White dwarf stars implicated in Type Ia supernova events

Darkchilde · #1 by **Darkchilde** » Dec 15, 2011 1:39 pm

From Nature: http://www.nature.com/news/early-observations-identify-star-at-heart-of-nearby-supernova-1.9646

A stellar explosion has helped astronomers to confirm the leading theory as to what causes type Ia supernovae. The explosion is the closest to the Solar System in the past 25 years, and was spotted a mere 11 hours after light from its eruption first reached Earth.

The favoured model suggests that a type Ia supernova is triggered when a white dwarf — an inactive star that crams roughly the mass of the Sun into the volume of the Earth — siphons material from a companion star. The extra mass triggers a thermonuclear explosion that blows the dwarf to smithereens.

Supernova SN 2011fe occurred in the Pinwheel galaxy, just 6.4 million parsecs (21 million light years) away from Earth. Analysing observations of the supernova made in August, a team of astronomers reports today in Nature1 that it has for the first time identified the type of star that exploded. Another team has narrowed down the probable nature of the companion star that triggered the eruption2.

Continued here: http://www.nature.com/news/early-observations-identify-star-at-heart-of-nearby-supernova-1.9646

1: http://dx.doi.org/10.1038/nature10644 : Supernova SN 2011fe from an exploding carbon–oxygen white dwarf star
2: http://dx.doi.org/10.1038/nature10646 : Exclusion of a luminous red giant as a companion star to the progenitor of supernova SN 2011fe

trubble76 · #2 by **trubble76** » Dec 20, 2011 11:45 am

Interesting stuff :thumbup:

klazmon · #3 by **klazmon** » Dec 20, 2011 12:26 pm

Darkchilde wrote:From Nature: http://www.nature.com/news/early-observations-identify-star-at-heart-of-nearby-supernova-1.9646

A stellar explosion has helped astronomers to confirm the leading theory as to what causes type Ia supernovae. The explosion is the closest to the Solar System in the past 25 years, and was spotted a mere 11 hours after light from its eruption first reached Earth.

The favoured model suggests that a type Ia supernova is triggered when a white dwarf — an inactive star that crams roughly the mass of the Sun into the volume of the Earth — siphons material from a companion star. The extra mass triggers a thermonuclear explosion that blows the dwarf to smithereens.

Supernova SN 2011fe occurred in the Pinwheel galaxy, just 6.4 million parsecs (21 million light years) away from Earth. Analysing observations of the supernova made in August, a team of astronomers reports today in Nature1 that it has for the first time identified the type of star that exploded. Another team has narrowed down the probable nature of the companion star that triggered the eruption2.

Continued here: http://www.nature.com/news/early-observations-identify-star-at-heart-of-nearby-supernova-1.9646

1: http://dx.doi.org/10.1038/nature10644 : Supernova SN 2011fe from an exploding carbon–oxygen white dwarf star
2: http://dx.doi.org/10.1038/nature10646 : Exclusion of a luminous red giant as a companion star to the progenitor of supernova SN 2011fe

I think it would have been a big surprise if something different had been found, given that Type Ia's are quite well modelled by the thermonuclear deflagration of a white dwarf at the Chandrasekhar limit. The recurrent Nova T Pyxidis, which had a flare up earlier this year is thought to be quite close to the Chandrasekhar limit. Each Nova blast not quite getting rid of all the mass it is accumulating between the outbursts. It's been over 400 years since the last Milky Way supernova was observed so it would be cool to get to see one (just as long as it isn't too close

).

Darkchilde · #4 by **Darkchilde** » Dec 20, 2011 1:09 pm

There are a few candidates for supernova events, like Betelgeuse for example. It would be cool if that star who is close but not as close went supernova and we got to watch it in our lifetimes...

trubble76 · #5 by **trubble76** » Dec 20, 2011 1:15 pm

If Type 1A supernovae are so predictable (in output, not timing), does anyone know what the maximum safe distance is? How many stars are close enough to sterilise us if they go blam?

Evolving · #6 by **Evolving** » Dec 20, 2011 4:08 pm

The majority of supernovae are not Type 1A, so if we are worried about proximity to a supernova, we need to consider all of them. (The reason why Type 1A supernovae are particularly interesting is that - if it is true that they are ALL caused by a white dwarf accreting enough matter to hit the Chandrasekhar limit, an assumption which has recently been called into question - they are excellent standard candles, because they all have the same absolute luminosity.)

How close any other kind of supernova can be to the Earth before we need to worry, depends on the size of the star. There is an absolute limit of about 100 solar masses: bigger than that, and radiation pressure overcomes gravity and blows the star apart before it can get going properly on the main sequence. Betelgeuse's mass is about 20 solar masses (it is very clearly visible from the Earth because it is so close, not because it is particularly luminous, as red giants go.)

Here is what NASA has to say about the answer to your question:

Astronomers estimate that, on average, about one or two supernovae explode each century in our galaxy. But for Earth's ozone layer to experience damage from a supernova, the blast must occur less than 50 light-years away. All of the nearby stars capable of going supernova are much farther than this.

The reason, by the way, why we have seen so few supernovae in our galaxy is (if the above statement is correct) because most of them are obscured by the rest of the galaxy getting in the way.