WISE finds coolest brown dwarfs ever seen!

By Phil Plait | August 24, 2011 6:29 am

How cool is this? Literally, the coolest: NASA’s Wide-field Infrared Survey Explorer has found the lowest-temperature brown dwarfs ever seen, the tail end of the stellar class of brown dwarfs called Y dwarfs. How not hot are they? This one (called WISE 1828+2650 if you’re playing brown dwarf bingo), spotted by WISE, has a surface temperature of 25° Celsius — that’s 80° Fahrenheit!

As I sit here and write this, it’s warmer outside my window than it is on the surface of that object!

Not only that, another Y dwarf they found, called WISE 1541-2250, may be the seventh-closest object in the sky outside our solar system. The distance found is not directly measured; it was calculated using the brightness of the brown dwarf. The distance was found using parallax. Even though it’s only about nine light years away, it’s incredibly faint. The only reason it was seen at all is that WISE is tuned to see in the far-infrared, where these things are far brighter than in visible light.

The most exciting part about this is it supports an idea I’ve had (and lots of others have had too) for a long time: Proxima Centauri may not be the closest object to the Sun. A Y-class brown dwarf could be even closer and still have evaded our detection. Even at four light years away — roughly how far Proxima Cen is — a Y star would be pretty hard to see. We may not know for a while yet, but it’s possible.

So what’s the deal with brown dwarfs? These are objects more massive than planets, but not massive enough to be true stars. Some astronomers classify stars as objects that can sustain nuclear fusion in their cores. In a star like the Sun, that’s due to its mass; there is enough crushing pressure in the core to fuse hydrogen into helium. A lower mass object, like a planet, can’t do that. It lacks the oopmh to squeeze atoms together tightly enough. The lower limit for this mass is about 75 times that of Jupiter, equivalent to about 7% of the mass of the Sun.

Somewhere between that mass and that of a planet is a brown dwarf. Definitions vary — I’ve seen some fun and lively arguments about it! — but most astronomers don’t consider brown dwarfs to be true stars. A BD might once have been able to fuse deuterium (an isotope of hydrogen) or lithium in its core, but that shuts off pretty quickly as the BD ages. By the time they’re a billion years old or so, they don’t generate their own energy, and just sit there cooling off. The lower mass they are, the more quickly they cool, and Y dwarfs are the coolest of them all. If you want to call them stars — and that’s fine with me — then this means these objects found by WISE are also most likely the lowest mass stars ever seen.

During the time it spent surveying the sky, WISE found at least six of these ultra-cool objects, ranging from 9 to 40 light years away. Due to the combination of the light they emit and the filters used by WISE, they appear green in WISE images… which brings up an interesting question: what color would these things appear if you were near one?

That’s hard to say. Low-mass stars, say down to about a tenth the Sun’s mass, look red. But as you look at cooler objects like brown dwarfs, things get complicated. For example, once the temperature is low enough, molecules like water and even methane can exist in the object’s atmosphere. These absorb certain colors of light, changing the color of the BD itself. There’s some thinking that very cool stars, like Y dwarfs, might be magenta in color! I’d love to see that. But that’s why the artist’s representation of a Y dwarf, shown here, is colored purple. No one’s really sure, though.

I find these objects pretty interesting for many reasons — I studied them briefly when I worked on Hubble, and we got a visible-light spectrum of the first brown dwarf ever discovered, called Gliese 229b. But more than that, I like things that push limits. What’s the difference between a brown dwarf, a star, and a planet? Making definitions is a dangerous game; even something as simple as "planet" can cause pretty good arguments. In this case, the definition of "star" gets fuzzy on the low end. What if an object fused deuterium, but only for ten minutes? What if it has enough mass to fuse deuterium but never could because its core never contained deuterium?

What nature is telling us, I think, is that definitions only serve to limit our imagination. Nature doesn’t work in definitions; only humans do that. Don’t worry about what to call something so much as worry about what it is.

Image credit: NASA/JPL-Caltech/UCLA.


Related posts:

- Two new nearby brown dwarfs found
- WISE finds the coolest star. Literally.
- The case of the brown dwarf that’s really red or possibly blue
- Dim, faint, and small is no way to go through life, son

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: brown dwarfs, WISE, y dwarfs

Comments (47)

  1. Derek

    so – would this thing have a solid surface??

  2. VinceRN

    Very cool star.

  3. Anchor

    “What nature is telling us, I think, is that definitions only serve to limit our imagination. Nature doesn’t work in definitions; only humans do that. Don’t worry about what to call something so much as worry about what it is.”

    Beautifully said Phil!

  4. JupiterIsBig

    What, no “click to dedwarfinate” line ?
    Did the word police get to you ?

    Brown and red dwarfs will forever remind me of Brian Cox’s line about how humanity might huddle up to one for a few billion years after the stellariferous age ends just like he was huddling up to a fire in the desert !

    [Then I read the previous post and find you already used an undwarfinate line, so I wasn't being original :-( ]

  5. Diederick

    Excellent. A star with its goldilocks zone on its surface.

  6. IVAN3MAN_AT_LARGE

    [...], has a surface temperature of 25° Celsius — that’s 80° Fahrenheit!

    Actually, that’s 77° F (as if I cared about bloody Fahrenheit!).

  7. J

    If the surface temperature is “only” 25 degrees Celsius, does it mean it is solid? As in, could you literally walk on the surface of this star and live?

  8. Lavocat

    I understand that the term “brown dwarf” is politically-incorrect. They prefer the term “swarthy little star” or SLS for short (pardon the pun).

    In any event, Phil, you just blew my mind. Again. It’s cooler INSIDE my house than it is on the surface of that stellar object!!?? Words fail me.

  9. Lavocat

    I meant to say “warmer”. But it’s cooler, too, with this new amazing information. Who’s to say this sort of thing isn’t the ever elusive “Planet X” that keeps popping up in the popular culture every decade or so? Might we have one of these strange things parked right outside our immediate solar system, somewhere in the Kuiper Belt or Oort Cloud?

    You’ve EASILY made my day AND week with this wild info.

  10. Jason

    Is it possible to find liquid water on these? Or would it just be water vapor? Is it possible to have a layer, some depth down that is water?

  11. Justin

    How long would a star like this maintain its temperature? I wouldn’t image that an 80° object sitting in space without generating energy would stay that warm for very long.

  12. Piper

    So, would one of these things be habitable? With a mass greater than Jupiter, it would probably have very high gravity (by human standards). And according to Wikipedia, they have a convective surface, so nothing solid to stand on.

    Would life be possible in an environment like that?

  13. Pete Jackson

    So WISE’s detectors are at 3.4, 4.6, 12 and 22 microns wavelength. So, based on Wien’s Law that the peak of a blackbody distribution is near 2900/T, where T is the temperature in Kelvin, then WISE 1541-2250 (T = 25C = 298K) presumably is seen brightest with the 12 micron detector.
    The 22 micron detector would be sensitive to far cooler objects, near 131K, about the temperature of Jupiter! If they find something there, I bet it would be closer than Proxima Centauri!

  14. Åsmund

    @Justin: It won’t keep its temperature. It is cooling very very very slowly. But the colder the brown dwarf is, the less energy it radiates, and the slower it cools. The time to cool from 35°C to 25°C is much longer than the time to cool from 1010°C to 1000°C.

  15. Really love that last paragraph, it’s so true!

  16. But with what precision is that temperature estimate? Considering what we are talking about is a) kinda-sorta a star, and b) 9 light years away, isn’t any temperature estimate going to be +/- 1000C anyway?

  17. allium

    As I sit here and write this, it’s warmer inside my skull than it is on the surface on that object!

  18. So one of these little suckers could sneak up on us, say, Dec. 21 of 2012?

  19. andy

    Should provide some insight into what we might expect to see when we finally get images of some of the radial velocity planet candidates. At that temperature the brown dwarf would be dark in visible light, unless it is being illuminated by something else (same goes for the late-type T dwarfs).

  20. DigitalAxis

    I find it very interesting that we’re in the temperature (and probably mass) range of planets. These objects may be ejected planets, not stellar-like objects that formed on their own.

    @9 Lavocat and 18 NCC-1701Z:

    It’s possible, but unlikely. If WISE could see these objects at a distance of 40 light years, they could CERTAINLY have spotted it at a distance of less than 1. The real problem is identifying it.

    Even at that distance, the orbital motion of a brown dwarf in solar orbit should be larger than the expected proper motion for a star (and if it was in a part of the sky they only scanned once, you’re out of luck.) For reference, the fastest moving star (as seen from Earth, right now) is Barnard’s Star, which takes about 180 years to cross an area of sky the size of the Moon. Solar system objects move that much in DAYS. WISE would probably assume the object was two detector glitches.

    The other problem is temperature: WISE could pick up an extremely cold object at, say, 10,000 AUs, but they might not recognize it as a brown dwarf, because they’d have no basis for comparison. Maybe with Jupiter?

    But anyway, 2012/Nemesis speculation is silly, because any object that could reach us next year would have to be… probably closer than Saturn right now.

    @16 James Curran: Temperatures can be determined more precisely than that. The existence of NH3 in the atmosphere basically requires a particular temperature range.

  21. X

    “What if it has enough mass to fuse deuterium but never could because its core never contained deuterium?”

    Then you should call SETI, the Nobel Prize committee and the PotUS, because you just discovered indisputable evidence of extraterrestrial intelligence? I wonder how the aliens managed to isotopically purify so many Jovian-masses of hydrogen.

  22. WISE finds coolest brown dwarfs ever seen!

    I thought that was Gary Coleman? <gdrfc>

  23. Tony

    Letting my imagination run with this….could you actually have an abundance of liquid water on one of these things? Would this object even have a solid surface the water could sit on, or would it be a warm slurry? one would imagine that these things would have a much higher surface gravity and would probably pick up a lot of dirt and dust from whatever was around.

    I can see a sci-fi author having a field day with one of these.

  24. Chief

    I would assume the gravity would be higher than all of our planets combined for a BD being the equivalent in mass and larger. It would be something to find bodies orbiting it as a mini solar system.

  25. Mike C

    I assume a similar composition to that of Jupiter or would they form differently. What I’m getting at is if you have an “atmosphere” of water on a brown dwarf…you could “see” lightning – do these emit anything in the radio spectra that would be detectable this far out?

  26. Geri Monsen

    Keep in mind also that Brown Dwarfs generate some heat simply from slow gravitational collapse, so not all of its temperture is simply due to leftover heat from when it was formed or went through a possible brief fusion phase. This keeps the brown dwarf from cooling off too quickly.

  27. Chris

    It’s so cool, it’s hot.

  28. Chris

    @#21
    LOL, thinking the same thing!

  29. Baramos

    So they aren’t really stars but certainly much bigger than gas giants…I guess they could call them ultra super gas giants or something!

  30. Kim

    @#21 X: Why do you think that much inlikely to have a body of deuterium-free gas? Ok, deuterium is everywhere since the Big Bang, but enough to fuse depends on when and where the brown dwarf was created, if it was a rich environment in that and other elements or not.

  31. Brian

    @20. DigitalAxis: is clearly thinking along the same lines as myself. Would a Brown Dwarf fall within the clasification of a “Rogue Planet?-that is a planet ejected from the orbit of a star? And related to this; What is the mass of the largest extra solar planet discovered to date and how does this compare to a Brown Dwarf?

  32. Russ

    With no light source, wouldn’t it just appear black?

  33. Steve Morrison

    I can see a sci-fi author having a field day with one of these.

    An SF writer already did, over fifty years ago. Georgi Gurevich wrote a story in Russian called “Infra Draconis” which postulated something very much like this; an English translation is collected in the anthology Soviet Science Fiction, with an introduction by Isaac Asimov. (ISBN-13 is 978-0020-16550-7 if anyone is interested in running down a copy.)

  34. Jen Deland

    How do we know that there are not enough things like this to account for the dark matter effects?

  35. #35: Gravitational lensing experiments, allegedly

    This brown dwarf is probably first-generation, because otherwise radioactive decay alone might keep it hotter than that. Planets/dwarfs in the 1-20 Mj range would have a similar radius as jupiter due to gravity’s effect on the cold gas, so the mass to surface area ratio is huge.

  36. Kitty

    #35 Jen, my understanding is that the effect of the gravity discrepancies is simply too great for dark (MACHO) objects like these to be responsible for it. I recall reading the gravitational discrepancies are both so off and so consistently off everywhere we can measure it, it just isn’t possible it’s all just stuff we can’t see yet.

    There are ideas like MOND which claim the discrepancies are miscalculations or mistakes in understanding gravity, but currently dark matter is the most accepted hypothesis as it seems to fit cleanly with other observations while no other proposals do.

    As a lay person, I used to have difficulty with the seemingly invented idea of dark matter but reading more about particles and particle creation at the beginning of everything made it easier to see how neutral, mass-bearing particles which don’t interact with photons could be possible. It helps dark matter seem ordinary :)

  37. Messier Tidy Upper

    Seven brown dwarfs now! Well done WISE guys* :-)

    I suggest they call the eighth brown dwarf they detect (assuming theyfuid another) “Snow White” so there’s Snowwhite & the seven other dwarfs. ;-)

    Great write up there BA too. :-)

    @29. Baramos : “So they aren’t really stars but certainly much bigger than gas giants…I guess they could call them ultra super gas giants or something!”

    Well brown dwarfs are intermediate boarderline objects between stars and planets. They’ve often been dubbed “failed stars” but “really successful Jupiters” does seem equally apt.

    @ 33. Steve Morrison :

    “I can see a sci-fi author having a field day with one of these.”
    An SF writer already did, over fifty years ago. Georgi Gurevich wrote a story in Russian called “Infra Draconis” which postulated something very much like this; an English translation is collected in the anthology Soviet Science Fiction, with an introduction by Isaac Asimov. (ISBN-13 is 978-0020-16550-7 if anyone is interested in running down a copy.)

    Thanks – I haven’t heard of that one. :-)

    Isaac Asimov himself has written stories including brown dwarfs as part of the settings – his ‘Nemesis’ novel features one closer than Proxima Centauri in the eponymous star system of red dwarf, brown dwarf and earth-like moon. Pretty sure Greg Bear had a (fictional) brown dwarf – an inhabited one even in the final star system reached in Anvil of Stars too. :-)

    @10. Jason : “Is it possible to find liquid water on these? Or would it just be water vapor? Is it possible to have a layer, some depth down that is water?

    It seems likely although even more probable is a layer or two of “hot ice” types of solid H2O that form even at very high temperatures under immense presures.

    For some cold old brown dwarfs, there may be an ocean under a thick atmosphere, then layers of hot ice down making up much of tehinetrabnl structures just as there are on massive exoplanets incl. some “super-Earths” (eg.Gliese 436 b) although I’m not 100% certain of this for brown dwarfs.

    ——

    * (WISE guys & girls – but then girls can be guys too metaphorically, right?

  38. Messier Tidy Upper

    D’oh! That’s meant to read :

    .. then layers of hot (high pressure) ice down beneath that ocean making up much of their internal structures ..

    See :

    http://en.wikipedia.org/wiki/Brown_dwarf

    for more about brown dwarfs.

    See :

    http://en.wikipedia.org/wiki/Gliese_436_b

    for “hot ice” exoplanet Gliese 436 b which is probably one of many such worlds. :-)

    Plus see :

    http://en.wikipedia.org/wiki/Nemesis_(Isaac_Asimov_novel)

    for Asimov’s Nemesis – the novel not his worst enemy! ;-)

    Note from there :

    Interestingly, the planetary system in the book included a Jovian planet named Megas in a very short-period orbit about its primary star. (Erythro is a moon of Megas.) This was a radical idea in 1989, but was vindicated with the discovery of the first extrasolar planet orbiting a sun-like star (51 Pegasi) in 1995, dubbed “Bellerophon”.

    Hmm.. I’m pretty sure I recall Megas being a brown dwarf not a superjovian so I’ll have to check that. I can vouch for that novel being a great read too. :-)

  39. Messier Tidy Upper

    Aha! Checked my copy of the novel and found that :

    “Megas is on the borderline. It’s either a very warm planet or a very dim brown dwarf .. [snip] .. it’s five times the mass of Jupiter and one thirtieth themass of Nemesis.”
    - Page 82, Nemesis, Isaac Asimov, Bantam Books, 1990.

    Which – despite the ambiguious description there – would seem to make “Megas” only a superjovian exoplanet because about 13 Jovian masses is required for brown dwarfdom as I understand things.

    For more about Bear’s novel Anvil of Stars see:

    http://en.wikipedia.org/wiki/Anvil_of_Stars

    but WARNING – contains SPOILERS!

    That’s a novel I’d strongly recommend too with some of the best aliens I’ve ever read. :-)

    @38. MTU :

    I suggest they call the eighth brown dwarf they detect (assuming they find another) “Snow White” so there’s Snowwhite & the seven other (brown)dwarfs.

    Incidentally, the nickname “Snow White” already belongs to another intermediate planet class body – the ice dwarf world “Snow White” or 2007 OR10 which is the fifth largest ice dwarf planet and is half Pluto’s size.

    See :

    http://www.eurekalert.org/pub_releases/2011-08/ciot-caf082211.php

    Although it seems the name “Snow Red” would actually have been more fitting there – perhaps a renaming to that is now called for! ;-)

    Not that giving the same name to two duiffrnt things is necessarily a cardinal sin anymore – after all, Hydra is both the largest constellation and one of Pluto’s many small moons.

  40. Messier Tidy Upper

    Typo correction for the last sentence in comment # 40 about Hydra’s dual meanings – duiffrnt = different.

    PS. For more about “hot high pressure ices” see :

    http://en.wikipedia.org/wiki/Ice#Phases

    Which answers the riddle of what ice, our Moon and Venus have in common – phases! ;-)

    The Anvil of Stars wikipage doesn’t actually state that the final “Leviathan” planetary system includes a brown dwarf – but from memory I’m fairly sure it does.

  41. “As I sit here and write this, it’s warmer outside my window than it is on the surface of that object!”

    But surely that’s misleading. If you were to view the earth from space you’d get about 255K ? So it’s much hotter than earth…

    jules

  42. Naomi

    So wait, is this the first non-Earth object (yes, yes, I know, the Earth has a fair range of temperatures) that’s actually at room temperature?

    I should go hang out there, I’m so sick of winter XD

  43. Messier Tidy Upper

    @ ^ Naomi : Our Moon is at room temperature too – as is Mercury – just very briefly. Of course the temperatures don’t stay “room-y” for long as they quickly soar wa-aay above or below that point going from extreme cold to extreme heat & vice-versa. The same applies to a number of eccentrically orbiting exoplanets too most likely. ;-)

    (Yeah, I’m guessing that’s not what you meant, sorry I am a pedant I’m afraid.)

    The Anvil of Stars wikipage doesn’t actually state that the final “Leviathan” planetary system includes a brown dwarf – but from memory I’m fairly sure it does.

    Hmm.. On checking the text I find this :

    “I we have one question,” Eye on Sky said. “Is this planet natural or artificial?”
    “Both,” Salamander said. “Once it was a small star. We have been changing it for thousands of years. First it was used as an energy and fuel source. Now, the easiest answer would be to say that it is artificial.”
    - Page 357, Anvil of Stars Greg Bear, Legend, 1992.

    That’s referring to the fourth planet of the Leviathan system dubbed Sleep by the Humans btw.

    I guess a brown dwarf could, at a stretch, be described as a small star. Surely it’d be easier to transform a brown dwarf into a world than a red dwarf even given god-like alien technology?

  44. Legion

    Maybe I missed it but what would the surface gravity be? And is it radioactive?
    In other words, could someone theoretically walk on one without being crushed, burned or irradiated?

  45. Jonny

    If this thing is at least 75 times the mass of Jupiter you can forget about walking on its surface. The gravity would crush anyone into a tiny grease spot …well anyone except Chuck Norris. So maybe Chuck Norris can fly out there and check-it out for us. He wouldn’t use a spaceship though, Chuck Norris doesn’t need spaceships.

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