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antoniseb
2006-Jun-23, 05:35 PM
Here (http://www.newscientistspace.com/article/dn9397-mysterious-xray-sources-may-be-lone-neutron-stars.html)'s a New Scientist article about how some/most/all of the xray sources in the galactic center might be old neutron stars accreting material from the denser clouds they are passing through.

trinitree88
2006-Jun-23, 08:16 PM
Here (http://www.newscientistspace.com/article/dn9397-mysterious-xray-sources-may-be-lone-neutron-stars.html)'s a New Scientist article about how some/most/all of the xray sources in the galactic center might be old neutron stars accreting material from the denser clouds they are passing through.

Antoniseb. I believe that story has a very familiar ring. The argument that a high redshift object could be a dense, compact object immersed in a tenuous gas cloud was one of the two original proposals for quasars that fell by the wayside in the 60's. Most theoreticians argued that it would soon exhaust the gas and vanish (they do, and have been seen to disappear on quasar population catalogs since then)...but at the time, only Doppler redshift would do for the concensus of the community.
As I have noted, both here on the boards and in the professional world at meetings...high transverse velocity pulsars can run through extended gas clouds,some...thousands of light years extant...for millenia...yielding high redshift objects. There is no reason to exclude the nearest galaxy to us...the Large Magellanic Cloud from such a fate. That of course means that a high redshift object will be associated with the lowest redshift galaxy to us (other than the Milky Way). Pete

antoniseb
2006-Jun-23, 08:44 PM
Pete, I was unable to parse what you were trying to communicate to me. The article was not talking about any visible objects, it was talking about X-Ray sources only. No redshift of any sort was mentioned in the article. I have no idea what you were talking about the LMC for, these are all near Sgr A*.

As a side note, the only things I've seen about red shift and neutron stars in terms of measured observations are that 511KeV annihilation gammas were seen redshifted down to about 400KeV from one neutron star's surface, but that was an entirely different study.

Note also that this New Scientist article was quoting a paper published in a Chinese Journal. The outside scientist quoted in the artile gave a neutral endorsement to the idea.

trinitree88
2006-Jun-23, 11:14 PM
Pete, I was unable to parse what you were trying to communicate to me. The article was not talking about any visible objects, it was talking about X-Ray sources only. No redshift of any sort was mentioned in the article. I have no idea what you were talking about the LMC for, these are all near Sgr A*.

As a side note, the only things I've seen about red shift and neutron stars in terms of measured observations are that 511KeV annihilation gammas were seen redshifted down to about 400KeV from one neutron star's surface, but that was an entirely different study.

Note also that this New Scientist article was quoting a paper published in a Chinese Journal. The outside scientist quoted in the artile gave a neutral endorsement to the idea.

Antoniseb. OK. I'll try again. My recollection for the discovery of quasars was that they had a H-spectrum that was energetically proportioned as the visible H-spectrum is according to Bohr's formulae, but that all of the lines were red-shifted to much longer wavelengths.
Two camps of thought arose as to the cause of this red-shifting:
1.The object emitting the spectrum had a high radial velocity component, and this was causing a doppler-shift of all the lines that were seen.If the object had been traveling at such a high relativistic speed, then one could infer that it was very far away, and hence extremely luminous. Read: power source unknown.
2. The ionized hydrogen emitting the spectra was in a very high gravitational field...i.e. a compact object such as a neutron star...as it did so. Then the lines would be gravitationally red-shifted. This second scenario would allow the object to be relatively nearby, hence not so luminous by inverse square law, and power source would fit standard physical models.

Shortly after the second scenario was proposed in the sixties, many in the astronomical community argued that a neutron star would rapidly deplete it's gas supply, and wink out. This was not observed initially, and it's merit as an explanation faded. Conclusion? Quasars were relativistically receding, at cosmological distances, and were powered by prodigious sources in order to be seen at those distances.
Since then two notable things have been learned:
3. A catalogue of quasars was published ~ 10 years ago. My recollection is coming across it in a fairly large folio format while reading other journal articles in the stacks at Hayden (MIT's main library). Of note was that the astrometric positions of a large number of them had moved in the sky...I'm thinking ~ 20%, but better check it out before I swear to it......and a smaller proportion had "disappeared"..or winked out (researchers spent what they thought was a fair amount of searching in the expected area, and could not locate the objects)
4. The statistical data on neutron stars is much improved. Many of them have appreciable transverse velocities, on the order of 200 km/sec. That would allow them to A) move their positions in a catalog over 30 years and
B) run through a gas cloud into a nearer vacuum, first dimming, then "winking" out.

This makes the second scenario for quasars more likely.
Additionally, the search for the host of discrete x-ray sources mentioned in the article does not necessarily exclude same said sources from also emitting in other parts of the spectrum, as gas swirling onto a neutron star would. My understanding of x-ray detectors is that large numbers of them are germaium detectors. An incident x-ray initiates a current in the detector which is proportional to the incident x-ray. It's a pretty linear response, but is not sensitive to the optical end of the spectrum..i.e. actinic radiation...of sufficient energy to be "seen" by the device.So,an x-ray astronomer's instrument wouldn't be searching for a redshifted H-spectrum...that'd be in the infrared-micro-radio range...and a germanium proportional detector is "blind" to those photons.
I would like to see an optical match to those sources, the way they multi-instrument the GRB afterglows.Nice.
Lastly, the article infers that the concept of a neutron star passing through an extended gas cloud is somehow novel...not so.."Gamma Ray Bursts a Halo of Neutron Stars at 400 Kiloparsecs? American Association of Physics Teachers Meeting, Olney Science Center, Harvard University, 1994, Pete's talk...with Matt Damon & Ben Affleck in the back row....but it was the unique numerical solution to the supernova problem they really liked(and wrote their GWH script on..:D ) Pete.

antoniseb
2006-Jun-23, 11:26 PM
OK, I now follow what you were trying to say.

These xray sources are in a dense part of the galaxy. Their positions can't easily be tied to specific infrared sources (optical is not observable). It would be interesting to see the spectra from these objects. I don't think you'd see much in the way of recombination photons.

trinitree88
2006-Jun-23, 11:49 PM
Antoniseb. Agreed that the spectra would be interesting. One of the things I learned in the Local Bubble discussion was that the more recent conferences asked that more researchers try to do imaging over the entire spectrum by using the instruments sensitive to each region simultaneously, so that daily superimposed computer models could be done. I realized that the various instruments , though exquisite in their areas, were like the six blind Hindus examining an elephant, each one gave a very different insight.:lol: Pete.