Slashdot Mirror

← Back to Stories (view on slashdot.org)

Proxima Centauri Might Not Be the Closest Star To Earth

Posted by samzenpus on from the hiding-behind-the-shine dept.

StartsWithABang writes The Alpha Centauri system consists of three stars, including Proxima Centauri, the closest star to Earth. But while main-sequence, hydrogen-burning stars are easy to find due to their visible light output, brown dwarfs — which only fuse the small amounts of deuterium they're born with — often emit no visible light at all, and can only be seen in the infrared. In 2013, WISE discovered a binary pair of brown dwarfs just 6.5 light years away, making them the third-closest star system to Earth, and leaving open the possibility that there may yet be brown dwarfs closer to us than any star, a question that it will take the James Webb Space Telescope to answer.

60 of 98 comments (clear)

  1. Are Brown Dwarfs Stars? by jfdavis668 · · Score: 5, Interesting

    I don't think brown dwarfs count as stars.

    1. Re:Are Brown Dwarfs Stars? by stox · · Score: 2

      Is the quality "star" one of mass, or energy output? Where between white and brown do you draw the line?

      --
      "To those who are overly cautious, everything is impossible. "
    2. Re:Are Brown Dwarfs Stars? by Anonymous Coward · · Score: 5, Informative

      Is the quality "star" one of mass, or energy output? Where between white and brown do you draw the line?

      The no-man's land between planet and star is a question of interior nuclear fusion: planets don't do it, stars do. But a brown dwarf is an object that does it - a little bit, early in life. Fusion of (normal) hydrogen into helium is pretty hard to do, but fusion of deuterium - hydrogen's heavier cousin - is easier. Brown dwarfs have enough central heat/pressure from gravitational contraction that they fuse all their deuterium away, quickly, and then fade into the night. It's thought that this no-man's land mass range is from about 13 to 80 Jupiter masses.

    3. Re:Are Brown Dwarfs Stars? by Sperbels · · Score: 2

      What about white dwarfs and neutron stars?

    4. Re:Are Brown Dwarfs Stars? by duck_rifted · · Score: 4, Informative

      Those are both post-main-sequence stars. Neutron stars happen post-supernova when their mass is too low for their gravitational collapse to compress them beneath the Schwarzschild Radius (which would make them black holes). The Scwarzschild Radius is the spherical radius resultant of calculations dependent upon mass; the distance from the center of a sphere to surface that the mass would need to be compressed into in order to become a black hole. I'm not sure whether the gravitational acceleration during collapse is countered by continued energy output, pressures resulting from electrons being pushed into higher energy levels such that the Pauli Exclusion Principle isn't violated, or some combination of both. Neutron stars are neat because they're basically enormous Bose-Einstein condensates.

      Your question about white dwarfs is spot-on though because those stars are pretty much what #49246567 describes. A star fuses enough hydrogen that the mass of its outer layers drops off, inner reactions then push that layer outward to form a red giant, the red giant sheds those outer layers, and a white dwarf is that hot, deuterium-rich star left behind. That star then cools and dims over time.

    5. Re:Are Brown Dwarfs Stars? by duck_rifted · · Score: 1

      Neutron stars are enormous Bose-Einstein condensates left over post-collapse when the gravitational acceleration of a star can't overcome pressures created as a secondary effect of the Pauli Exclusion Principle.

      White Dwarfs are exactly what the post above you describes. Hydrogen is fused into heavier deuterium that sinks to lower layers in a star until the outer layer is light enough that it gets pushed outward to form a red giant. Then, that outer layer is shed, leaving behind a bright, hot, deuterium rich core. The difference is that sooner or later, the deuterium starts to run out. Black dwarfs are completely expended white dwarfs. Brown dwarfs are easier to detect (but still not what you'd call easy to detect).

    6. Re:Are Brown Dwarfs Stars? by ShanghaiBill · · Score: 4, Informative

      Hydrogen is fused into heavier deuterium that sinks to lower layers in a star

      Stars do not produce deuterium. Any environment that can fuse normal hydrogen can easily burn up any deuterium that is present. Nearly all the deuterium in the universe is believed to be left over from the Big Bang. More info here.

    7. Re:Are Brown Dwarfs Stars? by duck_rifted · · Score: 1

      Okay, so it must be helium fusion going on in dwarfs then? I will look that up and read later (soon as I'm not a human jungle gym).

    8. Re:Are Brown Dwarfs Stars? by gman003 · · Score: 5, Informative

      There's a continuum of sorts between gas giant planets and dwarf stars, with a few notable points where you could draw the distinction. They all come from the same general start - a cloud of interstellar gas collapses into a spherical object. Depending on how big it is, you can get different objects.

      First you have gas giants, no fusion at all. This would be your Jupiter and Saturn type planets. Jupiter is actually about as big, volume-wise, as a gas giant can get. Add more mass, and it starts getting denser rather than bigger.
      At 13 Jupiter masses, you have enough gravitational pressure to fuse deuterium. This is what most astronomers define as a brown dwarf star, but others, and apparently you, consider it to still be a planet. Previous terminology included "substar", which I would not be opposed to. Deuterium isn't particularly common, so these objects glow very dimly, as far as stars go.
      At 65 Jupiter masses, you can start fusing lithium as well. This is one way to distinguish brown dwarfs from other stars - red dwarfs and yellow dwarfs, like our sun, consume their starting lithium very quickly, and so the presence of lithium spectra indicates a brown dwarf.
      At around 80 Jupiter masses, it starts fusing hydrogen, becoming a red dwarf, like Proxima Centauri. Still very dim, but at this point it's undeniably a star.
      At around 750 Jupiter masses, the star develops a more complex internal structure, and becomes a yellow dwarf, such as Sol.

      So where do you draw the line? Anywhere you want, but most astronomers settled on the simplest one: if it's undergoing fusion, it's a star, if it isn't, it's a planet.

    9. Re:Are Brown Dwarfs Stars? by rossdee · · Score: 2

      herve villechaize was a star

    10. Re:Are Brown Dwarfs Stars? by rogoshen1 · · Score: 1

      hmm, i think that's about 3/5 of a question sir. ...... what?

    11. Re:Are Brown Dwarfs Stars? by khallow · · Score: 1

      I believe most of the core of a white dwarf consists of iron nuclei and most of its internal heat comes from the supernova with a little additional gravitational compression over time, unless it happens to be pulling matter in, say from a star it orbits.

    12. Re:Are Brown Dwarfs Stars? by ShanghaiBill · · Score: 5, Interesting

      Okay, so it must be helium fusion going on in dwarfs then?

      In stars like our sun, the main process is the proton-proton chain. Deuterium is produced, but it is then almost immediately fused with an additional proton into He3, which then undergoes additional fusion to form He4.

      Stars bigger than 1.3 solar masses use the Carbon-Nitrogen-Oxygen Cycle to fuse hydrogen into helium in a reaction catalyzed by carbon.

      White dwarfs have little material left to fuse. They are mostly carbon and oxygen, but they are not big enough or hot enough to fuse the carbon or oxygen into heavier elements. So they slowly cool off and die.

       

    13. Re:Are Brown Dwarfs Stars? by FatdogHaiku · · Score: 1

      I don't think brown dwarfs count as stars.

      Grumpy is not gonna like this...

      --
      You have the right to remain sentient. If you give up the right to remain sentient, you will be elected to public office
    14. Re:Are Brown Dwarfs Stars? by Neil+Boekend · · Score: 3, Interesting

      The decay from white dwarf to black dwarf is slow. In fact it's so incredibly slow that the universe isn't old enough to have them in it yet.
      Estimates for the time it takes are 10^15 to 10^37 years, depending on factors like pronton decay and WIMP existence. The universe is "only" 13.8*10^9 years old.

      This makes their indetectability practically moot.
      Theoretically it's still fun to think about. The only ways to detect them with current physics would be occlusion (low detection chance) and gravitational influence (low detection range).

      --
      Well, I might have a way, but it only works on a semi spherical planet in a vacuum.
    15. Re:Are Brown Dwarfs Stars? by Neil+Boekend · · Score: 1

      There is at least one type of mud in that clear definition. Formation heat. During formation a lot of heat is generated, and that heat helps fusion. So young 12 Jupiter masses can fuse deuterium for a while, slowing the cooldown with the fusion energy.

      --
      Well, I might have a way, but it only works on a semi spherical planet in a vacuum.
    16. Re:Are Brown Dwarfs Stars? by WCMI92 · · Score: 1

      I was going to say much the same thing. If it doesn't do (or didn't do in the past in the case of white dwarfs) hydrogen fusion in the core is it really a star?

      I don't think that it is. Just being massive enough to emit some energy isn't enough. Jupiter, for example, gives off some heat but no one would argue that it's a star.

      --
      Corporatism != Free Market
    17. Re:Are Brown Dwarfs Stars? by WCMI92 · · Score: 2

      White dwarf and neutron stars are the remnants of stars that had core fusion during the main sequence.

      Brown Dwarf stars never had core hydrogen fusion and thus are failed stars. The smallest thing you can truly call a star is a Red Dwarf because they at least have core hydrogen fusion.

      --
      Corporatism != Free Market
    18. Re:Are Brown Dwarfs Stars? by WCMI92 · · Score: 4, Informative

      Your question about white dwarfs is spot-on though because those stars are pretty much what #49246567 describes. A star fuses enough hydrogen that the mass of its outer layers drops off, inner reactions then push that layer outward to form a red giant, the red giant sheds those outer layers, and a white dwarf is that hot, deuterium-rich star left behind. That star then cools and dims over time.

      Not all stars that were large enough to do core hydrogen fusion become red giants. Most red dwarf stars won't because they are fully convective, meaning that they will fuse almost all of their hydrogen in the "core" and not have hydrogen fusion in the shell (and no red dwarf has enough mass to do helium fusion). When low mass red dwarf stars run out of gas they simply pass directly to the white dwarf stage (burnt out core)

      --
      Corporatism != Free Market
    19. Re:Are Brown Dwarfs Stars? by Archtech · · Score: 1

      Indeed. While technically stars beyond any doubt, they aren't exactly the kind of stars we are looking for at the moment. (IMHO).

      --
      I am sure that there are many other solipsists out there.
    20. Re:Are Brown Dwarfs Stars? by tnk1 · · Score: 2

      Jupiter is producing more heat due to convection bringing core heat to the surface, it's not doing fusion. Like on Earth, core heat is due to the extreme pressures and radioactive materials heating the core to high temperatures. None of that pressure is enough to fuse nuclei together, however.

      Brown dwarfs will actually do fusion, but only a little of it, and only for a relatively short time since they only have enough mass to fuse heavy hydrogen nuclei, which is the easiest thing that you can fuse. The problem is that there isn't much of the heavy versions of hydrogen, and so you're not going to burn for very long, nor will you burn brightly.

       

    21. Re:Are Brown Dwarfs Stars? by Drumhellar · · Score: 1

      In a star like the Sun, Hydrogen burns into Helium, with Deuterium being a step along the proton-proton chain. When All the Hydrogen in the core is used up, the core contracts, and gets extremely hot. The layers outside of the core also contract, and a shell of hydrogen around the non-burning helium core begins to burn. The helium produced here sinks to the core, adding heat and mass. The added mass causes further contraction, and eventually the helium core starts burning, turning into carbon via the triple-alpha process. Eventually, the helium runs out, the core contracts again, a hydrogen shell starts burning, helium sinks to a shell around the carbon core, the hydrogen shell stops burning, contracts, another hydrogen shell starts burning, producing helium, which sinks to the helium layer, which eventually gets hot enough to start burning, producing carbon, which sinks to the carbon core, heating it up and causing it to contract from the added mass, which heats it up more, eventually getting hot enough for the Carbon-Nitrogen-Oxygen cycle to begin. This is what happens to a main-sequence star after it leaves the main sequence. Large stars do this in repeated steps and repeated layers, all the way up to iron, though when iron forms, disaster happens. During this repeated process of shell burning, the star will repeatedly shrink and contract over the scale of a few million years, losing mass in the process. For a star the mass of our Sun, the process will stop at Oxygen (I think). At this point, (and, once the various shells stop burning), the last of the outer layers float off into space, the core contracts, and fusion stops. This is a white dwarf. No fusion goes on - it's just a hot ball of degenerate gas (In the case of our Sun, a hot ball of mostly Oxygen). At this point, there isn't much in the way of gravitational contraction, glowing only from black body radiation. Just for fun, there are certain masses where this recurring balancing act of shell-core-shell-core burning doesn't work, and the star blows up - for example, when helium burning begins but there isn't enough mass external to the core to exert an inward pressure on the core, the helium core can blow itself apart.

  2. Intriguing headline.. by devon_halley · · Score: 5, Funny

    Surely the Sun is the closest star to Earth, right?

    1. Re:Intriguing headline.. by rubycodez · · Score: 4, Funny

      No, Linsey Lohan is, so drugged up she's rarely vertical

    2. Re:Intriguing headline.. by rudy_wayne · · Score: 2

      As long as Uranus doesn't get any closer to me, I'm OK with it.

    3. Re:Intriguing headline.. by kimvette · · Score: 1

      I wouldn't call her a star at this point. Train wreck, maybe.

      --
      The Christian Right is Neither (Christian nor right). See: Matthew 23, Matthew 25, Ezekiel 16:48-50
  3. yes, brown dwarfs can be stars by turkeydance · · Score: 1

    if they "identify" as stars.

    1. Re:yes, brown dwarfs can be stars by ultranova · · Score: 1

      if they "identify" as stars.

      Which they are unable to, since they're lifeless objects.

      Oh, I'm sorry, was that meant as a dig against some people who's existence bugs you for whatever reason? Have you considered getting professional help for your weird obsession?

      --

      Forget magic. Any technology distinguishable from divine power is insufficiently advanced.

  4. Place your bets... by billybob2001 · · Score: 4, Funny

    Proxima Centauri Might Not Be the Closest Star To Earth

    Put another way, Sol Might Be the Closest Star To Earth

    ...or perhaps Jupiter is?

    1. Re:Place your bets... by erice · · Score: 4, Informative

      Proxima Centauri Might Not Be the Closest Star To Earth

      Put another way, Sol Might Be the Closest Star To Earth

      ...or perhaps Jupiter is?

      Jupiter is not a brown dwarf. It is not massive enough to even burn deuterium. No fusion == no star

    2. Re:Place your bets... by by+(1706743) · · Score: 5, Informative

      ...or perhaps Jupiter is?

      Nope -- regardless of star status, Jupiter is farther away from the Earth than Sol.

    3. Re:Place your bets... by Anonymous Coward · · Score: 3, Funny

      Ok, deuterium, fine - no need to get heavy.

    4. Re:Place your bets... by Anonymous Coward · · Score: 1

      I would think excluding the sun would be a given. Also not one mention of Schulz's star, which (supposedly) 70,000 years ago came within 1 light year

    5. Re:Place your bets... by hcs_$reboot · · Score: 1

      Have a question for you since you seem knowledgeable and you are on a show-off mood. What would happen is someone gets close to Jupiter and lights a lighter?

      --
      Slashdot, fix the reply notifications... You won't get away with it...
    6. Re:Place your bets... by spauldo · · Score: 1

      Not the guy you were talking to, but I'll answer.

      Nothing. You've got fuel but no oxidizer.

      Jupiter has thunderstorms larger than our planet. If the atmosphere could burn, it would have done so long ago.

      --
      Those who can't do, teach. Those who can't teach either, do tech support.
    7. Re:Place your bets... by Maxwell'sSilverLART · · Score: 1

      How long does the fusion need to last to constitute a star? Arguably, the US and Russia have produced a number of stars quite close to Earth indeed, if only briefly.

      --
      Moderate drunk! It's more fun that way!
    8. Re:Place your bets... by catmistake · · Score: 1

      Proxima Centauri Might Not Be the Closest Star To Earth

      Put another way, Sol Might Be the Closest Star To Earth

      ...or perhaps Jupiter is?

      Depending on when the last periodical mass extinction was, Nemesis is.

      --
      The Admin and the Engineer
    9. Re:Place your bets... by tnk1 · · Score: 1

      Proxima Centauri Might Not Be the Closest Star To Earth

      Put another way, Sol Might Be the Closest Star To Earth

      ...or perhaps Jupiter is?

      The Earth is closer to the Sun than it is to Jupiter, so the point is moot no matter what you define Jupiter as.

    10. Re:Place your bets... by tnk1 · · Score: 1

      It needs to be self sustaining by burning its own mass using certain fusion reasons. When stars "start up" there's probably a spark like a fusion explosion somewhere in there that starts the reaction in the first place, but after that, it keeps going.

      Theoretically, you could say that if you put together a certain critical mass of fuel and maybe you compressed/nuked it to start it up, you might get a "star" for some period of time like a month or a year or 10,000 years or something, which is why we also have the concept of a "main sequence" star which will have a certain mass and follow the process of becoming a red giant then white dwarf and burn out. Those stars "live" for billions of years, and then peter out as white dwarfs over a trillion or so.

      So, you could probably produce a star from something like Jupiter, and I suppose it would be legit, but nuclear explosions don't count as stars themselves.

    11. Re: Place your bets... by Lodlaiden · · Score: 1

      They didn't produce theirs.

      --
      Suborbital [spaceflight] is the special olympics of spaceflight. - Rei
    12. Re:Place your bets... by toddestan · · Score: 1

      Even if it was, Earth is still closer to Sol than it is to Jupiter.

  5. Them are no stars... by 140Mandak262Jamuna · · Score: 4, Funny

    Come on brown dwarfs are not really stars. It is a con job to call them stars. It is like these New Jersey cruise sales boilerrooms selling "Masala Cruise with Bollywood stars" and then on board you see one guy who played the corpses in a murder mystery starring the Amir Khan and another who was the fourth thug beaten by Rajnikant enthiran the robot.

    --
    sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
    1. Re:Them are no stars... by NoKaOi · · Score: 4, Informative

      Sheesh, it's just semantics. Definitions are for communication, if they call them brown dwarfs then you know what they're talking about. The IAU's considered an object with a mass capable of fusing deuterium a brown dwarf, which is 13 Jupiter masses. Don't like it? Too bad, as long as it's qualified with "brown dwarf" then you know what they're referring to. So, the term "closest start to Earth" is another issue of semantics. In the context of this article, it means, "closest object outside of our own solar system with a mass over 13 Jupiters." Now, if they start handing out medals and big prize money to stars for being the closest to Earth, then go ahead and debate it, otherwise who cares?

    2. Re:Them are no stars... by techno-vampire · · Score: 2

      Sheesh, it's just semantics.

      I don't think that word means what you think it does.

      --
      Good, inexpensive web hosting
    3. Re:Them are no stars... by tnk1 · · Score: 1

      As we get most of their light in the infrared, they could very well be an actual brown color to our eyes depending on how it was illuminated. If you shined the light of an actual star on it from a short distance, it would probably be a very angry looking Jupiter. If there was no other illumination anywhere nearby, it would probably have a reddish glow like the color of a dying ember while it was fusing. After that, it would be indistinguishable from a gas giant planet.

  6. childish language by caviare · · Score: 2

    Wow, did you know that a binary system consists of literally two stars! And a pair of stars is like two stars also, awesome! So a binary pair must be like two doubly awesome stars. Party on dudes!

  7. lol by slashmydots · · Score: 1

    And the Red Dwarf is merely right over on Canadian television. That has to be closer.

  8. No one has said this yet... by l0n3s0m3phr34k · · Score: 1

    NIBIRU! hahahahahahaha

  9. Forgetting the obvious? by Anonymous Coward · · Score: 1

    The Sun, that big yellow fireball which appears in the sky during daylight hours when the weather is good, is in fact the closest star to the Earth.

    So this article is really about which star is the second closest to the Earth.

  10. Semantics by e065c8515d206cb0e190 · · Score: 4, Funny

    If it's not the closest, are we going to rename it?

    1. Re:Semantics by starless · · Score: 4, Funny

      If it's not the closest, are we going to rename it?

      Proximish Centauri??

    2. Re:Semantics by Anonymous Coward · · Score: 1

      Approximish Centauri.

    3. Re:Semantics by Roger+W+Moore · · Score: 2

      If it's not the closest, are we going to rename it?

      No, because it will presumably still be the nearest in the constellation of Centaurus. It's 'Proxima Centauri' not 'Proxima'

    4. Re:Semantics by waynemcdougall · · Score: 1

      If it's not the closest, are we going to rename it?

      No, because it will presumably still be the nearest in the constellation of Centaurus. It's 'Proxima Centauri' not 'Proxima'

      Constellations are not defined by a collection of stars at roughly the same distance. They are a collection of stars roughly close together, in a pattern _as viewed from Earth_. Apparently adjacent stars in the same constellation can vary in distance from earth by thousands of light years.

      So any newly discovered star closer to Earth is most likely to be in the scope of some other constellation.

      --
      Recycle PCs and build a wireless community network www.hillsborough.org.nz
    5. Re:Semantics by itzly · · Score: 1

      They can vary by a whole fuckload more than a few measly thousand light years.

      Stars that are part of a constellation are generally visible with the naked eye, which means that they are typically less than 1000 light years away. The furthest star that's visible with the naked eye (with good eyesight/conditions) is V762 Cas in the constellation of Cassiopeia at 16000 light years.

  11. Wrong name for that telescope by Kohlrabi82 · · Score: 1

    If the telescope is meant to detect brown dwarfs, why is it not called the Spud Webb Space Telescope?

  12. Well, ... by jandersen · · Score: 1

    of course not - the Sun is ;-)

  13. Not very surprising by Anonymous Coward · · Score: 1

    Since the discovery that Alpha Centauri was the closest neighboring star, and then the discovery of White Dwarfs and Red Dwarfs, there has been much speculation that there were closer stars than Alpha Centauri, and there was, it was discovered that Proxima Centauri was closer. If another star is discovered closer, it will be no different from last time it happened.

    Indeed the Nemesis proposal is a white, red, or brown dwarf companion to the Sun, responsible for extinction events

  14. Re:Dark Matter? by taiwanjohn · · Score: 1

    If the population of hard-to-spot brown dwarf stars turns out to be higher than previously thought, would the increased mass be enough to account for dark matter?

    --
    XML is like violence. If it doesn't solve your problem, you're not using enough of it. --AC
  15. Re:Dark Matter? by Anonymous Coward · · Score: 3, Informative

    No, or to be precise, not significantly. That calculation was done the other way around: what if all that dark matter was in the form of brown dwarfs, rogue planets, asteroids etc. Then it turns out you need such a huge number of such objects that they would definately be very very prominent in observations. So going back to the observational side of the question, given how hard it is to detect those things we get a very rough upper limit on their mass contribution. How close to that limit we actually are is something new observations try to answer and as in the case of the exoplanets it turns those things are way more comon than we thought initially. Still the upper limit on their total mass is such that they cannot account for more than a few percent of the dark matter.

    IIRC they are called MACHOS as opposed to WIMPS which is the kind of exotic particle people are looking into now. Astronomers suck at acronyms...