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

[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: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

[Neil Boekend]

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