N:dlzc D:aol T:com (dlzc) wrote:
Dear Sam Wormley:

"Sam Wormley" wrote in message
news:70RQe.292294$_o.100507@attbi_s71...

N:dlzc D:aol T:com (dlzc) wrote:


Stable neutron stars are 0.8 solar masses. How far down will
you define "too small to detect"?

Tell me where you get this figure of 0.8 solar masses for stable
neutron stars. Thanks.


http://zebu.uoregon.edu/~imamura/122/mar13/bhform.html
... greater than 2-3 solar masses are unstable

http://www-astronomy.mps.ohio-state....3/extreme.html
... neutron degeneracy pressure can sustain 1.2 -2 solar masses

http://www.ma.utexas.edu/mp_arc/c/05/05-190.pdf
... graph on page 28 (still about 0.5 to 2.2 solar masses)

I may have remembered a particular neutron star's mass, rather
than the "only stable neutron star mass" "or the upper limit on
neutron star mass is". Sorry for any confusion this might have
created.

David A. Smith



Acording to my references, observed masses of neutron stars:
M_ns = 1.01 to 1.73 solar masses, so if you know of observations
down to 0.80 solar masses, I'm all ears to find the references.

Upper limit: M_ns 2.9 solar masses, including any possible
contribution due to rapid uniform rotation (Kalogera and Baym, 1996).

For stars that explode as Type II supernovae, the neutron star masses
average M_ns = 1.28 or 1.73 solar masses; the average for those arising
from Type Ib supernovae is M_ns = 1.32 solar masses. This compares
favorably with the determination of a neutron star mass of
M_ns = 1.35 ± 0.27 solar masses for 17 system (Thorsett et al., 1993).
Radio observtions for four neutron binary star systems give M_ns = 1.01
to 1.64 solar masses (Finn, 1994), while neutron star masses inferred
from X-ray bnaries lie in the range M_ns = 1 to 2 solar masses (Bahcall,
1978; Joss and Rappaport, 1984; Lang, 1992).

Thanks
-Sam

N:dlzc D:aol T:com (dlzc) wrote:
http://www.universetoday.com/am/publ...e.html?1132005
... CMBR interacting with galaxies some 7 billion years ago...

This one seems to talk about all of the perceived variances in the CMBR
to be just effects of local galaxies creating an illusionary effect.
They can't seem to tell whether the variances are locally generated or
real ones.


MOND isn't the answer. Neither is Dark Matter, in my opinion.

snip

I suspect both Dark Matter and Dark Energy to end up being huge
fudge factors. I am usually wrong, however. Just don't look to
them to stay "unmodified and eternal".

David A. Smith

What do you expect the final answer will be? Perhaps these are effects
of as yet undiscovered properties of superstrings?

Yousuf Khan

Dear Yousuf Khan:

"Yousuf Khan" wrote in message
oups.com...
N:dlzc D:aol T:com (dlzc) wrote:
http://www.universetoday.com/am/publ...e.html?1132005
... CMBR interacting with galaxies some 7 billion years ago...

This one seems to talk about all of the perceived variances in
the CMBR to be just effects of local galaxies creating an
illusionary effect. They can't seem to tell whether the
variances
are locally generated or real ones.

The other two are more clear and in-line with expectations. The
CMBR is cooling. Doesn't mean (by itself) the Universe won't
collapse, or repetitively cycle, only that it is monotonically
cooling for the last 13 Gy and we cannot see "before" or "beyond"
it.

MOND isn't the answer. Neither is Dark Matter, in my opinion.

snip

I suspect both Dark Matter and Dark Energy to end up being
huge fudge factors. I am usually wrong, however. Just don't
look to them to stay "unmodified and eternal".

What do you expect the final answer will be? Perhaps these are
effects of as yet undiscovered properties of superstrings?

No, I'd go for G (and of course more since alpha can also contain
G) not being a Universal constant, but rather some relationship
to the "dynamo" at the center of the "star grouping in question".
But I'll say again, I am usually wrong.

David A. Smith

"YK" == Yousuf Khan writes:

YK Sam Wormley wrote:
There is more than one way to estimate the age of the universe.

New Age for the Universe

30 Jun 2005 - This week's Nature has a letter giving a new
determination of the age of the Universe based on the age of the
isotopes. 238U and 232Th are both radioactive with half-lives of
4.468 and 14.05 Gyrs but the uranium is underabundant in the Solar
System compared to the expected production ratio in
supernovae. This is not surprising since the 238U has a shorter
half-life, and the magnitude of the difference gives an estimate
for the age of the Universe. But the production ratio is poorly
known from nuclear physics models, so Dauphas (2005, Nature, 435,
1203) combines the Solar System 238U:232Th ratio with the ratio
observed in very old, metal poor stars to solve simultaneous
equations for both the production ratio and the age of the
Universe, obtaining 14.5 +2.8/-2.2 Gyr.

YK So this would indicate the very first Type II supernovas to have
YK occurred. How many years after the Big Bang would they expect the
YK first supermassive stars to have formed, and how many years later
YK would they be expected to explode?

The most massive stars can have lifetimes of order 100 million years.
Assuming that star formation in the early Universe is not
significantly different than in the current epoch, we should expect
that the first stars might very well have formed within 1000 million
years or 1 billion years after the Big Bang.

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"YK" == Yousuf Khan writes:

YK Bruce Scott TOK wrote:
Basically, although we see objects at distance we also see them in
the past and it is that which is relevant. We can see that the
state of the universe is different at high redshift than at zero
redshift, and due to the redshift distance relation this is
interpreted as a difference between past and present epoch. Note
that this has a frame-independent definition: proper time since the
initial singularity. When we speak of the age of the cosmos, we
are really giving a number to this coordinate in the
Robertson-Walker metric. We can extrapolate from observations
enough to tell that there is a fundamental limit to this epoch of
cosmic time regardless of how much of the spatial extent of the
universe we can see.

YK I assume you're talking about things like quasars, which we see
YK lot of in the past and in the distance, but not so much nearby. Is
YK it possible that these locations are so far off, that we only see
YK the brightest objects from there?

This sounds like you're asking about the Malmquist bias. Yes, as we
look farther away, only the brightest objects can be seen.

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No means no, stop rape. | http://patriot.net/%7Ejlazio/
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Joseph Lazio wrote:


The most massive stars can have lifetimes of order 100 million years.
Assuming that star formation in the early Universe is not
significantly different than in the current epoch, we should expect
that the first stars might very well have formed within 1000 million
years or 1 billion years after the Big Bang.


Evidence indicates that the first stars turned on as early as
200 million years after the big bang. Evidence also indicates
that massive stars ( 30 solar masses) last just a few million
years.