Definition of the sun's "death"?

In article , Odysseus wrote:
In article LADli.26938$Fc.8903@attbi_s21,
Sam Wormley wrote:

snip

Your book has an excellent diagram on page 459 relating the original
star mass to that of the final core mass (core mass being the mass of
whats left of the star at the end of its evolutionary processes).

What book is that? I assume your posting was taken from class notes --
what course?

Glad I wasn't the only one wondering about this. I looked at the thread
and other possibly related threads and couldn't work out what the
reference to "your book" was all about. I'd like to find out as well.

In article , Odysseus wrote:
In article LADli.26938$Fc.8903@attbi_s21,
Sam Wormley wrote:

snip

Your book has an excellent diagram on page 459 relating the original
star mass to that of the final core mass (core mass being the mass of
whats left of the star at the end of its evolutionary processes).

What book is that? I assume your posting was taken from class notes --
what course?

Google can be so useful sometimes. It's a direct quote from:

http://edu-observatory.org/mcc/homew...19/homework.ch.
18-19.html

Sam Wormley wrote:
Radium wrote:
Hi:

I just don't understand why the expansion of the sun into a red giant
would be classified as the sun's 'death'. As a red giant, the sun will
very much be alive as it is today. It will burn helium instead of the
hydrogen it burns today.

My definition of the "death of the sun", is when the sun ceases its
nuclear fusion. Fusion is what gives the sun its life.


Best,

Radium


Stars spend the majority of their "lives" on the main sequence, i.e.,
fusing hydrogen into helium. and the secondary, tertiary, etc. fusion
processes are short lived by comparison.

Star are born and stars die... just like us. The big massive stars have
but short lives, a few millions of years. Stars like our sun last for a
good 10 billions of years, and the little red stars like Barnard's Star
might last for 100 billion years. How long stars live, is determined by
their mass (which must be at least 80 Jupiter masses to sustain
thermonuclear fusion of hydrogen).

There are four (4) fates for the end of stars depending on their masses
and the masses of their cores:

Red/Brown Dwarfs - less than 0.6 Ms == Main Sequence 0.076-0.8 Ms
Stars less than about 0.6 solar masses, when nuclear fuel is used up,
gravitational collapse shrinks the star, but no more than the gas
temperature-pressure-volume laws of classical physics allow. We have
not found any white dwarf less massive than 0.6 solar masses. Part of
the answer is that the universe may not be old enough for lower mass
stars to have evolved off the main sequence.

White Dwarfs - 0.6 and 1.44 Ms == Main Sequence 0.8-8 Ms
Stars with core masses between 0.6 and 1.44 solar masses are
destined to become white dwarfs. White dwarfs are degenerate matter.
Further collapse is halted by electron degeneracy pressure. See pages
456-459 in your textbook. The vast majority of stars are in this mass
range and are destined to become white dwarfs

Neutron Stars - 1.44 and 2.9 Ms == Main Sequence 8-30 Ms
Core masses between 1.44 and 2.9 solar masses overcome electron
degeneracy pressure and collapse to form neutron stars, a star that is
essentially one gigantic nucleus. Further collapse is halted by neutron
degeneracy pressure.

Black Holes - 3 or more Ms == Main Sequence 30 Ms
But for cores with mass of 3 or more solar masses, neutron
degeneracy pressure does not stop the collapse and the star becomes a
black hole with zero physical size, but with all the mass. Gravity
really wins!

In each case, gravity eventually wins, but, to what extent is
determined by the mass and the relative pressures of the quantum
mechanical forces, electron and neutron degeneracy pressure. Your book
has an excellent diagram on page 459 relating the original star mass to
that of the final core mass (core mass being the mass of whats left of
the star at the end of its evolutionary processes).

Something I'd like to know:

Just what will be left of a star (that won't explode into a neutron star
or black hole) some 20 billion years from now. A cold, spinning sphere
of iron that you could walk on?

All stellar 'histories' that I have read (maybe I should say
understood), don't seem to elaborate on this.

As for the neutron star: Has there been any speculation as to how this
would appear if you could orbit one from a safe distance?

--
Stupot http://insignity.blogspot.com

Stuart Chapman nous a donc écrit :

Something I'd like to know:

Just what will be left of a star (that won't explode into a neutron
star or black hole) some 20 billion years from now. A cold, spinning
sphere of iron that you could walk on?

Not iron. Degenerate electronic matter is the constituent of a white dwarf.
Don't ask me the aspect of this matter
You could obviously walk on it, if you are not crushed by gravitation.
And in 20 billion years, this sphere of matter will surely be as cold as the
rest of the universe.

All stellar 'histories' that I have read (maybe I should say
understood), don't seem to elaborate on this.

As for the neutron star: Has there been any speculation as to how this
would appear if you could orbit one from a safe distance?

You could refer to this page
http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.html where you will find some
animation films about travelling to a neutron star.
The aspect of a neutron star must be a (quite) perfect sphere of iron, which
forms the crust of the star.

--
Norbert. (no X for the answer)
======================================
knowing the universe - stellar and galaxies evolution
http://nrumiano.free.fr
images of the sky http://images.ciel.free.fr
======================================

On Mon, 16 Jul 2007 16:06:14 +0200, "Norbert"
wrote:

Not iron. Degenerate electronic matter is the constituent of a white dwarf.
Don't ask me the aspect of this matter
You could obviously walk on it, if you are not crushed by gravitation.
And in 20 billion years, this sphere of matter will surely be as cold as the
rest of the universe.

I think that in just 20 billion years, you'd still get toasted pretty
well walking on the surface of a neutron star. It would still be a few
thousand degrees. Better give it at least a few hundred billion years if
you want it cool enough to walk on.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris L Peterson nous a donc écrit :

On Mon, 16 Jul 2007 16:06:14 +0200, "Norbert"
wrote:

Not iron. Degenerate electronic matter is the constituent of a white
dwarf. Don't ask me the aspect of this matter
You could obviously walk on it, if you are not crushed by
gravitation.
And in 20 billion years, this sphere of matter will surely be as
cold as the rest of the universe.

I think that in just 20 billion years, you'd still get toasted pretty
well walking on the surface of a neutron star. It would still be a few
thousand degrees. Better give it at least a few hundred billion years
if you want it cool enough to walk on.

I was talking about white dwarf. And from
http://www.journals.uchicago.edu/ApJ...864961312Guest
it seems that about 10 billion years will be enough.

Of course, for a neutron star, it will take a much much longer time

--
Norbert. (no X for the answer)
======================================
knowing the universe - stellar and galaxies evolution
http://nrumiano.free.fr
images of the sky http://images.ciel.free.fr
======================================

On Mon, 16 Jul 2007 17:11:52 +0200, "Norbert"
wrote:

I was talking about white dwarf. And from
http://www.journals.uchicago.edu/ApJ...864961312Guest
it seems that about 10 billion years will be enough.

Sorry, I was thinking white dwarf even while typing neutron star. And
from my reading of the referenced paper, a typical white dwarf
temperature will be about 15,000 K after 10 billion years... a little
warmer than I'd care to walk on! That temperature is also in line with
what you get modeling the luminosity function as a simple exponential
(which was the source of my time estimates elsewhere in this
discussion).

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris L Peterson nous a donc écrit :

On Mon, 16 Jul 2007 17:11:52 +0200, "Norbert"
wrote:

I was talking about white dwarf. And from
http://www.journals.uchicago.edu/ApJ...864961312Guest
it seems that about 10 billion years will be enough.

Sorry, I was thinking white dwarf even while typing neutron star. And
from my reading of the referenced paper, a typical white dwarf
temperature will be about 15,000 K after 10 billion years... a little
warmer than I'd care to walk on! That temperature is also in line with
what you get modeling the luminosity function as a simple exponential
(which was the source of my time estimates elsewhere in this
discussion).

Chris, you're right. My first reading of this article was a bit too fast.
I agree : I won't put my feet on such a star

--
Norbert. (no X for the answer)
======================================
knowing the universe - stellar and galaxies evolution
http://nrumiano.free.fr
images of the sky http://images.ciel.free.fr
======================================

On Jul 16, 3:06 pm, "Norbert"
wrote:
Stuart Chapman nous a donc écrit :

Something I'd like to know:

Just what will be left of a star (that won't explode into a neutron
star or black hole) some 20 billion years from now. A cold, spinning
sphere of iron that you could walk on?

Not iron. Degenerate electronic matter is the constituent of a white dwarf.
Don't ask me the aspect of this matter

Mostly at the surface chemically it will be carbon and oxygen when it
cools down enough to recombine from a plasma. And crystallisation is
believed to play a part in the cooling of white dwarfs when the
surface temperature falls below about 6000K (typically 5x10^9 years
after formation).

You could obviously walk on it, if you are not crushed by gravitation.
And in 20 billion years, this sphere of matter will surely be as cold as the
rest of the universe.

I think I would prefer to wait about 10^12 years for it to cool. By
then if current theories are correct it will be a roughly Earth sized
diamond with an iron core and very unpleasantly strong surface
gravity.

Various ZZ Cetae type white dwarf type stars are being studied to try
and understand their cooling processes.
eg http://www.aas.org/publications/baas...aas203/181.htm
more popular version
http://news.bbc.co.uk/1/hi/sci/tech/3492919.stm

Regards,
Martin Brown