Astronomers See Another Star Torn Apart By a Black Hole

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."

Comments

Why it gotta be a "black" hole?

[PopeRatzo]

I prefer "hole-of-color".

Unbelievable Gravity

[schwit1]

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

"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

[Anonymous Coward]

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

[feedayeen]

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

[Anonymous Coward]

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

[SpazmodeusG]

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

[Chris Burke]

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

[Anonymous Coward]

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 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. (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.

Will black hole devour dark matter, anti-matter?

[Taco Cowboy]

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

[Beryllium Sphere(tm)]

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

Re:End of the world

[ObsessiveMathsFreak]

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:Will black hole devour dark matter, anti-matter

[Yew2]

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?

Note exactly rare

[Manfre]

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

Re:Will black hole devour dark matter, anti-matter

[Trax3001BBS]

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

[robot256]

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

[Bengie]

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

I blame Q

[citking]

I think the Q continuum is at war again.

Re:Will black hole devour dark matter, anti-matter

[FrootLoops]

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,

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.

Re:Will black hole devour dark matter, anti-matter

[robot256]

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:How can you see something going into a black ho

[VortexCortex]

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 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:Will black hole devour dark matter, anti-matter

[Immerman]

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 de

You're both right

[Immerman]

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

[Immerman]

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 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:Will black hole devour dark matter, anti-matter

[Neil Boekend]

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