Remarkable white dwarf star possibly coldest, dimmest ever detected

Dne 27.6.2014 6:54, Yousuf Khan napsal(a):
On 25/06/2014 11:48 PM, Poutnik wrote:
Dne 26.6.2014 2:11, Michael J. Strickland napsal(a):
If that 1.44 for is for a "new" neutron star, maybe after 11 billion
years it's radiated away some of its mass.

Mike


Rather a white dwarf, passing CHS stability limit at 1.44 ,
does not end as 1.44 neutron star
after supernovae 1A explosion.

Part of mass is thrown to space.

In Type IA supernovas, it's not just a part of the mass that's thrown
into space, it's all of the mass that's thrown into space. There is no
core left behind at all in a Type IA. The white dwarf core is completely
obliterated after the supernova explosion, it doesn't get compacted into
a neutron star core.

No objection, it was my mistake.

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Poutnik

Wise man guards the words he says,
as they may speak about him more, than about the subject.

"Yousuf Khan" wrote in message

On 25/06/2014 8:11 PM, Michael J. Strickland wrote:
If that 1.44 for is for a "new" neutron star, maybe after 11 billion
years it's radiated away some of its mass.

Interesting theory. Radiating away 0.24 solar masses in 11 billion
years
would make for an extremely bright pulsar, probably brighter than most
supernovas, if it was all done in photons. Of course, it may have
radiated it away in neutrinos, which would be much harder to detect.
But
even if radiating it mostly in neutrinos, that would be a considerable
neutrino flux which we should be able to detect on Earth.

Yousuf Khan



I guess I'm also wondering if that 1.44 number is for the mass of the
star before collapse or after since it can lose mass during the
collapse/detonation?
Usually, I hear it stated that a star has to be at least X solar masses
to become a supernova/neutron starblack hole etc..., so I'm thinking the
1.44 probably refers to the initial mass prior to collapse and not the
currently emasured mass.


Mike


--
------------------------------------------------------------

Michael J. Strickland Reston, VA

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Dne 27.6.2014 7:31, Michael J. Strickland napsal(a):


I guess I'm also wondering if that 1.44 number is for the mass of the
star before collapse or after since it can lose mass during the
collapse/detonation?

Usually, I hear it stated that a star has to be at least X solar masses
to become a supernova/neutron starblack hole etc..., so I'm thinking the
1.44 probably refers to the initial mass prior to collapse and not the
currently emasured mass.


CHS limit is said to be maximum mass of a stabel white dwarf
before SN 1A explosion - no remnants-

or maximum mas of electron degenerate star inert core
before SN 2 star core collapse.

The current accepted value is 1.39.

I am still not sure if it depends
on element composition, as star inert core
contains heavier elements (by kernel mass )
than white dwarfs.

IMHO it should depend.

https://en.wikipedia.org/wiki/Chandrasekar_limit

There is stated a star needs at least 8 times Sun mass.

https://en.wikipedia.org/wiki/Type_II_supernova


--
Poutnik

Wise man guards the words he says,
as they may speak about him more, than about the subject.

On 27/06/2014 1:22 AM, Poutnik wrote:
Dne 27.6.2014 6:29, Yousuf Khan napsal(a):
On 25/06/2014 3:49 PM, Poutnik wrote:
Dne 25.6.2014 21:18, Yousuf Khan napsal(a):
On 25/06/2014 1:38 PM, Poutnik wrote:
Some references say the limit is 0.88-1.28 Solar mass.

http://arxiv.org/abs/astro-ph/0012321

Interesting, so you learn something new everyday. So that means at 0.88
solar masses, you may have some neutron stars that weigh less than some
white dwarfs.


Your original post mentions 1.2 SM pulsar,
what is less than maximum of 1.44 SM for dwarfs.

You're the one who mentioned neutron stars going from 0.88 to 1.28 solar
masses, therefore those would be all less than the 1.44 solar mass limit
for dwarfs.

No. 0.88-1.28 is estimated lower limit.
Limit is not the same as range.

Yes, but suppose you do have some examples of neutron stars at those
lower limits, whether it be 0.88 or 1.28 solar masses, those examples
would be smaller than some examples of white dwarfs at their higher
limits. Of course the highest limit for a white dwarf is 1.44 solar
masses. This would mean that neutron stars and white dwarfs could
overlap in their mass ranges.

Yousuf Khan

On 27/06/2014 1:24 AM, Poutnik wrote:
Dne 27.6.2014 6:54, Yousuf Khan napsal(a):
On 25/06/2014 11:48 PM, Poutnik wrote:
In Type IA supernovas, it's not just a part of the mass that's thrown
into space, it's all of the mass that's thrown into space. There is no
core left behind at all in a Type IA. The white dwarf core is completely
obliterated after the supernova explosion, it doesn't get compacted into
a neutron star core.
No objection, it was my mistake.

I think the reason that the white dwarf gets completely obliterated is
because it is only being held together by electron degeneracy rather
than neutron degeneracy. The electron degeneracy is a lot weaker than
neutron degeneracy. So when the final catastrophic supernova nuclear
reaction occurs, its bonds get completely loosened by the nuclear
reaction. However, it looks like a nuclear reaction isn't powerful
enough to blow apart a neutron star's bonds.

Yousuf Khan

On 27/06/2014 1:31 AM, Michael J. Strickland wrote:
I guess I'm also wondering if that 1.44 number is for the mass of the
star before collapse or after since it can lose mass during the
collapse/detonation?

It's the mass right before detonation. Actually, until now, I was also
assuming that the 1.44 Chandrasekhar Limit as the transition point
between white dwarf and neutron star, but I've since found out that
neutron stars can be possibly as low as 0.88 solar masses. So it looks
like the 1.44 figure is only the maximum size limit of a white dwarf,
and the point at which it detonates.

Usually, I hear it stated that a star has to be at least X solar masses
to become a supernova/neutron starblack hole etc..., so I'm thinking the
1.44 probably refers to the initial mass prior to collapse and not the
currently emasured mass.

Yes, that we can agree on.

Other limits I keep hearing about are that the initial mass of the core
of a star has to be at least 3.0 solar masses in order for it to become
a blackhole, rather than a neutron star. But I've seen that the smallest
solar blackhole discovered weighs in at 2.8 solar masses. So perhaps
there is an overlap in mass ranges for neutron stars and blackholes too?

Yousuf Khan

On 27/06/2014 2:21 AM, Poutnik wrote:
There is stated a star needs at least 8 times Sun mass.

https://en.wikipedia.org/wiki/Type_II_supernova

That's the overall mass of the star, rather than the core mass of the
star. The final core mass sets whether the star becomes a neutron star
or a blackhole. I think the core mass has to be at least 2.8 to 3.0
solar masses to become a blackhole.

Yousuf Khan

Dne 27.6.2014 16:33, Yousuf Khan napsal(a):
On 27/06/2014 1:22 AM, Poutnik wrote:


No. 0.88-1.28 is estimated lower limit.
Limit is not the same as range.

Yes, but suppose you do have some examples of neutron stars at those
lower limits, whether it be 0.88 or 1.28 solar masses, those examples
would be smaller than some examples of white dwarfs at their higher
limits. Of course the highest limit for a white dwarf is 1.44 solar
masses. This would mean that neutron stars and white dwarfs could
overlap in their mass ranges.

I am not an astronomer, I have just hobby interest.

I have handy only that example in OP,
where is binary system of 1.2M pulsar and 1.05M dwarf.

As neutron star is not evolution state of white dwarfs,
I do not see any paradox.


--
Poutnik

Wise man guards the words he says,
as they may speak about him more, than about the subject.

Dne 27.6.2014 16:37, Yousuf Khan napsal(a):

I think the reason that the white dwarf gets completely obliterated is
because it is only being held together by electron degeneracy rather
than neutron degeneracy. The electron degeneracy is a lot weaker than
neutron degeneracy. So when the final catastrophic supernova nuclear
reaction occurs, its bonds get completely loosened by the nuclear
reaction. However, it looks like a nuclear reaction isn't powerful
enough to blow apart a neutron star's bonds.


As SN 1A are like ignited huge carbon fusion bombs
with pretty well packed fusion material,

I do not wonder there is no remnant.

There are no remnants after exploded A or H bombs either.

--
Poutnik

Wise man guards the words he says,
as they may speak about him more, than about the subject.

Dne 27.6.2014 16:53, Yousuf Khan napsal(a):
On 27/06/2014 2:21 AM, Poutnik wrote:
There is stated a star needs at least 8 times Sun mass.

https://en.wikipedia.org/wiki/Type_II_supernova

That's the overall mass of the star, rather than the core mass of the
star. The final core mass sets whether the star becomes a neutron star
or a blackhole. I think the core mass has to be at least 2.8 to 3.0
solar masses to become a blackhole.


I did say star, not star core.

--
Poutnik

Wise man guards the words he says,
as they may speak about him more, than about the subject.