Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V11_3/V11_368.TXT

Internet Message Format | 1991-07-08 | 21KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/[e-mail] (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests)
          ID </afs/andrew.cmu.edu/usr1/ota/Mailbox/YaFEelK00VcJM:CU5v>;
          Mon,  7 May 90 01:42:10 -0400 (EDT)
Message-ID: <[e-mail]>
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Mon,  7 May 90 01:41:39 -0400 (EDT)
Subject: SPACE Digest V11 #368

SPACE Digest                                     Volume 11 : Issue 368

Today's Topics:
                Re: Our galaxy
           Re: Voyager Confirms Relativity
           Re: Voyager Confirms Relativity
            Re: Re: Dyson spheres?
      Re: Soviet VENERA Landers on the Surface of Venus.
           Re: Voyager Confirms Relativity
              Re: Fermi Paradox
           Re: Voyager Confirms Relativity
----------------------------------------------------------------------

Date: 6 May 90 19:42:51 GMT
From: philmtl!philabs!briar![e-mail]  (Robert Casey)
Subject: Re: Our galaxy

In article <[e-mail]> [e-mail] (Avery Ray Colter) writes:
>
>I kinda like "Milky Way".

I wonder if the Milky way was ever assigned a NGC number?  Like NGC1?  What is
the numbering scheme behind the NGC numbers, anyway?  Based on position in the
sky? or random?  If it is based on the position in the sky, I suppose the
Milky Way's "position" is where its center is in the sky.
------------------------------------------------------------------------------
"Don't try to live your life in one day"  Howard Jones

------------------------------

Date: 6 May 90 20:42:58 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!qucdn![e-mail]  (Arnold G. Gill)
Subject: Re: Voyager Confirms Relativity

In article <[e-mail]>, [e-mail] (Gordon
Booman) says:
>
>someone can illuminate me.
>
>Take a black hole.  Throw gas at it.  The gas falls in, heats up, at some
>point fuses, emmitting tons of energy.  If this happens in a thin layer, the
>radiation would have a nicely defined and highly red-shifted spectrum.  You
>can make it as red-shifted as you like by letting the layer be at the
>appropriate height above the event horizon.  OK?
>
>Quasars are just big black holes at normal galactic distances with thin fusing
>layers.  Mystery solved. :-)  Oh allright, why fusing in a layer, etc. but
>still, it's a **smaller** mystery now.  At least, closer :-)
>
>OK, why not?
     Then why is a specific quasar always seen at the same value for z?  Why
should the fusing layer be only found at a specific distance down the gravity
well?  You end up with a lot more questions than you are answering.
-------
 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
|  Arnold Gill                        |                                     |
|  Queen's University at Kingston     |     If I hadn't wanted it heard,    |
|  BITNET   : gilla@qucdn             |       I wouldn't have said it.      |
|  X-400    : [e-mail]  |                                     |
|  INTERNET : [e-mail]  |                                     |
 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

------------------------------

Date: 6 May 90 14:15:30 GMT
From: mcsun!hp4nl!philapd!ssp17![e-mail]  (Gordon Booman)
Subject: Re: Voyager Confirms Relativity

In article <[e-mail]> [e-mail] (Ron Baalke) writes:
>VOYAGER CONFIRMS RELATIVITY
>
>When photons escape the gravity of a massive object, they lose energy and
>their wavelengths increase correspondingly.  Such a gravitational redshift,
>amounting to just one part in a billion or so, was measured by Timothy P.
>Krisher and colleagues at NASA's Jet Propulsion Laboratory.  They used
>tracking data from Voyager 1's flyby of Saturn in 1980.
>...

OK, this reminds me of something I've been wondering about for years.  Perhaps
someone can illuminate me.

Take a black hole.  Throw gas at it.  The gas falls in, heats up, at some
point fuses, emmitting tons of energy.  If this happens in a thin layer, the
radiation would have a nicely defined and highly red-shifted spectrum.  You
can make it as red-shifted as you like by letting the layer be at the
appropriate height above the event horizon.  OK?

So why do we believe quasars are so far away?  They vary too fast to be as big
as they seemingly must be - to be so bright as they seemingly must be - to be
as red-shifted as they **are**.  There are quasars that seem to be connected to
galaxies that are much closer (i.e., have much smaller red-shift).  Two reasons
to believe that they're closer than they seem.  What evidence is there that
quasars really are as far off as their red-shifts indicate?

Quasars are just big black holes at normal galactic distances with thin fusing
layers.  Mystery solved. :-)  Oh allright, why fusing in a layer, etc. but
still, it's a **smaller** mystery now.  At least, closer :-)

OK, why not?
--
Gordon Booman SSP/v2b25  Philips TDS Apeldoorn, The Netherlands  [phone]
domain: [e-mail]             uucp:  ...!hp4nl!philapd!gordon

------------------------------

Date: 5 May 90 21:40:06 GMT
From: eru!luth!sunic!mcsun!ukc!tcdcs!swift.cs.tcd.ie!maths.tcd.ie![e-mail]  (Derek Bell)
Subject: Re: Re: Dyson spheres?


        Sorry if this has already been answered, but wouldn't the
presence of planets disrupt the orbits of the bodies making up the "shell"
of the sphere? (Or do you take them apart too?) What're the most serious
theoretical problems?
--
Derek Bell
[e-mail] [e-mail] [e-mail]

------------------------------

Date: 5 May 90 19:04:39 GMT
From: van-bc!oneb!iear![e-mail]  (Charlie Figura)
Subject: Re: Soviet VENERA Landers on the Surface of Venus.

In article <[e-mail]> [e-mail] writes:
>        VEGA 2, in tandem with VEGA 1, delivered the first balloon-
>    borne payloads into the thick Venusian atmosphere in June of 1985.
>    The probes also deposited two landers on the surface, and then
>    flew on for the first spacecraft encounters with Comet Halley in
>    March of 1986.  VEGA is the combined names of VENERA and HALLEY
>    (Halley in Russian is Gallei; there is no letter H in the Russian
>    alphabet).
>        Incidentally, the VEGA 2 lander survived on Venus' surface
>    for only 57 minutes.

    Okay, my source is a bit screwey....
Upon further analysis, I see that the atmospheric balloon
returned data for 46 hours before succumbing to the heat/pressure/
corrosion.
    The source (an astronomy textbook, blek) remarks that
Venera 16 deposited the lander & balloon, then was renamed
Vega 2, and continued to Halley's comet... It says the same
for Venera 5 & Vega 1.


    Still, it doesnt speak much for manned landers on Venus...

    (I'd rather forget my girlfriend's birthday....  :-(

------------------------------------------------------------
Charlie Figura    --  (cholly figura-Daemon) | "Can you sing?"
 ------- [e-mail] ---------  | "A little....
 "So *WHAT* if I'm a physics major??!?!?"  | ..I can dance."
------------------------------------------------------------

------------------------------

Date: 6 May 90 21:45:52 GMT
From: uoft02.utoledo.edu![e-mail]
Subject: Re: Voyager Confirms Relativity

In article <[e-mail]>, [e-mail] (Gordon Booman) writes:
> In article <[e-mail]> [e-mail] (Ron Baalke) writes:
>>VOYAGER CONFIRMS RELATIVITY
>>
>>When photons escape the gravity of a massive object, they lose energy and
>>their wavelengths increase correspondingly.  Such a gravitational redshift,
>>amounting to just one part in a billion or so, was measured by Timothy P.
>>Krisher and colleagues at NASA's Jet Propulsion Laboratory.  They used
>>tracking data from Voyager 1's flyby of Saturn in 1980.
>>...
>
> OK, this reminds me of something I've been wondering about for years.  Perhaps
> someone can illuminate me.
>
> Take a black hole.  Throw gas at it.  The gas falls in, heats up, at some
> point fuses, emmitting tons of energy.  If this happens in a thin layer, the
> radiation would have a nicely defined and highly red-shifted spectrum.  You
> can make it as red-shifted as you like by letting the layer be at the
> appropriate height above the event horizon.  OK?
>
> So why do we believe quasars are so far away?  They vary too fast to be as big
> as they seemingly must be - to be so bright as they seemingly must be - to be
> as red-shifted as they **are**.  There are quasars that seem to be connected to
> galaxies that are much closer (i.e., have much smaller red-shift).  Two reasons
> to believe that they're closer than they seem.  What evidence is there that
> quasars really are as far off as their red-shifts indicate?
>
> Quasars are just big black holes at normal galactic distances with thin fusing
> layers.  Mystery solved. :-)  Oh allright, why fusing in a layer, etc. but
> still, it's a **smaller** mystery now.  At least, closer :-)
>
> OK, why not?
> --
> Gordon Booman SSP/v2b25  Philips TDS Apeldoorn, The Netherlands  [phone]
> domain: [e-mail]             uucp:  ...!hp4nl!philapd!gordon


First of all the material in the accretion disk is not "fussing" since the
temperatures never get great enough for nuclear reactions.  The spectra
of black holes and quasars (including the whole E-M spectrum) can be modeled
reasonabaly well with blackbody energy distributions.  In the case of
quasars you need more than one BB which represent the temperature gradient
in the disk.

As for confirming the "cosmoligical redshift" that is still a hot topic.
I am not an expert on the subject.  If I remember there were some arguements
awhile back showing that at most one can get a grav redshift of about 0.62
while there are many quasars with z=1-3.  Plus there is other evidence like
the lyman alpha forest.  This is produced by light being absorbed by diffuse
clouds of gas between the quasar and the observer.  The absorption will
give the redshift of the cloud which is usually very large but less than
the quasar.  That cannot be explained with the grav redshift.  Gravitational
lensing also indicates that the quasars are trully very distant.  I am
sure there is more evidence.

Distances to some of the closer active galaxies have been determined reasonably
well and they seem consistent with their redshifts.

I would rather see confirmation that black holes exist.  Recent work with
quantum gravity suggest such critters may not even be possible (but there
still could be superdense solutions).



Bob Dempsey
Ritter Observatory

------------------------------

Date: 6 May 90 05:50:24 GMT
From: philmtl!philabs!briar![e-mail]  (Robert Casey)
Subject: Re: Fermi Paradox

In article <[e-mail]6> [e-mail] writes:
>
>     So now we have numbers (however imprecise) for Mrock and Mgas. If we
>say that the Earth is an "average" rocky planet, and that the mass of the
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If you look at the sizes of all the rocky (and icy) planets and moons in the
solar system, you'll notice that Earth is the largest.  So, the Earth is
larger than 'average'.  If this means anything is another question.

------------------------------

Date: 6 May 90 21:12:47 GMT
From: pacific.mps.ohio-state.edu!ohstpy![e-mail]
Subject: Re: Voyager Confirms Relativity

In article <[e-mail]>, [e-mail] (Gordon Booman) writes:
> In article <[e-mail]> [e-mail] (Ron Baalke) writes:
>>VOYAGER CONFIRMS RELATIVITY
>>
>> [deleted comments about confirmation of gravitational redshift predictions
>>  of GR using Voyager 1 tracking data]
>
> OK, this reminds me of something I've been wondering about for years.  Perhaps
> someone can illuminate me.

  Hang on, let me get my flashlight  :-)

> Take a black hole.  Throw gas at it.  The gas falls in, heats up, at some
> point fuses, emmitting tons of energy.  If this happens in a thin layer, the
> radiation would have a nicely defined and highly red-shifted spectrum.  You
> can make it as red-shifted as you like by letting the layer be at the
> appropriate height above the event horizon.  OK?

  Not OK.  The gas doesn't emit because it is undergoing thermonuclear fusion.
It emits because it is hot, but not quite *that* hot.  There have been models
which suggests that low-level thermonuclear processing might go on in massive
accretion disks around black holes (leading, among other things to Lithium
production, for example the work described in the Ph.D. dissertation of Li
Ping Jin at UChicago), but it contributes very little to the total energy
output of such systems.  The principal energy source even in these models is
still the release of gravitational energy as gas falls down the hole.

  The principal emission we see comes from regions far cooler and of far lower
density than required for thermonuclear reactions to occur.

  The emission-line spectrum we observe seems to arise from a rather large
volume, a few tens of light days across at least, as shown by time variability
studies.  In some well-observed objects, the central continuum source varies a
great deal, often attended by variations in the broadest emission-lines (these
lines are principally due to ionized Hydrogen) while relatively narrow lines
(say, lines of doubly ionized Oxygen) do not vary at all on any observed
timescale.  The narrow-line emitting regions must therefore be quite far away.
In some of the nearest objects, this narrow-line emitting gas has been
observed to extend as much as a few thousand parsecs, but most of the
narrow-line emitting volume seems confined to the few hundred parsec scale.
That the broad and narrow lines must arise from physically distinct regions is
most convincingly shown by details of the emission-line spectrum which seem to
require density stratification over about 5-7 orders of magnitude.

   In addition, in the best studied objects, changes in the line-emitting
regions are observed to *lag* behind changes in the central ionizing continuum
source brightness by a few days or so.  The response delay is due to light
travel time, as gas in the line-emitting regions should respond in a matter of
seconds to changes in the amount of ionizing radiation hitting them.  This
suggests in the highest density (broad) line-emitting regions, source sizes of
order a few light days.  The data are not yet good enough to contrain the
source geometry, but some models (like spherically symmetric shells) seem to
be in deep trouble.

> So why do we believe quasars are so far away?  They vary too fast to be as big
> as they seemingly must be - to be so bright as they seemingly must be - to be
> as red-shifted as they **are**.  There are quasars that seem to be connected
> to
> galaxies that are much closer (i.e., have much smaller red-shift).  Two
> reasons
> to believe that they're closer than they seem.  What evidence is there that
> quasars really are as far off as their red-shifts indicate?
>
> Quasars are just big black holes at normal galactic distances with thin fusing
> layers.  Mystery solved. :-)  Oh allright, why fusing in a layer, etc. but
> still, it's a **smaller** mystery now.  At least, closer :-)

  A very large body of evidence, Arp and Burbidge's "exceptions" not
withstanding, exists which establishes the case that quasars and related
phenomena are at cosmological distances.  A full summary would be a very long
review article, so I'll just address one of your points.

> OK, why not?

Gravitational redshift doesn't work - even if you have reasonably large
emitting volumes (much less the thin emitting layer you suggest, which simply
isn't remotely consistent with the body of data on quasars).

It works like this (arguments are originally due to Maarten Schmidt):

   In the spectra of quasars we observe bright, broad emission-lines of
Hydrogen and other elements.  At the telescope, we can measure a flux for the
Hydrogen-Beta line (for example) from a given quasar at some unknown distance.
The observed flux is, afterall, simply the number of H-beta photons - however
redshifted - entering the our spectrograph.  This gives us our first
"observable."  The second is the redshift we measures.  The quasar distance is
unknown.

   At the source, the intrinsic brightness of the H-beta emission-line region
is determined by the temperature and density of the line-emitting gas, and on
the total volume of the line-emitting region.  We can estimate the density and
temperature of the line-emitting gas using reasonably well-understood
diagnostics from the quasar spectrum.  The range of "derived" temperature and
density is fairly small compared to other observed (or derived) properties of
quasars, so in a sense, the H-beta emission-line flux we observe on earth
depends to a good approximation on the volume of the emitting region and the
distance to the quasar.  Thus, following Schmidt, we can write:

      Flux(H-beta) ~ V/D^2

where V is the volume of the line emitting region, and D is the distance to
the quasar.  Since Flux(H-beta) is an observable, for a given quasar, the
quantity V/D^2 is a constant, INDEPENDENT OF THE REDSHIFT MECHANISM.

   The gravitational redshift from a massive object is (to lowest order)
proportional to M/R, where M is the source mass, and R is distance of the
emitting-line region from the source size.  Thus, to get large gravitatonal
redshifts, you need either large masses or small emitting-region radii. Thus,
for a given mass and observed redshift, if we assume that the redshift arises
entirely due to a gravitational redshift, then we may estimate the size of the
emitting volume, V.  The fact that the gravitational redshift scales like M/R
tells us that larger gravitational redshifts require proportionally smaller
emitting volumes.  It is easy to show that the required emitting-region volume
is inversely proportional to the cube of the gravitational redshift for a
given mass.

   A smaller emitting volume implies that the intrinsic brightness of the
H-beta line-emitting region is proportionally smaller.  Since the observed
H-beta line-flux of the quasar is inversely proportional to the square of its
distance, this means that the quasar must be that much closer to us.  For
example, if you have to shrink the emitting volume by a factor of 2, you must
move the quasar 4 times closer to get the same observed H-beta emission-line
flux.

   For example, Schmidt picked the quasar 3C48, with a redshift of 0.37.  If
we assume 3C48 has a mass of 1 solar mass, and that the observed redshift is a
pure gravitational redshift (no cosmology), then to produce the observed
H-beta flux, 3C48 would be at a distance of about 10 km.  For masses of order
10^11 solar masses (about the mass of the Milky Way), the distance would be
about 10 kpc (kiloparsecs), still within the effective confines of our own
galaxy.  This is bad news, as the gravitational effects of such a massive
object right on top of the Milky Way would be extreme, and are yet unobserved.
Note also, this was for just ONE quasar, there are thousands catalogued.

   We now know of quasars with redshifts as high as 4.7, which means even more
trouble (you can easily work out from the arguments above that for a given
quasar Mass and flux of H-beta, the inferred distance for a pure gravitational
redshift is inversely proportional to the 3/2 power of the observed redshift).

   The bottom line is that having a purely (or even largely) gravitational
redshift for quasars results in absurd consequences.  The "alternatives"
required by the assertions by Arp and Burbidge (and collaborators) that the
quasar redshift is non-cosmological depend not on invoking the gravitational
redshift, but on some unspecified "new physics."  They have yet to propose a
self-consistent model for the observed large redshifts that explains other
observed properties of these objects.   Apparent bridges between low redshift
galaxies and high-redshift quasars not withstanding (there are very few good
examples), the non-cosmological redshift picture seems to be quickly loosing
ground.

------------------------------

End of SPACE Digest V11 #368
*******************