Some colliding white dwarfs can reignite fusion rather than go supernova

Colliding white dwarfs give each other a new lease on life
"Astronomers recently discovered the rather memorably named SDSS
J010657.39–100003.3, which is a binary star system composed of two white
dwarfs, one of which is 17% the Sun's mass, while the other is about
43%. The two orbit each other at a distance of just 140,000 miles, which
is even closer than the distance between the Earth and the Moon. The two
rotate each other at about a million miles per hour.

When white dwarfs collide, one of two things can happen: if the combined
masses is greater than 140% of the Sun, the collision creates a
supernova. But in this case, the white dwarfs will actually reignite
nuclear fusion, creating a brand new star just like our Sun that will,
after another few billion years of renewed life, cool down into yet
another white dwarf."
http://ca.io9.com/5801997/colliding-...-lease-on-life

On 5/16/11 12:36 AM, Yousuf Khan wrote:
Colliding white dwarfs give each other a new lease on life
"Astronomers recently discovered the rather memorably named SDSS
J010657.39–100003.3, which is a binary star system composed of two white
dwarfs, one of which is 17% the Sun's mass, while the other is about
43%. The two orbit each other at a distance of just 140,000 miles, which
is even closer than the distance between the Earth and the Moon. The two
rotate each other at about a million miles per hour.

When white dwarfs collide, one of two things can happen: if the combined
masses is greater than 140% of the Sun, the collision creates a
supernova. But in this case, the white dwarfs will actually reignite
nuclear fusion, creating a brand new star just like our Sun that will,
after another few billion years of renewed life, cool down into yet
another white dwarf."
http://ca.io9.com/5801997/colliding-...-lease-on-life


Since white dwarf contain little or no hydrogen the later ain't gonna
happen. Two white dwarfs would likely create a Type I supernova or
form a neutron star.

On 5/16/11 9:05 AM, Sam Wormley wrote:
On 5/16/11 12:36 AM, Yousuf Khan wrote:
Colliding white dwarfs give each other a new lease on life
"Astronomers recently discovered the rather memorably named SDSS
J010657.39–100003.3, which is a binary star system composed of two white
dwarfs, one of which is 17% the Sun's mass, while the other is about
43%. The two orbit each other at a distance of just 140,000 miles, which
is even closer than the distance between the Earth and the Moon. The two
rotate each other at about a million miles per hour.

When white dwarfs collide, one of two things can happen: if the combined
masses is greater than 140% of the Sun, the collision creates a
supernova. But in this case, the white dwarfs will actually reignite
nuclear fusion, creating a brand new star just like our Sun that will,
after another few billion years of renewed life, cool down into yet
another white dwarf."
http://ca.io9.com/5801997/colliding-...-lease-on-life



Since white dwarf contain little or no hydrogen the later ain't gonna
happen. Two white dwarfs would likely create a Type I supernova or
form a neutron star.



Related Paper: On Type Ia supernovae from the collisions of two
white dwarfs
http://arxiv.org/abs/0907.3915

On 16/05/2011 10:05 AM, Sam Wormley wrote:
Since white dwarf contain little or no hydrogen the later ain't gonna
happen. Two white dwarfs would likely create a Type I supernova or
form a neutron star.

Depending on the size of the white dwarf remnants, they would contain a
lot of helium at the very least, and they can restart helium fusion
rather than hydrogen fusion.

Besides, when a white dwarf goes Type Ia supernova, what do you think
makes it go kablooey? It was a runaway fusion process.

Yousuf Khan

On 5/17/11 1:02 AM, Yousuf Khan wrote:
On 16/05/2011 10:05 AM, Sam Wormley wrote:
Since white dwarf contain little or no hydrogen the later ain't gonna
happen. Two white dwarfs would likely create a Type I supernova or
form a neutron star.

Depending on the size of the white dwarf remnants, they would contain a
lot of helium at the very least, and they can restart helium fusion
rather than hydrogen fusion.

Besides, when a white dwarf goes Type Ia supernova, what do you think
makes it go kablooey? It was a runaway fusion process.

Yousuf Khan

And because the components are degenerate matter, the fusion will
be runaway!

On May 15, 10:36*pm, Yousuf Khan wrote:
Colliding white dwarfs give each other a new lease on life
"Astronomers recently discovered the rather memorably named SDSS
J010657.39–100003.3, which is a binary star system composed of two white
dwarfs, one of which is 17% the Sun's mass, while the other is about
43%. The two orbit each other at a distance of just 140,000 miles, which
is even closer than the distance between the Earth and the Moon. The two
rotate each other at about a million miles per hour.

When white dwarfs collide, one of two things can happen: if the combined
masses is greater than 140% of the Sun, the collision creates a
supernova. But in this case, the white dwarfs will actually reignite
nuclear fusion, creating a brand new star just like our Sun that will,
after another few billion years of renewed life, cool down into yet
another white dwarf."http://ca.io9.com/5801997/colliding-white-dwarfs-give-each-other-a-ne...

They'll also have to encounter a substantial molecular cloud of
hydrogen and helium. Is there one of those nearby?

More likely it'll just soft-nova and become another white dwarf,
because there's not enough combined mass or impact velocity to
supernova.

http://translate.google.com/#
Brad Guth, Brad_Guth, Brad.Guth, BradGuth, BG / “Guth Usenet”

On 5/16/11 2:53 PM, Brad Guth wrote:
On May 15, 10:36 pm, Yousuf wrote:
Colliding white dwarfs give each other a new lease on life
"Astronomers recently discovered the rather memorably named SDSS
J010657.39–100003.3, which is a binary star system composed of two white
dwarfs, one of which is 17% the Sun's mass, while the other is about
43%. The two orbit each other at a distance of just 140,000 miles, which
is even closer than the distance between the Earth and the Moon. The two
rotate each other at about a million miles per hour.

When white dwarfs collide, one of two things can happen: if the combined
masses is greater than 140% of the Sun, the collision creates a
supernova. But in this case, the white dwarfs will actually reignite
nuclear fusion, creating a brand new star just like our Sun that will,
after another few billion years of renewed life, cool down into yet
another white dwarf."http://ca.io9.com/5801997/colliding-white-dwarfs-give-each-other-a-ne...

They'll also have to encounter a substantial molecular cloud of
hydrogen and helium. Is there one of those nearby?

More likely it'll just soft-nova and become another white dwarf,
because there's not enough combined mass or impact velocity to
supernova.

http://translate.google.com/#
Brad Guth, Brad_Guth, Brad.Guth, BradGuth, BG / “Guth Usenet”

Carbon/Oxygen core makes up at least 99% of the White Dwarf's mass.

On May 16, 3:55*pm, Sam Wormley wrote:

... but in this case, the white dwarfs will actually reignite
nuclear fusion, creating a brand new star...

and then wrote...

Carbon/Oxygen core makes up at least 99% of the White Dwarf's mass.

Just to make sure that I understand, would it then the case here that
it would be the carbon and/or oxygen that would start fusing, since
there is no other fuel available? Doesn't either of these elements
require extraordinary temperatures and pressures to do so? It doesn't
seem intuitive to me that there would be enough pressure available
from such a lightweight star.

Isn't it possible that a merger of such stars would only result in a
proportionally larger white dwarf @ 60% the mass of the sun? Aren't
there white dwarfs out there now that have a mass which is 60% of Old
Sol? I found an article here...

http://articles.adsabs.harvard.edu//...00247.000.html

.... which lists plenty of white dwarfs with masses in this range.

I find it curious that the article you referenced states that "in this
case, the white dwarfs will actually reignite nuclear fusion, creating
a brand new star just like our Sun", since our sun still has most of
the hydrogen it started with and these guys have none... but perhaps
I'm missing something here.

\Paul A

On 5/16/11 6:29 PM, palsing wrote:
On May 16, 3:55 pm, Sam wrote:

... but in this case, the white dwarfs will actually reignite
nuclear fusion, creating a brand new star...

and then wrote...

Carbon/Oxygen core makes up at least 99% of the White Dwarf's mass.

Just to make sure that I understand, would it then the case here that
it would be the carbon and/or oxygen that would start fusing, since
there is no other fuel available? Doesn't either of these elements
require extraordinary temperatures and pressures to do so? It doesn't
seem intuitive to me that there would be enough pressure available
from such a lightweight star.

Since 1.44 solar masses cannot be held up by electron degeneracy
pressure and we see the Type Ia supernovae, I'm assuming that the
collapse generates sufficient conditions for the fission (not fusion).

If exceeding the Chandrasekhar limit of 1.44 solar masses creates
a Type IA supernova, I'm betting that two colliding white dwarfs
will do similar.






Isn't it possible that a merger of such stars would only result in a
proportionally larger white dwarf @ 60% the mass of the sun? Aren't
there white dwarfs out there now that have a mass which is 60% of Old
Sol? I found an article here...

http://articles.adsabs.harvard.edu//...00247.000.html

... which lists plenty of white dwarfs with masses in this range.

I find it curious that the article you referenced states that "in this
case, the white dwarfs will actually reignite nuclear fusion, creating
a brand new star just like our Sun", since our sun still has most of
the hydrogen it started with and these guys have none... but perhaps
I'm missing something here.

\Paul A

On May 16, 4:35*pm, Sam Wormley wrote:

* *If exceeding the Chandrasekhar limit of 1.44 solar masses creates
* *a Type IA supernova, I'm betting that two colliding white dwarfs
* *will do similar.

Sam, I would agree with this, but aren't we talking about a merger in
this case that is considerably less than the 1.44 mass limit, a total
which is, in fact, is less than 50% of that limit?

By the way, correct or not, the Wiki article...

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

.... makes it quite clear that both carbon and oxygen fusion (and not
fission) have a prominent role in type IA supernovae, although it also
makes it quite clear that not all the details are, well, quite
clear :-)

\Paul A