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The Secret Origin Story of Brown Dwarfs

Artist's impression of a Y-dwarf, the coldest known type of brown dwarf star. (NASA/JPL-Caltech)

Sometimes called failed stars, brown dwarfs straddle the line between star and planet. Too massive to be “just” a planet, but lacking enough material to start fusion and become a full-fledged star, brown dwarfs are sort of the middle child of cosmic objects. Only first detected in the 1990s, their origins have been a mystery for astronomers. But a researchers from Canada and Austria now think they have an answer for the question: where do brown dwarfs come from?

If there’s enough mass in a cloud of cosmic material to start falling in upon itself, gradually spinning and collapsing under its own gravity to compress and form a star, why are there brown dwarfs? They’re not merely oversized planets — they aren’t in orbit around a star. They’re not stars that “cooled off” — those are white dwarfs (and are something else entirely.) The material that makes up a brown dwarf probably shouldn’t have even had enough mass and angular momentum to start the whole process off to begin with, yet they’re out there… and, as astronomers are finding out now that they know how to look for them, there’s quite a lot.

So how did they form?

According to research by Shantanu Basu of the University of Western Ontario and  Eduard I. Vorobyov from the University of Vienna in Austria and Russia’s Southern Federal University, brown dwarfs may have been flung out of other protostellar disks as they were forming, taking clumps of material with them to complete their development.

Basu and Vorobyov modeled the dynamics of protostellar disks, the clouds of gas and dust that form “real” stars. (Our own solar system formed from one such disk nearly five billion years ago.) What they found was that given enough angular momentum — that is, spin — the disk could easily eject larger clumps of material while still having enough left over to eventually form a star.

Model of how a clump of low-mass material gets ejected from a disk (S. Basu/E. Vorobyev)

The ejected clumps would then continue condensing into a massive object, but never quite enough to begin hydrogen fusion. Rather than stars, they become brown dwarfs — still radiating heat but nothing like a true star. (And they’re not really brown, by the way… they’re probably more of a dull red.)

In fact a single protostellar disk could eject more than one clump during its development, Basu and Vorobyov found, leading to the creation of multiple brown dwarfs.

If this scenario is indeed the way brown dwarfs form, it stands to reason that the Universe may be full of them. Since they are not very luminous and difficult to detect at long distances, the researchers suggest that brown dwarfs may be part of the answer to the dark matter mystery.

“There could be significant mass in the universe that is locked up in brown dwarfs and contribute at least part of the budget for the universe’s missing dark matter,” Basu said. “And the common idea that the first stars in the early universe were only of very high mass may also need revision.”

Based on this hypothesis, with the potential number of brown dwarfs that could be in our galaxy alone we may find that these “failed stars” are actually quite successful after all.

The team’s research paper was accepted on March 1 into The Astrophysical Journal.

Read more on the University of Western Ontario’s news release here.

About 

A graphic designer in Rhode Island, Jason writes about space exploration on his blog Lights In The Dark, Discovery News, and, of course, here on Universe Today. Ad astra!

Comments on this entry are closed.

  • Peristroika May 4, 2012, 10:29 PM

    At first, I wanted dark matter to be real. I was excited over the possibility of so much stuff out there that we had yet to understand. The more the experts delve, however, the more I wonder whether we’ll ever find it at all. It certainly does smack of the search for the luminiferous ether of several decades ago. I’m finding myself on the “undecided” side, more and more.

    • Shootist May 4, 2012, 11:05 PM

      “the researchers suggest that brown dwarfs may be part of the answer to the dark matter mystery”

      I believe they are suggesting that, at least part of, DM is ordinary baryonic matter (da stuff we are made of, you know? Atoms?). Which, Willy of Occam would agree I believe, is the simplest explanation.

      The “luminiferous ether” isn’t/wasn’t supported by observations. The fact that galaxies exhibit more angular momentum than Einstein/Newton’s physics would allow, makes the boffins believe there is mass (matter) that cannot be seen (dark). Understand now?

      • Peristroika May 4, 2012, 11:50 PM

        Is that as condescending as you get? I’m sure you can pull out even the teensiest bit more superiority. I know all that, and if you’d actually read my post, would have clued into the fact that I didn’t ask what it was, how it behaved or why we believe something needs to be out there. The ether of past days WAS supported by observations in the same way that DM is today. That is why serious science looked for it, built structures to understand it and was puzzled as anything when it became clear it wasn’t there.

      • Peristroika May 4, 2012, 11:50 PM

        Is that as condescending as you get? I’m sure you can pull out even the teensiest bit more superiority. I know all that, and if you’d actually read my post, would have clued into the fact that I didn’t ask what it was, how it behaved or why we believe something needs to be out there. The ether of past days WAS supported by observations in the same way that DM is today. That is why serious science looked for it, built structures to understand it and was puzzled as anything when it became clear it wasn’t there.

        • TheDirtBoy May 5, 2012, 1:11 AM

          I too was a fan of the dark matter idea at first. The idea of an exotic material that can’t be seen or measured directly, that could potentially unlock the deepest darkest secrets of the universe if we can find a way of understanding it. Then, as attempted explanations started rolling in, each more convoluted than the last, reality hit me. I realized that dark matter is no different than luminiferous ether or the cosmological constant or any of the other failed ideas throughout history. I now see dark matter for what it was always intended to be, a place holder, a hole in human knowledge. If history has taught us anything it’s that even the smartest of us can be (and most often are) completely wrong. It’s called progress and we’ve been through it many times before.

          • Zoutsteen from Holland May 5, 2012, 1:57 AM

            The actual reference for darkmatter is Missing Observed Mass. But somehow MOM sounded less mysterious than darkmatter.

            MOND is an alternative to the darkmatter or Missing Observed Mass model. (MOND = MOdified Newtonian Dynamics)

            In the end, it will be either MOM or that.
            :-)

          • Rik Van Riel May 6, 2012, 2:05 AM

            Look at the rotational curve for M94 (NGC 4736). That observation makes MOND somewhat less likely than dark matter…

          • philip davis May 6, 2012, 4:27 PM
        • Shootist May 5, 2012, 1:37 PM

          No, I was being polite. In my mind you lumped DM with bad science. It isn’t.

          EM travels in waves (observation). Ponds have waves. Maybe EM is like waves on a pond? So it went. The observers knew they needed an explanation, to fit what was observed, so they invented ‘ether’ and tried to make it fit.

          The difference:

          Excess galactic angular momentum also needs an explanation, but the bright people doing this work haven’t invented (out of whole cloth) an explanation to fit the observation. They continue to search for the missing mass.

          • Peristroika May 6, 2012, 11:00 PM

            You read a lot into words that don’t exist. Maybe that explains why you’re happy to look for dark matter where it may not exist.
            Let me point out that Ether was based on fairly basic understanding of the cosmos, having never been beyond our own small sphere. One can be excused for supposing what might lie beyond our experience. However, your own example perfectly illustrates the parallel I described.

            EM travels in waves…
            Galaxies rotate en masse

            Ponds have waves
            Massive galaxies would seem solid

            Maybe EM is like waves on a pond
            Maybe there is some stuff we can’t see

            So they invented DM and tried to make it fit!

            Simply because modern science is current does not mean it’s infallible, or that it doesn’t make its own suppositions. We have MUCH to learn about even fairly basic things like stars, let alone whole galaxies. Searching for missing mass may be the wholly wrong direction. It may not be there at all.

        • Jack Jacobsen May 6, 2012, 9:34 AM

          The smart-ass attitude just shows that he does not understand that we are modelling reality based on inference and conjecture. The emphasis should be on modelling..

      • Peristroika May 4, 2012, 11:50 PM

        Is that as condescending as you get? I’m sure you can pull out even the teensiest bit more superiority. I know all that, and if you’d actually read my post, would have clued into the fact that I didn’t ask what it was, how it behaved or why we believe something needs to be out there. The ether of past days WAS supported by observations in the same way that DM is today. That is why serious science looked for it, built structures to understand it and was puzzled as anything when it became clear it wasn’t there.

  • Tony Power May 5, 2012, 8:23 AM

    Just out of curiosity, what would happen if fusion was to be artificialy started in one of these brown dwarfs? Say by detonating a nuclear bomb in it? Does it have enough mass to fight the force pushing it apart or does it just blow apart? On that point what would happen if some super technologicaly advanced end-of-the-world cult launches a nuclear bomb into Jupiter? do we get a second sun or do we all die as our atmosphere burns thanks to the nova size H-Bomb?

    • magnus.nyborg May 5, 2012, 9:15 AM

      The fusion would peter out over time, as the generated heat would leak out faster than it would be produced, the core slowly cools off and fusion ends.

      A certain amount of mass is required in order to allow fusion at sufficient rate that it doesnt peter out, and that mass is about 0.08Msun.

      Edit: Hydrogen fusion that is, deuterium can fuse at a lower mass, and is one reason why large brown dwarfs are somewhat hot, but the fuel soon runs out. Also lithium beryllium and boron can participate in some nuclear processes and produce some heat, but they also run out very quickly.

    • Zoutsteen from Holland May 5, 2012, 9:55 AM

      I’ll start with what brown dwarfs are first:
      A brown dwarf weighs in at about 13-75 Jupiters
      With this amount of Mass, there is already fusion happening within the brown dwarf.
      At ~13 Jupiter masses, this is Deuterium, or Hydrogen with 1 extra neutron.
      At ~65 Jupiter masses, the fusion will also consume Lithium
      At ~75 Jupiter masses, the fusion will be Hydrogen itself. And we start calling it a red dwarf.

      If Hydrogen Fusion could be artificialy started, than this would only last for a very very short time. The Fusion itself would require continuous energy to keep it going. And it takes a lot to do so. A massive amount.

      Fusion itself would not blow Jupiter or the brown dwarf apart though. Nothing more but a short period of glowing and than it dims again.

      But destroying Jupiter sized planets …. I only know that if we’ld throw Earth at Jupiter, then even than nothing more would happen than leaving Jupiter burping and complaining we didn’t add mayonaise or ketchup.

      Hope this answered your question Tony.

      • Tony Power May 5, 2012, 11:24 AM

        Thanks to you both. I had always wondered but had never had any where or anyone I could ask and get a decent answer.

      • brundall May 6, 2012, 1:08 PM

        So how warm/hot are Brown Dwarfs? Are they warm enough to sustain a goldilocks zone of any kind?

  • Zoutsteen from Holland May 5, 2012, 9:59 AM

    Apologies Magnus, I left this page open for a bit and replied before refreshing.
    Didn’t want to ninja your reply.

    • magnus.nyborg May 6, 2012, 7:47 AM

      What ninja? You explained with different words the same thing, that only makes the explanations better.

  • Torbjörn Larsson May 5, 2012, 1:26 PM

    Ah, the mysteries of formation and size of the population of brown dwarfs! I don’t know much about that, but I note the paper suggests a new way besides two main models and claim it has less of stress to it. I.e. it would be somewhat easier to match this one to predictions.

    I am less certain about the claim that this formation mechanism could predict low mass stars among the first population stars. They formed under quite different conditions than the ones Basu et al seem to have considered. Dark matter was much more important to gather baryonic mass, and since hydrogen molecules are piss poor coolers compared to other molecules and dust the systems were much larger and hotter than later molecular clouds. The Jeans mass were 3 (!) orders of magnitude larger.

    As for the dark matter discussion, I hope I don’t sound too condescending when I note that:

    – We can observe dark matter uniquely now. I.e. gravity lensing predicts dark matter, and dark matter only in cases of cluster collisions. (Say, the Bullet cluster, but also many more.)

    – Similarly, we can reject all other theories by now. Everything they predict dark matter predicts better, and there are cases like the cluster collisions or the formation of the first stars described above, where they fail spectacularly.

    – I’m no expert, but we have been told by them that these MACHOs (Massive Astrophysical Compact Halo Objects) can’t predict much of the observed mass, in halo’s or elsewhere:

    “Studies of big bang nucleosynthesis and gravitational lensing have convinced most scientists[5][68][69][70][71][72] that MACHOs of any type cannot be more than a small fraction of the total dark matter. … According to A. Peter: “…the only really plausible dark-matter candidates are new particles.”

    The future of dark matter seems bright, not brown.

    • Zoutsteen from Holland May 6, 2012, 8:44 AM

      Larsson, maybe you can help me out on this …
      http://www.youtube.com/watch?v=oKb2tCtpvNU

      Just a document where gravitational information delay is incorporated at the grand scale is good enough for me.
      No bullet galaxy though, as that’s been scrutinized through a different filter.

      ty in Advance!

    • philip davis May 6, 2012, 4:55 PM
    • Peristroika May 6, 2012, 11:12 PM

      No, that wasn’t condescending at all, Torb. Just stating facts or our current understanding. My doubts (and I’m not saying there is no dark matter, I’m not that full of myself) are based on the fact that much of the underlying science is in flux. With current understanding, dark matter fills the bill, yet…remains impossible to detect. Similar to the Higgs Boson and the entire Higgs mass theory. Constrained perhaps but not detected at all. Methinks the melon-headed men may be working in the wrong directions and only when we rethink our base models will we be able to see how in some unforseen way, it all begins to come together.

  • lcrowell May 5, 2012, 1:26 PM

    The composition of the universe is approximately 73% dark energy, which is some form of quantum vacuum physics with gravity, 23% dark matter and 4% luminous or baryonic matter. It is then clear there is over 5 times the amount of DM than ordinary matter. The search for DM can involve so called MACHO, or massive objects, but the data clearly points to WIMPS, weakly interactimg matter particles, as the dominant component. Objects such as cold brown dwarfs or rogue planets and the rest might increase luminous or baryonic matter’s role in the universe by a fraction of a percent, but these are very unlikely to constitute 5 times the amount of matter we observe in gas and stars.

    LC

    • kultivator May 5, 2012, 10:53 PM

      These stats are based on our flawed and incomplete observations and understanding of the universe.

      Don’t think there’s conclusive proof that the missing matter is non-baryonic in nature – this research points to yet another source of baryonic matter that alters the scales, albeit slightly.

      Since nobody really has much of a handle of cumulative mass within the Oort / Kuiper and possibly other groupings of matter in our local neighbourhood – with all due respect, how can we take these stats with any degree of seriousness at this point in time?

      • lcrowell May 6, 2012, 2:39 AM

        The distribution of dark matter is mostly outside the actual galaxies. By weak gravitational lensing maps of dark matter have been plotted.

        If this were ordinary matter then it would interact by the electromagnetic field. This would dissipate energy from the system and it would clump, just as there are nebula and stars in the galaxy. The lack of such interactions suggests this form of matter is different from luminous or baryonic matter

        LC

        • ft_c May 6, 2012, 6:43 PM

          The distribution of dark matter is mostly outside galaxies? What on earth do you mean by that?! That it hovers on the outside? That certainly cannot be true… Or are you saying it exists in regions of space where baryonic matter doesn’t?? Please provide a link or reference, I’ve had a little search and can’t find these maps. Thank you!

          • lcrowell May 6, 2012, 7:35 PM

            You might want to do a search, even here on UT. Dark matter around a galaxy is called a halo. It is a spherical region filled with DM with the galaxy in the middle. There can of course be dwarf galaxies and globular clusters there, but DM is not confined to just the volume of a galaxy.

            LC

          • lcrowell May 6, 2012, 7:35 PM

            You might want to do a search, even here on UT. Dark matter around a galaxy is called a halo. It is a spherical region filled with DM with the galaxy in the middle. There can of course be dwarf galaxies and globular clusters there, but DM is not confined to just the volume of a galaxy.

            LC

          • ft_c May 7, 2012, 11:24 AM

            Thanks LC yes I understand how dark matter supposedly works, but I thought you were saying that weak grav. lensing maps of dark matter had been recorded in regions of space where baryonic matter is not present. The only thing I know of like that is the train wreck cluster… If there are any more examples you know of though would be great to see! Thanks

          • lcrowell May 7, 2012, 1:22 PM

            Take a look at

            http://hubblesite.org/newscenter/archive/releases/2007/01/image/a/grav

            which gives an review of how weak lensing is used to map the large scale distribution of dark matter.

            LC

          • ft_c May 9, 2012, 1:28 PM

            Thanks, sorry only just got round to looking at this. I have actually seen this before, but it is not definitely mapping dark matter! Only gravity. I had wondered whether there were some mapping of gravitational fields that wasn’t using trad. matter to position it. I suppose this isn’t possible on distances this great. I’m just looking for examples of clumps of dark matter/gravitational regions that definitely could not be attributable to ordinary matter. Best, FC

          • lcrowell May 9, 2012, 2:35 PM

            Dark matter is by definition some form of matter which has gravity but no apparent electromagnetic interaction by which it can be detected otherwise.

            LC

          • ft_c May 9, 2012, 4:36 PM

            Indeed, it’s very convenient. What happens to the ‘c’ in e=mc^2?! What type of energy is this matter composed of? If EM radiation can produce particle pairs exhibiting mass, and dark matter is produced by the same EM radiation exhibiting mass, it must subsequently disappear out of the EM field in order to evade EM interaction. The neutrino of course exists in the EM field too. It’s as if 2 universes exist together, sharing (well, swapping) energy and gravitational fields… More weird than quantum weirdness. Incidentally, I think solutions to QM will provide answers to the extra gravity…and the expansion of the universe! But I mean to ask serious questions as I am keeping an open mind to the idea. Also, to my knowledge so far, DM and ordinary matter have always been found in the same ratio. If there are any studies counter to this I’d love to see!
            Best
            FC

          • ft_c May 12, 2012, 6:37 PM

            Any feedback on that previous comment LC? Am I on the wrong track/questions making sense?! Thanks

          • lcrowell May 12, 2012, 9:11 PM

            I think this is pretty much a dying thread. Yes there are problems with what you post or are trying to think. For one thing the neutrino does not interact electromagnetically, for it has no electric charge.

            LC

      • magnus.nyborg May 6, 2012, 8:34 AM

        The cumulative mass of the Oort-cloud would still be on the same order of the amount of elements heavier than hydrogen and helium, wich places it still around 1% of the total mass.

        If dark matter where simply matter that we havent discovered, the discrepancy would be a factor 500.

        Some of it might be jupiter-sized planets, brown dwarfs and what not, and I am not going to assume anything about it, but either something is wrong, or something is missing (even in our understanding). But Oort-clouds, planets and brown dwarfs do definitely not constitute a mass of 5x the mass of all the other detected mass, because it cannot be.

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    • Jonathan Archer May 6, 2012, 2:52 PM

      That’s what we ‘think’ universe are, not what ‘actually’ universe is

      • lcrowell May 6, 2012, 3:34 PM

        Science is not about proving things or finding what nature “actually is.” It is about working on consistent models which are tested by measurement and observation. A theory supported by a good body of evidence is considered to be effective, but never proven. A theory found to not be supported is then falsified outside some domain of experience that might support it.

        LC

  • SAM223 May 5, 2012, 11:32 PM

    Is it possible to add material, say, hundreds of asteroids, into an existing brown dwarf to let it go into creating a normal star? Or would it take the mass of a whole star just to start this one?
    Or what?? Could it’s life be extended by doing so?
    Would the temperature go up to increase the goldilocks zone significantly enough?
    I am writing a SF story about a race that does just that and I need a better understanding of all these possebilities.
    Anyone?
    Thanks for your help.

    • magnus.nyborg May 6, 2012, 7:53 AM

      You need about 75 jupiters merged to make a borderline red dwarf, 2-3 times more jupiters than that to make a star with somewhat of a reasonable habitable zone.

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