Vampires and thrillseekers rejuvenate dead stars

By Phil Plait | December 23, 2009 11:00 am

I have a tale of death, near death, and undeath to weave for you, but first, gaze upon the jewel-like beauty of the glittering denizens of M30:

hst_acs_m30

This image was taken by the Advanced Camera for Surveys on board the Hubble Space Telescope. I had to cut it and compress it drastically to get it to fit on the blog, so you very much want to click on it to embiggen it massively and see it in its fully resolved glory.

The image is of the insanely beautiful globular cluster M30, an ancient city of a few hundred thousand stars located 28,000 light years away in the constellation of Capricornus. The cluster is ancient, about 13 billion years old, making it as old or even older than the Milky Way itself. The core of the cluster is unusually dense as such things go, which is why it was studied. Where better to find vampires and thrillseekers?

Like people, stars are born, age, and die. Stars born with more mass tend to die off more quickly, consuming their fuel at far higher rates than their lower-mass brethren. These stars tend to be blue, so in an old cluster like M30 you’d expect to see no blue stars at all; they should all be long gone. And yet, there are quite a few — astronomers call them blue stragglers. Where did they come from?

One theory, which has been borne out by observations, is that blue stragglers are in tight binary systems, with a dead star in such close proximity to a normal star that it can siphon off the normal star’s gas, using it to rejuvenate itself. This would make them vampires, of course, sucking the life force of other stars in an attempt to stay young.

But another idea was that dead stars might also physically collide with other stars and merge, forming a single star that would burn blue and bright. In an environment like that near our own Sun this kind of collision can almost literally never happen; even considering the entire Milky Way Galaxy over its entire lifetime a head on collision has probably never happened out here in the stellar suburbs.

But that cluster M30 is pretty densely populated with stars, and collisions are far more likely. What observations like this one of the cluster (and also of an ancient cluster called NGC 188) have shown is that the blue stragglers appear to have two different sub-groups; one that appears to have come from the vampire stars, and another from stars that have collided: thrill-seekers, stars that have physically slammed into each other and merged, their combined mass separating them from the other blue straggler group.

Blue stragglers have been known since the 1950s, and the idea that they were pulling gas off nearby stars was proposed to explain them, too, but it’s only with our modern instrumentation that we can not only show that this is true, but that a second, far-fetched-sounding scenario of collisions also contributes.

I find it wonderful and extremely uplifting that an image as spectacular and gorgeous as the one above — it became my desktop wallpaper as soon as I saw it! — not only satisfies our desire for beauty and art, but can also be tapped to deliver incredible science that boosts our awe of what Nature can do. I love that we can understand such things, but you know what I love even more? The idea that we have only begun to understand the Universe.

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (33)

  1. Hmm…that could explain vampires that sparkle when sunlight hits them…

    I have this image of a bunch of crazy teens jetting around in their convertible starmobile, playing chicken with oncoming balls o’ plasma.

  2. “The idea that we have only begun to understand the Universe.”

    Well, I’m glad that “climate science” is settled so we can get to work on the rest of it.

  3. Chris A.

    Ahh, M30, the bane of my existence (the lone object that prevented me from completing a Messier Marathon a few years ago, invisible in bright morning twilight)!

  4. Who says science can’t be beautiful?

  5. Paul

    I think calling the merger model “zombies” would fit better with your vampires…

  6. Actually, Paul, I thought of that too… after I posted this. Sigh. But funny. :)

  7. vanderleun (#2) you are rapidly approaching troll status. Give it a rest, please, especially in posts where it’s off topic.

  8. bk

    oh, shiiiny… my new wallpaper… thats just stunning. Edit: damn… its a bit blurry =( i’ll check the massive one, doubt i’ll see any change though…

  9. Harman Smith

    Wow, the high-resolution version of that picture is dazzling.

  10. Big Al

    You can almost convince yourself it is in 3-D when embiggened. How many years of observations would be necessary to get views that would show relative motion within the cluster. Sigh, probably way too many for me to live long enough to see it. Beautiful, though.

  11. Gus Snarp

    So cool. You keep making me change my wallpaper, but this one is perfect for the holidays!

  12. DrFlimmer

    Wallpaper? Indeed. And yes, perfect for the upcoming days!

  13. Really, blue stragglers? I think most of those blue stars are just helium-burning “horizontal branch” stars.

  14. DrFlimmer

    @ Michael:

    Aren’t those supposed to be red?

  15. Number 6

    Would a star-star collision rate as a type-III supernova? Has one ever been seen or suspected?

  16. rob

    i would really like to see stars collide. talk about fireworks!

  17. Larry

    My god, it’s full of stars! I wonder what the sky would look like from a perspective located deep within that cluster.

  18. andy

    Incidentally the well-known star Regulus is likely in the “vampire” class of blue straggler system (though not being in a globular cluster it isn’t technically a blue straggler). In 2008 it was discovered to have a white dwarf binary companion in a close orbit. It is likely that the primary star accreted both mass and angular momentum from the companion when it went through its red giant stage, and is now a rapidly-rotating B-type star.

    Regulus has yet more episodes of mass transfer ahead of it: when the primary goes through its own red giant stage, it will transfer mass back to the white dwarf, forming a common envelope binary. After that there are several possibilities, including that it may eventually evolve into an AM Canum Venaticorum-type binary (a cataclysmic variable involving mass transfer between two white dwarfs).

  19. Grant

    Nice galaxy in the upper left hand corner.

  20. Scott Smith

    Judas Priest, Phil. You should hand out some eye protection before urging people to embiggenfy that image. Dang near burnt out my optic nerves when I largenated it, sitting here in the dark. I wonder if I need to find a corneapractic now? ;-)

  21. StevoR

    Beautiful. I totally agree with that last paragraph there BA. Spot on. :-D

    Please BA,when it comes to a another “top 10 pictures of 2009″ I’m gonna have to do an “Oliver Twist” and ask “Please sir can we have some more?” Preferably once this year actually ends so these & other magnificent images ,i>(who knows what’s still to come) don’t miss out!

    I’d have to add this one & one of the Jupiter impact and the ‘Janus shadowed by Saturn’s rings’ and the Shuttle-ISS as an artificial “sunspot” & ‘Titan’s Kraken mare glints’ & some more from Cassini and a few others too to my top ten list if I were you.

    (Which, I guess luckily for you, unluckily for me I’m not! ;-) )

    @ 2. vanderleun : I agree with you but I also agree with the BA that this is NOT the place to raise this issue. Please save it for a specific greenhouse / AGW thread – which I’d like to see more of & *much* more skeptically viewed by our blogger & host here.

    @19. Grant Says:

    Nice galaxy in the upper left hand corner.

    Sorry but I can’t see that one. Not in the image provided above anyhow. :-(
    Do I need to click the embiggened version to spot it? Is it a spiral or elliptical or other?

    @ 18. andy Says:

    Incidentally the well-known star Regulus is likely in the “vampire” class of blue straggler system

    Very true – & this spinning up of Regulus A by its (now) white dwarf companion may have helped create Regulus’es flattened shape. Although the even more egg-shaped Achernar has no known companions and is too massive & thus young to be accompanied by a white dwarf so its clearly not the whole or only reason for such stellar distortion. BTW Achernar about 6-8 solar mass is on the border of stars that will go supernova.

    Ken Croswell has a good page or two on his website about this with Regulus – see :

    http://kencroswell.com/RegulusWhiteDwarf.html

    &

    http://kencroswell.com/RegulusIsOblate.html

  22. Todd W

    Thanks mate for that quote back in the Holey Rollers post
    “You are my sun, my moon, my starlit sky. Without you, I dwell in darkness.”
    That, combined with this image, made a great christmas card for the “wife to be”.

    Regards
    John

  23. RBH

    Phil, you wrote

    The cluster is ancient, about 13 billion years old, making it as old or even older than the Milky Way itself.

    Doesn’t 13 billion years put in the close company of the very first galaxies in the universe post-Big Bang? The oldest I’ve seen referred to is 750my post-Big Bang, which is about where “13 billion years old” would put M30, no?

  24. Cyberdraco

    I literally had goosebumps when I visualized a Cosmic vampire star…How wonderful it is to be star stuff.

  25. Alan T

    WOW! Sorry, best i could do after retrieving my jaw from the floor.

  26. Peter B

    What a fascinating pair of concepts.

    I’m trying to wrap my head around the idea that one star extracts material from its binary twin. In particular I’m thinking about what happens to the siphonee – as it loses material, the relative masses of the two stars will change, which presumably must affect the orbit of the two stars around each other. Could someone explain what happens as this process continues? Would the siphoned star orbit inwards as it lost mass? Would the gas in the vicinity act like an atmosphere providing aerobraking for a spacecraft? Does this mean the siphoned star will eventually crash into its larger twin? Enquiring minds want to know!

  27. @DrFlimmer, HB stars are blueish to yellowish, but more luminous than main sequence stars of the same color. When you look at a high-res color image of a globular cluster, you mostly see the luminous red giant and AGB stars, and then the next brightest stars are the blueish HB stars. The main sequence stars (including the rare blue stragglers) are much fainter. E.g., see the HR diagram figure in the middle of these lecture notes: http://tinyurl.com/y989emb

    Oh, here’s a better color-vs.-brightness plot for the globular M13: http://tinyurl.com/y875qj8

  28. Gary Ansorge

    25. Peter B:

    I rather doubt there would be any orbital degeneration, as the total mass of this two star system would be constant but the common center of gravity would shift as mass is transferred from one star to the other.

    GAry 7

  29. toasterhead

    What does the age of a cluster refer to, exactly, and how is it determined? Is it the time at which that group of stars began aggregating around a common center of gravity, or is it determined by looking at the chemical composition and estimating how many life-cycles the stars within the cluster have been through?

  30. andy

    Mass transfer does change the orbital semimajor axis. IIRC, for conservative mass transfer (no mass lost from the system), transfer from the more massive star to the less massive one causes decrease of semimajor axis, transfer from the less massive star to the more massive one causes increase of semimajor axis.

  31. Way cool! I’m still trying to understand how light has mass. When rays of light pass by black holes, they bend. Where the gravity is really strong, the light doesn’t escape at all. Anyone?

  32. Darren

    Maybe the stars are being transported from a black hole and are just coming out of an event horizon then speeding off into space. I just cant see how that many stars can coexist without running into each other.

  33. I wonder: are there any estimations at how long a star merger would take? Is there ANY chance to actually catch one in the process? Are there any known stars that are about to merge in this way in said cluster (or any other)?

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