Astronomers Find New Type of Supernova
Yousuf Khan
dwarf - Softpedia
"Supernovae are the huge explosions that accompany the end of a massive
star's burning cycle. When the detonations occur, the outer layers over
the former core are violently thrown away, and the core itself may
collapse into a black hole, or into a neutron star, or simply a small,
helium-based star, known as a white dwarf. In precisely this type of
celestial bodies, long thought to be essentially uninteresting,
astronomers have recently discovered a new type of supernova. In this
instance, they explain, the helium on the surface of the white dwarf
simply detonates, Space reports. "
http://news.softpedia.com/news/Astronomers-Find-New-Type-of-Supernova-126260.shtml
YKhan
A different source of the story makes the implications more clear.
They've discovered a stage half-way between a Nova and a Type Ia
Supernova. In this case, a white dwarf isn't accumulating mass from a
companion red giant star, but from a companion smaller white dwarf.
Since it's harder to take away mass from another tightly-packed white
dwarf than it is to take it from a loose ball of gas like a red giant,
the primary white dwarf doesn't gather enough mass to completely
explode to smithereens in a full Type Ia supernova. But it does gather
enough mass to be more than just a Nova.
Yousuf Khan
New Type of Supernova Discovered
"According to Bildsten, a Type .Ia blast requires two white dwarfs of
unequal masses circling each other.
The more massive star is made of carbon and oxygen, while its
companion consists mostly of helium.
Gravity from the larger white dwarf slowly pulls helium from the
surface of its neighbor, and the siphoned gas builds up into a shell
around the star.
After tens of millions of years, that shell reaches a critical mass
threshold, at which point it detonates in a luminous but short-lived
explosion.
Since only the helium shell explodes, both white dwarfs remain intact
after the blast, and the cycle could potentially repeat. "
http://news.nationalgeographic.com/news/2009/11/091106-new-supernova-type.html
Dan Birchall
> A different source of the story makes the implications more clear.
> They've discovered a stage half-way between a Nova and a Type Ia
> Supernova. In this case, a white dwarf isn't accumulating mass from a
> companion red giant star, but from a companion smaller white dwarf.
> Since it's harder to take away mass from another tightly-packed white
> dwarf than it is to take it from a loose ball of gas like a red giant,
> the primary white dwarf doesn't gather enough mass to completely
> explode to smithereens in a full Type Ia supernova. But it does gather
> enough mass to be more than just a Nova.
Interesting... I wonder whether these will repeat, then? Accreting
novae tend to, if I recall.
On the other hand, if the co-orbiting red dwarves have a degrading
orbit, then eventually they should merge, potentially leading to a
super-Chandrasekhar-mass type Ia supernova such as SN2007IF (q.v.
CBET 1059). Which would also make for some good observing. :)
--
djb@ | Dan Birchall, Night Operation Assistant, Subaru Telescope/NAOJ.
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Yousuf Khan
> Interesting... I wonder whether these will repeat, then? Accreting
> novae tend to, if I recall.
Yes, that is one of the implications. Except I think that unlike a
repeating nova, the explosions might be powerful enough to destroy some
part of the surface of accreting white dwarf away. In a full-blown Type
Ia supernova, the whole white dwarf is obliterated, completely blown out
into the wind, no trace of it remains. So in this half-blown Type Ia,
maybe a partial amount of the surface gets blown away with each blast,
so that both white dwarfs start to get smaller with each blast.
> On the other hand, if the co-orbiting red dwarves have a degrading
> orbit, then eventually they should merge, potentially leading to a
> super-Chandrasekhar-mass type Ia supernova such as SN2007IF (q.v.
> CBET 1059). Which would also make for some good observing. :)
Yes, that's likely the outcome, that eventually both white dwarfs will
merge, probably into a neutron star or black hole.
Yousuf Khan
YKhan
Curiously, this is the second time within a year that they have come
up with a new, weak type of supernova. The other one was earlier this
year with supernova SN 2008ha, which was also distinguished by the
fact it was discovered by a 14-year old girl.
The Strange Case of Supernova SN2008ha | Universe Today
"But if SN2008ha is a Type II supernova, where did the hydrogen go?
The answer might be mass loss. Some stars are so massive and luminous
that they lose their outer hydrogen layers in strong outflowing
stellar winds. And because they're so massive, their cores collapse
into a black hole without transfering energy to the outer layers of
the star, which may explain the low luminosity of the explosion."
http://www.universetoday.com/2009/06/09/the-strange-case-of-supernova-sn2008ha/
gb
It doesn't simply detonates.
The ice skating balerina spins up as the star is shrinking and
shrinking once it begins collapsing, focusing its energies toward a
catastrophic spinup reaction.
gb
The universe's most powerful explosion. Only bigger are electron or
neutron stars which are much sturdier in structure and much rarer. The
big bang might be a result of a collapsing electron or neutron star,
very rare. Energies inflate as this is not an energy based explosion,
but a gravity-spin, or gravity spinoff. Electromagnet star or nuclear
star spinoff produces nature's nuclear bomb or big bang.