Star age Measurements

Dear Steve Willner:

On Thursday, May 23, 2013 3:38:10 PM UTC-7, Steve Willner wrote:
In article ,

dlzc writes:

*Please understand that I mean by pure hydrogen,
the = initial mix the Big Bang is supposed to have
produced (and note that this was established by
observation of the mix, and not fundamental physics...

On the contrary, there are theoretical calculations
of the light nuclide abundances. Do a web search on
"Big Bang Nucleosynthesis." Observations agree with
theory. I'm not sure which is considered more
accurate nowadays.

This is not my dog. We will see what the OP does with it.

To play Devil's advocate, should some form of
continuous Bang be going on (= or white holes,
or evaporating proto black holes),

or invisible fairies (but evaporating black holes
would not be adding to total mass)

.... but could be adding hydrogen...

a pure* hydrogen star does not have to be old.

Logically correct, but there is no evidence for
creation of new matter.

We have not been looking very long. I tend to agree with you. New discoveries (a close cold galaxy 5 - 10 years ago) are due to improvements in observation.

One would have to ask, though, if low-metal stars are
forming now, why don't we see any low-metal gas?

With space filled (in some sense) with ionized hydrogen and oxygen missing 5 electrons, how would we know if some of the hydrogen was new?

globular clusters are assumed to be old ,
because there was a Big Bang, and that was the only
time pure* hydrogen was available.

No. As has been written in this thread, globular
clusters are assumed to be old because of their HR
diagrams.

Which was in turn, scaled in light of a Big Bang.

In particular, the clusters contain no main
sequence stars more massive than a fairly
small value. That's because (in the standard view),
all stars with larger mass have evolved away from
the main sequence.

Better. Much better.

Hence the OPs reference to circular argument

was mistaken.

I seem unable to get you to see that he really was not.

They also have been stripped of their dust

What makes you think globular clusters ever had
dust (though they probably did)? More relevant,
they have been stripped of gas, or the gas was
entirely used up in forming the stars. What that
has to do with anything being discussed here
escapes me.

"The oldest stars..."

(see below, and assuming they were the cores =
of smaller galaxies that lost their "disc stars"
to the larger galaxy).

Globular clusters were the cores of galaxies?! Why
would you suggest that?

They seem extremely similar to the center of a spiral galaxy. They also have black holes.
http://arxiv.org/abs/1207.3795

We cannot image individual stars outside the
Milky Way.

If you mean image the stellar surfaces, that's
true. It's only possible for stars that are both
nearby and physically large. If you mean see a
star as separate from other stars in the same galaxy,
that's not entirely true. Bright stars can be
resolved in nearby galaxies and supernovae even in
distant galaxies. Cepheid variables, fore example,
are particularly important for distance measurements.

.... and even then it is non-trivial to locate the container galaxy.

So what we see, are illuminated dust clouds in
more distant areas

I have no idea what you mean by this.

It would help if you did not cut the quote off mid-sentence.

Galaxies in general are seen as we see the Milky Way
by naked eye: patches of light spread over a
finite area on the sky.

Or the bullet cluster, where "all" the dust is removed, and we can see none of the stars.

The light comes from stars that are not resolved
individually, as Galileo discovered for the Milky
Way. Dust has nothing to do with it (in visible
light) except that dust extinction diminishes the
light that would otherwise be seen.

When yo look at a nebula, say the ring nebula, what is its most prominent feature, the white dwarf, or the nebula?

(Reflection from dust is seen in a few rare
cases but contributes a miniscule fraction of
the total light.)

OK, unless you have something for me, you can end this as you see fit.

David A. Smith

In article ,
"Mike Dworetsky" wrote:

snip

Various attempts have been made to model the "Population III" stars that
would have been the first to condense from the original gas mixture. There
would have been no dust--because there was no carbon, silicon, etc.
However, these cannot be compared observationally because no such stars have
been found, yet.

If earlier stars were bigger than those of later generations, as has
been suggested, one wouldn't expect many of them to be left in a
non-degenerate state, having made their trips off the main sequence eons
before the Sun was formed. Unless their evolution takes a different
course from higher-metallicity stars, any of Pop. III still surviving
would be small, long-lived dwarfs. It's only in recent years we've been
able to detect or characterize faint red dwarfs beyond our immediate
neighbourhood (lists of the N nearest stars are still getting updated
every couple of years, where N is a surprisingly small number), which
may not be representative of the Galaxy as a whole.

--
Odysseus

On May 22, 8:54*pm, (Steve Willner) wrote:
On 17/05/2013 6:44 PM, David Levy wrote:
So the science is measuring the star age based on the fundamental Idea
of the Big bang.

Not true, as others have written. *In any case, the Big Bang is now
so well supported by so many lines of evidence that using it as a
constraint on star ages is justified.


'Big bang' is so logically corrupt that it requires a dysfunctional
mind to ignore the internal inconsistencies or rather,the acceptance
of logical consistency.

Because the idea of past is bumped up to present observations as an
evolutionary timeline it means that the oldest galaxies being the
furthest in a smaller Universe will generate, by logical consistency,
the perception that the nearest galaxies are the youngest in a larger
Universe.I wouldn't know what to make of people who propose such a
structure but that is exactly what the wider view looks like.







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

Odysseus wrote:
In article ,
"Mike Dworetsky" wrote:

snip

Various attempts have been made to model the "Population III" stars
that would have been the first to condense from the original gas
mixture. There would have been no dust--because there was no
carbon, silicon, etc. However, these cannot be compared
observationally because no such stars have been found, yet.

If earlier stars were bigger than those of later generations, as has
been suggested, one wouldn't expect many of them to be left in a
non-degenerate state, having made their trips off the main sequence
eons before the Sun was formed. Unless their evolution takes a
different course from higher-metallicity stars, any of Pop. III still
surviving would be small, long-lived dwarfs. It's only in recent

Yes, this is correct, and the search goes on. But so far, nothing like a
Pop III dwarf star has been found. Some stars of astonishingly low metal
abundance have been found (10^-3 to 10^-4 of solar abundances, IIRC). For
various reasons involving the dynamics of older stars, the search is usually
conducted by examining stars in the galactic halo.

years we've been able to detect or characterize faint red dwarfs
beyond our immediate neighbourhood (lists of the N nearest stars are
still getting updated every couple of years, where N is a
surprisingly small number), which may not be representative of the
Galaxy as a whole.

Arguments that we do not see Pop III stars because we happen to be located
in a special area of the Galaxy where they do not occur, suffer from the
violation of the Principle of Mediocrity, or the Copernican Principle, which
says that we are not located in a special or privileged place.

To claim it is true requires special pleading.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

On May 24, 8:37*am, "Mike Dworetsky"
wrote:

Arguments that we do not see Pop III stars because we happen to be located
in a special area of the Galaxy where they do not occur, suffer from the
violation of the Principle of Mediocrity, or the Copernican Principle, which
says that we are not located in a special or privileged place.


You display all the traits of a cult mind and this trumped up idea of
the 'Copernican Principle' which is merely late 20th century junk
imposed on history.

The objection of the Pope in the Galileo affair had nothing to do with
a supposed central Earth nor a stationary Sun,the genuine astronomical
objections which still hold true today was whether the facility for
predicting astronomical events like eclipses and transits as days and
dates within the calendar framework be also used to extrapolate the
planetary dynamics of the Earth -

"Here lurked the danger of serious misunderstanding. Maffeo Barberini,
while he was a Cardinal, had counselled Galileo to treat Copernicanism
as a hypothesis, not as a confirmed truth. But ‘hypothesis’ meant two
very different things. On the one hand, astronomers were assumed to
deal only with hypotheses, i.e. accounts of the observed motions of
the stars and planets that were not claimed to be true. Astronomical
theories were mere instruments for calculation and prediction, a view
that is often called ‘instrumentalism’. On the other hand, a
hypothesis could also be understood as a theory that was not yet
proved but was open to eventual confirmation. This was a ‘realist’
position. Galileo thought that Copernicanism was true, and presented
it as a hypothesis, i.e. as a provisional idea that was potentially
physically true, and he discussed the pros and cons, leaving the issue
undecided. This did not correspond to the instrumentalist view of
Copernicanism that was held by Maffeo Barberini and others. They
thought that Copernicus’ system was a purely instrumental device, and
Maffeo Barberini was convinced that it could never be proved. This
ambiguity pervaded the whole Galileo Affair."

http://www.unav.es/cryf/english/newlightistanbul.html

When the unfortunate Flamsteed correlated a rotating celestial sphere
with a rotating Earth using the 24 hour AM/PM cycle within the
365/365/365/366 day framework so began empirical homocentricity which
is the worst of the worst.so bad that the astronomers before
Copernicus sought out arguments for the Earth's motions as it would
create the horror of homocentricity where every point would be the
center of the Universe -

"Thereupon you will see-- through the intellect..that the world and
its motion and shape cannot be apprehended. For the universe will
appear as a wheel in a wheel and a sphere in a sphere-- having its
center and circumference nowhere. . . " Nicolas of Cusa 16th century

Mediocrity principle indeed !,try looking in the mirror.




To claim it is true requires special pleading.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

Thanks All

David: Hence, for example - if it took the Earth 5 Billion year to cool down the surface and set the first solid rocks and ground, than by definition its age is 5 + 4.5 Billion years. Do you agree?
Yousuf: In principle that could be true, but in practice the oldest pieces of
space rock we have ever observed in the solar system date to 4.55by.
David: This is a critical issue. The Earth or the moon could be a molten ball on their birthday as follow: "Our planet was probably still mostly a molten ball of rock, and the impact of the Moon did little to change that". Hence, there is a chance that it took some time for the Erath & the Moon to cool down and set the first solid rocks. Therefore, by adding all the factors, there might be an error in their age estimation... This might lead us to an error in the age estimation of the solar system and so on.
Martin: The age of the oldest terrestrial rocks corroborates the age of the solar system from meteorites (by being less, as expected), but is not used to determine the solar system age.
dlzc (David A. Smith): .... assuming they start with pure hydrogen, a resultant of the Big Bang. The "theory" compared against assumes eh star stars with pure hydrogen, and the star's composition is compared to a composition-with-age chart.

So yes, the age of the oldest meteorites is clear. But, this can only give us the minimum lever of the Solar system age.
By : http://www4.nau.edu/insidenau/bumps/...meteorite.html
"Their findings dated the piece at 4.568 billion years old, or nearly 2 million years older than the oldest materials found in other meteorites… For nearly 10 years they have classified and studied more than 1,000 meteorites, which include 22 lunar and 14 Martian meteorites, and have published dozens of research papers on the topic."
Out of the Billion over Billion meteorites & Asteroids we have verified the age of about 1000. We have found that the oldest is about 4.568 Billion years old. Does it mean that there is no possibility that there are some others which might be older???
The upper lever of the solar age can't be determined by only 1000 pcs which we have in our hand. Therefore it can only give us an indication that the lower limit age of the solar system or even the Earth is 4.568 billion years.
With Regards to the Earth – Yes, we must measure the age of the "oldest terrestrial rocks". Unfortunately, as the petroleum is located deep in the ground, it's quite clear that the majority of the oldest terrestrial rocks are located today deep in the ground. As over 70% of the Earth is cover with Oceans, then, there is a chance that there is no access today to the real oldest terrestrial rocks. Therefore, the rocks which are considered to be the oldest terrestrial rocks, give us an indication for the Min. age of the Earth.
Even so, those oldest terrestrial rocks might be molten lava on the day that the Earth was born. We don't know for sure how long it took for the Earth to cool down and set the first solid rock. Therefore, even those achievable oldest terrestrial rocks can't give an indication for the real age of the Earth.

David: So, the star age measurements is based on the BBT. Therefore, if the science is using the current star age measurements to confirm the BBT
then by definition it sounds like circular argument.
Mike: No, you misunderstand this. Star ages are based on observations of stars, and comparisons with the theory of stellar structure and evolution.

By Wiki – "Stellar populations are categorized as I, II, and III… Soon after the Big Bang, without metals, it is believed that only stars with masses hundreds of times that of the Sun could be formed;
Hence – the whole Idea of the stellar population is based on the BBT. Therefore, by definition this is a circular argument!!!
Even so, there are some other issues as follow:
By Wiki - http://en.wikipedia.org/wiki/Stellar_evolution
"A stellar evolutionary model is a mathematical model that can be used to compute the evolutionary phases of a star from its formation until it becomes a remnant... Accurate models can be used to estimate the current age of a star by comparing its physical properties with those of stars along a matching evolutionary track.[26]"
Hence – the stellar evaluation model is based on the fundamental idea of comparing a star with a matching evolutionary track. This is O.K. if you base the theory on the BBT and you know for sure the age of the matching evolutionary stars. Unfortunately we also don't know for sure even the age of the Earth. So how can we set this kind of matching process???
With regards to the BBT – I fully agree with David A. Smith.

dlzc (David A. Smith): .... assuming they start with pure hydrogen, a resultant of the Big Bang. The "theory" compared against assumes eh star stars with pure hydrogen, and the star's composition is compared to a composition-with-age chart.

But what if they didn't start with pure Hydrogen??? What if it started differently??? How can we know for sure what is correctd theory???
With regards to Steve message -

Steve: The Big Bang is now so well supported by so many lines of evidence that using it as a constraint on star ages is justified…
I suppose the Big Bang model could turn out to be wrong (though whatever
replaces it will have to look a lot like the Big Bang through the last 10 or so Gyr), but Steady State is out.

Hence, In one hand you write that just by setting the BBT as the mainstream of the modern science, it is justified to use it for star age measurements, So it is O.K. for you to use the BBT in a circular argument. In the other hand you mention that there is a chance (even a very small chance...) that the BBT will be turned out wrong.
Therefore, I strongly suggest that the science should not verify and set the age measurements based on BBT & its supportive theories!!!
We must find a correct process for age measurments!!!

David Levy wrote:
Thanks All

- David: Hence, for example - if it took the Earth 5 Billion year to
cool down the surface and set the first solid rocks and ground, than
by definition its age is 5 + 4.5 Billion years. Do you agree? -
- Yousuf: In principle that could be true, but in practice the oldest
pieces of
space rock we have ever observed in the solar system date to 4.55by.
- - David: This is a critical issue. The Earth or the moon could be a
molten ball on their birthday as follow: "Our planet was probably
still mostly a molten ball of rock, and the impact of the Moon did
little to change that". Hence, there is a chance that it took some
time for the Erath & the Moon to cool down and set the first solid
rocks. Therefore, by adding all the factors, there might be an error
in their age estimation... This might lead us to an error in the age
estimation of the solar system and so on. -
- Martin: The age of the oldest terrestrial rocks corroborates the
age of the solar system from meteorites (by being less, as
expected), but is not used to determine the solar system age.
dlzc (David A. Smith): .... assuming they start with pure hydrogen,
a resultant of the Big Bang. The "theory" compared against assumes
eh star stars with pure hydrogen, and the star's composition is
compared to a composition-with-age chart. -
So yes, the age of the oldest meteorites is clear. But, this can only
give us the minimum lever of the Solar system age.
By : http://www4.nau.edu/insidenau/bumps/...meteorite.html
"Their findings dated the piece at 4.568 billion years old, or nearly
2 million years older than the oldest materials found in other
meteorites… For nearly 10 years they have classified and studied
more than 1,000 meteorites, which include 22 lunar and 14 Martian
meteorites, and have published dozens of research papers on the
topic." Out of the Billion over Billion meteorites & Asteroids we
have verified the age of about 1000. We have found that the oldest is
about 4.568 Billion years old. Does it mean that there is no
possibility that there are some others which might be older???
The upper lever of the solar age can't be determined by only 1000 pcs
which we have in our hand. Therefore it can only give us an indication
that the lower limit age of the solar system or even the Earth is
4.568 billion years.
With Regards to the Earth – Yes, we must measure the age of the
"oldest terrestrial rocks". Unfortunately, as the petroleum is located
deep in the ground, it's quite clear that the majority of the oldest
terrestrial rocks are located today deep in the ground. As over 70% of
the Earth is cover with Oceans, then, there is a chance that there is
no access today to the real oldest terrestrial rocks. Therefore, the
rocks which are considered to be the oldest terrestrial rocks, give
us an indication for the Min. age of the Earth.
Even so, those oldest terrestrial rocks might be molten lava on the
day that the Earth was born. We don't know for sure how long it took
for the Earth to cool down and set the first solid rock. Therefore,
even those achievable oldest terrestrial rocks can't give an
indication for the real age of the Earth.
- David: So, the star age measurements is based on the BBT.
Therefore, if the science is using the current star age measurements
to confirm the BBT
then by definition it sounds like circular argument. -
- Mike: No, you misunderstand this. Star ages are based on
observations of stars, and comparisons with the theory of stellar
structure and evolution. -
By Wiki – "Stellar populations are categorized as I, II, and
III… Soon after the Big Bang, without metals, it is believed
that only stars with masses hundreds of times that of the Sun could be
formed;
Hence – the whole Idea of the stellar population is based on the
BBT. Therefore, by definition this is a circular argument!!!

No, the idea of stellar populations originated with Walter Baade's
observations comparing young disk populations in spiral galaxies with old
populations in the halo. These ideas were presented long before anyone
proposed the Big Bang Theory.

The idea of an even older "Pop III" was proposed much later.

Even so, there are some other issues as follow:
By Wiki - http://en.wikipedia.org/wiki/Stellar_evolution
"A stellar evolutionary model is a mathematical model that can be used
to compute the evolutionary phases of a star from its formation until
it becomes a remnant... Accurate models can be used to estimate the
current age of a star by comparing its physical properties with those
of stars along a matching evolutionary track.[26]"
Hence – the stellar evaluation model is based on the fundamental
idea of comparing a star with a matching evolutionary track. This is
O.K. if you base the theory on the BBT and you know for sure the age
of the matching evolutionary stars. Unfortunately we also don't know
for sure even the age of the Earth. So how can we set this kind of
matching process???

You look up all the gas laws, including how to deal with degenerate gases,
then you add knowledge of nuclear reactions from laboratory experiments, for
which published reaction rates exist, then you make a numerical model of a
star using gravitation and thermodymamics, and calculate what such a star
would look like as it ages. A good computer programmed for numerical
calculations of stellar structure including time steps is needed. You then
compare the theory and observation and look for a match. If a set of models
of a particular age matched the distribution of star colours and magnitudes
in a cluster and then for a set of models then you can determine the age of
the cluster. BBT absolutely does not come into it.

With regards to the BBT – I fully agree with David A. Smith.
- dlzc (David A. Smith): .... assuming they start with pure
hydrogen, a resultant of the Big Bang. The "theory" compared against
assumes eh star stars with pure hydrogen, and the star's composition
is compared to a composition-with-age chart. -
But what if they didn't start with pure Hydrogen??? What if it
started differently??? How can we know for sure what is correctd
theory???
With regards to Steve message -
- Steve: The Big Bang is now so well supported by so many lines of
evidence that using it as a constraint on star ages is
justified… I suppose the Big Bang model could turn out to be
wrong (though whatever replaces it will have to look a lot like the
Big Bang through the last 10 or so Gyr), but Steady State is out. -
Hence, In one hand you write that just by setting the BBT as the
mainstream of the modern science, it is justified to use it for star
age measurements, So it is O.K. for you to use the BBT in a circular
argument. In the other hand you mention that there is a chance (even a
very small chance...) that the BBT will be turned out wrong.
Therefore, I strongly suggest that the science should not verify and
set the age measurements based on BBT & its supportive theories!!!
We must find a correct process for age measurments!!!

Too many exclamation marks. Calm down and think.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

In article ,
"Mike Dworetsky" wrote:

Odysseus wrote:

snip

If earlier stars were bigger than those of later generations, as has
been suggested, one wouldn't expect many of them to be left in a
non-degenerate state, having made their trips off the main sequence
eons before the Sun was formed. Unless their evolution takes a
different course from higher-metallicity stars, any of Pop. III still
surviving would be small, long-lived dwarfs. It's only in recent

Yes, this is correct, and the search goes on. But so far, nothing like a
Pop III dwarf star has been found. Some stars of astonishingly low metal
abundance have been found (10^-3 to 10^-4 of solar abundances, IIRC). For
various reasons involving the dynamics of older stars, the search is usually
conducted by examining stars in the galactic halo.

years we've been able to detect or characterize faint red dwarfs
beyond our immediate neighbourhood (lists of the N nearest stars are
still getting updated every couple of years, where N is a
surprisingly small number), which may not be representative of the
Galaxy as a whole.

Arguments that we do not see Pop III stars because we happen to be located
in a special area of the Galaxy where they do not occur, suffer from the
violation of the Principle of Mediocrity, or the Copernican Principle, which
says that we are not located in a special or privileged place.

To claim it is true requires special pleading.

JFTR I wasn't claiming anything of the kind, but pointing out that our
observational knowledge of such objects is comparatively poor, and -- as
your mention of the galactic halo suggests -- the oldest generation may
be less likely to be found here in the galactic disc than elsewhere, for
reasons having nothing to do with 'exceptionalism' but with the way the
structure of the Galaxy has evolved. We're also poorly placed to spot
faint, cool objects near the hub, for example, because of the dust and
gas in the intervening arms -- nothing special to the solar system
itself, but a fact of life anywhere in the mid-outer to outer portions
of the disc.

--
Odysseus

Odysseus wrote:
In article ,
"Mike Dworetsky" wrote:

Odysseus wrote:

snip

If earlier stars were bigger than those of later generations, as has
been suggested, one wouldn't expect many of them to be left in a
non-degenerate state, having made their trips off the main sequence
eons before the Sun was formed. Unless their evolution takes a
different course from higher-metallicity stars, any of Pop. III
still surviving would be small, long-lived dwarfs. It's only in
recent

Yes, this is correct, and the search goes on. But so far, nothing
like a Pop III dwarf star has been found. Some stars of
astonishingly low metal abundance have been found (10^-3 to 10^-4 of
solar abundances, IIRC). For various reasons involving the dynamics
of older stars, the search is usually conducted by examining stars
in the galactic halo.

years we've been able to detect or characterize faint red dwarfs
beyond our immediate neighbourhood (lists of the N nearest stars are
still getting updated every couple of years, where N is a
surprisingly small number), which may not be representative of the
Galaxy as a whole.

Arguments that we do not see Pop III stars because we happen to be
located in a special area of the Galaxy where they do not occur,
suffer from the violation of the Principle of Mediocrity, or the
Copernican Principle, which says that we are not located in a
special or privileged place.

To claim it is true requires special pleading.

JFTR I wasn't claiming anything of the kind, but pointing out that our
observational knowledge of such objects is comparatively poor, and --
as your mention of the galactic halo suggests -- the oldest
generation may be less likely to be found here in the galactic disc
than elsewhere, for reasons having nothing to do with
'exceptionalism' but with the way the structure of the Galaxy has
evolved. We're also poorly placed to spot faint, cool objects near
the hub, for example, because of the dust and gas in the intervening
arms -- nothing special to the solar system itself, but a fact of
life anywhere in the mid-outer to outer portions of the disc.

I'm happy to accept your explanation. The wording of the last sentence
suggested my interpretation.

One point worth making is that the halo is a preferred searching ground in
part because halo stars are known to be preferentially of low metal
abundance. On the other hand, the galactic hub is generally richer in heavy
elements than the part of the galactic plane near the Sun. What you say is
possible, but I think unlikely.

Any remaining Pop III stars would be around 1/2 solar mass or less, hence
very faint intrinsically, making the search difficult. There have been
theoretical discussions of why such small stars might never have formed, but
I don't know if that is still an accepted view.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

SW One would have to ask, though, if low-metal stars are
SW forming now, why don't we see any low-metal gas?

In article ,
dlzc writes:
With space filled (in some sense) with ionized hydrogen and oxygen
missing 5 electrons, how would we know if some of the hydrogen was
new?

What gas has oxygen missing five electrons? More to the point, I
thought you were suggesting stars forming out of "new hydrogen" that
lacks metals. If that's happening, where is this low-metallicity
gas, and why don't we see it?

SW As has been written in this thread, globular
SW clusters are assumed to be old because of their HR diagrams.

Which was in turn, scaled in light of a Big Bang.

Why do you continue to assert that? As has been explained _multiple_
times in this thread, the cluster ages are based entirely on atomic
physics. In other words, we observe a cluster with a maximum main
sequence luminosity of, say, half a solar luminosity. Via stellar
evolution theory (detailed computer models), stars of that luminosity
have about 0.8 solar masses and take about 9 Gyr to evolve off the
main sequence. (I'm making up all the numbers, but they are probably
in the ballpark.) Thus the cluster is 9 Gyr old. This has nothing
whatever to do with the Big Bang.

The models might, of course, be wrong (though they are well tested on
the Sun, for example, and other stars for which one can measure
independent masses or structures), but there is nothing circular
about the reasoning.

Or the bullet cluster, where "all" the dust is removed, and we can
see none of the stars.

You have some strange misconception, but I'm baffled by what it could
be. Are you equating "dust" with "dark matter?" Dust is dark in
visible light, but it isn't what is meant by "dark matter." In
particular, most dust glows quite nicely in the infrared, and in any
case there are direct methods of detecting dust. In all cases I can
think of, it is a tiny fraction of the mass.

Interpretation of the Bullet Cluster has nothing to do with dust.

When yo look at a nebula, say the ring nebula, what is its most
prominent feature, the white dwarf, or the nebula?

What does this have to do with the light from galaxies? A gaseous
nebula is an extended source of light. Sizes run from perhaps a
tenth of a parsec to tens of parsecs. A collection of stars, if you
have high enough resolution, can be separated into individual
objects. Separations are typically a parsec near the Sun and
somewhat smaller in globular clusters or galactic cores. (If you
have resolution 7 or 8 orders of magnitude better than a parsec, you
could resolve the stellar surfaces themselves, but that's quite a
leap from resolving the cluster or galaxy.)

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