How to shut down the Sun?

On Jul 27, 6:24*pm, dlzc wrote:
http://www.gemini.edu/node/73

If I understand the cartoon correctly,

Yes, sorry about the quality...

the "donor object" was a star losing mass
during its own evolution. *Much of the mass
lost was then collected by the white dwarf
companion. *That's a much different scenario
than one in which the companion _causes_
the mass loss.

I guess I am confused how a star with a companion can lose mass in
some "normal" evolutionary process, but that process does not (?)
occur in similar stars that do not have companions ouside the Roche
limit? *Are they just "stars with massive dark companions"? *Or are we
believing that the donor became a red giant, and all its "hydrogen"
was transferred to the acceptor star?

As I understand the implications from that article, the white dwarf
and the red dwarf companion were initially far away from each other.
They spiraled towards each other over time, until now they are no
further away from each other than the surface of the Earth from the
surface of the Moon. And also they are no longer a white dwarf/red
dwarf pair, but now a white dwarf/brown dwarf pair since most of the
red dwarf's mass has been stripped away from it to the point where it
no longer qualifies as a red dwarf.

Now why they started spiraling towards each other might have happened
when the white dwarf's progenitor star evolved into a red giant.
During that time, it's atmosphere might have enveloped the red dwarf,
and the atmsopheric drag brought them closer together. Something like
this may have happened to a different star system too, WD0137-349,
where a brown dwarf got encompassed inside the atmosphere of a red
giant and spiraled in towards it. These two stories sound remarkably
alike actually.

Brown Dwarf Survives Jonah Episode With Red Giant
"Astronomers using ESO's Very Large Telescope
have discovered a binary system in which a Jupiter-sized brown dwarf
is orbiting an Earth-sized white dwarf. What's unusual about the
arrangement, however, is the brown dwarf once actually orbited inside
its companion when the white dwarf grew into a red giant."
http://www.spacedaily.com/reports/Br...ant_ 999.html

But in the case of EF Eridanus the smaller object may have started out
life as a red dwarf rather than a brown dwarf like in WD0137-349. EF
Eri only ended up being the size of a brown dwarf after much
evolution.

In the case of EF Eri, I suspect that the white dwarf, during its red
giant phase, initially enriched the mass of the red dwarf, where the
red dwarf gorged on the red giant's swollen atmosphere. Enriching it
to the point where it was almost 50-100% the mass of the Sun, but it
ended up way too close to the white dwarf. Then it was the white
dwarf's turn to gorge on the atmosphere of the previous red dwarf.
What the primary gave to the secondary, it then took it back with
interest.

Yousuf Khan

In article ,
dlzc writes:
http://en.wikipedia.org/wiki/Nuclear_fusion

That's mostly about fusion reactions potentially useful for
terrestrial reactions. Remember, the average hydrogen atom in the
center of the Sun will wait several billion years before it undergoes
fusion; that reaction rate is not practical for power reactors (and
even less so for bombs).

The page you want is the one I gave earlier:
http://en.wikipedia.org/wiki/Proton-proton_chain

No neutrons involved.

http://hyperphysics.phy-astr.gsu.edu...solneu.html#c1

Not sure what relevance this has, but again the link to the pp cycle
http://hyperphysics.phy-astr.gsu.edu...procyc.html#c2
shows that the reactions don't involve neutrons.

I guess I am confused how a star with a companion can lose mass in
some "normal" evolutionary process,

The same way(s) a star without a companion loses mass. During
typical mass-loss phases of evolution, mass is driven off the surface
by radiation pressure, often when solid particles form in a cool
atmosphere. If the star is isolated, the mass escapes from the star
and adds to ambient interstellar gas and dust (some of which will
later form new stars), but if the star is in a multiple system, some
of the mass lost may land on one or more companion stars. Both mass
loss and subsequent accretion have implications for stellar orbits.

I've seen decent discussions of stellar mass loss (and subsequent
recycling of the ISM into stars) on the web, but the Wikipedia entry
isn't very helpful, and the first page of Google references seems to
be mostly academic papers on specific topics, not a general overview.
Maybe you'll have better luck with a more careful search.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

Dear Steve Willner:

On Jul 28, 10:26*am, (Steve Willner) wrote:
In article ,

writes:
http://en.wikipedia.org/wiki/Nuclear_fusion

That's mostly about fusion reactions potentially
useful for terrestrial reactions. *Remember, the
average hydrogen atom in the center of the Sun
will wait several billion years before it undergoes
fusion; that reaction rate is not practical for
power reactors (and even less so for bombs).

The page you want is the one I gave earlier:
http://en.wikipedia.org/wiki/Proton-proton_chain

No neutrons involved.

http://hyperphysics.phy-astr.gsu.edu...solneu.html#c1

Not sure what relevance this has,

It indicates that we have not yet accounted for all the neutrinos
necessary to result from the p-p chain reaction you keep pointing to.

but again the link to the pp cycle
http://hyperphysics.phy-astr.gsu.edu...procyc.html#c2
shows that the reactions don't involve neutrons.

I understand that is the model. But we are still shy neutrinos
(missing about 70%). Maybe not for long...

I guess I am confused how a star with a
companion can lose mass in some "normal"
evolutionary process,

The same way(s) a star without a companion
loses mass. *During typical mass-loss phases
of evolution, mass is driven off the surface by
radiation pressure, often when solid particles
form in a cool atmosphere. *If the star is isolated,
the mass escapes from the star and adds to
ambient interstellar gas and dust (some of which
will later form new stars),

Any significant mechanisms besides supernovae and "solar wind"? Just
off the top of your head... keywords...

but if the star is in a multiple system, some
of the mass lost may land on one or more
companion stars. *Both mass loss and
subsequent accretion have implications for stellar
orbits.

I've seen decent discussions of stellar mass
loss (and subsequent recycling of the ISM into
stars) on the web, but the Wikipedia entry
isn't very helpful, and the first page of Google
references seems to be mostly academic
papers on specific topics, not a general overview.
Maybe you'll have better luck with a more careful
search.

Thanks...

David A. Smith

In article ,
YKhan writes:
As I understand the implications from that article, the white dwarf
and the red dwarf companion were initially far away from each other.
They spiraled towards each other over time,
....
Now why they started spiraling towards each other might have happened
when the white dwarf's progenitor star evolved into a red giant.
During that time, it's atmosphere might have enveloped the red dwarf,
and the atmsopheric drag brought them closer together.

I suspect conservation of angular momentum might have more to do with
the orbit change than atmospheric drag in the red giant atmosphere.
Unfortunately, I didn't find any good resources on the web but that
was with only the most cursory search. Perhaps a better search would
turn up notes for some graduate course on binaries and accretion.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On Jul 28, 5:18*pm, (Steve Willner) wrote:
I suspect conservation of angular momentum might have more to do with
the orbit change than atmospheric drag in the red giant atmosphere.
Unfortunately, I didn't find any good resources on the web but that
was with only the most cursory search. *Perhaps a better search would
turn up notes for some graduate course on binaries and accretion.

Well, when a star goes red giant, it loses a little bit of mass (which
becomes its planetary nebula), so to conserve angular momentum, the
companion would have to get further away. However, since the red giant
also gets less dense and balloons up to extraordinary sizes, it's
outer atmosphere might actually outrace the companion's orbital shift.
So it would necessarily have to be atmospheric drag that brings its
companion closer since angular momentum should take it out further.

Yousuf Khan

YKhan wrote:

In the case of EF Eri, I suspect that the white dwarf, during its red
giant phase, initially enriched the mass of the red dwarf, where the
red dwarf gorged on the red giant's swollen atmosphere. Enriching it
to the point where it was almost 50-100% the mass of the Sun, but it
ended up way too close to the white dwarf. Then it was the white
dwarf's turn to gorge on the atmosphere of the previous red dwarf.
What the primary gave to the secondary, it then took it back with
interest.

I don't see how it's possible to reduce it to a substellar mass in
this
way, given how radius varies with mass.

Andrew Usher

On Jul 28, 10:26*pm, Andrew Usher wrote:
I don't see how it's possible to reduce it to a substellar mass in
this
way, given how radius varies with mass.

Well, I added the speculative narrative about the system before the
first star was a white dwarf. The latter part of the narrative I took
straight from the original article link about EF Eri itself. The
original article didn't speculate at all about the system pre-white
dwarf.

From the original link, about 500 million years ago, the companions
were 3 million km from each other, with the secondary star being a
near-Solar mass star with a volume similar to slightly larger than the
Sun (it may have puffed up slightly due to the onset of mass
transfer). Then about 200 million years ago, the secondary was much
smaller and cooler, having lost significant mass to the white dwarf;
and the companions had spiraled in towards each other to 1.5 million
km (half of the 500 million year distance). Today, the secondary is
700 thousand (half of the 200 million year distance), and the mass is
much smaller again.

Yousuf Khan

YKhan wrote:

Well, I added the speculative narrative about the system before the
first star was a white dwarf. The latter part of the narrative I took
straight from the original article link about EF Eri itself. The
original article didn't speculate at all about the system pre-white
dwarf.

Where's the original article you refer to? You only posted this:

http://www.spacedaily.com/reports/Br...ant_ 999.html

which can't be it.

From the original link, about 500 million years ago, the companions
were 3 million km from each other, with the secondary star being a
near-Solar mass star with a volume similar to slightly larger than the
Sun (it may have puffed up slightly due to the onset of mass
transfer). Then about 200 million years ago, the secondary was much
smaller and cooler, having lost significant mass to the white dwarf;
and the companions had spiraled in towards each other to 1.5 million
km (half of the 500 million year distance). Today, the secondary is
700 thousand (half of the 200 million year distance), and the mass is
much smaller again.

Yes, but the mass-radius relation reverses between a few times Jupiter
and the hydrogen-burning mass; the primary's gravity could only make
this worse. So if it were sufficiently close to reduce it below the
minimum hydrogen-burning mass, it should continue to do so until the
secondary is below Jupiter's mass.

Andrew Usher

In article ,
dlzc writes:
http://en.wikipedia.org/wiki/Proton-proton_chain
It indicates that we have not yet accounted for all the neutrinos
necessary to result from the p-p chain reaction you keep pointing to.

You're several years out of date. The neutrinos switch "flavors" on
the way to Earth. This was proposed decades ago but finally
confirmed fairly recently. (Sudbury Neutrino Observatory was a key
part of the confirmation, so you might want to search on that.) I
don't have the best references at hand, but a detailed article is at
http://pdg.ift.unesp.br/2009/reviews...ino-mixing.pdf

I expect a search on "neutrino flavor mixing" would turn up more.

I've never heard of anyone (besides you) even hinting that neutrons
are important for stellar energy production. They are important for
element building during supernova explosions, though.

[stellar mass loss]
Any significant mechanisms besides supernovae and "solar wind"? Just
off the top of your head... keywords...

The big contributors to returning mass to the interstellar medium are
supernovae, novae, and asymptotic giant branch stars. Ordinary red
giants, red supergiants, and Wolf-Rayet stars contribute less, and
ordinary main sequence stars virtually nothing. All this is from
memory; I probably have left out some contributors and may be
remembering relative contributions wrong. I tried web searches on
various combinations of interstellar, matter, medium, stellar, and
mass loss but didn't find anything really helpful. (To be fair, I
only briefly glanced at the first page of results; there may be good
resources farther down.)

There were, I believe, some good posts in this newsgroup some while
ago. One post I found was
http://groups.google.com/group/sci.a...051b768c773f6b

but I see it deals with dust in particular rather than mass loss in
general.

One caution is that the whole subject of mass loss from stars is not
well understood theoretically. Some aspects are understood, and
there are lots of observational data, but we are very far from having
a complete picture.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

In article ,
YKhan writes:
Well, when a star goes red giant, it loses a little bit of mass (which
becomes its planetary nebula), so to conserve angular momentum, the
companion would have to get further away.

That's part of the story, yes. What happens when the matter accretes
onto a less massive companion?

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA