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The Supernova next door?

  1. Dec 8, 2015 #1
    I was looking at the article about Sirius Wikipedia, and it said that Sirius A would become a red giant in about a billion years, then settle down to a white dwarf.

    I felt this can't be right! If Sirius A becomes a red giant, how long until Sirius B passes the Chandrasekhar limit and becomes a type Ia supernova? Sirius B is relatively heavy for a white dwarf (just under the Sun's mass) and ominously is currently covered in hydrogen. There is a sub-Chandrasekhar limit model for type Ia supernovas that has the star coated in hydrogen which then burns to helium which flashes to start a two explosion supernova. Is that why solar mass and heavier white dwarfs are hard to find? Or just that once a white dwarf starts gaining mass, it soon becomes a supernova?

    Anyway, if the Sirius system is not going to explode for millions of years, it won't be anywhere near the solar system then. But it is interesting to think that we have a genuine type 1a progenitor close at hand to study.
     
  2. jcsd
  3. Dec 8, 2015 #2
    The ingredients for a 1a supernova are certainly there.
    I guess a big factor in whether that actually can happen will be the distance between the two stars.
    If the white dwarf Sirius B is not close enough to the red giant Sirius A, then it might not be possible for it to pick up enough extra material to pass the Chandrasekhar limit
     
  4. Dec 8, 2015 #3
    The orbital period Sirius B is just over 50 years which puts it an average of 20 AU from Sirius A. Not a threat to pick up much mass from Sirius A in the immediate future, but there is the double detonation path to evaluate. When Sirius A goes through its red giant phase? (About a billion years from now...) Most of the mass of Sirius A will eventually be blown off, and it is hard to imagine Sirius B not picking up the 0.4 Solar mass needed to go type 1a.

    None of this means that it will go supernova tomorrow, or in the next million years. But if the system will inevitably end up in a 1a supernova, or especially if it won't, this looks like a nice PhD thesis sized chunk of work.
     
  5. Dec 8, 2015 #4

    SteamKing

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    Even closer to home than Sirius A, good ole Sol will also become a red giant, but in about 5 billion years or so.

    There are apparently two kinds of SN Ia type explosions: one is due to additional material accreting on a white dwarf and then exploding; the other occurs when two white dwarves collide with one another. Both type of explosions leave very little behind.

    https://en.wikipedia.org/wiki/Type_Ia_supernova

    I wouldn't lose any sleep over Sirius. On the other hand, Betelgeuse (Alpha Orionis) is already a red giant, it has about 7-20 solar masses, and it's less than 650 LY away.

    https://en.wikipedia.org/wiki/Betelgeuse

    Never having studied a SN event so close to earth, and because Betelgeuse is a solitary star, like the sun, it's hard for astronomers to pin down even how massive the star is, let alone predict the true path of its demise.
     
  6. Dec 8, 2015 #5
    About half of one percent is quite a lot considering that the red giant will likely be blowing away it's outer shell more or less uniformly in every direction, and not particularly in a direction where the white dwarf is able to capture it.
     
  7. Dec 8, 2015 #6

    Chronos

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    Just to offer some peace of mind, earth has no neighbors that pose any threat for probably a billion years. Since earth will be virtually uninhabitable after another billion years, little cause for concern over death by supernova..
     
  8. Dec 8, 2015 #7
    Betelgeuse will certainly become a supernova well before Sirius B. Not much of a risk to earth, since it is about 100 times further away. Also which type of supernova Betelgeuse will become is the subject of fierce argument--but type 1a is the one type not mentioned. On the other hand...there are some suspicions that Betelgeuse is a double or triple star. The blankets of stellar atmosphere, warm dust, and ejected mass from Betelgeuse could make detecting a (white dwarf) companion invisible. If so, we could have a nearby supernova in our lifetimes. Eta Carina (which is a double start, one massive, one hypermassive) is another ten times further away, and no one really has a handle on its evolution. But at 90 solar masses, the primary doesn't have long to live.
     
  9. Dec 8, 2015 #8
    But Sirius B won't be far away. In fact it probably will be passing through Sirius A's extended photosphere part or all of the time. And if Sirius B forms an accretion disk (they don't only form around black holes) it could act like a parachute to spiral Sirius B into Sirius A. If Sirius B's orbit was twice as large, I would guess that the type 1a chance was low to non-existent. If Sirius B were orbiting Betelgeuse at the same distance it orbits Sirius A, it would go supernova in well under 100,000 years. (Flame retardant: The best distance and size estimates for Betelgeuse are uncertain.)
     
  10. Dec 10, 2015 #9
    It's a joke that we've gone 400 years without a visible SN, a galaxy this size should be furnishing one every 50 years or so.
     
  11. Dec 10, 2015 #10

    SteamKing

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    We can't be sure that the MW is not doing its job. Those SNs could all be on the other side of the galactic core.

    The radio source known as Cassiopeia A was found to be a SN remnant which is thought to have exploded around 1680, yet there were no records of anyone observing such a celestial event on earth. It is thought that Astronomer Royal John Flamsteed might have observed the light of this explosion, but attributed his sighting to an otherwise unremarkable star.

    https://en.wikipedia.org/wiki/Cassiopeia_A

    There may be all kinds of stars blowing up, but the light for some reason doesn't reach earth.
     
  12. Dec 10, 2015 #11
    Yes, but I did say 'visible' SNs. Then again it looks like there was nothing from 1181 to 1572 either, so maybe I'm being greedy.
     
  13. Dec 10, 2015 #12

    SteamKing

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    To be sure, during that period, there were great societal upheavals in Europe, and astronomical observations were way down the list of priorities.

    As in Europe during this period, China also suffered great upheavals, first with invasions by the Mongols, and after they fell, followed by a period of plagues. Again, survival trumped astronomy.
     
  14. Dec 10, 2015 #13

    davenn

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    not sure where you got that info from ??

    the last naked eye visible SN was in 1987 that marked a 300 odd yr period since the previous naked eye visible one. and that was in our satellite galaxy, the LMC


    Dave
     
  15. Dec 10, 2015 #14

    SteamKing

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    Well, SN1987A was located in the Large Magellanic Cloud, which is not inside the MW proper. The distance to the dead star is estimated to be 160,000 LY from earth, which is way out there by any measure.

    https://en.wikipedia.org/wiki/SN_1987A
     
  16. Dec 10, 2015 #15

    davenn

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    \yeah I stated that :)
     
  17. Dec 10, 2015 #16

    davenn

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    actually saw it, photo'ed it and even photo'ed comet Wilson and it in the same part of the sky
    That was cool to get a SN and a comet in the same 50mm lens frame ( 35mm film camera)

    Dave
     
  18. Dec 10, 2015 #17

    davenn

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    and that there is a really important factor, we only see a small portion of our galaxy

    and as such we would have to use occurrence of SN's in other similar galaxies to get a feel for occurrence rates


    Dave
     
  19. Dec 11, 2015 #18
    I've been thinking about that since June. I think it is most likely possible, but questionable.

    Although possible, the two stars are a bit far away and with drift even further apart as Sirius A loses mass as it goes through the Red Giant Phrase. They currently are both separated by an average of 20 AU. Although mass with fall somewhat onto Sirius B, it likely would not reach the Chandrasekhar Limit in the time it would take. Most likely, it would spent part of its time as a dwarf novae. Because of this, during outbursts, the star will lose part of the mass it gained each time. At the most, it would approach under 1.1-1.2 SM. with the dwarf of Sirius A being .73 SM. However, we can't quite rule out that this is true. Mira (Omicron Ceti) was recently found to be accreting mass to it's White Dwarf Companion. Mira A is currently in the later phrases of it's AGB phrase, and is known for it's 13 LY long trail of gas it's left since entering the phrase. It's already lost a lot of mass, and likely was less massive than Sirius on the Main-Sequence at 1.90 SM given it's age of 6 GY. The space between the Mira binary is 70 AU, or 3.5 times the distance between Sirius A and B. Likely is it accreting because of the material that is slowly ejected by A each variability period. It is a slow, steady, stream coming in, giving the dwarf time to process it's material. Telescopes have shown a hook off of Mira, showing it is powerful enough to directly pull mass. But, given their separation, Mira B is likely less mass than Sirius B at .7-.8 SM.

    But, Back to Sirius. The possibility still exists, but is somewhat unlikely. Most Type 1a SN candidates are very close, with orbital periods of under 3 years or less. at 50.1 years, who knows, that's usually a period for novae. But I will look into it more.
     
  20. Dec 11, 2015 #19

    davenn

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    its phase, not phrase :smile:
     
  21. Dec 11, 2015 #20
    Oops. Thanks for the correction!
     
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