The case of the brown star that's really red or possibly blue

By Phil Plait | January 29, 2010 12:11 pm

Brown dwarfs are poorly named: they’re not really brown. They’re objects that are too small to really be called stars; they lack the oomph needed to fuse hydrogen into helium in their cores, which is the the mark of a true star. Because of this, they are far cooler than actual stars. Since cool stars are red, you’d think brown dwarfs would actually be really red.

And they are. Unless they’re blue.

Yeah, let me explain this one. First, here are two images of a newly discovered brown dwarf, perhaps the coolest ever seen, and certainly one of the closest to the Earth:

sdss1416b

[Click to redgiantize.]

The star SDSS1416+13A is the brighter one in the image, and is a regular ol’ brown dwarf. The other star is its lower mass and cooler companion, called SDSS1416+13B. How cool is it? Scientists estimate that it’s at about 200 Celsius (400° F). I ate chicken last night hotter than that! So as stars go, 1416+13B is pretty cool.

Observations taken some time apart show that the two stars are in fact binary, orbiting around each other. Since we don’t know exactly how far away these two are, we can’t say exactly just what their masses are, but the way they give off light is a dead giveaway they are both brown dwarfs. It’s possible to estimate their distance, and scientists think they are between 15 and 50 light years away. That makes them very close to us as stars go! The Milky Way is 100,000 light years across, so these guys are basically sitting in our front yard.

Now, let me take a sec to explain some jargon. Blue light has a shorter wavelength than red light. Because of this, astronomers sometimes use the words "blue" and "red" as adjectives, meaning shorter and longer wavelengths, respectively. So blue is bluer than red, and red is redder than blue. Duh. But they can also say with a straight face that red is bluer than infrared, and infrared is redder than red! That’s because red has a shorter wavelength than IR, and is therefore "bluer", while the IR is longer wavelength than red, and is therefore "redder". Got it? It actually makes sense, and you eventually get used to it. I’ll be using this jargon below, so be ye fairly warned.

The pictures above are false color; both are in infrared light (the left is from the ground-based UKIRT telescope, while the one on the right is from the space-based Spitzer telescope). You might expect that since 1416+13B is cooler than its companion, it should be giving off more long-wavelength (redder) IR light. But in the case of the left image, the blue color still means 1416+13B is giving off more light at the shorter (bluer) end of the IR part of the spectrum. What gives?

Brown dwarfs are weird, that’s what gives. They have atmospheres almost like planets do, and that air is filled with methane, water vapor (steam!), and sometimes even vaporized iron for hotter ones — in cooler brown dwarfs, that iron precipitates out… in other words, it rains molten iron droplets!

In the case of 1416+13B, the atmosphere is cool enough that methane and steam absorb the light coming from below. Those two molecules are picky about what light they absorb, and they soak up quite a bit of IR at different wavelengths, allowing other wavelengths through. So what’s happening here is that some of the redder IR light gets sucked up, while bluer IR passes right through. What we see from outside is the star emitting bluer IR light, so images taken in IR make the star look blue.

This spectrum, taken with the Subaru telescope, might help:

sdss1416spectrum

Think of the vertical axis telling you how much light the gas in the star’s atmosphere lets through, and the horizontal is the color. Bluer IR is on the left, redder on the right. You can see that a handful of blue colors blast right through, but the star emits very little in the red. So when we look at it with our infrared telescopes, we see it looking blue.

Mind you, to our eyes, this guy would look very, very red. But that’s in visible light, off to the left (blue) of this graph.

So, given all this, why does the star look red in the Spitzer image? Aiiiiieeee!

OK, don’t panic. That’s because Spitzer looks at a different part of the IR spectrum. It sees light at 3.6 and 4.5 microns, well off to the right (red) of the spectrum shown above. In those wavelengths, 1416+13B looks redder.

So here we have a brown dwarf that looks red, or maybe blue. It all depends on how you look at it.

But that’s the whole point! By looking at stars at different wavelengths, we can find out a lot about them. In this case, we can estimate the distance to the star, its temperature, and even what’s in its atmosphere… all from hundreds of trillions of kilometers away!

Things like this never cease to amaze me. Science! I love this stuff.


Related posts:
Dim, faint, and small is no way to go through life, son
Astronomers weigh in on teeny stars
Welcome to our tiny family


Image credits: JAC/UKIRT, Spitzer Space Telescope, University of Hertfordshire, and Subaru Telescope (NAOJ), University of Hertfordshire.

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

Comments (53)

  1. Kelli

    This is really interesting. We did enough wavelength type labs in my astronomy class last fall that I get what you’re talking about. Astronomy is stellar! (sorry)

  2. Cheyenne

    Cool post. All of these Astronomy pics are so much better with the explanation from the good doc.

    “I ate chicken last night hotter than that!” WOW! How tough are Astronomers? They eat 400 degree chickens!

  3. Yeah, but who’s on first?

    – Jack

  4. Rob

    Mmmmm, plasma chicken.

  5. Jamey

    So, is it the same compounds resulting in the blue deficiency in the Spitzer segment of the spectrum, or are they different/unknown compounds?

    And would an alternate way of looking at this be that the star is brighter than expected at some wavelengths, and dimmer than others?

    I wonder if we have enough instrumentation above the atmosphere to get a good continuous spectrum all the way from soft x-rays to reasonably long-wave radio?

  6. CW

    “Brown dwarfs are weird, that’s what gives. They have atmospheres almost like planets do, and that air is filled with methane, water vapor (steam!), and sometimes even vaporized iron for hotter ones — in cooler brown dwarfs, that iron precipitates out… in other words, it rains molten iron droplets!”

    Sounds like they are almost like a gas giant planet? If this is the case, does this mean that Jupiter was very, very, very close to becoming a brown star?

  7. Which way to go with this?

    Option “A” would be the obvious toilet humor “Don’t it make my brown star blue” song lyric.

    Option “B” would be something about Pygmies in Space.

    Option “C” would be bacon.

    BACON!

  8. Beavis

    LOL Brown star.

  9. TW

    Man that was some over cooked chicken…

  10. ad

    The diagram says 16A and 16B, your text talks about 13A and 13B. So which is it?

  11. Only 400 degrees F? That’s barely hot enough to scorch paper. Paper’s ignition point is 451 degrees F; learned that from Ray Bradbury. Great Pasta, I’ve used solar ovens hotter than the surface of this star!

  12. Torbjörn Larsson, OM

    They’re objects that are too small to really be called stars; they lack the oomph needed to fuse hydrogen into helium in their cores, which is the the mark of a true star.

    Or they are possibly “blue”, objects that are too big to really be called planets; they have the oomph to be fully convective throughout. [Snatched from Wikipedia.]

    … er, I meant to say: “BACON!”

  13. ethanol

    Sounds like they are almost like a gas giant planet? If this is the case, does this mean that Jupiter was very, very, very close to becoming a brown star?

    It looks like the smallest brown dwarfs are about 13 Jupiter masses, so not really.

    What really amazes me is that we can spot a 200C object not much larger than Jupiter more than 15 light years away just based on the warmth emanating from its surface. I am looking forward to the results from WMAP to see whether there are any other gas giants in the far outer solar system or brown dwarfs closer than proxima centauri.

  14. cmflyer

    I think that’s an awesome way to help students think about the EM spectrum, especially red-shift. I’ll use it!

  15. blf

    hmm…too small and cold to be a star, too large to be a planet. I guess it’s the textbook definition of a brown dwarf.

    But I agree with @13, it is really amazing that we can spot these things.

  16. Doug

    Ok, so I’m no expert on IR telescopes, astronomic photography, or most anything else for that matter. But I noticed a couple things about the pictures:

    1) The ground-based image seems sharper/clearer than the spitzer image — I would have expected the opposite. Is this due to the different wavelength being examined?

    2) Some stars (or galaxies, I suppose) are visible in one but not the other. Again, is this caused by the wavelength, air interference, or light-gathering capabilities?

  17. MadScientist

    “I ate chicken last night hotter than that!” (400F)

    You do know that you’re not supposed to eat the flambee while it’s still on fire, don’t you? Not even if you’re an aspiring flame-eater.

    What object’s spectrum is that which was shown from Subaru? There’s a lot of (earth’s) CO2, CH4, and H2O absorption in that region shown, with those peaks appearing in the typical bands used for near-infrared astronomical observations, so that spectrum could be of just about any celestial object (including the moon) and demonstrates how the earth’s atmosphere filters the light.

  18. Gary

    Wow, that’s amazing. I didn’t know brown dwarfs could have such low temperatures. Have any artists attempted to depict what such a cool brown dwarf might look like up close?

  19. Jon Niehof

    There’s something seriously tragic about the fact that I recognize plots made with IDL now…

  20. Emily

    @anothermike Yeah, that really puts it in a new light when I think that the “surface” of the star would be at just the perfect temperature for baking biscuits…

  21. Wondering

    But, why or how are the precipitating iron droplets molten at 400 F or less in the cooler brown dwarfs ? Are there other temperature considerations somehow involved ?

    Thanks

  22. Plutonium being from Pluto

    Awesome news & post – thanks BA. :-)

    But I thought I read something somewhere sayin brown dwarfs would actually be a sort of mauve colour?

    Cool system in more ways than one but more information please – whats the most likely distance and orbital separation between the two brown dwarfs? Any possibility of exoplanets around one or other or both of these star-cross-gas giants?

    Also what magnitude are these at and what would be their apparent magnitudes seen from 1 AU or how bright would they be if they replaced our Sun?

    Or, as another way of looking at it, from what distance away would these brown dwarfs have an apparent magnitude of minus twenty-seven equal to our Sun?

    What would the internal structure of such objects be like – a barely fusing core overlain by something like a thick Hot Jupiter outer atmosphere? Or star-like plasma throughout?

    So many questions, such facsinating objects.

    Does anyone know and care to enlighten us here please? BA? Anybody?

    Personally, I like to think of Brown dwarfs not as “failed stars” but rather as “really sucessful Superjovians!” ;-)

  23. Messier Tidy Upper

    @22. Wondering Says:

    But, why or how are the precipitating iron droplets molten at 400 F or less in the cooler brown dwarfs ? Are there other temperature considerations somehow involved ?

    Not sure about other temperature considerations but I’m pretty sure *age* is a big factor here – the younger the hotter.

    Mass also matters & again, I think I’d be right in saying the more massive ones stay hotter for longer while the less massive ones cool off quickly.

    Do we know how old these two brown dwarfs are?

    Am I right in thinking these objects fuse deuterium very slowly then cease doing so and just cool down gradually to some point where they end up like huge inert balls of gas? Do they reach the point where they become “degenerate” like white dwarfs or just get to be really cold compressed gas?

    What would an old brown dwarf be like and has there been enough time for any to have “finished” or they like red dwarfs in lasting many times longer than our universe has been around for yet?

    Would these brown dwarfs – like Jovian gas giants – have metallic hydrogen layers somewhere or develop them at some point once their cores cease fusing Deuterium? I know they are fully convective and material circulates throughout them but they still have atmospheres, cores and some internal strcuture to them don’t they? Or do they?

  24. Plutonium being from Pluto

    Correction sorry :

    Also what magnitude are these at and what would be their apparent magnitudes seen from 1 AU or how bright would they be if they replaced our Sun?

    is supposed to read :

    “Also what magnitude are these at their current distance – and what would be their apparent magnitudes seen from 1 AU or how bright would they be if they replaced our Sun?”

    Any chance an amateur astronomer with a sufficently large scope could spot these or an astrophotographer could capture them on a CCD image or something – what equipment would be needed to do so?

    Amazing to imagine what these half-star half-superjovian objects would look like from a large moon-like planet. I’m picturing something like Ganymede or Titan only bigger and closer and something like a red (blue? mauve?) hot Jupiter.

  25. StevoR

    @ 23. me as “Plutonium being from Pluto” :

    But I thought I read something somewhere sayin brown dwarfs would actually be a sort of mauve colour?

    Actually, what I remembered reading came via this related link from your “Welcome to our tiny family” post which is linked under the main article above :

    http://www.nd.edu/~bennett/moa07blg192/

    Which shows an artists conception comparison of the MOA-2007-BLG-192L system which may be either a red dwarf star or a brown dwarf with an accompanying low-mass icy Super-Earth exoplanet :

    Artist’s conception of the newly discovered planet MOA-2007-BLG-192Lb orbiting a brown dwarf “star” with a mass of only 6% of that of the Sun. Theory suggests that the 3-earth-mass planet is made primarily of rock and ice. Observational and theoretical studies of brown dwarfs reveal that they have a magenta color due to absorption by elements such as Sodium and Potassium in their atmospheres. … [& then] An alternate artist’s conception of the planet MOA-2007-BLG-192Lb, under the assumption that the host star has a mass of 9% of that of the Sun, which is also consistent with the microlensing data. This would be a red dwarf star about 100 times brighter than the brown dwarf, but 1000 times fainter than the Sun.

    (Emphasis mine.)

    Sorry to further muddy the waters and mix the colours but which is the right colour – blue, red or mauve? As you said it depends upon what wavelengths your viewing the brown dwarf at but to the unaided eye would it be – red or mauve or brown or even for an old “brown” dwarf too dark to see at all esp. given we’re “seeing”” in “heat?” ;-)

    Would these brown dwarfs have bands of colours and spots – seen them pictured that way too.

    Wish we could see one close up or get some real photos of one from a passing starship or something! ;-)

    @ 14. ethanol Says:

    “Sounds like they are almost like a gas giant planet? If this is the case, does this mean that Jupiter was very, very, very close to becoming a brown star?” It looks like the smallest brown dwarfs are about 13 Jupiter masses, so not really. What really amazes me is that we can spot a 200C object not much larger than Jupiter more than 15 light years away just based on the warmth emanating from its surface. I am looking forward to the results from WMAP to see whether there are any other gas giants in the far outer solar system or brown dwarfs closer than Proxima Centauri.

    I agree & it amazes and deeply impresses me too that we can detect these objects and even more so exoplanets from earth and, for HST and Spitzer, near-earth space. :-)

    But WMAP? Don’t you mean WISE?

    PS. Awesome post again BA -loved this one, thanks! :-)

    PPS. Oh & BACON since it seems to be the thing to say! ;-)

    – StevoR a.k.a. Plutonium being from Pluto

  26. Plutonium being from Pluto

    One very last thing if I might :

    When are we going to give such signficant and remarkable objects as this one some proper easily pronounceable, memorable, plain english names rather than dull, unpronounceable, unmemorable numerical designation codes!?!?

    After all how do you pronounce & how can you really talk to non-astronomical general folks about something “named” MOA-2007-BLG-192Lb or the like?

    These objects are pretty marvellous and fascinating objects but faced with having to recall and pronounce such as “MOA-2007-BLG-192Lb” most people will struggle and resort to “that one” or suchlike or, worse, just not mention them at all. Which is sad and annoying & I do think actually hinders communicating astronomy to our broader society and even astronomy generally. :-(

    If we must have such codes as “names” can we at least try and keep it to no more than say four numerals? Sigh.

    But ideally, once objects like this are found to be remarkable – literally worth remarking & talking about – can’t we give them *proper* names like say ‘The Balsawood Planet’ is informally but often used for TrES-4 or ‘Polydeuces’ for Pollux b or ‘Bellopheron’ is for 51 Pegasi b and so on? Surely we can do that?

    This is a pet gripe of mine that I’ve discussed before & I don’t want to bore y’all but really it bugs me badly. Can’t we *do* something about this?

  27. Wondering

    @ 24 Messier …

    But the temperature is given to us as “estimated” be 400 F and the estimate is probably merely due to the small uncertainty about the distance. This is why I asked if there are ‘other’ temp considerations not mentionned to explain how the precipitating iron got to be “molten”.

    Also, the cores of brown dwarfs don’t fuse deuterium or anything as BA told us. Brain fart there no doubt, lol. But i would guess that if they are closer to a ‘star’ than Jupiter then they probably could have hydrogen cores at metallic density or maybe even carbon cores of diamond, who knows. Maybe BA could chime in on that.

    @ TrevoR

    Maybe this particular brown dwarf simply doesn’t have any sodium or potassium in its atmosphere so it is the color we are measuring it to be without conflict that other dwarfs might be magenta colored by the mechanism you cite. Just speculating though.

  28. Joshua

    Can we name it Plasma Chicken?

  29. m.j.

    Did anyone else picture themselves sailing on an ocean of molten iron with hardened iron droplets pelting them in the face?

  30. Pi-needles

    A small nit to pick: “Brown Star” Star?

    As the BA himself points out:

    They’re objects that are too small to really be called stars; they lack the oomph needed to fuse hydrogen into helium in their cores, which is the the mark of a true star.

    & then ignores his own words:

    The star SDSS1416+13A is the brighter one in the image, and is a regular ol’ brown dwarf. The other star is its lower mass and cooler companion, called SDSS1416+13B

    See where could be a tad confusing? They’re not *stars* they’re brown dwarfs – not quite stars but a bit more than just planets. Sorta halfway between.

    @ 29. m.j. Says:

    Did anyone else picture themselves sailing on an ocean of molten iron with hardened iron droplets pelting them in the face?

    I am now! ;-)

  31. ethanol

    But WMAP? Don’t you mean WISE?

    Whoops. WMAP was cool too, though.

  32. Spectroscope

    @ 30 Pi-needles :

    They’re not *stars* they’re brown dwarfs – not quite stars but a bit more than just planets. Sorta halfway between.

    Actually, brown dwarfs *are* classified as stars – stellar spectral classes L & T to be precise.

    As stellar expert James Kaler notes:

    For decades, astronomers predicted the existence of substars we now call “brown dwarfs,” stars too small and light (of insufficient mass, less than 0.073 solar masses) to run the full nuclear fusion process (from ordinary hydrogen to helium). After all, the star formation process should “know” nothing of the conditions under which nuclear reactions should turn on. Brown dwarfs (which are still called “stars”) turned out to be so cool that only new infrared technologies could find them. We now know they are very common, so common that new classes, L and T (cooler than M) had to be made for them. Between 0.073 solar masses (78 Jupiter-masses) and 13 Jupiter-masses, brown dwarfs do fuse their natural deuterium (heavy hydrogen, with an extra neutron) to helium. Below 13 Jupiters, fusion stops altogether. As noted above, the lower end of brown dwarf masses is not known. They quite likely overlap the masses of planets. Planets are by current definition made from the “bottom up,” accumulated from dust in disks surrounding new stars, while stars (including brown dwarfs) are made from the “top down,” by direct condensation from interstellar gases. But here even the definitions become confused and might overlap as well.

    Source: http://stars.astro.illinois.edu/sow/star_intro.html#brown via Kaler’s ‘Stars’ website: http://stars.astro.illinois.edu/sow/sowlist.html

  33. Ben Burningham

    Just to throw a spanner in the works: SDSS1416A, the brighter component, might actually be a star. Our best estimate for its mass just now is right on the stellar/substellar boundary at about 75 times the mass of Jupiter, although this estimate also hangs on the age estimate for the system (which is about 10 billion years).

    You can read it all in more detail here: http://arxiv.org/abs/1001.4393

  34. katesisco

    Does this mean that we should read Milton/DeGrazie and the theory that our Sol is an exploded star that resulted in proto-Jupiter strongly magnetically strung back to Sol, a tube in which the other planets formed from proto-Jupiter?

    Or should we just read S W Carey Earth, Universe, Cosmos?

    Or maybe reference the current work of O Manuel of Rolla, MO whose students have amassed data showing the elements are ordered inside of Sol indicating a prior nova?

  35. I’m a bit surprised that 200ºC is hot enough for stuff to emit light… OK, most of it is infrared but you said it would look very red in the visible spectrum. So my question may be silly but… what kind of matter emits visible light at 200ºC?

  36. Mark Hansen

    Anothermike, you’ve picked a not-so-good source for paper flash point. Don’t remember where (may have been watching the extras with the movie version) but Bradbury basically admitted he guesstimated the flashpoint. Turns out he was about 200ºF off. According to the “Handbook of physical testing of paper, Vol. 2″, and their figures don’t take into account variables such as lignin content, flashpoint is in the region of 350º C or 662º F. Whatever the flashpoint, it’s a great book.

  37. Gary Ansorge

    38. Inti

    He wasn’t referring to VISIBLE light. That generally starts at a temp of around 1500 to 2000 degrees F.

    Try placing your hand next to a pan of boiling water; you’ll feel the infra red radiation coming from the 100 degree C water.

    The cooler any matter is, the longer the wavelength of radiated energy it gives off. At absolute zero, matter radiates no energy at all, not even radio waves. This is one definition for absolute zero. The cosmic microwave background radiation is equivalent to a body radiating at a temp of about 2.7 Kelvins, ie, very long radio waves.

    GAry 7

  38. Wondering

    So, still wondering how the iron droplets get to be molten. Maybe they are first kicked up from deeper in the *star* where temperatures are presumably hotter ?

    Phil ??????????????

  39. Thanks Gary. What got me confused is this line:

    Mind you, to our eyes, this guy would look very, very red. But that’s in visible light, off to the left (blue) of this graph.

    So this brown dwarf doesn’t actually emit visible light at all?

  40. Someone should refer to arXiv:1001.2743, an earlier paper by Scholz identifying this as an interesting object and giving a distance for the system 1416+13AB. Given the distance of 8 pc and the fluxes from Burningham etal, and assuming a radius of 0.1 R(sun) the effective temperature is more like 610-690 K. Definitely chicken flambe.

    The B component will be a 60-70 sigma detection in WISE data. The A component is even brighter, and the separation will be resolved by WISE.

  41. Messier Tidy Upper

    @ 36. Ben Burningham Says:

    Just to throw a spanner in the works: SDSS1416A, the brighter component, might actually be a star. Our best estimate for its mass just now is right on the stellar/substellar boundary at about 75 times the mass of Jupiter, although this estimate also hangs on the age estimate for the system (which is about 10 billion years).

    Thanks! That’s great info & link there – much appreciated. :-)

  42. Pi-needles

    Having been thinking about the name “brown dwarfs” some more, I’ve come to the conclusion that the most accurate name for these objects would be “infra-red dwarfs” or even “heat dwarfs” instead.

    After all their “redder than red” in terms of the electromagnetic spectrum and so that’s the next logical step there & its also accurately descriptive in terms of how we (mainly?) detect & view them correct?

    Anyone with me for seeing if we can change the BD name to “IR / heat dwarfs”? ;-)

  43. Ben Burningham

    @ 44. Ned Wright

    Careful with that distance, the paper that was posted by Scholz is not yet accepted for publication, and I suspect significant revisions will be required before it is.

    I’m not sure how you’ve gone about calculating that Teff, but be aware that it is not a trivial step to go from the Spitzer magnitudes to fluxes for these objects, and then to effective temperature even given a distance. These objects do not have blackbody-like spectra.

    But yes, WISE will find many objects this cool. We’re all very much looking forward to seeing what’s out there :-)

    and
    @ 18. MadScientist

    The subaru spectrum is the spectrum of SDSS1416B, and it has been corrected for the absorption due to the Earth’s atmosphere.

  44. mike burkhart

    Some white stars apper green in color also the sun and moon can apper in diferent colors maybe some of this is that humans are one of few animals that can see in color on Earth

  45. CharonPDX

    What amazes me is that this “star” is cooler than the surface of Venus!

  46. Messier Tidy Upper

    @ ^ CharonPDX : Me too. Cold “stars” indeed!

    Plus they’ve since found even colder brown dwarfs – room temperature – if my vague memory of reading something in one astronomy magazine suffices. :-)

  47. Messier Tidy Upper

    Aha! Found it! :-)

    In the July 2012 ‘Sky &Telescope’ magazine article titled “Misfit Stars” by Kristina Grifantini. (Pages 22 -27) According to one caption :

    “.. WISEP J1828+2650 currently the coldest known free-floating brown dwarf. A thermometer on this failed stars visible surface would read a lower temperature than that measured by a thermometer stuck in a person’s mouth.”

    In the text it is described as one of 8 Y-class brown dwrfas six of which were discovered by the WISE space observatory. They add that it is “..only as warm as earth on a summer’s day : 300 K” (page 24) and another contender for literally coolest brown dwarf – WD 0806-661B – which orbits a white dwarf star is described as having “short sleeve conditions” as well! (Page 25.) 8)

    Good article there that I’d highly recomend. Knew I’d read something about this recently! ;-)

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