Dead star systems

Hi there,

Is there an estimate of how many defunct solar systems are "floating
around" out there in our Milky Way? Such as an estimated ratio of
burning stars vs burnt out ones? Since the nearest "active" star system
is ~3+ light years away (Alpha C) is it possible that dead stars (such
as cold white dwarfs) are even closer and more plentiful than visible
burning stars? As I understand it these old star cinders still exist
after burning out but are just dark and highly massive, possibly
penetrating our oort cloud? Any insights on this?
Thanks.

veggie king wrote:
Hi there,

Is there an estimate of how many defunct solar systems are "floating
around" out there in our Milky Way? Such as an estimated ratio of
burning stars vs burnt out ones? Since the nearest "active" star system
is ~3+ light years away (Alpha C) is it possible that dead stars (such
as cold white dwarfs) are even closer and more plentiful than visible
burning stars? As I understand it these old star cinders still exist
after burning out but are just dark and highly massive, possibly
penetrating our oort cloud? Any insights on this?
Thanks.

AFAIK they are called black dwarves, and AFAIK the Universe is not old
enough for them to exist because they take so long to cool down enough.

The only "dead" stars are neutron stars and black holes.

Dear veggie king:

On Dec 17, 10:03*am, (veggie king) wrote:
Hi there,

Is there an estimate of how many defunct solar
systems are "floating around" out there in our
Milky Way? Such as an estimated ratio of
burning stars vs burnt out ones? Since the nearest
"active" star system is ~3+ light years away (Alpha
C) is it possible that dead stars (such as cold white
dwarfs) are even closer and more plentiful than
visible burning stars? As I understand it these old
star cinders still exist after burning out but are just
dark and highly massive, possibly penetrating our
oort cloud? Any insights on this?

The local vicinity will have none of them, since they would be
occluding stars, and if supermassive, would be detectable via
gravitational lensing.

David A. Smith

Thanks for the replies.
Black dwarfs - had not heard of that designation before now, the older I
get the harder is it to keep pace

Also hard to believe that these haven't had time to cool off yet, esp
the ones that spent their fuel during the very early years of the Milky
Way. With the recent announcement of the tripling of stars (due to the
well hidden brown dwarfs) wouldn't it be even harder to detect all the
black dwarfs out there?

Dear veggie king;

On Dec 18, 9:04*am, (veggie king) wrote:
Thanks for the replies.
Black dwarfs - had not heard of that designation before
now, the older I get the harder is it to keep pace

*Also hard to believe that these haven't had time to cool
off yet, esp the ones that spent their fuel during the very
early years of the Milky Way. With the recent
announcement of the tripling of stars (due to the well
hidden brown dwarfs) wouldn't it be even harder to detect
all the black dwarfs out there?

If a star had enough mass to sustain fusion, it would asymptotically
approach complete loss of hydrogen (etc.),and would not continue to
burn its fuel at a linear rate. Which means it'll go red for a long
time, before it goes black. Like billions of years.

On 12/18/2010 11:04 AM, veggie king wrote:
Thanks for the replies.
Black dwarfs - had not heard of that designation before now, the older I
get the harder is it to keep pace

Also hard to believe that these haven't had time to cool off yet, esp
the ones that spent their fuel during the very early years of the Milky
Way. With the recent announcement of the tripling of stars (due to the
well hidden brown dwarfs) wouldn't it be even harder to detect all the
black dwarfs out there?


The universe is 13.7 billion years old. The earliest white dwarfs would
be only a few hundred million years after that, maybe 13.6 billion years
ago. It will take several hundred billion years for the white dwarfs to
cool down to black dwarf status, as the only method of cooling down in
empty space is through radiation.

Yousuf Khan

Thanks again for the feedback on this topic.

But if it takes that much time (100s of billions of years) for a white
dwarf to cool into a black dwarf then would it be safe to assume that
black dwarfs really do not exist....yet?

On 19/12/2010 10:47 AM, veggie king wrote:
Thanks again for the feedback on this topic.

But if it takes that much time (100s of billions of years) for a white
dwarf to cool into a black dwarf then would it be safe to assume that
black dwarfs really do not exist....yet?

Yes, unless something surprising is waiting for us to discover. Then in
that case, it would mean we need to reevaluate our knowledge of
thermodynamics.

Yousuf Khan

Well Yousef, nothing much surprises me anymore . After growing up
during a time when our solar system was believed to be formed by another
star grazing the sun tearing away material to form the planets then I'm
sure we're in for some doozie surprizes. And to think, now-today we
believe that the Earth's moon formed in a similar collision-like manner,
go figure. Enjoy the mystery!

Thanks again for your astronomical insights.

In article ,
(veggie king) writes:
Is there an estimate of how many defunct solar systems are "floating
around" out there in our Milky Way? Such as an estimated ratio of
burning stars vs burnt out ones?

For the latter, there's only an upper limit. Last time I checked,
which was several years ago, there was still room for white dwarfs
with ages of order 13 billion years to make up a nontrivial fraction
of the nonbaryonic dark matter. I've forgotten what temperature
these stars would have (though calculations exist), but a couple of
thousand kelvins might be about right. It would take some work to
put numbers on all this, and I don't have time right now. You might
try asking in sci.astro.research to see whether any posters have
looked more recently than I have.

Whether very old stars might have planets is a far more difficult
question. There's a pulsar (or more than one now?) with planets, so
it might be possible.

is it possible that dead stars (such
as cold white dwarfs) are even closer and more plentiful than visible
burning stars?

Most of the old white dwarfs should have masses near the
Chandrasekhar limit (1.4 solar masses), or at least that's what I'd
expect. Thus there probably can't be more of them than main sequence
stars, and if the white dwarfs have a halo distribution, the expected
distance to the nearest one would be many parsecs at least.
Individual objects would be very difficult to detect and recognize,
so I doubt the presence of one or two within a few parsecs can be
ruled out by existing observations.

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