Forgot your password?
typodupeerror
Space Science

Astronomers See Another Star Torn Apart By a Black Hole 127

Posted by samzenpus
from the dr.-reinhardt-approved dept.
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."
This discussion has been archived. No new comments can be posted.

Astronomers See Another Star Torn Apart By a Black Hole

Comments Filter:
  • by PopeRatzo (965947) on Wednesday May 02, 2012 @06:54PM (#39873721) Homepage Journal

    I prefer "hole-of-color".

  • Unbelievable Gravity (Score:5, Informative)

    by schwit1 (797399) on Wednesday May 02, 2012 @07:10PM (#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?

    • by Anonymous Coward on Wednesday May 02, 2012 @08:33PM (#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: (Score:3, Interesting)

        by 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

        • by SpazmodeusG (1334705) on Wednesday May 02, 2012 @09:03PM (#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.

          • by Chris Burke (6130)

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

            Try tidal forces.

          • by Anonymous Coward on Wednesday May 02, 2012 @10:43PM (#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.

          • by Lando (9348)

            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.

            • by Lando (9348)

              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.

    • 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

    • by feedayeen (1322473) on Wednesday May 02, 2012 @08:44PM (#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.

    • 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.

      • by Chris Burke (6130) on Wednesday May 02, 2012 @09:13PM (#39874827) Homepage

        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.

        • 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.

          • by Chris Burke (6130)

            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.

          • by ultranova (717540)

            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.

            First, tidal forces [wikipedia.org] will tear the star apart, then the resulting ring of gas will heat up due to friction (since layers closes to the hole will move faster), which causes the gas to radiate away its potential energy and spiral into the hole.

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

    • by mcgrew (92797) *

      You have to remember that the black hole has a mass millions of times that of the star. A pebble next to a mountain. And it didn't "out-gravity" it, gravity doesn't work that way. Your mass pulls the earth with the same force that the earth pulls on you. The star tugs at the black hole with the same force that the black hole tugs on the star, but the black hole is so big it no more notices the star than the earth notices an ant. There's already a comment explaining how the difference in gravity from one sid

      • by MickLinux (579158)

        I would think that the SC radius would indicate that relativistic gravity [for want of a better term] does not behave quite the same as classical gravity. Therefore, there will be some different gravitational effects.

        Also, there's plenty that's lighter than hydrogen.

        There's hydrogen nuclei, for example.
        There's electrons.
        There's quarks in that state of being ripped apart from each other, just as a new quark / antiquark pair is forming... which in normal physics would cancel out the old quark, leaving the n

  • How is this different from a quasar?

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

    • by osu-neko (2604)

      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...

    • by Shoten (260439)

      I don't get it. You ask the question, and post a link to the answer? A quasar is a supermassive black hole at the center of a galaxy. This (what the Slashdot post refers to) is a more normal black hole that happens to be next to a star, and is going 'NOM NOM NOM' on it.

  • There was supposed to be an earth-shattering kaboom!
  • 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?

  • by Nesa2 (1142511)
    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.
  • Note exactly rare (Score:4, Interesting)

    by Manfre (631065) on Wednesday May 02, 2012 @08:43PM (#39874641) Homepage Journal

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

    • 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.

    • 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.

    • by l0ungeb0y (442022)

      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.

    • Doesn't matter, it's still awesome.
  • 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 (Score:4, Funny)

    by citking (551907) <(jay) (at) (citking.net)> on Wednesday May 02, 2012 @10:01PM (#39875095) Homepage
    I think the Q continuum is at war again.
    • Give the guy a break. Laser watches and exploding pens don't work too well on a four million solar mass super villain.

  • our galaxy?

    Anyone with some astrophysics background want to describe what this would be like? Is it directional? would we be fried if we were in the beam? or would it just look pretty in the day and night sky?

    Just curious for someone in the field to describe it.

    • by Coren22 (1625475)

      IANAAP (Astrophysicist)

      My understanding of this event is that it required a black hole from the center of the galaxy, such as Sgr A* in the center of the milky way. My guess, is that the jets would be faced perpendicular to the galaxy, so we would see them from the side. It might be bright, but from so far away in our galaxy and not head on, I doubt it would have an effect on us. I am more concerned about Betelgeuse going supernova as it is rather close.

  • by Shoten (260439)

    Which star is Courtney Love dating now, then?

  • Reading the article I am struck by just how little fact and data this is based on. This is something that happened 2.7 billion light years away and this is one possible explanation for what happened. I have no idea of how likely it is to be the correct explanation, but I didn't read anything that told me that it was the only explanation.

    With that in mind, I am happy to float the possibility that this flash in a very distant galaxy, very long ago, was actually a mega-strike in a intergalaxial war. I have abs

  • by g0bshiTe (596213)

    Although rare, this is the second time such a thing has been seen; the other was just last year."

    We've seen 2 in a year, how freakin rare can they be?

"The algorithm to do that is extremely nasty. You might want to mug someone with it." -- M. Devine, Computer Science 340

Working...