Some colliding white dwarfs can reignite fusion rather than go supernova

On May 19, 10:57*am, Yousuf Khan wrote:
On 19/05/2011 12:48 PM, Brad Guth wrote:









On May 18, 11:07 pm, Yousuf *wrote:
On 18/05/2011 3:25 PM, Brad Guth wrote:

Apparently there are binary or possibly trinary white dwarfs that if
combined would far exceed the 1.44 Ms supposed limits, so there's no
telling what will happen when those merge into one over-mass white
dwarf.

In a trinary system, you can tell what's going to happen, one of the
WD's will be either kicked out of the system, or at least kicked into a
higher orbit.

* * * * *Yousuf Khan

That kinda make sense. * What's the repulsive force that's of a
greater force than gravity, keeping the third WD from ever being
consumed or combined into either of the other WDs?

The repulsive force is gravity itself, more specifically momentum. In
order for one of the WD's to lose energy and get closer, the third WD
has to gain energy and go to a higher orbit. The smallest of the WD's
will always get pushed out. Depending on the mass ratios between them,
the smallest one will either get pushed to a higher orbit or get pushed
out completely.

* * * * Yousuf Khan

Once again, basic physics confounds brad guth.

I'm glad you grasp the importance of angular momentum - keep that in
mind the next time a question about why dark matter remains diffuse
comes up.

On 5/19/11 12:59 PM, Steve Willner wrote:
In ,
Sam writes:
Steve, is there a mechanism (other that supernovae or collapse) that
results in a degenerate star reverting back to a state the obeys gas,
temperature, pressure laws?

Su heating. (I don't see how supernova or collapse makes matter
non-degenerate unless you are thinking of a SN destroying the whole
star.)

Matter is degenerate when the degeneracy pressure, which depends on
density, exceeds the gas pressure, which depends on both density and
temperature. Make the temperature high enough, and the matter ceases
to be degenerate. I don't know whether this would happen or not in a
merger of helium white dwarfs, but I don't see why it couldn't.
Apparently people are actually trying to model such mergers (which
maybe shouldn't surprise me), but I don't know enough to comment on
the results.

I did manage to find what might be the original paper that started
this thread: Kilic et al. 2011 MNRAS 413, L101. There's a preprint
at http://arxiv.org/abs/1103.2354 . The paper doesn't actually say
much about what will happen when the stars merge, but it refers to a
preprint by Dan et al. at http://lanl.arxiv.org/abs/1101.5132 and
concludes "The two WDs will merge in 37 Myr and most likely form a
core He-burning single subdwarf star." I don't understand that
outcome -- I'd expect a red giant star -- but don't have time to
study the Dan et al. preprint. If somebody does have time to study
it, please post a summary here.

What the Kilic+ paper does say is that the visible star is the 0.17
solar mass white dwarf. It's about 1.1 Gyr old and 2.4 kpc distant
from the Sun, part of the Galactic halo population. The secondary
star is invisible, but it has to be a compact object of roughly 0.4
solar masses. On statistical grounds, it's more likely to be a white
dwarf than a neutron star or black hole, but as far as I can tell,
the latter two possibilities can't be ruled out. (A red dwarf or
subdwarf is ruled out by the physical size of the orbit, 0.32 solar
radii.) Unless I missed it, the paper says nothing about the past
history of the system, but it must have been interesting.


Thanks!
-Sam

On 5/19/11 12:52 PM, Yousuf Khan wrote:
On 19/05/2011 12:37 PM, Sam Wormley wrote:
On 5/19/11 1:07 AM, Yousuf Khan wrote:
On 18/05/2011 3:25 PM, Brad Guth wrote:
Apparently there are binary or possibly trinary white dwarfs that if
combined would far exceed the 1.44 Ms supposed limits, so there's no
telling what will happen when those merge into one over-mass white
dwarf.

In a trinary system, you can tell what's going to happen, one of the
WD's will be either kicked out of the system, or at least kicked into a
higher orbit.

Yousuf Khan

What about a system like
http://stars.astro.illinois.edu/sow/castor.html

None of that system are currently white dwarfs, but will likely be
some day.

That's not the point. Brad was trying to say that in a trinary WD
system, that there could be a three-way collision between the WD's. I'm
saying that one of the WD's will be kicked up and away before there is a
simultaneous 3-way collision.

Yousuf Khan

The arguments are not dependent on whether the bodies are white
dwarfs, mail sequence stars, or black holes. The dynamics are the
same. http://en.wikipedia.org/wiki/Three-body_problem

On May 19, 10:57*am, Yousuf Khan wrote:
On 19/05/2011 12:48 PM, Brad Guth wrote:









On May 18, 11:07 pm, Yousuf *wrote:
On 18/05/2011 3:25 PM, Brad Guth wrote:

Apparently there are binary or possibly trinary white dwarfs that if
combined would far exceed the 1.44 Ms supposed limits, so there's no
telling what will happen when those merge into one over-mass white
dwarf.

In a trinary system, you can tell what's going to happen, one of the
WD's will be either kicked out of the system, or at least kicked into a
higher orbit.

* * * * *Yousuf Khan

That kinda make sense. * What's the repulsive force that's of a
greater force than gravity, keeping the third WD from ever being
consumed or combined into either of the other WDs?

The repulsive force is gravity itself, more specifically momentum. In
order for one of the WD's to lose energy and get closer, the third WD
has to gain energy and go to a higher orbit. The smallest of the WD's
will always get pushed out. Depending on the mass ratios between them,
the smallest one will either get pushed to a higher orbit or get pushed
out completely.

* * * * Yousuf Khan

So there's really no way that WDs or anything of mass can ever join up
or merge into one? (are you certain about that?)

? Gravity & Momentum always = Repulsion ?

Seems we've seem any number of items merge into our sun, as well as
Jupiter, or was that an illusion?

http://www.wanttoknow.info/
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Brad Guth, Brad_Guth, Brad.Guth, BradGuth, BG / “Guth Usenet”

On 19/05/2011 6:26 PM, Brad Guth wrote:
On May 19, 10:57 am, Yousuf wrote:
The repulsive force is gravity itself, more specifically momentum. In
order for one of the WD's to lose energy and get closer, the third WD
has to gain energy and go to a higher orbit. The smallest of the WD's
will always get pushed out. Depending on the mass ratios between them,
the smallest one will either get pushed to a higher orbit or get pushed
out completely.

Yousuf Khan

So there's really no way that WDs or anything of mass can ever join up
or merge into one? (are you certain about that?)

Just in a 3-body situation. You cannot have simultaneous 3-way mergers.
However, you can have sequential 2-way mergers, WD A & B merge, followed
some long time later by WD C joining them.


Yousuf Khan

On May 19, 12:48*pm, Brad Guth wrote:
On May 18, 11:07*pm, Yousuf Khan wrote:

On 18/05/2011 3:25 PM, Brad Guth wrote:

Apparently there are binary or possibly trinary white dwarfs that if
combined would far exceed the 1.44 Ms supposed limits, so there's no
telling what will happen when those merge into one over-mass white
dwarf.

In a trinary system, you can tell what's going to happen, one of the
WD's will be either kicked out of the system, or at least kicked into a
higher orbit.

* * * * Yousuf Khan

That kinda make sense. * What's the repulsive force that's of a
greater force than gravity, keeping the third WD from ever being
consumed or combined into either of the other WDs?

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

Gravity is winning. White dwarfs being squeezed harder and harder,and
in the process keeping very hot and bright. Gravity always wins the
cosmic balancing acts,but in some cases it takes a very long time.
White dwarfs fit TreBert

On May 19, 5:05*pm, Yousuf Khan wrote:
On 19/05/2011 6:26 PM, Brad Guth wrote:

On May 19, 10:57 am, Yousuf *wrote:
The repulsive force is gravity itself, more specifically momentum. *In
order for one of the WD's to lose energy and get closer, the third WD
has to gain energy and go to a higher orbit. The smallest of the WD's
will always get pushed out. Depending on the mass ratios between them,
the smallest one will either get pushed to a higher orbit or get pushed
out completely.

* * * * *Yousuf Khan

So there's really no way that WDs or anything of mass can ever join up
or merge into one? (are you certain about that?)

Just in a 3-body situation. You cannot have simultaneous 3-way mergers.
However, you can have sequential 2-way mergers, WD A & B merge, followed
some long time later by WD C joining them.

* * * * Yousuf Khan

OK, that kinda makes sense. Perhaps Sirius(C) got taken in by Sirius
(A) or (B) unless it was tossed entirely out to begin with.

What would happen to us if even a small wandering/rogue WD of 0.5 Ms
smacked into our sun? (would our sun merely bulk-up to 3e30 kg, and
carry on?)

What if our sun was only worth 1e30 kg to begin with, and it merged or
joined up with another wandering/rogue 1e30 kg star of similar
properties?

How often does our solar system get to encounter the Sirius Oort
cloud?

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