Astronomers weigh in on teeny stars

By Phil Plait | June 2, 2008 12:30 pm

More brown dwarf news came out of the last press conference: the masses of some of the lowest mass brown dwarfs have been found using the powerful Keck telescope in Hawaii. They did this by precisely measuring the orbits of binary brown dwarfs, and from the well-known equations of how bodies orbit one another the masses were found.

Images of the two brown dwarf binary systems from the Keck telescope. Credit: Michael Liu (IfA, U Hawaii) and Trent Dupuy and Michael Liu (IfA, U Hawaii), respectively.

Amazingly, one binary system (2MASS 1534-2952AB) appears to be comprised of two brown dwarfs each of which have only 3% the mass of the Sun! This makes them the lowest mass and coldest objects (outside of extrasolar planets orbiting other stars) for which a mass has been found. Another binary (HD 130948BC) was measured as well, and each star has a mass of 5.5% the mass of the Sun — and as you can see in the image above, this pair orbits a third star which is more like the Sun, which is why it appears so much brighter.

While this is pretty nifty in and of itself, it gets better when these masses are compared to the theoretical masses of the brown dwarfs derived from the equations expected to describe them, and then looking at the other characteristics of the failed stars. When that’s done, the first pair is cooler than expected, and the second pair warmer! That means the theories need to be tweaked a bit. It’s probably not anything hugely serious, but it’s interesting nonetheless.

Both binaries are about 50 light years from the Earth — if they were much farther away they’d be too hard to study, even with Keck — and in both pairs the stars are separated by about twice the Earth-Sun distance.

Note to my readers: if you like any of these news stories coming out of this meeting, then please feel free to click the yellow Digg button to help spread the word! Thanks.

Comments (17)

  1. Kaptain K

    Couldn’t the temperature variance be due to age? IIRC, brown dwarfs start out burning deuterium, so very young ones would be hotter than expected if compression heating was the sole source of internal heat.

  2. Andy Hefner

    Nice to see a return to astonomy-related postings.

  3. alfaniner

    There are no small roles, only small stars.

  4. Sili

    I assume that the second pair is warmer than what can be explained by their grown up neighbour, right?

    I mean, I’d expect them to be warmer with that big furnace in their backyard.

  5. Gavin Flower

    Hmm…

    A minor correction… you had used
    “appears to be comprised of two brown dwarfs”
    which should be replaced by either of
    “appears to be composed of two brown dwarfs”
    or
    “appears to comprise two brown dwarfs”.

    According to my Oxford dictionary “comprise” means “be composed of”!!!

    …Now I can get back to enjoying the fascinating article…

  6. Fascinating stuff! I’m writing and illustrating a sci-fi graphic novel and doing research on everything from star formation to theoretical gravity engines. I just can’t get enough science!

  7. Utakata

    Andy Hefneron wrote:

    “Nice to see a return to astonomy-related postings.”

    That’s Obama and Clinton orbiting each other on the top left. The big green one on the bottom right is McCain.

  8. TomAschenbach, I don’t know that I would characterize gravity engines and other things of that nature as scientific, hence the name science fiction.

  9. Brian

    Now if only we can get the Jovian planets to merge. Would there be enough mass to form a brown dwarf?

  10. Mount

    So if I was looking to buy a house on a planet, err moon, that was orbiting a pair brown dwarfs, that were orbiting a larger star… Would that be a good neighbohood or not?

    The seasons would sure be interesting!

  11. Ronn Blankenship

    Phil wrote:

    “Note to my readers: if you like any of these news stories coming out of this meeting, then please feel free to click the yellow Digg button to help spread the word! Thanks.”

    If I may ask what may to some seem a dumb question: what exactly does doing this accomplish?

  12. Alan B.

    Brianon:

    Now if only we can get the Jovian planets to merge. Would there be enough mass to form a brown dwarf?

    A brown dwarf is generally defined as at least 12 Jupiter masses.

  13. Steve P.

    If the Helix Nebula is the Eye of God, then these are surely the eyes of Satan and his pal The Hulk. Interestingly, the Hulk’s ad appears on this page.

    Cue Bette Midler:

    “The Hulk is watching us, the Hulk is watching us, the Hulk is watching us…..

    from a distance.”

  14. Irishman

    Ronn Blankenship said:
    > Phil wrote:
    > “Note to my readers: if you like any of these news stories coming out of this meeting, then please feel free to click the yellow Digg button to help spread the word! Thanks.”

    >If I may ask what may to some seem a dumb question: what exactly does doing this accomplish?

    Generally degrade the quality of the comment posts. ;-)

    Seriously, I’ll take a WAG. Digg is a social networking site that works by having users rate stories. The more positive ratings the story gets, the higher it goes in the list, sort of like getting closer to the front page. Ergo, clicking the Digg button will add a tick to the popularity of the article on the Digg site, moving it ever so higher in the rankings, thus attracting more attention, so more people will see it and thereby learn, and possibly come over here and annoy us with witless comments.

  15. StevoR

    # Utakata on 02 Jun 2008 at 4:11 pm


    “Andy Hefneron wrote:

    “Nice to see a return to astonomy-related postings.”

    That’s Obama and Clinton orbiting each other on the top left. The big green one on the bottom right is McCain.”

    Nah! Obama is the big star! After all, he’s the best American presidential candidate well pretty much since JFK and maybe ever. ;-)

    McCain, well his light was never very bright and is fading with his increasing age & (c)oldness. He’s your worst Presidential candidate since .. well Bush the lesser.

    So its the Big bright star of Obama being orbited by his rivals Bill & Hilary Clinton (also stars but dimmer ones) with a (hypothetical) long-dead cratered barren and useless Moon-like world representing that old turkey McCain on the far distant outskirts of this Symbolic Political Brown Dwarf system. ;-)

    Really, from this non-Americans’ POV, I honestly cannot understand why anyone would even imagine voting for the currently in power pro-war, anti-science Retardican party or an ancient, semi-senile and probably about to go incontinent old fool whose main claim to fame was being shot down by enemy forces decades ago and whose campaign promise is “.. 100 more years in the hellish quagmire of Vietnam ..er .. Iraq!” ;-)

    … & isn’t it amazing how absolutely any topic can be turned into politics … Sigh. :-(

  16. StevoR

    # Alan B. on 03 Jun 2008 at 5:50 am
    “Brianon:

    Now if only we can get the Jovian planets to merge. Would there be enough mass to form a brown dwarf?

    A brown dwarf is generally defined as at least 12 Jupiter masses.”

    … & I don’t think there’s enough mass even if you could somehow combine Jupiter, Saturn, Ouranos & Neptune all together …

    Pretty sure, Jupiter accounts for most of the mass of the solar system that isn’t in the Sun.

    Amazing images & good coverage of the story -Thanks BadAstronomer!

    Plus of course we’ve just had more brilliant (possible) brown dwarf news in the next story on MOA-2007-BLG-192Lb (& for flips sake astronomers, let’s give such objects decent real names!* Such unwieldy labels impede communication to the public. ) and its low-mass planet.

    Clearly, its a good week for brown dwarfs! 8)

    ——
    * I suggest following the Barnard’s Star, Van Maanen’s Star, Plaskett’s star(s) tradition & renaming MOA-2007-BLG-192Lb “Bennett’s star” because he’s the lead astronomer on the discovery team. If he makes another big discovery for another such star then he gets to name it some other reasonable name. That’s dignified, shorter, pronounceable and an incentive for people to study astronomy. Or call it “the Moa star” (although as a big project / survey we could end up with many of them – Moa-1, Moa-2 etc .. too many?) or perhaps we could use a name from the constellation or nearby stars alternatively or something … anything .. other than such wretched catalogue “names”! Please!

  17. StevoR

    Or again, on better names for MOA-2007-BLG-192Lb how about we follow the Moa theme but shift to other flightless birds for other interesting or significant systems discovered by that survey project.

    For examples; the first major find (say, MOA-2007-BLG-192Lb ) could be called the Moa star, the next one the Emu star, then the Ostrich star, the Cassowary star, the Penguin star, et cetera …

    After all there’s already a Peacock star (Alpha Pavonis) see :

    http://www.astro.uiuc.edu/~kaler/sow/peacock.html

    ;-) :-) 8)

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