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

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

[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: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: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

[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

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

[Anonymous Coward]

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.

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.