Hyperfast Star Ejected from the Large Magellenic Cloud

Occasionally, stars minding their own business around the supermassive black hole at the center of our galaxy get chucked out of the Milky Way, never to return. Fraser wrote about the discovery of two of these exiled stars, hurling away at the mind-blowing speed of over 1 million miles an hour. A recent study of another shows that not all of them originate in the center of our own galaxy.

New results from astronomers at the Carnegie Institute show that one star rocketing away from the Milky Way hearkens from the Large Magellanic Cloud, our neighboring galaxy. There have been ten such hypervelocity stars discovered, but where this one came from was quite a conunudrum.

Named HE 0437-5439, it’s nine times the mass of the Sun, and is traveling at 1.6 million miles an hour (2.6 million km an hour). The origin of the star has been a mystery until now because of its youth: it is 35 million years old, but it would have taken 100 million years to get to its current location if it were from the center of the Milky Way.

This meant that the star either came from somewhere else, or had to have formed out of the merger of two low-mass stars from the Milky Way, a so-called “blue straggler.”

Carnegie astronomers Alceste Bonanos and Mercedes López-Morales, and collaborators Ian Hunter and Robert Ryans from Queen’s University Belfast took measurements of the composition of the star – the first time this has been done on any hypervelocity star – and determined that its metal-poor makeup pointed towards the Large Magellanic Cloud as the former home of the castaway.

Bonanos said,“We’ve ruled out that the star came from the Milky Way. The concentration of [heavy] elements in Large Magellanic Cloud stars are about half those in our Sun. Like evidence from a crime scene, the fingerprints point to an origin in the Large Magellanic Cloud.�

Hypervelocity stars get their kick of energy from their interaction with a black hole. The stars were once part of a binary system, and as one star in the system gets captured by the black hole, the other is abruptly released, booting it clear out of the galaxy.

The mere fact that the Large Magellanic Cloud produced this hyperfast star hints at the presence of a black hole there, which has never previously been observed to exist.

Source: Carnegie Institute Press Release

18 Replies to “Hyperfast Star Ejected from the Large Magellenic Cloud”

  1. Is there any evidence that this particular Hspeed star has any flux in mass? is the speed constant? please reply. Thank you.

  2. Change in mass? Change in speed? What do you mean?

    Conservation of mass and energy preclude such changes.

  3. There are a few typos in this article, namely the 1 million miles (a distance, not a speed), and the conversion from mph to kph, which seems to have lost a factor of one million somewhere or other.

  4. I’m not sure what you’re complaining about with “…hurling away at the mind-blowing speed of over 1 million miles.”

    That’s really slow because the Falcon does the Kessel Run in 12 parsecs.

  5. Hmm I can walk 2.6 km an hour. Shouldn’t I be hurtling out of the galaxy too?

  6. I noticed the typos too. “1 million miles� is a statement of distance, not of speed. The author probably meant to add “per hour� to the end of that. He also thinks in English units, but giving the metric equivalent in parenthesis. However, in the metric equivalent of “1.6 million miles an hour�, he writes “2.6 km an hour� instead of “2.6 million km an hour�. Also, he is a bit careless with abbreviations. If he spells out “million miles an hour� then he should also spell out “kilometers an hour�.

    In ruling out the origin as the Milky Way, he writes, “The concentration of elements in Large Magellanic Cloud stars are about half those in our Sun.� Gas in the Magellanic Clouds in general is metal poor as compared to gas in our own galaxy. He should have inserted the word “heavy� before the word “elements�. Without that word, the sentence lacks meaning. A higher mass star will have a higher density, and therefore a higher concentration of elements, than a low mass star. The subject changes without that word.

    As others have noted, the author was less than clear on the mechanism for how a black hole might accelerate a star.

  7. Confused? If, a binary star system got close enuf’ to an Black Hole for one of the stars to be consumed, why would the gravational pull of the Black Hole release it’s effects on the remaining star and not gobble-it-up, as well?

    Are you suggesting, that a “slingshot” effect has been created by the Black Hole itself and its energy transferred to boosting, or knockin’ a homerun with the remaining star — outta’ the Magellanic Park?

    A Black Hole at the center of the Magellanic Cloud? Believe the Magellanic Cloud is made-up of gaseous vapors and dust from it’s self-termination… where’s the Black Hole?

    Very confusing, doesn’t make sense? Sorry, plese re-explain!

  8. Yup, I’m slightly confused too. Someone didn’t have their morning coffee before writing, now did they 😉

  9. typos aside (as I’m sure I’m not in a position to comment), the curious thing is a star traveling independently at such speed, assuming over the billions of year this has happened quiet a lot, the first stars would have burnt out and their massive cores would be traveling unseen very quickly in any direction … I wonder how close to us one would need to be before we’d notice it?

  10. Yeah, the writing was fast and loose but let’s get some things straight. The large Magellenic Cloud is so named because of what it looks like, not because of what it is made of. It is a satellite galaxy to our own and is made of stars and dust as is our own. It has no discernable symmetry so does not suggest a black hole centre. However, we have been finding black holes in the centre of more and more galaxies that we did not think would contain one. The description of how a binary star system is absorbed into a black hole is complex and difficult to describe without mathematics. I’m sure it has something to do with the conservation of momentum when one of the pair crosses the event horizon and the other is no longer orbitting but has the added momentum of being at the extreme inside of an accretion disk of a super massive black hole. You can see where there might be occasion for it to have accumulated quite a few “parsecs” or even “millions of miles”. Thank you to the folks who threw in the witticisms…nice to get a laugh here.

  11. Steve, with the speed of these things, and the size (which precludes us from having any say as to where it goes) we probably wouldn’t spot one until it was far too late. It would be well within the boundaries of our solar system before we knew it was there barring some sharp eyed infrared telescope being trained into the right quadrant that week. The likelihood is akin to reaching out your hand out of a car window and grabbing a Blue Morpho moth on the first try.

  12. Sorry about the typos, folks. I changed them to reflect the actual numbers and measurements, and not how Han Solo would have measured it. Touché with the Kessel Run joke 🙂

    A bit about how hypervelocity stars are ejected. Fraser’s article linked to in the beginning of the story explains it a little as well. Essentially, because of the conservation of angular momentum, when the one star in a binary system gets captured, the other has nothing more to rotate around. Think of spinning a ball attached to a string around your head, and then letting that ball go. Your hand is the star that gets trapped by the black hole, and the string – which is the gravitational bond between the two – is disrupted and lets the ball go free. The ball is just like the star that goes flying off, only at millions of miles (per hour, of course).

    As for the LMC black hole possibility: the mechanisms for creating hypervelocity stars is still in the works like many things in astronomy, but it’s been posited that the only way it can happen is through this interaction with a black hole. This discovery is tantalizing because of that fact, making it all the more cool! New Scientist had an article that focused on other researchers who postulate about a black hole in the LMC because of the star written about here. Check that out at: http://space.newscientist.com/article/dn11019

  13. I have not read one intelligable response to this article.
    Turn of the computer guys and go back to your reruns of star trek.

  14. Here’s an intelligable response:
    I don’t know where to begin here:

    D. Madison says: “Gas in the Magellanic Clouds in general is metal poor as compared to gas in our own galaxy. He should have inserted the word “heavyâ€? before the word “elementsâ€?. Without that word, the sentence lacks meaning. A higher mass star will have a higher density, and therefore a higher concentration of elements, than a low mass star.

    Oh my….
    Higher mass stars tend to be large, and mostly hydrogen and other light elements. They do not have a higher concentration of elements than, say, a red dwarf. It’s density may not be greater either. Compare Wolf-Rayet stars with white dwarfs.

    The word “heavy” is problematic too. Heavy elements in astronomy are anything greater than oxygen or so.

  15. Does anyone know where this star is currently located ,where its heading ,and the distance between our galaxy and the large Cloud ,edge to edge so to speak ?

  16. Nicholas:

    Appreciate your reply to my original post questioning the binary-star theory. Have for some unknown reason been thinking about the physics, and am convienced it could not have a binary-star.

    Tour example of a ball attached to a string and swung around your head doesn’t work, as the fulcrum would not be your hand, but instead a point somewhere in between depending of the size of the objects and the gravtional properties shared between them.

    However, believe your on the right track, but instead of a binary-star… it could have been accelerated by a TRINARY STAR, whereas, the larger (or, 1st) star was trapped by the black hole’s gravational pull, and it’s release was an accelerated by a close pass of the remaining star (or, 3rd star) around the remaining (or, 2nd star) accelerating it out of the grational pull of its’ sisters, both of which were gobbled-up by the black hole.

    Just a thought, but the fulcrum would not be your, therefore, in my mind (at least) it doesn’t fit the physics.


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