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Some colliding white dwarfs can reignite fusion rather than go supernova



 
 
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  #21  
Old May 17th 11, 07:03 AM posted to sci.astro.amateur,sci.astro,sci.physics
Yousuf Khan[_2_]
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Default Some colliding white dwarfs can reignite fusion rather than gosupernova

On 16/05/2011 3:53 PM, Brad Guth wrote:
They'll also have to encounter a substantial molecular cloud of
hydrogen and helium. Is there one of those nearby?


Why would need to find a cloud? They're likely already made of helium.

Yousuf Khan
  #22  
Old May 17th 11, 07:09 AM posted to sci.astro.amateur,sci.astro,sci.physics
Androcles[_43_]
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Default Some colliding white dwarfs can reignite fusion rather than go supernova


"Yousuf Khan" wrote in message
...
| On 16/05/2011 3:53 PM, Brad Guth wrote:
| They'll also have to encounter a substantial molecular cloud of
| hydrogen and helium. Is there one of those nearby?
|
| Why would need to find a cloud? They're likely already made of helium.
|
| Yousuf Khan

They are for more likely to be made of bull****. Why would (you) need to
make up idiotic crap?





  #23  
Old May 17th 11, 07:10 AM posted to sci.astro.amateur,sci.astro,sci.physics
Yousuf Khan[_2_]
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Default Some colliding white dwarfs can reignite fusion rather than gosupernova

On 16/05/2011 6:55 PM, Sam Wormley wrote:
Carbon/Oxygen core makes up at least 99% of the White Dwarf's mass.


Not if they're small white dwarfs. Some white dwarfs stop at the helium
stage. Take a couple of those small white dwarf husks and bang em
together, and you can restart helium fusion. The examples they gave here
are a 0.4 solar mass white dwarf and a 0.1 solar mass white dwarf merger.

In the end, it'll probably end life as another carbon-oxygen white dwarf.

Yousuf Khan
  #24  
Old May 17th 11, 07:16 AM posted to sci.astro.amateur,sci.astro,sci.physics
Yousuf Khan[_2_]
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Default Some colliding white dwarfs can reignite fusion rather than gosupernova

On 16/05/2011 7:29 PM, palsing wrote:
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.


The article listed white dwarfs in the range of 0.43 for primary and
0.17 for secondary. The primary would be a carbon-oxygen WD and the
secondary would be a helium WD. The helium being deposited on the
surface as the secondary is ripped apart can then restart helium fusion
due to the combined gravity of the merged WD.

Yousuf Khan
  #25  
Old May 17th 11, 09:22 AM posted to sci.astro.amateur,sci.astro,sci.physics
Yousuf Khan[_2_]
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Default The end of star-making days

On 16/05/2011 8:16 PM, herbert glazier wrote:
Sam my G=EMC^2
predicts the days of star making has to end.(no more interstellar gas
for gravity to compress. Gravity still will do what it does best and
that is to evolve the stuff it created. The end is when all it
created is left in black holes,neutron stars,and white dwarfs. Sam
They are not really the end,but that is the spacetime with no universe
life,or any physical matter. Cheer up Sam it will always have
"time,space energy,and gravity" Its my last picture,so Sam Get the
picture TreBert


It's going to take a while to reach that point. There's more mass within
the intergalactic gas between galaxies, than there is in the galaxies
themselves. If a galaxy runs out of gas, its central blackhole will stop
blowing gas away, and instead that gas will fall back into the galaxy,
restarting star formation. Or even more wildly, the intergalactic gas
will start forming new baby galaxies between the old galaxies. I figure
this stage will last a trillion years (or two orders of magnitude older
than the universe is now), with continuous cycles of gas falling into
old galaxies and/or new baby galaxies forming.

Yousuf Khan
  #26  
Old May 17th 11, 09:52 AM posted to sci.astro.amateur,sci.astro,sci.physics
Yousuf Khan[_2_]
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Default Some colliding white dwarfs can reignite fusion rather than gosupernova

On 16/05/2011 7:21 PM, Eric Gisse 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.


A factor of 4 or so closer in separation compared to the Hulse-Taylor
pulsar system, but with significantly less mass. And no pulsar for
timing.

This system will decay via gravitational radiation too. Wonder how
long it'd take.


37 million years, according to the article.

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...


I wonder what type of supernova that would be. Not a 1a - that's a
helium flash from accretion, and not a II which is a core
collapse...probably be rather noisy, perhaps a candidate the fast
variety of GRB's?


Depending on the mass and mass ratios between the two white dwarfs, the
choices a (1) sub-luminous SNe Ia, (2) super-luminous SNe Ia, or (3)
no supernova at all, just a re-awakening of stellar nucleosynthesis.
Obviously the subject of previously mentioned article is about the #3
possibility, where the two WD's won't approach the Chandrasekhar limit
even after merger.

However, for much larger WD's where their combined mass exceeds the
Chandrasekhar Limit, the following study suggests that the difference in
mass between the primary and secondary WD's makes a difference to what
kind of SNe Ia explosion will occur. They suggest that since there is
more mass being ejected, but the kinetic energy is the same, the ejecta
is travelling at lower speeds, thus producing the sub-luminous SNe Ia
effect.

[1102.1354] Violent mergers of nearly equal-mass white dwarf as
progenitors of subluminous Type Ia supernovae
http://arxiv.org/abs/1102.1354

Yousuf Khan
  #27  
Old May 17th 11, 04:11 PM posted to sci.astro.amateur,sci.astro,sci.physics
Sam Wormley[_2_]
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Default Some colliding white dwarfs can reignite fusion rather than gosupernova

On 5/17/11 12:33 AM, palsing wrote:
On May 16, 9:53 pm, Sam wrote:

If this paper is accurate
http://adsabs.harvard.edu/abs/2011MNRAS.tmpL.233K


Completely off-topic for this thread, but in that paper it says that
some of the data was obtained using the 2.1 meter telescope at
McDonald in Texas. I have had the pleasure of using that same
telescope optically from dusk to dawn on 3 occasions, once in 2000 and
a full weekend in 2006. 82" of glass, 812X at the lowest power and sub-
arc-second seeing on one night makes for very memorable and
remarkable experiences.

If you like such observing reports, mine is here...

http://www.pnalsing.com/82-report

\Paul A


Thanks Paul!
-Sam

  #28  
Old May 17th 11, 04:16 PM posted to sci.astro.amateur,sci.astro,sci.physics
Sam Wormley[_2_]
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Default Some colliding white dwarfs can reignite fusion rather than gosupernova

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!
  #29  
Old May 17th 11, 04:19 PM posted to sci.astro.amateur,sci.astro,sci.physics
Sam Wormley[_2_]
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Default Some colliding white dwarfs can reignite fusion rather than gosupernova

On 5/17/11 1:16 AM, Yousuf Khan wrote:
On 16/05/2011 7:29 PM, palsing wrote:
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.


The article listed white dwarfs in the range of 0.43 for primary and
0.17 for secondary. The primary would be a carbon-oxygen WD and the
secondary would be a helium WD. The helium being deposited on the
surface as the secondary is ripped apart can then restart helium fusion
due to the combined gravity of the merged WD.

Yousuf Khan


We are dealing with degenerate matter here--the fusion will be
a run-a-way blowing the thing to smithereens.


  #30  
Old May 17th 11, 04:24 PM posted to sci.astro.amateur,sci.astro,sci.physics
Sam Wormley[_2_]
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Default Some colliding white dwarfs can reignite fusion rather than gosupernova

On 5/17/11 1:10 AM, Yousuf Khan wrote:
On 16/05/2011 6:55 PM, Sam Wormley wrote:
Carbon/Oxygen core makes up at least 99% of the White Dwarf's mass.


Not if they're small white dwarfs. Some white dwarfs stop at the helium
stage. Take a couple of those small white dwarf husks and bang em
together, and you can restart helium fusion. The examples they gave here
are a 0.4 solar mass white dwarf and a 0.1 solar mass white dwarf merger.

In the end, it'll probably end life as another carbon-oxygen white dwarf.

Yousuf Khan


Large enough stars that cannot ignite a fusion process beyond helium
burning will *create* a degenerate white dwarf. No fusion process goes
on in white dwarf stars unless on the surface (nova) or during
collapse (supernova).


 




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