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Thread: Unstable local stars?

  1. #1
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    Unstable local stars?

    Greetings

    <disclaimer> I'm a newbie amateur </disclaimer>

    I was browsing through my stars & planets guide looking at the southern cross (crux) and the stars around it. My attention was particularly drawn to the two bright stars next to it in Centauris, alpha and beta that are particlularly visible here. The guide tells me that alpha centauri is a (trinary?) system containing the closest star to sol, alpha proxima, and that this is a flare star, changing in magnitude rapidly over a relatively short period of time.

    My questions: although I know Sol is supposed to have plenty of life left in her yet, what about neighbouring stars? I think alpha centauri is ~4ly away. I don't know if being a 'flare' star means it is unstable or nearing the end of its lifecycle, but if it (or any other neighbouring star) was to explode/supernova/whatever, could our solar system be bombarded by dangerous levels of radiation? Are there many old/unstable stars within ~50ly radius of us?

    I'm not trying to be alarmist, it is just a point of interest for me.

  2. #2
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    Red dwarf stars like Proxima Centauri have lifespans in the hundreds of billions of years. We'll be loooooooooooooooonnnnnnnggg gone before even the first of them enters middle age. Many red dwarfs are flare stars. I myself don't know the mechanism, but they commonly exhibit flare activity that puts our own sun to shame. There's nothing unstable about them.

    Alpha and Beta Centauri are G-class stars very similar to our own Sun. I don't remember exactly, but I think they are a little older than Sol. G-class stars ending their lives swell up into red giants and expel large clouds of gas for a while, then gracefully die out and become white dwarfs. They do not go supernova. It takes a very massive star to do that.

    There was a thread a while back about the possible threat of supernovae. It looks like it's not much of one at all. Read it here:
    http://www.badastronomy.com/phpBB/viewtopic.php?t=3590

  3. #3
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    Of course, no chat on supernovae risks should be without the infamous eta c. picture:

    http://antwrp.gsfc.nasa.gov/apod/ap980816.html


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    Thanks for the info, figures that it would have been discussed before.

    Also- that picture of Eta Carinae is absolutely mind boggling.

  5. #5
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    One of the stars of Alpha Centauri is a G2 dwarf just like Sol, but the other is a bit cooler. It's K1 type.

    I presume that red dwarfs are much lighter than yellow dwarfs, hence why their fusion doesn't go as strong, so perhaps it's just that red dwarfs are capable of chucking out more stuff than heavier stars, where the material might get pulled back in due to gravity. A pure guess though.

  6. #6
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    Quote Originally Posted by Glom
    One of the stars of Alpha Centauri is a G2 dwarf just like Sol, but the other is a bit cooler. It's K1 type.

    I presume that red dwarfs are much lighter than yellow dwarfs, hence why their fusion doesn't go as strong, so perhaps it's just that red dwarfs are capable of chucking out more stuff than heavier stars, where the material might get pulled back in due to gravity. A pure guess though.
    D'oh, you're right. I was under the impression that alpha was a little hotter, and beta was just a little cooler than Sol, maybe G5 or G6. I didn't know it was in another class altogether. Live and learn. Still, I'd think K-class stars would behave pretty close to G's in stellar evolution. They'll just live a bit longer.

    According to this link, the flares of Proxima are caused by a very chaotic magnetic field.

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    F, G and K don't have a heck of a lot between them.

    I think you also need to be a bit careful with the notation. Greek letters are reserved for Bayer designations. Beta Centauri is otherwise known as Hadar and sits 4 west of Alpha Centauri. When distinguishing between the stars that are so close that they have the same Bayer designation, numbers are used.

    GSC 9007:5849, the G2V type star, is designated Alpha-1 Centauri. GSC 9007:5848, the K1V type star, is designated Alpha-2 Centauri.

    A similar thing happens in Orion. There are two stars designated Theta Orionis. SAO 132314, otherwise known as Trapezium a O6pe :-? type star is Theta-1 Orionis, while SAO 132321, a O9.5Vpe :-? type star is Theta-2 Orionis.

  8. #8
    Quote Originally Posted by David Hall
    [According to this link, the flares of Proxima are caused by a very chaotic magnetic field.
    The sun's activity is likely driven by its magnetic field, which becomes twisted
    and contorted in the turbulent convective zone just below the surface of the
    sun. For cool stars, the convective zone is much deeper, and
    the stars show an increase in both the number and energy of the flares
    and sunspots. So it is not surprising that Proxima Centauri is a
    flare stare.

    Interestingly, there is a significant relation between the age of a flare star
    and the luminosity of its brightest flares. Luckily, Proxima Centauri seems to
    be the same age as its companion stars (5-6 billion years or so).

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    That would make sense. In hotter stars, material too deep in ionises completely, losing all its electrons, and so it cannot carry heat. Therefore, it cannot participate in convection and so the convection currents are smaller causing less magnetic stuff. In cooler stars, material can hold onto its electrons even deeper down so the convective zone can be bigger. This gives rise to more chaotic current which make the magnetic field go all evil on us.

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    [quote="kurtisw"]
    Quote Originally Posted by David Hall
    [According to this link, the flares of Proxima are caused by a very chaotic magnetic field.
    The sun's activity is likely driven by its magnetic field, which becomes twisted
    and contorted in the turbulent convective zone just below the surface of the
    sun.

    This is a very interesting point. My encyclopedia of astronomy (circ 2001) says that we have found the north magnetic pole of the sun but not the south. Seems as though it is very difficult to locate. I wondered how we ever found it at all with the sun rotating at different speeds. i.e. the north and south poles rotate at a different speed than the equator. This leads me to wonder do all stars rotate at different speeds? Personal note: The drive from Flagstaff on 89A going south down to Sonora is one of the most beautiful places on the earth.

  11. #11
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    Ulysses will sort it out. No south pole's gonna hide from us.

  12. #12
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    Quote Originally Posted by Jobe
    Thanks for the info, figures that it would have been discussed before.

    Also- that picture of Eta Carinae is absolutely mind boggling.
    No worry mate, everything has been discussed before. that doesn't stop anyone.

  13. #13
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    Quote Originally Posted by David Hall
    Many red dwarfs are flare stars. I myself don't know the mechanism, but they commonly exhibit flare activity that puts our own sun to shame. There's nothing unstable about them.
    Short article on flare stars at the Internet Stellar Database.

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