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Star Smaller Than Some Planets Found

Posted by Zonk on from the on-the-way-to-a-hole-in-space dept.

Abhishek writes "Astronomers have found the tiniest full-fledged star known, an object just 16 percent bigger than Jupiter. It is smaller than some known planets that orbit other stars. The star is a companion to a Sun-like star toward the center of our Milky Way Galaxy. It was found and measured by observing changes in the light output of the system when the smaller star passes in front of the larger star from our vantagepoint. This would give a better idea of brown dwarfs or failed stars. The star has been named OGLE-TR-122b. This discovery also marks the possibility of stars that look strikingly like planets."

17 of 138 comments (clear)

  1. Interesting... by Ianoo · · Score: 4, Insightful

    I've read in other places that there needs to be a critical mass for a big cloud of hydrogen to begin fusion, otherwise it ends up as something like Jupiter. What might be the reason for this star burning when other similarly sized objects do not? Gravitational effects from the companion star imparting extra energy? Any physicists care to speculate?

    1. Re:Interesting... by selectspec · · Score: 5, Informative

      The article is misleading confusing "size" with "mass". This new star has 95 times the mass of Jupiter. However, it's density is so great that its physical size is only slightly larger. Density is the trigger key for fusion.

      --

      Someone you trust is one of us.

    2. Re:Interesting... by DoubleEdd · · Score: 3, Informative

      The Chandrasekhar limit is 1.4 solar masses, and is quite irrelevant to the lower limit on the mass of hydrogen which will form a star.

      This star has no bearing on the Chandrasekhar limit.

    3. Re:Interesting... by Minwee · · Score: 4, Informative
      I think you are confused. The Chandrasekhar limit is the upper mass limit for a stable white dwarf star -- A star whose core exceeds that mass will become degenerate and collapse into a neutron star or "black hole" while one below the limit will be able to support itself and remain a white dwarf until it burns out and dies.

      The Chandrasekhar has to do with the _death_ of stars, not their birth. To be considered a star all you need is sustained hydrogen fusion at the core, not electron degeneracy. While it's interesting that we are seeing a dense low mass star the value of L C is in no danger of being rewritten.

      To learn more, why not search the Internet?

    4. Re:Interesting... by LurkerXXX · · Score: 4, Funny
      Likely it was rebels fleeing from an Alliance Heavy Cruiser. As they were slingshoting around the larger star, they decided to launch one of their thermonuclear torpeados into the gas giant orbiting it, triggering the thermonuclear reaction that the proto-star was incapable of initiating on it's own. Luckily for the rebels the unexpected flood of radition from the new star was enough to temporarily blind the sensors of the Alliance Cruiser, allowing them to escape.

      But that's just my hunch.

    5. Re:Interesting... by Mr.+Bad+Example · · Score: 3, Funny

      > What might be the reason for this star burning when other similarly sized objects do not?

      Sheer impotent RAGE.

  2. Aren't neutron stars "stars"? by turnstyle · · Score: 4, Insightful

    Aren't neutron stars "stars"? And aren't they smaller than planets?

    --
    Here's what I do: Bitty Browser & Andromeda
    1. Re:Aren't neutron stars "stars"? by nefele · · Score: 4, Informative

      Neutron stars were stars at one point, but they're not stars in the same sense that the Sun is. When a Sun-like star ends its lifecycle with a (super)nova burst, it gets rid of most of its mass, and the rest collapses into a small neutron 'star', or a black hole if the mass was sufficiently large.

      IANAP, but I think no thermonuclear reactions take place in neutron 'stars' (or maybe just not enough to sustain the emission of light, so they're not easily visible). So basically neutron stars are just dead stars.

    2. Re:Aren't neutron stars "stars"? by LokieLizzy · · Score: 5, Informative
      Not quite. Actually, not at all. A sun-like star doesn't end its life cycle with a nova burst, or anything like that. Rather, it swells into a red giant, and eventually *slowly* puffs out its outer layers and forms a planetary nebula, with a white dwarf at its center. Stars that (go) Nova are typically several times larger than our sun, and stars that go supernova can be hundreds of times larger than our Sun (hence their names: red or blue supergiants). Sirius (brightest star in the night sky) is an example of a blue supergiant, while Antares (the heart of the Scorpion) is a red supergiant. After supernovaing, it's *these* stars that can form neutron stars or black holes. But not our sun, or stars in close mass to our sun -- those form planetary nebulae, and white dwarves.

      Furthermore, neutron stars aren't dead -- they often radiate a hell of a lot of energy. Those that do are called *Pulsars* -- that's where all those directional radio/x-ray waves come from in deep space -- they spin like lighthouses, you see.

      --
      My digital rights don't need management.
    3. Re:Aren't neutron stars "stars"? by LMCBoy · · Score: 4, Informative

      You are a lucky man, Lord Pillage; you now have a golden opportunity to expand your horizons by learning all about white dwarfs and neutron stars, and about the stark and dramatic physical differences between them.

      Enjoy!

      --
      Liberal (adj.): Free from bigotry; open to progress; tolerant of others.
  3. that's no star... by HawkinsD · · Score: 3, Funny

    That's no star... That's a space station!

    --
    Never attribute to malice that which can be explained by mere idiocy.
  4. They're only small stars by eclectro · · Score: 3, Funny

    until the Oscar awards.

    Thank you, I'm here all week.

    --
    Take the cheese to sickbay, the doctor should see it as soon as possible - B'Elanna Torres, "Learning Curve"
  5. Quadrupole-induced polarization? by Sheetrock · · Score: 4, Funny
    There is a possibility, albeit a small one, that an overload of the phase coupling relay reaction in a solar furnace (star) could trigger a non-catastrophic split.

    If a star is smaller than the conditions necessary for supernovae, and is struck with a star of the same size, you will end up with quadrupoles flying off in different directions. Needless to say this is rare, which makes this quite an exciting find!

    --

    Try not. Do or do not, there is no try.
    -- Dr. Spock, stardate 2822-3.




  6. Stars "looking" like planets ? by Dozix007 · · Score: 3, Insightful

    I think it should be noted that the way we look at stars and planets could never really lead to that mistake. Radiation emitted by a stellar body is analyzed and it is then determined "what" the stellar body is. It is impossible to misinterpret an extremely hot stellar body with a relatively cool planet.

    1. Re:Stars "looking" like planets ? by Fex303 · · Score: 3, Funny
      It is impossible to misinterpret an extremely hot stellar body with a relatively cool planet.

      I dunno... After a few drinks I've been known to think all kinds of things have hot bodies.

  7. Don't panic... by hanssprudel · · Score: 3, Informative


    Before anyone starts panicing about Juptier collapsing into a companion star to the sun, and screwing over our whole solar system pretty royally - please note that while this star is only 16% larger than Jupiter in volume, it contains 95 times as much mass.

  8. Re:So again, why? by Ckwop · · Score: 4, Informative

    Been a long time since I was I was into nuclear phys, but how can it maintain that density with such (relatively) small mass? The process of fusion, which tends to expand a star, equally balances gravity which tends to contract a star. Seems to me a normal star would expand due to fusion.

    Basically, it doesn't make sense that it can maintain being 1/10 the mass of the sun and 50x as dense. This means its fusion output must be tiny (little to balance gravity), but why? Is it mainly made of non-hydrogen mass? They should be able to tell the elemental composition from the spectrum. And how could it have such little fusion and not be a brown dwarf?

    Wish this press release had some science in it.

    Actually, you got the right answer! The star has expanded due to nuclear fusion taking place it just hasn't expanded dramatically because it doesn't take a dramatic amount of fusion to support a star with so little mass.

    The reason fusion is needed to support a star is because the heat generated through contraction is radiated in to space. The energy lost through this process needs to be replaced to keep the volume of the star constant - and fusion provides this energy.

    There are two reasons why a star this small can exist. The first is the low mass of the star. The smaller the mass of the star the less heat it takes less energy to raise the tempreture of the entire star. This means it takes less energy to maintain the tempreture of the star and this means less fusion.

    The second reason is surface area. The Sun has a surface area of approximately 6 x 10^20 meters compared with Jupiter's 6.4 x 10^18 meters. This star is only slightly larger than Jupiter in terms of volume and so will have a comparable surface area. This means that the radiation of heat in the star will not be as efficient as in the sun and that means less fusion is required to keep the tempreture of the star constant.

    Since the tempreture, among other things, determines the size of a star both of these factors allow the star to remain balanced and still stay fairly compact. So while it suprising that stars this small exist it is not inconsistent with theory.

    Simon.