Failed Stars Oddly Rare

Astronomers surveying our solar neighborhood for brown dwarfs have been thrown a surprise: these "failed stars" are a lot less common than previously thought.

During its 14-month mission, NASA’s Wide-field Infrared Survey Explorer (WISE) took snapshots of more than 500 million celestial objects from its vantage point 326 miles (525 kilometers) above Earth’s surface. Scientists originally thought that catalog would include an equal number of normal, hydrogen-burning stars and “failed stars” called brown dwarfs. But new investigations into the WISE data have shown that the number of brown dwarfs in our solar neighborhood is far lower than expected.

Astronomers have found that the number of brown dwarfs in our solar neighborhood, shown in this artist's rendition, is much lower than expected. Blue circles are previously known brown dwarfs, and red circles are brown dwarfs identified for the first time by WISE. Click on the image for a larger version.
NASA/JPL-Caltech
Astronomers arrived at the new estimate, which puts the ratio at roughly six normal stars for every one brown dwarf, by looking at WISE objects within 26 light-years of the Sun. Although they found seven new members of the coldest brown dwarf class, called Y dwarfs, that only brought the total number of brown dwarfs in our region of space to 33. That number falls far short of the 211 hydrogen-burning stars in the same volume. Study coauthor Davy Kirkpatrick (Caltech) says it’s likely this ratio is typical of most of the rest of the galaxy: the solar neighborhood contains roughly the same number of stars as other parts of the galaxy — except for those furiously forming stars.

Brown dwarfs form with too little mass to sustain nuclear fusion in their cores. After burning through their initial store of fuel the objects gradually cool off, glowing faintly at infrared wavelengths with the leftover heat of the gravitational collapse that formed them. Y-class brown dwarfs are the oldest and coolest of the group and are notoriously difficult to detect. One such object, WISEP 1828+2650, is only about 80° Fahrenheit (27° Celsius), making it the coldest known star-like body.

An artist's impression of brown dwarf WD 0806-661 B (right foreground) orbiting a white dwarf at a large distance.
NASA Goddard Space Flight Center/Francis Reddy
Normal stars burn through their constituent materials, fusing heavier and heavier elements inside themselves until they eventually throw much of that material back out into interstellar space. But brown dwarfs never progress beyond the early stages of star formation, meaning they still contain the original (unadulterated) materials they were born with, says Kirkpatrick. “You can think of them as little time capsules,” he says, windows into the chemical history of the region of the galaxy where they formed.

While the low number of dwarfs won't necessarily wreak havoc with star formation theories, it does mean that astronomers have fewer examples to work with.

There may be more Y dwarfs hiding in the WISE data, but almost certainly not enough to match the previous one-to-one estimate, the study’s authors conclude in their paper, which will appear in the July 10 Astrophysical Journal. NASA put the WISE telescope into hibernation mode after it completed its primary science missions last year, so future space-based efforts to locate more brown dwarfs will have to wait for instruments such as the James Webb Space Telescope, currently scheduled for a 2018 launch.

12 thoughts on “Failed Stars Oddly Rare

  1. Bruce

    Remember the article several months ago; “How Many Unbound Planets in Milky Way?” In it Monica Young reported on a paper claiming that there could be as many as 100,000 unbound planets per star in our galaxy. “Planets” in this case were anything from sub-stellar brown dwarfs down to Pluto sized objects. Stephen Craft’s interesting article here kinda blows the doors off the upper end of their estimate, doesn’t it?

  2. Mike W. Herberich

    … plus, there goes the remnant of a weak hope for a dark matter candidate heard here and there.

  3. Bruce

    Indeed Mike, that’s true. I had wondered the same thing upon reading the Nomad planets story and had posted a question about these “planets” perhaps solving the missing mass problem. Dr. Young herself answered that even 10^5/star planets wouldn’t be enough mass to fill the bill. So “dark matter” retains it’s non-baryonic abundance and it’s strangeness, at least for now. We must take the universe as we find it to actually be, regardless of our preconceived notions, and be willing to modify our thinking accordingly, don’t you think?

  4. Mike W. Herberich

    Absolutely, Bruce! After all: that is how we all perceive of science, is it! Really nicely and concisely put, your last sentence there! It just so happens that I watched a TV program last night, summarizing in a half hour the current state of affairs, with dark matter, dark energy, dark flow and all … what an amazing achievement of the combined brightest heads and resources of all times up to now: that Socrates with his "scio nescio" ("I know I ignore!) is closer to the "truth" than anything and anybody else! It truly is an amazing, fascinating time we have the privilege and luck to be living in!

  5. Bruce

    Whoa there, partner. Mike, I think you read more into my last post than I intended to imply. I enjoy science, but I didn’t mean that it should be placed on a pedestal, as it were. It’s good to remember that in the quest for actual truth science has often gone up what turned up to be dead ends. Science is a human endeavor, and humans are imperfect. The intellectually pure “quest for truth” is often sullied by things like greed, envy, pride and arrogance. Scientists, like people in other fields, have been known to cheat, fudge their data, or omit findings that weaken their theory in the pressure to publish. I agree with you that this is a fascinating time to be alive, but not primarily for man’s scientific advancements. (To learn my main reason see Daniel 12:1-4, when a time when “the true knowledge will become abundant” was foretold. I think we’re in this time now.)

  6. Mike W. Herberich

    Bruce, did you notice the quote marks around the word "truth"? My intention was to underline your very last sentence because I think that beautifully summarizes what Rod called the Galilei method plus what science SHOULD be/ do and we all should always and everywhere (at least try to) implement. It IS difficult though, agreeably, sometimes next to impossible. That (we!) humans are humans everywhere and at all times (as far as we know) with all the shortcomings, but all the wonderful things also, is surely indisputable for anyone who has lived longer than a day in this world. I did not intend to put (all) science PEOPLE on a pedestal as better people than others. Yet, the scientific endeavor as such (which I would NOT qualify as "intellectually pure": I don’t think there is such a thing as PURE intellect) is extremly important. …

  7. Mike W. Herberich

    Another point I wanted to make is that people like Socrates (at a time when science meant a much broader thing altogether) obviously arrived at a result -just by philosophizing?!- which sounds very familiar to us, knowing the percentages of all dark (=unknown, theoretically introduced!) entities vs. the measurable, observable. Daniel: I looked it up in my (German, Lutheran) bible and found it pretty mute. Anyway, me being as non-religious as can be (to state it mildly!), my mental resorts are more of the sorts of Kant, etc. Reason and compassion are not only NOT mutually exclusive but rather do condition each other. And I go with the joke: prophecies are rather difficult to make … especially when the pertain to the future! That is why I like your sentence "… as we actually find it to be … willing to modify thinking …"!

  8. Bruce

    Thanks for the explanations Mike. And I’m sorry if I over-reacted to your comment. I must admit that, being sort of a red-necked Texan (my wife cringes when I mispronounce nuclear), a lot of what you write goes right over my head. But we do share at least two things, appreciation for humor and a fascination for what’s out there. Or, not out there, which brings me to the point of this post. The S&T article starting this thread shows us that brown dwarfs (no problem with the use of “dwarf” here, they are much smaller than the sun) are likely to be much less common than theories predicted. That’s what prompted my “be willing to modify thinking” statement. I have no idea why they would be rare except for this, what possible useful purpose does a brown dwarf serve? They can’t warm a planet, all they can do is cool off. If there were vast numbers of them they’d be hazardous to navigation :)

  9. Mike W. Herberich

    No sweat, Bruce. On re-reading my own comments, I sometimes wonder what this guy intended to say :-{ ! Your certainly right about humor and fascination. Nuclear: go check dict.leo.org, click the info button, pick "Definition/ Pronunciation (American)"; that will give you something to rub your wife’s nose in ;-] ! Dwarfs: maybe one should consider calling them politically more correctly … like "brown growth challenged futiles" … or so :-D ! As for their purposefulness: what good are ALL these objects out there anyway … they just make us doubt, question and think, don’t they!? :-| (that was an (antithetical) pun, by the way … just to anticipate enraged flames!)

  10. Bruce

    Hey Mike, don’t feel bad, “I sometimes wonder what this guy intended to say,” just means your completely normal, just like everyone else who reads your posts. :) As for myself, as everyone can tell I’m quite opinionated, but since I’m very “willing to modify my thinking” the set of all people who agree with me completely oscillates between 0 and 1, myself included. I suggest we call this phenomenon the Mayfield-Herberich Uncertainty Principle. (MHUP, perhaps?) For more astronomically inspired humor, all who have signed up and logged in can enter the S&T article title I referenced in the first post in this thread into the search field. The excellent article you’ll pull up inflates the balloon that Stephen Craft’s article here pops, as it were, but the humor is found in the long conversation Dr. Monica Young’s first article generated. You’ll find the origin of my “dwarf” comments, as well as my most embarrassing misspelling ever. :0

  11. Mike W. Herberich

    Thanks, Bruce, for categorizing me with the normal: 1 out of a billion terrestrials … but, hey, that’s a start ;-]. I guess you wouldn’t like my suggestion for rearranging MHUP into HUMP, would you? … just because it’d put MY initial before yours … or because it doesn’t make sense at all in this sequence anyway? Dr. Monica Young’s 1st article: I checked on your lead, but found only 1 post of yours with no misspelling or reference to dwarfs, really. Did I miss out on something?

  12. Bruce

    Mike, if guys exactly you are one in a billion there must be 6 more of you out there … Since you’ve got me vastly outnumbered I’ll suggest the compromise acronym HMUP. I am sorry you’re having difficulty pulling up “How Many Unbound Planets in Milky Way.” I typed this title into the search keyword field earlier today and the story was the first item in the list. You ARE missing out if you can’t check it out Mike. The article was excellent and it generated 27 comments (with all doubles deleted). In reviewing these posts I discovered something I’d forgotten: The guy who got me started into dwarf comments is another very humorous Mike! (One of the other 6, perhaps?)

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