects.

And, antimatter is just like normal matter, it just carries an opposite charge because it's made from different versions of subatomic particles. It's not that exotic - we make antimatter all the time - go to a hospital and get a PET scan. "Dark matter", on the other hand... we have no idea what that is.

Re:Will black hole devour dark matter, anti-matter (0)

Anonymous Coward | more than 2 years ago | (#39874461)

Dark matter is just stuff they cant see, anti-matter is differnt, assuming it would make it to the event horizon without coming in contact with matter, and going poof into pure energy, it would still go in. I suppose it would come into contact with regular matter at the point and go poof but it doesnt matter at that point since even the energy emitted wouldnt be able to escape and the black hole wouldnt lose any mass because keeping with E=MC^2 the sum of the energy would still have the same mass as the matter itself.

Re:Will black hole devour dark matter, anti-matter (1)

Trax3001BBS (2368736) | more than 2 years ago | (#39874825)

Will black hole's gravity pull pulls in dark matter and/or anti-matter?

Gravity effects everything, it's the most powerful fundamental force of all.

"The Elegant Universe" book, CD and Series by Nova
http://www.pbs.org/wgbh/nova/physics/elegant-universe-dimensions.html [pbs.org] freaking ads I can't get past them.
Uses a pool table as an example, the only thing that escapes a pool table is sound.
Sound being gravity, which exerts it's force in all dimensions.

Gravity rated 4th in strengths of the fundamental forces, yet the force it exerts in all dimensions added together,
gravity sucks big time.

Re:Will black hole devour dark matter, anti-matter (2)

Roachie (2180772) | more than 2 years ago | (#39875895)

Correction: Gravity affects everything, its the weakest fundamental force of all .

Glad I could help.

You're both right (3, Informative)

Immerman (2627577) | more than 2 years ago | (#39876245)

GP said "most powerful" which is not synonymous with strongest. For example, conspiracy theories aside, the US president is probably one of the single most powerful men on the planet, but it's a matter of force multiplication, in a test of strength I'd bet on most any bodybuilder that challenged him.

In the case of gravity it's more a matter of force division. The nuclear forces fall off very rapidly with distance, becoming effectively nonexistent at even molecular scales. Magnetism fairs better, but still falls off with the inverse cube, becoming negligible at any significant distance. That leaves the electrostatic force as the only real challenger at long range, and it's bi-polarity causes opposite charges to tend to clump together in equal quantities, neutralizing it's effects.

And thus gravity is left standing as the long-range champion, free to shape the universe as it sees fit with little interference from it's myopic stronger cousins.

Re:You're both right (1)

flargleblarg (685368) | more than 2 years ago | (#39876333)

Interesting. I've long known that gravity is O(r^-2) and that magnetism is O(r^-3), but didn't know that nuclear forces trailed off even more rapidly than that. What power do they trail off with?

Re:You're both right (3, Informative)

Immerman (2627577) | more than 2 years ago | (#39876495)

The nuclear force is a bit weird as it's due to quantum-mechanical interactions between the quarks of the associated hadrons. I don't pretend to really understand it, but they have some lovely diagrams and animations on wikipedia [wikipedia.org] that will leave you convinced that either we're misunderstanding what's going on or God has a wacky sense of humor.

Short answer, the nuclear force is a very strong attractor at around one femtometer, becomes repulsive at distances less than 0.7 femtometers, and decreases to insignificance by about 2.5 femtometers. It's actually a residual force that originates with the strong interaction between quarks, which is a force that reaches a strength of about 10,000N at a limiting distance of roughly the size of a hadron, and then remains constant regardless of how much farther apart the coupled quarks move. So yeah, no matter how you look at it it's not at all analogous to the macroscopic forces.

Re:You're both right (1)

flargleblarg (685368) | more than 2 years ago | (#39876543)

My God, that's nasty / crazy / weird!

Re:Will black hole devour dark matter, anti-matter (5, Interesting)

Immerman (2627577) | more than 2 years ago | (#39876177)

Well, we've created antimatter in the lab and it seems to behave very much like normal matter, it just has the opposite charge (for protons/electrons) and Baryon number (a QM property). So I suspect it would behave very much like normal matter, in fact I doubt we can actually tell whether a celestial object/event involves matter or antimatter, though it seems fairly likely that all the "native" matter in a particular galaxy will be the same type, otherwise it would have mutually annihilated whenever a gas cloud of one kind interacted with it's opposite, though a matter galaxy could conceivably capture a rogue star from a passing antimatter galaxy - as long as the rogue star never exploded or hit something directly it would likely be indistinguishable except for a *very* faint and diffuse halo where its antimatter-based solar wind contacted and annihilated the interstellar medium.

Dark matter though... that's an interesting question. As far as we can tell it only interacts gravitationally so it will never glow or collide with anything, since both are EM interactions. The Bullet Cluster would seem to indicate that it even passes right through other dark matter. Which raises an interesting question, while it could presumably be sucked into a black hole's event horizon it might continue to behave just as bizarrely, possibly even being able to escape again somehow. We just have no idea what the stuff is, it's even possible that it's not matter at all, but rather a phenomena symptomatic of a fundamental misunderstanding of the nature of reality, much as black-box radiation in the 1800s led to the development of quantum mechanics and radically altered our understanding of the universe. It was widely believed at the time that we basically understood everything about physics, with just a few loose ends still to tie up (BB radiation, the cause of spectral lines, and a couple others). Instead those loose ends led to the unraveling of virtually everything we thought we knew and opened the door to something far stranger.

There's also the possibility that black holes don't exist at all and the question is nonsensical. We have evidence of ultra-massive non-luminous objects, but little if any for the existence of the defining characteristic of black holes, an event horizon. We assume they are black holes because our theories say that anything that massive would collapse into a singularity, but think about it - we're postulating that a body can become so dense that it creates a region of space where the laws of physics themselves to break down! There are several competing theories that make such a situation impossible, one that I like is based on the fact that Einstein treated gravity as a special case - all other energy fields generate a gravitational field based on their energy density. Einstein felt that it would be "double dipping" to have gravitational fields do so and discarded the idea. However, if we rework the equations assuming that they do in fact do so then we find that as the gravitational field strength becomes extreme the "secondary" gravity generated by the extreme energy density of the "primary" field pulls back against the primary source, causing the field strength to plateau at a level less than that required to create an event horizon, regardless of the density of the central object. If that, or some other mechanism, puts an upper limit on gravitational field strength it seems likely that the ultramassive objects are simply some sort of exotic quark-degenerate matter that happens to be non-luminous. As far as I can remember photons are radiated when (1) charges accelerate through space (as with radio transmissions), (2) electrons descend to a lower orital, and (3) nuclear processes result in lower binding energies. I don't know much QM, but it seems likely that (4) quark bindings and transmutaions that result in "left-over" energy would be a final source, and the only one that might apply to a neutron star, which are apparently directly observable (I couldn't find much in the way of details). In a quark-degenerate star it seems like even 4 might no longer apply, and it would thus be completely invisible unless it passed directly in front of a star, which would be very unlikely considering that the entire mass of the Milky way (~3e42 kg) packed into only neutron star density (~5e17kg/m^3) would occupy a sphere only 226,000km across, less than 1/12 the size of the sun, or 60% larger than Jupiter. Gravitational lensing would be the only evidence we'd ever be likely to see.

Re:Will black hole devour dark matter, anti-matter (1)

flargleblarg (685368) | more than 2 years ago | (#39876325)

^^ This was one of the most interesting posts I've ever read on Slashdot.

Re:Will black hole devour dark matter, anti-matter (1)

Neil Boekend (1854906) | more than 2 years ago | (#39876609)

IANAP, but I'd postulate that, assuming dark matter obeys the laws of time dilation, it would behave exatly as normal matter beyon the Schwartzschild radius of a black hole. Time would stop due to extreme time dilation and thus the particle would effectively stop at the Schwartzschild radius. Then the black hole would be a tiny bit more massive, the Schwartzschild radius would be a tiny bit bigger.

Re:Will black hole devour dark matter, anti-matter (1)

Taco Cowboy (5327) | more than 2 years ago | (#39876659)

I had to read, and re-read your comment 3 times before I begin to understand

Many thanks !

End of the world (-1)

Anonymous Coward | about 2 years ago | (#39873701)

Suppose it is raining and you run under a tree for shelter. What do you do when the rain soaks through that tree? Run to another tree? No. That tree is soaked through too.

The universe has apparently aged enough to build up a sufficient number of black holes that events like this are becoming common place. It is only a matter of time now before a rogue black hole passes close enough to Sol to destroy all life.

Happy 2012.

Re:End of the world (0, Offtopic)

Anonymous Coward | about 2 years ago | (#39873769)

Yeah, finally, after 14 billion years of existence, the universe went from this event never happening to happening all the time in under a year. And now the earth's existence will end because, you know, since this happens all the time now and since we're right next to the black hole in the center of our galaxy, a star being torn apart is sufficiently close to destroy all life.

I find your ideas insightful and I would like to sign up for your newsletter.

Re:End of the world (1, Funny)

Anonymous Coward | more than 2 years ago | (#39874981)

This is all clearly Obama's fault. Two stars torn apart in one year? You never saw this during the Bush administration.

Why is Obama crippling our black hole defenses?

Re:End of the world (0)

Anonymous Coward | about 2 years ago | (#39873859)

If we 3D print enough scrith we can build a Ringworld.

Re:End of the world (0)

Anonymous Coward | about 2 years ago | (#39874099)

Do you know how much ABS filament costs? Are you insane?

Re:End of the world (2)

gstrickler (920733) | about 2 years ago | (#39873891)

We'll never get to witness that, either Sol will become a red giant first, consuming anything that still lives on the earth, or, the gravity of the black hole with eat the earth before Sol succumbs. Either way, we'll already be dead.

Unless, of course, you have reservations at Milliway's

Re:End of the world (1)

VortexCortex (1117377) | more than 2 years ago | (#39874889)

We'll never get to witness that, either Sol will become a red giant first, consuming anything that still lives on the earth, or, the gravity of the black hole with eat the earth before Sol succumbs. Either way, we'll already be dead.

Unless, of course, you have reservations at Milliway's

Considering this year's Earth Day slogan, [earthday.org]
There may yet be another option... [google.com]

Re:End of the world (4, Funny)

ObsessiveMathsFreak (773371) | about 2 years ago | (#39874089)

It is only a matter of time now before a rogue black hole passes close enough to Sol to destroy all life.

The odds of such an event are... [sunglasses]....Astronomical.

Re:End of the world (1)

Anonymous Coward | more than 2 years ago | (#39874805)

Yeeeeeaaaaahhhhhh!

Re:End of the world (1)

Sardaukar86 (850333) | more than 2 years ago | (#39874401)

Don't be ridiculous.

I'm not nearly lucky enough for such a thing to happen!

Why it gotta be a "black" hole? (5, Funny)

PopeRatzo (965947) | about 2 years ago | (#39873721)

I prefer "hole-of-color".

Re:Why it gotta be a "black" hole? (1, Funny)

Anonymous Coward | about 2 years ago | (#39873777)

The correct term is "African-American" hole

Re:Why it gotta be a "black" hole? (1)

Anonymous Coward | about 2 years ago | (#39873823)

Damn you and your petty regionalism!

Re:Why it gotta be a "black" hole? (0)

Anonymous Coward | about 2 years ago | (#39873835)

AA-Hole?

Re:Why it gotta be a "black" hole? (1)

Jackie_Chan_Fan (730745) | about 2 years ago | (#39873893)

I dont get it.

Re:Why it gotta be a "black" hole? (2, Funny)

PopeRatzo (965947) | more than 2 years ago | (#39875143)

I dont get it.

Use more Axe body spray.

Re:Why it gotta be a "black" hole? (0)

sjames (1099) | about 2 years ago | (#39874105)

If it's first spotted in the U.K. is it a British African-American hole?

Re:Why it gotta be a "black" hole? (-1)

Anonymous Coward | about 2 years ago | (#39874125)

The correct term is "African-American" hole

My first reaction was LOL

I stopped my laughter in midway when I realized that it's not Political Correct to laugh at "sensitive matter"

Re:Why it gotta be a "black" hole? (-1)

game kid (805301) | about 2 years ago | (#39873817)

Hmph. Another member of the Universal Association for the Advancement of Colored Holes. You must've half-died when Wolf Blitzer called them "so massive, and so black" when that comet passed over them.

One thing's certain: I don't support the United Negro Singularity Fund, because a star is a terrible thing to waste.

Re:Why it gotta be a "black" hole? (1)

PopeRatzo (965947) | more than 2 years ago | (#39875655)

You must've half-died when Wolf Blitzer called them "so massive, and so black"

That's such a coincidence. Your sister uttered those same exact words.

Re:Why it gotta be a "black" hole? (1)

bored_engineer (951004) | about 2 years ago | (#39873841)

Wait! Wouldn't this would be a "hole-of-no-color?"

Re:Why it gotta be a "black" hole? (0)

Anonymous Coward | more than 2 years ago | (#39874559)

In Canada, that would properly be "hole-of-colour".

Star torn apart by black hole (0)

Anonymous Coward | about 2 years ago | (#39873735)

George Clooney and Oprah Winfrey in an octagon match

Re:Star torn apart by black hole (0)

Anonymous Coward | about 2 years ago | (#39873785)

That would be 'black ho'

Unbelievable Gravity (5, Informative)

schwit1 (797399) | about 2 years ago | (#39873827)

In this article the scale of the gravity comes into focus:
http://news.sciencemag.org/sciencenow/2012/05/giant-black-hole-shreds-and-swal.html?ref=hp [sciencemag.org]

"Before its fiery demise, when the star was about as far from its nemesis as Pluto is from the sun, the black hole stripped off its hydrogen envelope."

At 3.5 billion miles the black hole is able to out-gravity a star of its own hydrogen atmosphere. Am I reading that right?

Re:Unbelievable Gravity (5, Informative)

Anonymous Coward | more than 2 years ago | (#39874539)

At 3.5 billion miles the black hole is able to out-gravity a star of its own hydrogen atmosphere. Am I reading that right?

Yes, that's right. The way it happens is this: the star is in orbit around the black hole. The edge of the star closest to the black hole is in one orbit, and the opposite edge of the star is in another orbit. So they'd drift apart, if the star's gravity weren't holding them together. If this effect is large enough, then the star's gravity isn't enough to counteract it, and different parts of the star head off in their own separate orbits.

Your average stellar-mass black hole (the sort you get left over after some types of supernova) wouldn't be able to do this at 3.5 billion miles. But the black hole in this story is one of the supermassive ones you get at the centres of galaxies, with a mass 3,000,000x that of the sun. Also, the star in question is a red giant, which has a huge, puffy atmosphere (something like 0.2 billion miles across), which makes it easier to strip off: the opposite edges of it are in *very* different orbits around the black hole, so they pull apart more easily.

Re:Unbelievable Gravity (3, Interesting)

Anonymous Coward | more than 2 years ago | (#39874681)

Hey, I think I can maths this one out.

Say that the black hole has mass M, and the star has mass m. The radius of the star is r, and the distance between the black hole and the centre of the star is R. So the edge of the star closest to the black hole is at a distance of (R-r), and experiences a gravitational field from the black hole of:

G M / (R-r)^2

where G is the gravitational constant. (Don't worry - this will drop out eventually.) The edge of the star farthest from the black hole is at a distance of (R+r), so it experiences a gravitational field of:

G M / (R+r)^2

The difference between these two values tells us how fast these different bits of the star would accelerate away from each other, if they weren't being held together. Doing a bit of algebra (and assuming that r is a lot less than R, to make a few approximations), I get:

G M / (R-r)^2 - G M / (R+r)^2
  = ( (R+r)^2 - (R-r)^2 ) * G M / (R+r)^2 / (R-r)^2
  ~= 4 R r G M / R^4
  = 4 r G M / R^3

But both edges of the star are also being pulled together by the star's gravity, with a strength of

G m / r^2

So, from the gravitational force of the star alone, they'd be accelerating together at twice this value (each with that much acceleration towards the centre of the star). The point at which the star starts getting stripped of material is when these two effects (star getting pulled apart; star holding itself together) exactly balance, i.e.

4 r G M / R^3 = 2 G m / r^2

hence:

2 M / m = (R/r)^3

So, let's say that the star has the same mass as the sun, and the black hole has 3,000,000x that, so (M/m) = 3,000,000. Let's also say that the star is 0.2 billion miles across (r = 0.1 billion miles). Then we get:

R = (0.1 billion miles) * (6,000,000)^(1/3) = 18 billion miles

So the black hole would start stripping off the star's atmosphere when it's about five times as far away as Pluto is from the sun.

Re:Unbelievable Gravity (4, Informative)

SpazmodeusG (1334705) | more than 2 years ago | (#39874789)

Good maths and all but there's one thing you need to consider- If you're in stable orbit you don't actually fall inwards.

The sun for example has twice the pull on the moon as the earth (do the maths and see for yourself). It doesn't fall into the sun because it's in a stable orbit.

Likewise in this example. It's not a case of the black hole pulling more than the sun at a given distance. It can, but it's not all that relevant, plenty of orbiting bodies have more gravity pull from a nearby larger mass than they exert themselves but that's not what determines whether or not something gets pulled into the larger body.

What does determine whether or not something gets pulled into the larger body is if something disrupts the orbit. In this case the most likely culprit is charged particles from the event horizon stripping the sun of its outer layers.

Re:Unbelievable Gravity (1)

Chris Burke (6130) | more than 2 years ago | (#39875285)

In this case the most likely culprit is charged particles from the event horizon stripping the sun of its outer layers.

Try tidal forces.

Re:Unbelievable Gravity (4, Interesting)

Anonymous Coward | more than 2 years ago | (#39875345)

Good maths and all but there's one thing you need to consider- If you're in stable orbit you don't actually fall inwards.

I think you've misunderstood my posts. I agree that a pointlike object in a circular orbit will remain in a circular orbit, absent any external factors. However, a non-pointlike object is actually in a range of orbits - different orbits for different parts of the object - and will drift apart unless held together. (Note that the separate parts, after this, will still be in orbit.) This is the same effect [wikipedia.org] that produces the tides on Earth; when an orbiting body is close enough to be torn apart by this effect, it's the Roche limit [wikipedia.org] . (You'll see a derivation equivalent to mine in both of those articles.)

Another way of thinking of it: as you say, it's not a case of the black hole pulling more than the star at a given distance. Instead, it's a matter of the difference between the pull of the black hole on different parts of the star being greater than the gravity of the star holding itself together.

I'm not sure where you got the idea that I was talking about the star being pulled into the black hole. That happens, certainly, but through a range of other effects: primarily, I would guess, through friction between the star and other material in orbit around the black hole. (You ascribed it to charged particles from closer to the event horizon, but these are emitted in jets perpendicular to the accretion disk, rather than omnidirectionally.)

Finally, I apologise for making an argument from authority, but I am an astronomer, though this isn't my exact field of research. I don't expect you to take my word for it, but I hope this will persuade you to read my posts in enough detail to understand the point you've missed.

Re:Unbelievable Gravity (2)

Lando (9348) | more than 2 years ago | (#39876503)

Um, no orbits are caused by falling. The fact that the moon is in orbit around the earth doesn't mean that it is not also falling around the sun. Just because the earth is orbiting around the sun, doesn't mean it's not also in orbit around the galaxy.

Re:Unbelievable Gravity (1)

Lando (9348) | more than 2 years ago | (#39876519)

Hmmm, also terminology you are using seems a bit wrong. The fact is that you aren't falling towards an object if you are in orbit because the horizontal velocity is such that even though you are being drawn together your horizontal position is keeping you from ever hitting. Again, you are always falling towards the object, stable orbit just means your horizontal velocity causes you to miss all the time.

Re:Unbelievable Gravity (1)

Jeremy Erwin (2054) | more than 2 years ago | (#39874545)

If Sagitarius A* is a supermassive black hole, with a mass of, say, 4.1 million solar masses, its radius is probably no more than 6.25 light hours-- 45 AU. This star drifted within 5.2 light hours-- 37 AU.

"light hours" have the advantage of conveying just how large a light year is--63240 AU, or (if you must), 5.87 trillion miles.

Or, to put another way.

Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.--Douglas Adams

Re:Unbelievable Gravity (3, Informative)

feedayeen (1322473) | more than 2 years ago | (#39874651)

At 3.5E billion miles, the gravitational acceleration from the black hole, which is about 3 million times the size of the sun is 12 meter per second squared, roughly the same as the Earth's gravity.

The star was described as being a red giant, using generous assumptions here favoring the star, the mass of the star being 10 times our own size and it's radius being 50 million miles, the surface gravity is about 0.2 meters per second squared, which is lower than Pluto's.

The star's orbital momentum helps it here since the acceleration due to this would roughly cancel out all of the gravitational acceleration, however this is at the center of mass, 50 million miles away from the surface. At this distance, the core of the star is only experiencing 97% of the gravity as the outside. That difference of 3% amounts to 0.36 meters / second squared of acceleration that was not canceled out at the surface.

Re:Unbelievable Gravity (1)

SpazmodeusG (1334705) | more than 2 years ago | (#39874675)

Gravity alone doesn't selectively pick out hydrogen and leave helium behind. I'm guessing that's more the usual atmospheric escape when an object gets too close to a mass of charged, high velocity particles. Earth can't hold onto it's hydrogen against the suns solar wind. In this case a sun can't hold out against a black holes radiation.

Re:Unbelievable Gravity (3, Informative)

Chris Burke (6130) | more than 2 years ago | (#39874827)

Giant stars like this are layered, with the heaviest elements that are undergoing fusion in the center and lighter ones as you go outward. So the black hole ripped away the hydrogen because that was what was the farthest out and thus bound the weakest to the star.

Re:Unbelievable Gravity (1)

SpazmodeusG (1334705) | more than 2 years ago | (#39874895)

It's not a matter of experiencing more gravity though. The sun has more pull on the moon than the earth. That doesn't mean the moon gets pulled into the sun. The hydrogen on the outer layers of this sun would still have more or less the same orbital velocity as the rest of the sun. There has to be something disrupting the orbit.

Re:Unbelievable Gravity (1)

Chris Burke (6130) | more than 2 years ago | (#39875271)

The hydrogen on the outer layers of this sun would still have more or less the same orbital velocity as the rest of the sun.

No it wouldn't, because the gravity gradient is very steep, and the star large. So the closer part of the star would like to have a substantially higher orbital velocity than the center of mass of the star, and would tend to want to be stripped off. A more massive (but equal size) star would hold onto its outer layers for longer. But once it comes too close, then the black hole's gravity (gradient) is simply too great and the star is ripped apart. Nothing needs to disturb it except said gravity.

Re:Unbelievable Gravity (2)

MillionthMonkey (240664) | more than 2 years ago | (#39875027)

Gravity does pick out some elements more than others. The Boltzmann distribution of helium atoms tails out at a much lower velocity than the distribution of hydrogen atoms. Near the top of the atmosphere, you will see many more hydrogen atoms than helium atoms shooting outward at escape velocity. This is why on Earth, we only have a tiny bit of helium to fill our balloons that came from radioactive decay of heavy elements, and most of it will someday make it into space.

Re:Unbelievable Gravity (0)

Anonymous Coward | more than 2 years ago | (#39876149)

Earth's atmosphere has had plenty of time to mix, so it's had time to reach its equilibrium state, in which the lighter molecules are more common higher up in the atmosphere. But a star's atmosphere is much thicker and denser, and the time it would take to thoroughly mix is greater than the lifetime of the star.

So you're right: if you left a star for long enough, it would end up with a higher concentration of hydrogen in the outer layers, and helium near the core. But in this case, the concentration of helium in the core is higher than you'd expect from that effect, for a somewhat simpler reason: fusion in the core is turning the hydrogen into helium.

Re:Unbelievable Gravity (1)

pwnyxpress (2597273) | more than 2 years ago | (#39874685)

Sounds like this black hole was almost as powerful as Bain Capital under Romney...

Roche Limit (2)

Immerman (2627577) | more than 2 years ago | (#39876401)

If you want to learn more about the phenomena this [wikipedia.org] might be a good place to start. That's the distance at which a satellite will be torn apart into a ring by the gravitational shear of its primary. First gasses, then liquids (both fluids, but liquid's higher density and stronger inter-molecular attraction would let it get closer), and finally, even rigid bodies will get torn apart. I would guess a star could be roughly modeled as a liquid body with a gasseous atmosphere. The formulas don't really account for bodies with non-uniform density, but I'm betting the atmosphere would elongate far more readily than the denser than the much higher density core and cross the limit much in advance of the rest of the star.

An interesting feature is that the Roche Limit is independent of the mass of the satellite, it's only the mass of the primary and density of the satellite that matters. Conceivably you could have two identical stars tearing each other apart as they approach their Roche Limits, though they'd probably just end up merging into a single rapidly-spinning star instead of forming an awesome ring-shaped star. Still, with enough angular momentum you might at least get an extremely flattened ovoid, that'd be kinda cool.

How is this different from a quasar? (2)

flyhigher (643174) | about 2 years ago | (#39873849)

How is this different from a quasar?

http://en.wikipedia.org/wiki/Quasar [wikipedia.org]

Re:How is this different from a quasar? (0)

Anonymous Coward | about 2 years ago | (#39873933)

Similar mechanism, less fuel?

Re:How is this different from a quasar? (2)

osu-neko (2604) | about 2 years ago | (#39873961)

How is a water droplet different from an ocean?

The material is the same, but it's a matter of scale. A single star ripped apart in a singular event does not a quasar make...

Hopefully it was Lindsay Lohan (-1)

Anonymous Coward | about 2 years ago | (#39873865)

The star that is. That was torn apart. I'm here all week.

Was it wearing a hoodie? (-1)

Anonymous Coward | about 2 years ago | (#39873957)

Then the star can shoot it in self-defense. You know, cuz it's black.

Re:Was it wearing a hoodie? (0)

busyqth (2566075) | about 2 years ago | (#39874085)

Wait does the hoodie play a part here or not? Is this just a lame attempt at current-events-race-related humor?

Re:Was it wearing a hoodie? (-1)

Anonymous Coward | about 2 years ago | (#39874141)

OK, maybe it was carrying a bag of Skittles. Then you can totally shoot it.

Where's the kaboom? (0)

NoNonAlphaCharsHere (2201864) | about 2 years ago | (#39874047)

There was supposed to be an earth-shattering kaboom!

And they did not report it to proper authorities! (0)

anwyn (266338) | about 2 years ago | (#39874205)

I bet those Astronomers did not report the event to the proper authorities! I bet they don't even know who to report to.

How can galactic central maintain an orderly galaxy, if astronomers are going to be apathetic?

Aliens (1)

Nesa2 (1142511) | about 2 years ago | (#39874211)

Might just as well be alien armada making it's way though galaxy destroying every planet for fuel. Let's not poke around there too much.

How can you see something going into a black hole? (0)

Anonymous Coward | more than 2 years ago | (#39874599)

I apologize if it's a dumb question, but isn't the whole point of a black hole that not even light escapes?

Re:How can you see something going into a black ho (4, Interesting)

VortexCortex (1117377) | more than 2 years ago | (#39875869)

I apologize if it's a dumb question, but isn't the whole point of a black hole that not even light escapes?

The gravity tore apart the star before it entered the black hole. Watching all the videos about black holes and space might lead one to think that orbits are easy to achieve, but after I ran some particle simulations [google.com] using simple Newtonian physics in my game engine, I noticed that most particles will slingshot around a source of heavier gravity when they approach, and be flung too far away for gravity to recapture it. In a stellar nursery this sling shot effect places a limit on the star's size, the other main contributing factor being initial density of the nebula. This is true for black holes as well as planets or asteroids approaching a star. So, although some of the star will fall into the black hole, a lot more of it gets flung away from the black hole -- It's a classic case of Conservation of angular momentum...

They're seeing what happens when something gets close to a black hole, not goes into it. You can see things "going into a black hole" before they've reached the event horizon. Also: In my sim, elliptical orbits that didn't result in the object being flung away became tighter and rounder orbits over time.

That schools don't have kids play with simple sims like these in class is Ridiculous! My high-school age little brother hasn't played a traditional game in three weeks. Since I gave him the gravity sim (particle engine stress test) to play with -- all he does is simulate solar systems and formation of stars, or big stars eating little stars, etc. It's the first time I've ever seen him interested in space beyond the Halo Universe! He asked me about Quantum Physics yesterday!

Re:How can you see something going into a black ho (1)

Mathness (145187) | more than 2 years ago | (#39876289)

Better watch him careful or he might build a spaceship [imdb.com] . :P

Note exactly rare (3, Interesting)

Manfre (631065) | more than 2 years ago | (#39874641)

This scenario was observed twice in two years. Not exactly rare when you realize how little of the sky we watch.

Re:Note exactly rare (1)

VortexCortex (1117377) | more than 2 years ago | (#39874963)

This scenario was observed twice in two years. Not exactly rare when you realize how little of the sky we watch.

So what if they're not early adopters? That doesn't make their statement invalid. Hell, most people don't even know about the new S.I. steak units.

Re:Note exactly rare (1)

FrootLoops (1817694) | more than 2 years ago | (#39875581)

From the article,

Events like this are rare; they probably only happen every 100,000 years or so per galaxy. So the astronomers looked at 100,000 galaxies, giving them good odds they’d see something like this once per year. Their gamble paid off.

Re:Note exactly rare (2)

l0ungeb0y (442022) | more than 2 years ago | (#39875613)

Considering that it's an event that's estimated to occur once every hundred thousand years per galaxy, I'd say it's rare. The fact that they watched over 100,000 galaxies, and got 1 per year as estimated does not diminish the sheer volume of galaxies watched nor decrease the rarity of the event.

Re:Note exactly rare (1)

Neil Boekend (1854906) | more than 2 years ago | (#39876681)

Doesn't matter, it's still awesome.

It's not that hard to find anymore... (1)

bughunter (10093) | more than 2 years ago | (#39874943)

Astronomers See Another Star Torn Apart By a Black Hole

What a coincidence... last night I watched Another Black Hole Torn Apart by a Massive Star. (Number 19, I think...)

As usual, the ending was no surprise. Some stellar material was ejected, and then Fin.

I blame Q (3, Funny)

citking (551907) | more than 2 years ago | (#39875095)

I think the Q continuum is at war again.

Re:I blame Q (1)

Ukab the Great (87152) | more than 2 years ago | (#39875303)

Give the guy a break. Laser watches and exploding pens don't work too well on a four million solar mass super villain.

Cough (1)

ezwip (974076) | more than 2 years ago | (#39875117)

These guys are wrong so often that an event occurring 2.7 billion light years away is probably inaccurate.

Old news (0)

Anonymous Coward | more than 2 years ago | (#39875439)

Reddit covered this 2.7 billion years ago. Slashdot is always late to the party but it was never this bad when Taco was in charge.

Black holes are just like wolves (0)

Anonymous Coward | more than 2 years ago | (#39875653)

Black holes tear things apart. This is just like wolves. People often find it surprising, that something as simple -as a pack of wolves- can tear a family apart. (Thanks again S.N.L.)

Your mom... (0)

Anonymous Coward | more than 2 years ago | (#39875857)

I can't believe your mom wandered as far as 2.7 billion light years away to eat an entire star...
She's even bigger than I imagined.

Fuzzy mosaics (0)

Anonymous Coward | more than 2 years ago | (#39875975)

Can someone explain to me how astronomers can tell with any accuracy exactly what they're looking at in these photos? I mean I know that they look for gravitic lensing or other "tell tale signs" but it just seems that every article I see about some amazing thing happening in deep space that the scientists are looking at pictures of stars that have been censored by Japanese porn studios. Anyway if someone could shed some light on this for me I'd be very grateful

What we are seeing is a History (0)

Anonymous Coward | more than 2 years ago | (#39876797)

Frankly its astonishing to imagine that we just witnessed a even which occured 2.7 billion years ago ( which is the distance that took light to reach us )

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