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Is Alpha Centauri, the closes star to the solar system?

  1. May 4, 2006 #1
    is Alpha Centauri, the closes star to the solar system?
  2. jcsd
  3. May 4, 2006 #2


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  4. May 4, 2006 #3


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    Essentially yes. Alpha Centauri is a multiple system. The closest member is something called Proxima Centauri - it is a dwarf.
  5. May 4, 2006 #4
    thx a lot for the website, i m very interested in space things, are they in the category of "astronomy" and "cosmology", and are "astronomy" and "cosmology" the same thing, if you have anymore good site please post them, thx.
  6. May 4, 2006 #5


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    No, astronomy and cosmology are not the same thing. Cosmology is the study of the univeverse as a whole. Examples of this would be like studying the big bang and the evolution of the universe. Astronomy is the study of matter in outerspace essentially like stars and blackholes.
  7. May 4, 2006 #6
    Cosmology tends to be more speculative and theoretical and is the science of the universe as a whole. There are few limits to cosmology. Astronomy is the study of the 'stuff' out there, with no philosophy needed.
  8. May 5, 2006 #7
    This is certainly not correct. In this day and age, we are able to measure large scale properties of chunks of the universe big enough to say non-speculative things about the Universe. See for example data from WMAP, the 2 degree field galaxy redshift survey and the sloan digital sky survey. WMAP in particular measure the microwave background radiation, whilst the 2 galaxy surveys measure redshifts for hundreds of thousands of galaxies spread out over a large volume.
  9. May 5, 2006 #8
    thx alot for the information, is very helpful!!
  10. May 5, 2006 #9


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    Well, I just stumbled across this article.

    Any thoughts?

    Of course, this could belong in Ivan's Skepticism & Debunking forum. :biggrin:
    Last edited: May 5, 2006
  11. May 6, 2006 #10


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    The question of whether the Sun has a companion, possibly a brown dwarf, sometimes called Nemesis, has regularly been suggested.

    The first reason it was thought it might exist was as a periodic disturber of the Oort cloud of comets, which then fell sunwards causing periodic mass extinctions on Earth.

    However whether mass extinctions actually do occur at regular intervals is highly problematic. Infra-red surveys such as by IRAS in the 1980's have really closed the parameter space in which such an object may exist. It is now almost inconceivable that such an object should exist without it already being detected.

    Plenty of room though for "Planet X"s such as Sedna out there .

  12. May 6, 2006 #11


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    I agree with Garth. IRAS has virtually ruled anything that remotely resembles 'Nemesis'.
  13. May 6, 2006 #12


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    "...Sedna moves in resonance with previously published orbital data for a hypothetical companion star..."

    How much data does one need about the orbits of

    1] a newly disocovered body of which we've seen only a tiny, tiny arc of its orbit, and
    2] a hypothetyical body, never even seen

    to determine if they are resonant with each other?
  14. May 6, 2006 #13


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    They didn't mention what resonance. 2:1, 3:2? And why would Sedna's eccentricity fade with time. That doesn't make any sense unless it frequently passes through a belt of material at perihelion. And if you want to believe that it is, then maybe its orbit is circularizing. Maybe it was once more elliptical. Imagine its orbital period used to be 100,000 years. It just wouldn't pass through perihelion often enough to for any belt at its perihelion distance to significantly affect its orbit.

    Regarding Nemesis stirring up the Oort Cloud on a periodic basis and sending comets crashing into Earth, here's something I don't understand:

    Oort Cloud comets are believed to be at about 60,000 AU. They should have an orbital speed of ~120 m/s. For them to drop to the inner solar system, they would need to have this orbital speed reduced to less than ~1.5 m/s. Comets whose velocity is changed to ~2m/s won't drop much closer to the Sun than Jupiter. ~5 m/s and above, and they don't even make it as close to the Sun as the Kuiper Belt. So the inner solar system is a very small target.

    And those that do get sent to the inner solar system have another lottery they must win. Earth is a very small target in the inner solar system. To get hit, the comet must be in the ecliptic when it crosses the 1AU mark. And even if it is, The Earth, with its 12000 km diameter and 1 billion km orbital track around the Sun, only occupies 1/75000 of its orbit at a time.

    So it would take millions of comets falling to the inner solar system for every hit. Would Nemesis be able to alter the velocities of millions of comets such that their new orbital velocities are in the small window of 0-1.5 m/s?
  15. May 6, 2006 #14


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