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From: Yousuf Khan on 14 Mar 2010 03:26
Steve Willner wrote:
> In article <4b998f24$1(a)news.bnb-lp.com>,
> Yousuf Khan <bbbl67(a)spammenot.yahoo.com> writes:
>> What quantitative conclusions can't be derived from the model we have
>> now?
>
> The dependence of luminosity on mass, for one.
>
>> But when it comes to Type Ia, I think we can pretty well say that a
>> bigger mass will result in a bigger blast.
>
> You have yet to give any reason "we" can say any such thing. It
> could be true, but there is _no evidence_ from either theory or
> observation so far as I know.

For the theory, I don't know what else I can say beyond what I've
already said.

As for observation, the couple of blasts already identified as possible
dual-white-dwarf SN Ia's, where identified because of their extra
luminosity.

> There are at least two scenarios consistent with the observation that
> local SNe Ia are good standard candles:
>
> 1. All or nearly all come from accretion onto white dwarfs and
> therefore all progenitors have the same mass when they explode,
> giving constant luminosity.

I agree with this, my feeling is most SN Ia's are standard gas-accretion
type. The only question is what portion aren't? How significant are
these latter type? Do they become more significant with the age of the
universe?

> 2. Some or all come from white dwarf mergers, and their progenitor
> masses vary, but there is some regulation or feedback in the
> explosion process that produces nearly constant luminosity
> regardless of mass.
>
> I know of no evidence to rule out either scenario, but the original
> observation that started this thread would be more consistent with 2.
> The dependence of luminosity on stretch might also be more consistent
> with 2. That's a very long way from saying 2 is correct, of course.
> The evidence simply doesn't exist.

In the case of dual-white-dwarf mergers, there are two paths that can be
taken: (1) produce SN Ia, or (2) produce neutron star. Let's say the
path taken depends on the mass of the two original WD's. If the two WD's
together are nearly equal mass and higher than the Chdskr limit, they
will most likely produce a neutron star. If the two WD's are together
over the Chdskr limit, but one is much heavier than the other, then
it'll likely produce an SN Ia. Let's only consider this latter case for
the purposes of this discussion.

The heavier WD will tear apart the lighter one as they get closer.
Enough material from the lighter one will accumulate on the heavier one
to take it right to the edge of the Chdrskr limit, and it will blow up
as an SN Ia. So far that's exactly the same as a gas-accretion SN Ia.
Where the additional power comes from is from the remnants of the
lighter WD that wasn't torn away by the heavier WD. The remnant of the
light WD is now even lighter, and it no longer has any enough
self-gravitation to remain in degenerate matter form. This release of
gravitational pressure will destroy this remnant explosively too. So
you'll have two explosive contributions to an overall explosion that
will be much more than just a standard SN Ia explosion by itself.

Yousuf Khan
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