mullen@ecsvax.UUCP (Mike McMullen) (04/04/85)
I don't pretend to be an astrophysicist. The answer I present here was given to me by a friend who is one , however. "Neutron stars have typical surface temperatures of a million degrees K, so they are the "color" of X-ray photons (i.e., way past the ultra- violet side of the visible color spectrum). That assumes they radiate somewhat like blackbody emitters, which is about what the sun does. But at any rate, the X-ray astronomers have measured their surface emission and they generally fit a blackbody spectrum at 1 million degrees. You wouldn't want to observe them from up close with your own eyeballs." Makes sense if you think about it for a minute.
cooper@pbsvax.DEC (Topher Cooper HLO2-3/M08 DTN225-5819) (04/05/85)
I read a monograph, surveying what was then known about the
structure and behavior of neutron stars, about 13 years ago.
Sorry I don't have a citation, but it was one of a major
series of monographs in physics. Most of it was way beyond
me, but it was nicely written with the consequences of the
calculations and formula described in comprehensible English.
If you can find it I recommend it, though it is undoubtedly
out of date.
One of the interesting results was, that for a stable neutron
star, the pressure at the surface was insufficient to cause
degeneracy of the matter (i.e., the surface would be fairly
ordinary atomic matter).
It was speculated that that matter would be mostly or wholly
iron (the trough in the curve of binding energy). It would
be expected that the "typical" neutron star would have a
very intense magnetic field, a result of compression of the
"ancestral" stars ordinary magnetic field. This field would
be expected to be intense enough to cause the iron from the
surface to form into "hairs" similar to the lines of iron
filings formed with a bar magnet.
I also seem to remember that there was a shallow (a meter or
two) atmosphere, but I'm afraid I don't remember what it was
composed of. As best I remember it, this atmosphere resembled
a good vacuum.
Neglecting the atmosphere, then, the color would be that of
iron at the temperature of the neutron star, red-shifted
appropriately for the intensity of the gravitational field
and the distance from which the star's surface is being
observed. From close up the hair would have the effect
of providing some visual texture.
In the absence of a companion star dumping matter onto its
surface, a stabilized neutron star has no source
of energy. It would therefore eventually cool to the 3K
background level. However, my guess is that it would take
a LONG time to cool to anything like this level. I would
guess a very high initial temperature (it started life as
a star with a run-away nuclear reaction, then was compressed
extrodinarily), and it has a low (to say the least) surface area
relative to its mass. At any given time in history, you would
therefore expect to find a wide range of temperatures for
neutron stars. Take your pick.
Topher Cooper
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ARPA/CSNET: cooper%pbsvax.DEC@decwrlherbie@watdcsu.UUCP (Herb Chong [DCS]) (04/07/85)
In article <1523@decwrl.UUCP> cooper@pbsvax.DEC (Topher Cooper) writes: >It was speculated that that matter would be mostly or wholly >iron (the trough in the curve of binding energy). It would >be expected that the "typical" neutron star would have a >very intense magnetic field, a result of compression of the >"ancestral" stars ordinary magnetic field. This field would >be expected to be intense enough to cause the iron from the >surface to form into "hairs" similar to the lines of iron >filings formed with a bar magnet. > <..> > Topher Cooper would this not then imply (because of the extremely rough surface) that the star would radiate as an almost perfect black body? an outside observer would see (ignoring many things such as atmosphere) a redshifted black body at the temprature of the surface. Herb Chong... I'm user-friendly -- I don't byte, I nybble....
pmk@prometheus.UUCP (Paul M Koloc) (04/08/85)
> It would > be expected that the "typical" neutron star would have a > very intense magnetic field, a result of compression of the > "ancestral" stars ordinary magnetic field. > It's probably true that most neutron stars have very intense magnetic field densities, but probably NOT the result of compression of the "ancestral" star state. In fact, that ancestral field is swept away by the outward snow plow action of the outer plasma mantle of the star as the mantle is driven by the release of energy arising from the "gravitational collapse of the inner core of the star. It is sort of an inverse inverse pinch. The field of the collapsed star probably has its origin from unified field related processes which are not yet known, or well understood, but may well be mass density, star body spin and precession related. I like crimson. -- +-------------------------------------------------------+--------+ | pmk@prometheus: (301) 445-1075 | FUSION | | Prometheus II Ltd., College Park, MD 20740-0222 | this | | ..!{umcp-cs,seismo}!prometh!pmk | decade | +-------------------------------------------------------+--------+
js2j@mhuxt.UUCP (sonntag) (04/10/85)
> > It would > > be expected that the "typical" neutron star would have a > > very intense magnetic field, a result of compression of the > > "ancestral" stars ordinary magnetic field. > > It's probably true that most neutron stars have very intense magnetic > field densities, but probably NOT the result of compression of > the "ancestral" star state. In fact, that ancestral field is swept > away by the outward snow plow action of the outer plasma mantle > of the star as the mantle is driven by the release of energy arising > from the "gravitational collapse of the inner core of the star. > It is sort of an inverse inverse pinch. The field of the collapsed > star probably has its origin from unified field related processes > which are not yet known, or well understood, but may well be mass > density, star body spin and precession related. I like crimson. > | pmk@prometheus: (301) 445-1075 | FUSION | Since most stars revolve about their axes, wouldn't a neutron star, being a collapsed star, be expected to revolve extremely quickly about it's axis? And revolving so quickly, wouldn't it be expected to have an intense magnetic field if it has a reasonable charge? Why aren't these well understood effects sufficient to explain a neutron star's intense magnetic field? -- Jeff Sonntag ihnp4!mhuxt!js2j "You're from Joisey? I'm from Joisey!" "Which exit?"