Remarkable white dwarf star possibly coldest, dimmest ever detected

It's only 3000K in temperature, and possibly 11 billion years old (as
old as the Milky Way)! It was only detected because it was paired up
with a pulsar, which was the first thing detected in the system. They
then noticed some anomalies in the pulsar's timings, and then it was
clear that the pulsar must've had a companion.

The pulsar and the white dwarf are remarkably close in mass to each
other: the pulsar has 1.2 solar masses, while the dwarf has 1.05 solar
masses. The pulsar seems like it's on the low end of the mass scale for
neutron stars (I always thought they had to be over the Chandrasekhar
Limit of 1.4), while the dwarf seems pretty massive for a dwarf.

http://www.astronomy.com/news/2014/0...-ever-detected

Yousuf Khan

On Wednesday, June 25, 2014 6:59:47 AM UTC-7, Yousuf Khan wrote:
It's only 3000K in temperature, and possibly 11 billion years old (as

old as the Milky Way)! It was only detected because it was paired up

with a pulsar, which was the first thing detected in the system. They

then noticed some anomalies in the pulsar's timings, and then it was

clear that the pulsar must've had a companion.



The pulsar and the white dwarf are remarkably close in mass to each

other: the pulsar has 1.2 solar masses, while the dwarf has 1.05 solar

masses. The pulsar seems like it's on the low end of the mass scale for

neutron stars (I always thought they had to be over the Chandrasekhar

Limit of 1.4), while the dwarf seems pretty massive for a dwarf.



http://www.astronomy.com/news/2014/0...-ever-detected



Yousuf Khan

And it's likely much older than 16 GY in order to be that cool. Otherwise, what cooled it off so quickly?

Dear Yousuf Khan:

On Wednesday, June 25, 2014 6:59:47 AM UTC-7, Yousuf Khan wrote:
The pulsar and the white dwarf are remarkably
close in mass to each other: the pulsar has
1.2 solar masses, while the dwarf has 1.05
solar masses. The pulsar seems like it's on
the low end of the mass scale for neutron
stars (I always thought they had to be over
the Chandrasekhar Limit of 1.4),

Chandrasekhar limit is the threshold that separates atomic matter (stars) from degenerate matter (neutron stars - lose heat - black holes).

while the dwarf seems pretty massive for a dwarf.

Nah. "Dwarf" just means it is dense, so is smaller than a star that still has some hydrogen to fuse.

David A. Smith

On 06/25/2014 03:59 PM, Yousuf Khan wrote:
It's only 3000K in temperature, and possibly 11 billion years old (as
old as the Milky Way)! It was only detected because it was paired up
with a pulsar, which was the first thing detected in the system. They
then noticed some anomalies in the pulsar's timings, and then it was
clear that the pulsar must've had a companion.

The pulsar and the white dwarf are remarkably close in mass to each
other: the pulsar has 1.2 solar masses, while the dwarf has 1.05 solar
masses. The pulsar seems like it's on the low end of the mass scale for
neutron stars (I always thought they had to be over the Chandrasekhar
Limit of 1.4), while the dwarf seems pretty massive for a dwarf.

IMHO CHS limit 1.44 M_sol applies only to white dwarf stability.

Not all neutron stars evolve from a white wharfs,
as not all supernovas are type 1A.

For true supernova 1A creation a neutron star from a dwarf
there is significant mass loss.

http://www.astronomy.com/news/2014/0...-ever-detected


Yousuf Khan


--
Poutnik

A wise man guards words he says,
as they may say about him more, than he says about the subject.

On 06/25/2014 04:25 PM, dlzc wrote:
Dear Yousuf Khan:

On Wednesday, June 25, 2014 6:59:47 AM UTC-7, Yousuf Khan wrote:
The pulsar and the white dwarf are remarkably
close in mass to each other: the pulsar has
1.2 solar masses, while the dwarf has 1.05
solar masses. The pulsar seems like it's on
the low end of the mass scale for neutron
stars (I always thought they had to be over
the Chandrasekhar Limit of 1.4),

Chandrasekhar limit is the threshold that separates atomic matter (stars) from degenerate matter (neutron stars - lose heat - black holes).


Chandrasekhar limit is the threshold that separates
degenerate matter ( dwarfs ) from neutron-like matter (neutron stars ).

while the dwarf seems pretty massive for a dwarf.

Nah. "Dwarf" just means it is dense, so is smaller than a star that still has some hydrogen to fuse.

Rather mostly carbon and oxygen, with neon and magnesium if evolved
from heavier stars.
( with some hydrogen an helium at surface layers, especially in fusiun
material collection of Nova cycle )


--
Poutnik

A wise man guards words he says,
as they may say about him more, than he says about the subject.

On 25/06/2014 10:09 AM, Brad Guth wrote:
And it's likely much older than 16 GY in order to be that cool. Otherwise, what cooled it off so quickly?

Perhaps the interactions with the pulsar's magnetic field? You've heard
of magnetic cooling, right?

Yousuf Khan

On 25/06/2014 11:04 AM, Poutnik wrote:
On 06/25/2014 03:59 PM, Yousuf Khan wrote:
The pulsar and the white dwarf are remarkably close in mass to each
other: the pulsar has 1.2 solar masses, while the dwarf has 1.05 solar
masses. The pulsar seems like it's on the low end of the mass scale for
neutron stars (I always thought they had to be over the Chandrasekhar
Limit of 1.4), while the dwarf seems pretty massive for a dwarf.

IMHO CHS limit 1.44 M_sol applies only to white dwarf stability.

Not all neutron stars evolve from a white wharfs,
as not all supernovas are type 1A.

Maybe, but my assumption was that you needed the 1.44 solar masses to
maintain a neutron degeneracy pressure.

Yousuf Khan

On 25/06/2014 10:25 AM, dlzc wrote:
Chandrasekhar limit is the threshold that separates atomic matter (stars) from degenerate matter (neutron stars - lose heat - black holes).

while the dwarf seems pretty massive for a dwarf.

Nah. "Dwarf" just means it is dense, so is smaller than a star that still has some hydrogen to fuse.

Both white dwarfs and neutron stars are considered degenerate matter.
The white dwarfs have electron degeneracy, while neutron stars have
neutron degeneracy.

Yousuf Khan

Dne 25.6.2014 18:26, Yousuf Khan napsal(a):
On 25/06/2014 11:04 AM, Poutnik wrote:
On 06/25/2014 03:59 PM, Yousuf Khan wrote:
The pulsar and the white dwarf are remarkably close in mass to each
other: the pulsar has 1.2 solar masses, while the dwarf has 1.05 solar
masses. The pulsar seems like it's on the low end of the mass scale for
neutron stars (I always thought they had to be over the Chandrasekhar
Limit of 1.4), while the dwarf seems pretty massive for a dwarf.

IMHO CHS limit 1.44 M_sol applies only to white dwarf stability.

Not all neutron stars evolve from a white wharfs,
as not all supernovas are type 1A.

Maybe, but my assumption was that you needed the 1.44 solar masses to
maintain a neutron degeneracy pressure.

In my understanding you need the 1.44 solar mass
for gravity to overcome electron degeneracy pressure
for gravity collapse
and gravity driven kernel - electron fusion.

I suppose there would be a big hysteresis in process reversal.
IMHO, there is not many NS below limit not because they are unstable,
but because there were more strict conditions for their creation.

Some references say the limit is 0.88-1.28 Solar mass.

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

--
Poutnik

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

On 25/06/2014 1:38 PM, Poutnik wrote:
In my understanding you need the 1.44 solar mass
for gravity to overcome electron degeneracy pressure
for gravity collapse
and gravity driven kernel - electron fusion.

I suppose there would be a big hysteresis in process reversal.
IMHO, there is not many NS below limit not because they are unstable,
but because there were more strict conditions for their creation.

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.

Yousuf Khan