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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.

6 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 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.

    2. 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.

    3. 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.

       

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

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

  3. 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.