Still lower noise radio astronomy (was: low-noise amplifiers for radio astronomy )

John (Liberty) Bell wrote:
Joseph Lazio wrote:

I've posted it before, but it might be useful to
post again this link to a stellar evolution
simulation, URL:
http://www.mhhe.com/physsci/astronom.../Hr/frame.html .

This applet does not seem to give credible results.

Try making sure you are doing a VALID test before
dismissing a well accepted tool whose output is
inconvenient to your arguments.

Setting the star's mass to that of the Sun gives
an initial luminosity of 1.72 times the Sun's,
and after 4.8 billion years (now) this rises to 5
times.

Ummm, the sun's mass _now_ wouldn't be the correct
mass to stick in for "the sun at birth", nor does a
star "poof" into existence; there has to be a
period when fusion has begun but emitted energy is
too low to sweep away gas and so mass is still
accumulating. Simplistic tests don't convey much.

Last time I checked the Sun was not 5 times as
bright as it is.

Try finding out what the correct starting figure is,
or work backwards from the current state to see what
the sun's mass _was_ at birth.

I am, therefore, disinclined to trust its figures
and timescales for the evolution of other stars.

You need to break your repeated habit of distrusting
what you don't understand.

When astronomers look at a group of stars, the
easiest thing to do is measure their color. The
"bluer" the color of the group of stars, the more
hot, young stars are in the group.

Agreed

Suppose one starts with a group of stars all born
at essentially the same time. In 0.01 Gyr, all
of the stars more massive than about 20 solar
masses will be gone, in 0.02 Gyr all of the stars
more massive than about 10 solar masses will be
gone,

Well, that certainly seems to rule out a
preponderance of such stars in the observed
galaxies. Assuming a typical galaxy of stars of ~
10^11 solar masses, and 1 month for the visibility
persistence of a supernova, that would work out at
> 40 supernovas simultaneously visible per
galaxy. That would have been noticed.

Sigh. Did you see the word "suppose"?

Did you understand *at all* that what was being done
for you was the presenting to you of an INTELLECTUAL
EXERCISE, and not an attempt to describe a real
situation in a real galaxy in the real universe?

Stars in galaxies are _not_ "born essentially at the
same time", they are born spread out across the life
of the galaxy from its birth until the galaxy runs
out of sufficient gas concentrations or triggering
events or both to foster star creation.

and in 0.1 Gyr, all of the stars more massive
than about 5 solar masses will be gone.

Ditto. That would work out to 16 supernovas
simultaneously visible per galaxy. That too would
have been noticed.

"Suppose" you take the time to understand what is
being said before you dismiss its applicability to
your claims.

The _point_ is that the light from "hot blue giant"
stars is _always_ going to be scarce, because even
though individually brilliant, they don't last long.

The clue is that if that light is particularly
deficient, you are learning something extra about
the unavailability or earlier superavailability of
one of "sufficient raw material for star birth"
and/or "sufficient triggering events for star birth"
and/or "sufficient temporal and spatial coincidence
of the prior two items".

Heck, wait a full 1 Gyr and all of the stars more
massive than *2 solar masses* will be gone.

Ditto. Even that appears to work out as 4
supernovas simultaneously visible per galaxy. That
too would have been noticed.

*Shudder*

Sure it would, *IF* all the stars in the life of the
galaxy were created at the inception of the galaxy
*AND* all the galaxies were created at just the
right time for that concentration of brand new stars
to be what we're seeing now.

Sigh.

People type to you for some other reason than to
elicit your unthinking dismissal of what they've
said. Responses like this one of yours prolong
discussions to no avail. A single point needs to be
explained over and over to someone who refuses to
consider responses until overwhelmed by their
accumulation in bulk from multiple correspondents.

Rather than dismissing science and math, try to do
something useful: INVENT a mechanism that can
reconcile what is seen and known locally with what
we see in these ancient galaxies.

1) Do shockwaves somehow (massive black hole jets
maybe) travel _between_ those antique and so more
closely spaced galaxies, using up the available raw
material for stars quickly?

2) Are early galaxies internally "clumpier", perhaps
due to more frequent galaxy collisions and near
misses among more closely spaced galaxies [or
minigalaxies too small to be seen from here], so
that cascading star creation events eat
star-engendering mass into stars much much faster?

3) Do those early galaxies start life on average
significantly smaller in diameter for the same or
greater mass, due to the intermediate scale texture
of the antique universe being "tighter", so, again,
that star stuff gets consumed faster than in
recent universe galaxies that start on average at
larger diameters and smaller masses?

4) Were tiny galaxies more numerous in the ancient
universe, due to the greater intermediate scale
density of raw material in a smaller universe? Could
those galaxies exist/have existed but (now) be
unnoticed from this distance, and be having lots of
"spooky effects like random birdshot" whizzing
through and among the galaxies we _can_ see?

5) Is there some single, conservative change in the
very nature of space and/or time between the ancient
universe and now that would explain what we see?

[None of that needs to make a speck of sense, I'm
not one of those who can "do the math".]

There's lots of room for speculation, expecially for
the speculation that turns out to have explanatory
power, but not much room for letting laziness make
you cause yourself to avoid analyzing facts
furnished to you that distress you, in these
discussions.

FWIW

xanthian.

John (Liberty) Bell wrote:
Joseph Lazio wrote:

Suppose one starts with a group of stars all born at essentially the
same time. In 0.01 Gyr, all of the stars more massive than about 20
solar masses will be gone, in 0.02 Gyr all of the stars more massive
than about 10 solar masses will be gone,

Well, that certainly seems to rule out a preponderance of such stars
in the observed galaxies. Assuming a typical galaxy of stars of ~
10^11 solar masses, and 1 month for the visibility persistence of a
supernova, that would work out at 40 supernovas simultaneously
visible per galaxy. That would have been noticed.

and in 0.1 Gyr, all of the
stars more massive than about 5 solar masses will be gone.

Ditto. That would work out to 16 supernovas simultaneously visible
per galaxy. That too would have been noticed.

Heck, wait
a full 1 Gyr and all of the stars more massive than *2 solar masses*
will be gone.

Ditto. Even that appears to work out as 4 supernovas simultaneously
visible per galaxy. That too should have been noticed.

Incidentally, the above figure appears to hit or surpass the lowest
limit on the rate of supernovas required to explain galaxy
observations at ~ 3 Gyr. These require stars constructed from material
that has passed through "repeated" supernova stages, to explain
percentages of matter beyond iron. Even if we assume this merely means
just over 2 supernovas per star mass, over that timespan, that still
works out at~ 2 x 10^11 / 2 x 10^9 = 100 Sun masses of supernova per
galaxy per year.

Consequently, it still seems to me that we should see something like
commensurate light from supernovas as from galaxies, at high z, if
galactic evolution is to fit comfortably into the alloted timespan.

Since others here seem quite complacent about this timespan, I presume
I must be missing something that astronomers know.

Can anyone tell me what it is?


John Bell
(Change John to Liberty to bypass anti-spam email filter)

Joseph Lazio wrote:
"J(B" == John (Liberty) Bell writes:

JB Joseph Lazio wrote:
I've posted it before, but it might be useful to post again this
link to a stellar evolution simulation, URL:
http://www.mhhe.com/physsci/astronom.../Hr/frame.html .

JB This applet does not seem to give credible results. Setting the
JB star's mass to that of the Sun gives an initial luminosity of
JB 1.72 times the Sun's, and after 4.8 billion years (now) this
JB rises to 5 times.

Heh, yes, this does seem discrepant. I can only assume that the input
models must be too coarsely quantitized.

See Kent Paul Dolan's comment

JB Last time I checked the Sun was not 5 times as bright as it is.

Actually, since its start on the main sequence some 5 Gyr ago, the Sun
has increased its luminosity. The factor is not 5x, more like 50%.
This effect is known as the "faint early Sun paradox."

JB I am, therefore, disinclined to trust its figures and timescales
JB for the evolution of other stars.

While quantitatively apparently not accurate, the applet is still
qualitatively correct: More massive stars have shorter lifetimes, and
the more massive the star the shorter the lifetime.

The lifetime-mass relation for main-sequence stars scales something
like
(lifetime) \propto M^{-3} .
Crudely, we might expect a 10 solar mass star to have a lifetime some
1000 times shorter than that of the Sun, or about 0.01 Gyr. There are
published models that allow one to be more accurate, but the essential
point is unchanged.


When astronomers look at a group of stars, the easiest thing to do
is measure their color. The "bluer" the color of the group of
stars, the more hot, young stars are in the group.

JB Agreed

Suppose one starts with a group of stars all born at essentially
the same time. In 0.01 Gyr, all of the stars more massive than
about 20 solar masses will be gone, in 0.02 Gyr all of the stars
more massive than about 10 solar masses will be gone,

JB Well, that certainly seems to rule out a preponderance of such
JB stars in the observed galaxies. Assuming a typical galaxy of
JB stars of ~ 10^11 solar masses, and 1 month for the visibility
JB persistence of a supernova, that would work out at 40
JB supernovas simultaneously visible per galaxy. That would have
JB been noticed.

I'm not quite sure how you got to this result, but no matter.

It is quite simple. Assume mean star mass is 10 Sun, then star quantity
is 10^10 / galaxy.
Mean time to supernova is 2 x 10^7 years, hence 500 supernovas per
year.

As I
recall, the original issue was the apparent "maturity" of "young"
galaxies. The point I was making was that one could have a relatively
youthful group of stars, yet they would have a relatively late-type
color.

Yes, but as I pointed out in response to the moderator's note, I was
referring to heavy metal content, as opposed to colour=temperature=mass
(I mean here related to not equal).

Both your and that consideration appear to require a pretty spectacular
frequency of supernovas in early galaxies, especially since Kent Paul
Dolan's comment indicates that second generation stars would have
longer 'fuses'

See also my comment under new title "Galactic Evolution".

John Bell
(Change John to Liberty to bypass anti-spam email filter)

Sorry, in my just sent post I referred twice th the posting of Kent
Paul Dolan. I meant, of course, the more constructive posting of


John

Kent Paul Dolan wrote:
People type to you for some other reason than to
elicit your unthinking dismissal of what they've
said.

Your above rant appears to be based on your own misunderstanding of why
the 'tool' gave incorrect results, inflamed, no doubt, by your
annoyance over my showing on 26 September, that you were talking
nonsense then too.

See response of (Ted) @ richmond.edu for the real reason why the 'tool'
gave incorrect results.

I see little point in responding in further detail to your posting,
beyond giving this advice: if you are "not one of those who can 'do the
math'", then don't knock those who can (do the maths).

John Bell
(Change John to Liberty to bypass anti-spam email filter)

[Mod. note: quoted text trimmed. Please try to focus on science,
rather than personal history, otherwise I will have to start rejecting
posts again -- mjh]

"JB" == John (Liberty) Bell writes:

JB Joseph Lazio wrote:

Suppose one starts with a group of stars all born at
essentially the same time. In 0.01 Gyr, all of the stars more
massive than about 20 solar masses will be gone, in 0.02 Gyr all
of the stars more massive than about 10 solar masses will be
gone,

JB Well, that certainly seems to rule out a preponderance of such
JB stars in the observed galaxies. Assuming a typical galaxy of stars
JB of ~ 10^11 solar masses, and 1 month for the visibility
JB persistence of a supernova, that would work out at 40 supernovas
JB simultaneously visible per galaxy. That would have been noticed.

I'm not quite sure how you got to this result, but no matter.

JB It is quite simple. Assume mean star mass is 10 Sun, then star
JB quantity is 10^10 / galaxy. Mean time to supernova is 2 x 10^7
JB years, hence 500 supernovas per year.

May I gently suggest that a mean stellar mass of 10 solar masses seems
perhaps a bit high?


As I recall, the original issue was the apparent "maturity" of
"young" galaxies. The point I was making was that one could have a
relatively youthful group of stars, yet they would have a
relatively late-type color.

JB Yes, but as I pointed out in response to the moderator's note, I
JB was referring to heavy metal content, as opposed to
JB colour=temperature=mass (I mean here related to not equal).

*If* I've tracked down the appropriate press releases (by hunting back
through the Google archives to your previous posts), I still think
that my point stands. Hot stars burn out quickly, potentially leaving
one with a galaxy that looks fairly reddish, which often gets
translated in press releases to meaning "old" or "mature." The colors
may be reddish, and the stars "late-type," but that doesn't
necessarily mean "old." (Of course, "old" is itself a rather
non-specific term.)

As for the metal content, when hot stars run out of fuel, they
collapse and form supernovae, spraying metals all over their
surroundings.

By way of context, I'm not saying that there are not issues to
research or that we understand everything. However, I have yet to be
convinced that (1) the broad picture doesn't make sense, and (2) press
releases are the appropriate place to try to understand the details.


JB Both your and that consideration appear to require a pretty
JB spectacular frequency of supernovas in early galaxies, [...].

I think that's broadly consistent with what we know. Most
(essentially all) gamma-ray bursts (GRBs) are seen at relatively large
distances (z ~ 1). GRBs (at least the long variety) are thought to
be the result of the collapse of massive stars, and there are far more
GRBs in the distant Universe than locally.

Also, a quick ADS search finds a paper by Nugent et al., URL:
http://adsabs.harvard.edu/cgi-bin/np...pJ...645..841N
, which describes some of the difficulties in observing (at least a
class of) Type II supernovae. This suggests to me that high redshift
supernovae from early galaxies (e.g., at z ~ 3) are not detected
because we do not yet have the sensitivity, except when the supernovae
also produce GRBs.

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Sorry. In that last posting, I mixed up the names of two respondents,
which won't make sense if you check those postings.

John (Liberty) Bell wrote:
Joseph Lazio wrote:
"J(B" == John (Liberty) Bell writes:

JB Joseph Lazio wrote:
I've posted it before, but it might be useful to post again this
link to a stellar evolution simulation, URL:
http://www.mhhe.com/physsci/astronom.../Hr/frame.html .

JB This applet does not seem to give credible results. Setting the
JB star's mass to that of the Sun gives an initial luminosity of
JB 1.72 times the Sun's, and after 4.8 billion years (now) this
JB rises to 5 times.

Heh, yes, this does seem discrepant. I can only assume that the input
models must be too coarsely quantitized.

See Kent Paul Dolan's comment

This should read: See comment of

JB Last time I checked the Sun was not 5 times as bright as it is.

Actually, since its start on the main sequence some 5 Gyr ago, the Sun
has increased its luminosity. The factor is not 5x, more like 50%.
This effect is known as the "faint early Sun paradox."

JB I am, therefore, disinclined to trust its figures and timescales
JB for the evolution of other stars.

While quantitatively apparently not accurate, the applet is still
qualitatively correct: More massive stars have shorter lifetimes, and
the more massive the star the shorter the lifetime.

The lifetime-mass relation for main-sequence stars scales something
like
(lifetime) \propto M^{-3} .
Crudely, we might expect a 10 solar mass star to have a lifetime some
1000 times shorter than that of the Sun, or about 0.01 Gyr. There are
published models that allow one to be more accurate, but the essential
point is unchanged.


When astronomers look at a group of stars, the easiest thing to do
is measure their color. The "bluer" the color of the group of
stars, the more hot, young stars are in the group.

JB Agreed

Suppose one starts with a group of stars all born at essentially
the same time. In 0.01 Gyr, all of the stars more massive than
about 20 solar masses will be gone, in 0.02 Gyr all of the stars
more massive than about 10 solar masses will be gone,

JB Well, that certainly seems to rule out a preponderance of such
JB stars in the observed galaxies. Assuming a typical galaxy of
JB stars of ~ 10^11 solar masses, and 1 month for the visibility
JB persistence of a supernova, that would work out at 40
JB supernovas simultaneously visible per galaxy. That would have
JB been noticed.

I'm not quite sure how you got to this result, but no matter.

It is quite simple. Assume mean star mass is 10 Sun, then star quantity
is 10^10 / galaxy.
Mean time to supernova is 2 x 10^7 years, hence 500 supernovas per
year.

As I
recall, the original issue was the apparent "maturity" of "young"
galaxies. The point I was making was that one could have a relatively
youthful group of stars, yet they would have a relatively late-type
color.

Yes, but as I pointed out in response to the moderator's note, I was
referring to heavy metal content, as opposed to colour=temperature=mass
(I mean here related to not equal).

Both your and that consideration appear to require a pretty spectacular
frequency of supernovas in early galaxies, especially since Kent Paul
Dolan's comment

Again, this should read: 's comment

indicates that second generation stars would have
longer 'fuses'

See also my comment under new title "Galactic Evolution".

John Bell
(Change John to Liberty to bypass anti-spam email filter)

"John (Liberty) Bell" wrote in message
...
Sorry. In that last posting, I mixed up the names of two respondents,
which won't make sense if you check those postings.

John (Liberty) Bell wrote:
.....
See Kent Paul Dolan's comment

This should read: See comment of

Ted Bunn:

http://www.richmond.edu/~ebunn/

HTH
George

Joseph Lazio wrote:
"JB" == John (Liberty) Bell writes:

JB Joseph Lazio wrote:

Suppose one starts with a group of stars all born at
essentially the same time. In 0.01 Gyr, all of the stars more
massive than about 20 solar masses will be gone, in 0.02 Gyr all
of the stars more massive than about 10 solar masses will be
gone,

JB Well, that certainly seems to rule out a preponderance of such
JB stars in the observed galaxies. Assuming a typical galaxy of stars
JB of ~ 10^11 solar masses, and 1 month for the visibility
JB persistence of a supernova, that would work out at 40 supernovas
JB simultaneously visible per galaxy. That would have been noticed.

I'm not quite sure how you got to this result, but no matter.

JB It is quite simple. Assume mean star mass is 10 Sun, then star
JB quantity is 10^10 / galaxy. Mean time to supernova is 2 x 10^7
JB years, hence 500 supernovas per year.

May I gently suggest that a mean stellar mass of 10 solar masses seems
perhaps a bit high?

Certainly. But that is simply another reason for ruling out a
"preponderance" of such stars.

As I recall, the original issue was the apparent "maturity" of
"young" galaxies. The point I was making was that one could have a
relatively youthful group of stars, yet they would have a
relatively late-type color.

JB Yes, but as I pointed out in response to the moderator's note, I
JB was referring to heavy metal content, as opposed to
JB colour=temperature=mass (I mean here related to not equal).

*If* I've tracked down the appropriate press releases (by hunting back
through the Google archives to your previous posts), I still think
that my point stands. Hot stars burn out quickly, potentially leaving
one with a galaxy that looks fairly reddish, which often gets
translated in press releases to meaning "old" or "mature." The colors
may be reddish, and the stars "late-type," but that doesn't
necessarily mean "old." (Of course, "old" is itself a rather
non-specific term.)

I do understand what you are saying here (and have for some time).
The most relevant reference was
http://www.aip.org/enews/physnews/2004/split/668-1.html
particularly the last paragraph, which you cover below.

As for the metal content, when hot stars run out of fuel, they
collapse and form supernovae, spraying metals all over their
surroundings.

Agreed. The question I am asking is whether there are enough of them to
give the observed concentrations of heavy metals, at the observed z
shifts, in the timescales currently predicted by GR.

By way of context, I'm not saying that there are not issues to
research or that we understand everything. However, I have yet to be
convinced that (1) the broad picture doesn't make sense,

I would agree that the broad picture certainly does make sense. What I
am particularly interested in is whether the numbers really add up,
within the believed timescales. This is not because I am a Luddite. It
is because I am investigating a different relativistic field equation,
which, in addition to having other apparent advantages, also suggests
that timescales between high z epochs could be longer than established
GR theory predicts.

and (2) press
releases are the appropriate place to try to understand the details.

I would agree, but they at least provide a convenient starting point
for subsequent examinations. Unfortunately, the Gemini Deep Deep Survey
link from that particular press release (to the Gemini Observatory
website), no longer connects to anything.

JB Both your and that consideration appear to require a pretty
JB spectacular frequency of supernovas in early galaxies, [...].

I think that's broadly consistent with what we know. Most
(essentially all) gamma-ray bursts (GRBs) are seen at relatively large
distances (z ~ 1). GRBs (at least the long variety) are thought to
be the result of the collapse of massive stars, and there are far more
GRBs in the distant Universe than locally.

I would certainly hope so, at least qualitatively. Although we seem to
have additional temporal 'elbow room', it is not enough to allow
spectacularly different physics in the distant visible universe.

Also, a quick ADS search finds a paper by Nugent et al., URL:
http://adsabs.harvard.edu/cgi-bin/np...pJ...645..841N
, which describes some of the difficulties in observing (at least a
class of) Type II supernovae. This suggests to me that high redshift
supernovae from early galaxies (e.g., at z ~ 3) are not detected
because we do not yet have the sensitivity, except when the supernovae
also produce GRBs.

I certainly did not get that impression from the abstract.
They say this study is "based on five events at redshift up to
z~0.3" and conclude "thus demonstrating the feasibility of
measuring the expansion history."

Are you referring to a specific location within the paper itself?

John Bell
(Change John to Liberty to bypass anti-spam email filter)

John (Liberty) Bell wrote:
http://www.aip.org/enews/physnews/2004/split/668-1.html
Unfortunately, the Gemini Deep Deep Survey
link from that particular press release (to the Gemini Observatory
website), no longer connects to anything.

*shudder*

http://www.google.com/search?q=%22Ge...Deep+Survey%22

==

http://www.gemini.edu/index.php?opti...ask=view&id=18

xanthian.