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Fraser
2005-Jun-08, 06:11 PM
SUMMARY: If you could look into the sky with gamma ray eyes, you'd see gamma ray bursts, and other sources of gamma radiation across the night sky. If you could fine tune your eyes to only see a very specific colour of gamma rays, the one associated with the annihilation of matter and antimatter, you'd see wash of energy, but not coming from any specific location. Astronomers using the European Space Agency's INTEGRAL space telescope have developed one of the best pictures yet of this exotic energy.

View full article (http://www.universetoday.com/am/publish/search_positronium.html)

What do you think about this story? Post your comments below.

antoniseb
2005-Jun-08, 06:14 PM
It's interesting to think about that much antimatter.
Curiously though, this is just the positrons, we have no idea yet how much annihilation there is of anti-protons in the galaxy because we don't yet have equipment that can do a sensitive all-sky survey at such high energy gammas.

om@umr.edu
2005-Jun-08, 06:34 PM
I am delighted that astronomers are thinking about other forms of matter.

Positronium is an electron and an anti-electron in hydrogen-like orbits, spiraling toward annihilation with the emission of two 0.511 MeV gammas moving in opposite directions. Those who have operated gamma-detectors have seen these peaks at 0.511 MeV and the sum peak at 1.022 MeV frequently.

I hope astronomers will also start thinking about trying to detect anti-neutrinos.

Neutrinos are emitted in the decay of proton-rich nuclei.

Anti-neutrinos are emitted in the decay of neutron-rich nuclei.

Measurements on the emission of anti-neutrinos from stars will tell us if there are neutron-rich nuclei there.

With kind regards,

Oliver
http://www.umr.edu/~om

dave_f
2005-Jun-08, 06:47 PM
Originally posted by om@umr.edu@Jun 8 2005, 01:34 PM
I hope astronomers will also start thinking about trying to detect anti-neutrinos.

I might be off-base with this question, but aren't neutrinos and anti-neutrino's the same particle, since it's a chargeless (neutrally charged) particle?

Don Alexander
2005-Jun-08, 07:03 PM
aren't neutrinos and anti-neutrino's the same particle, since it's a chargeless (neutrally charged) particle?

Depends on whether they are Dirac or Majorana particles. Photons are neutral and, moving at the speed of light, can't be overtaken which would change their helicity, thus they are Dirac particles and their exact own anti-particles.

It's unclear if Neutrino's are also Dirac particles.

This is probably highly technical, but it popped up via a humble Google search, so there should be more to find:

arxiv.org/abs/hep-ph/9910357

lswinford
2005-Jun-08, 08:20 PM
Well, I learned something from this piece. I learned of positrons and anti-matter in school, but anti-matter was mostly a momentary product of the accelerators in the big particle physics labs. There was talk that maybe other galaxies might be made of full anti-matter existences such as ours, and the vast and presumeably empty space between galaxies was the insulation that kept one from annihilating the other. Mostly, it was a theoretical oddity. On the collision of an electron and positron the product was light--photons. Now I see that these photons are gamma rays and at a specific wavelength or energy. Now, instead of antimatter annihilation in the early moments of the big bang, we have an on-going production with an ongoing destruction, and it even happens here in our own galaxy. To borrow a Cheech and Chong expression that sounded appropriate, "Far out!"

om@umr.edu
2005-Jun-08, 09:37 PM
Originally posted by dave_f+Jun 8 2005, 06:47 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (dave_f &#064; Jun 8 2005, 06:47 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-om@umr.edu@Jun 8 2005, 01:34 PM
I hope astronomers will also start thinking about trying to detect anti-neutrinos.

I might be off-base with this question, but aren&#39;t neutrinos and anti-neutrino&#39;s the same particle, since it&#39;s a chargeless (neutrally charged) particle? [/b][/quote]
They are different particles, dave.

Neutrinos (v) from the Sun were first seen in the Homestake Mine by their capture on Cl-37 to drive backward the natural decay of Ar-37 by electron capture (EC):

Natural process: Ar-37 -(EC)-> Cl-37
Neutrino detector: Cl-37 + v -> Ar-37

Anti-neutrinos (anti-v) from the Sun could be seen by their capture on Cl-35 to drive backward the natural decay of S-35 by electron emission (EE):

Natural process: S-35 -(EE)-> Cl-35
Anti-neutrino detector: Cl-35 + anti-v -> S-35

The need for the latter measurement was noted last year in Physics of Atomic Nuclei 67 (2004) 1983-1988.

With kind regards,

Oliver
http://www.umr.edu/~om

Greg
2005-Jun-08, 10:38 PM
The SMBH at the center of the galaxy is most likely the predominant source of the positrons. Compton is a good instrument, but certainly no the penultimate gamma ray detector. More detailed instruments of the future may be able to detect point sources. The rather large amount of antimatter we are talking about here indicates to me that the only thing capable of producing it would be the SMBH. Why did compton not detect a significant concentration near it, then? Easy one to answer, it has been quiet for 350 years. Should it awaken, I will bet you we will see the source antimatter factories we can&#39;t now. I am providing a link below (which requires adobe acrobat to open) that goes into the reasoning behind this, although not in alot of detail. (look around page 12 of 16)
universe.nasa.gov/be/roadmap/Chapter-6.pdf
Here is a link to an article from the forum about when our SMBH was last active.
www.universetoday.com/am/publish/ our_black_hole_active.html?2612005 - 23k -

dave_f
2005-Jun-09, 01:43 AM
Originally posted by om@umr.edu+Jun 8 2005, 04:37 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (om@umr.edu &#064; Jun 8 2005, 04:37 PM)</td></tr><tr><td id='QUOTE'>
Originally posted by dave_f@Jun 8 2005, 06:47 PM
<!--QuoteBegin-om@umr.edu@Jun 8 2005, 01:34 PM
I hope astronomers will also start thinking about trying to detect anti-neutrinos.

I might be off-base with this question, but aren&#39;t neutrinos and anti-neutrino&#39;s the same particle, since it&#39;s a chargeless (neutrally charged) particle?
They are different particles, dave.

... (snip) ...

With kind regards,

Oliver
http://www.umr.edu/~om[/b][/quote]
Thank you Oliver. I have better knowledge of classic definitions than modern ones and to this day I&#39;m still guilty of assuming an anti-particle is defined by its electrical charge only.

Though this does beg the question: Should an anti-particle that doesn&#39;t fit the above criteria (opposite electric charge) be called something other than an "anti-particle"? Good science is built on good nomenclature. Should this point be considered?

om@umr.edu
2005-Jun-09, 02:13 AM
Originally posted by dave_f@Jun 9 2005, 01:43 AM
Should an anti-particle that doesn&#39;t fit the above criteria (opposite electric charge) be called something other than an "anti-particle"?
Good question, dave.

I don&#39;t know the answer.

Many of us have had thoughts about "particles" and "anti-particles" that are incorrect.

For example, I always assumed "particles" are more abundant than "anti-particles".

But "anti-neutrinos" are far more abundant than "neutrinos" on old planet Earth. That is because this planet is made mostly of heavy, neutron-rich nuclei that emit electrons and "anti-neutrinos" when they decay.

It is widely assumed, on the other hand, that stellar luminosity comes from fusing light nuclei together to form proton-rich nuclei that that emit positrons and "neutrinos" when they decay.

"Neutrino" detectors were set up to confirm that hypothesis.

"Anti-neutrino" detectors might tell us if there are neutron-rich nuclei inside stars too.

With kind regards,

Oliver
http://www.umr.edu/~om

Nereid
2005-Jun-09, 07:19 AM
Originally posted by om@umr.edu+Jun 9 2005, 02:13 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (om@umr.edu &#064; Jun 9 2005, 02:13 AM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-dave_f@Jun 9 2005, 01:43 AM
Should an anti-particle that doesn&#39;t fit the above criteria (opposite electric charge) be called something other than an "anti-particle"?
Good question, dave.

I don&#39;t know the answer.

Many of us have had thoughts about "particles" and "anti-particles" that are incorrect.

For example, I always assumed "particles" are more abundant than "anti-particles".

But "anti-neutrinos" are far more abundant than "neutrinos" on old planet Earth. That is because this planet is made mostly of heavy, neutron-rich nuclei that emit electrons and "anti-neutrinos" when they decay.

It is widely assumed, on the other hand, that stellar luminosity comes from fusing light nuclei together to form proton-rich nuclei that that emit positrons and "neutrinos" when they decay.

"Neutrino" detectors were set up to confirm that hypothesis.

"Anti-neutrino" detectors might tell us if there are neutron-rich nuclei inside stars too. [/b][/quote]
This (http://www.pas.rochester.edu/~pavone/particle-www/Summer%20Institute/Talks2004/julie__&#39;s%20standard%20model%202.pdf) (rather large PDF) is a nice, 45-page Powerpoint-style summary of the Standard Model of particle physics (for something that won&#39;t cause your PC to crash while your browser is downloading the PDF, try this excellent overview (http://particleadventure.org/particleadventure/), from the Lawrence Berkeley National Laboratory).

The key things are:
a ) a neutral particle can (and does) have an anti-particle counterpart; it&#39;s not only charge which makes the difference
b ) we all recognise that the Standard Model cannot be the last word (there was an excellent summary - by Gordon Kane? - in an issue of Scientific American, a few years ago, on its limits), but the regimes where it fails are far beyond what we can examine in our labs today (except, perhaps, CP violation (http://physicsweb.org/articles/world/14/8/9/1)).

Moseley
2005-Jun-09, 10:02 AM
Thanks very much for the particle adventure link Nereid, that is most helpful & easy to take in.

Jürgen
2005-Jun-09, 01:01 PM
Originally posted by Greg@Jun 8 2005, 10:38 PM
The SMBH at the center of the galaxy is most likely the predominant source of the positrons. Compton is a good instrument, but certainly no the penultimate gamma ray detector. More detailed instruments of the future may be able to detect point sources. The rather large amount of antimatter we are talking about here indicates to me that the only thing capable of producing it would be the SMBH. Why did compton not detect a significant concentration near it, then? Easy one to answer, it has been quiet for 350 years. Should it awaken, I will bet you we will see the source antimatter factories we can&#39;t now. I am providing a link below (which requires adobe acrobat to open) that goes into the reasoning behind this, although not in alot of detail. (look around page 12 of 16)
universe.nasa.gov/be/roadmap/Chapter-6.pdf
Here is a link to an article from the forum about when our SMBH was last active.
www.universetoday.com/am/publish/ our_black_hole_active.html?2612005 - 23k -
We&#39;re not talking about Compton here, but about SPI aboard INTEGRAL. And SPI can very well discriminate between a point source at the galactic centre, such as the SMBH, or an extended source, such as the galactic bulge. Indeed, we significantly can exclude emission from a single point or point-like source&#33; We&#39;re not seeing the SMBH, we&#39;re seeing extended emission. You could argue that positrons from the SMBH may diffuse away and therefore are producing extended emission when they annihilate. But there is no reason that these positrons stop at the border of the galactic bulge and do not diffuse in the galactic disk. Conversely, SPI sees emission that is well fit by the morphology of the galactic bulge, hence it is very likely that the positron source is also physically associated with the galactic bulge and that positron diffusion is negligible.
By the way, with IBIS on INTEGRAL a point source could be located to around 10 arcmin or better, yet no such source is seen in the IBIS data. 511 keV is clearly not coming from a single point-source such as the SMBH.

wstevenbrown
2005-Jun-09, 01:34 PM
Jurgen:
Can you elaborate (or provide references) on exactly what was seen by SPI and IBIS? It&#39;s my understanding that the pair productions are thought to originate from the gammas that arise from relativistic hadronic jets (of which there might be many more than one). 511 KEV is an annihilation signature-- wouldn&#39;t that be expected to follow the matter distribution-- clear sailing thru the interior of a SN bubble, followed by a higher probability of annihilation in the much denser wall of the bubble? Best regards-- Steve

Jürgen
2005-Jun-09, 02:30 PM
Originally posted by wstevenbrown@Jun 9 2005, 01:34 PM
Jurgen:
Can you elaborate (or provide references) on exactly what was seen by SPI and IBIS? It&#39;s my understanding that the pair productions are thought to originate from the gammas that arise from relativistic hadronic jets (of which there might be many more than one). 511 KEV is an annihilation signature-- wouldn&#39;t that be expected to follow the matter distribution-- clear sailing thru the interior of a SN bubble, followed by a higher probability of annihilation in the much denser wall of the bubble? Best regards-- Steve
Dear Steve,

The SPI observations are documented in our paper (astro-ph/0506026), the IBIS observations are in (astro-ph/0501123). SPI has seen extended emission of 511 keV line emission from the bulge region of our Galaxy with a FWHM extension of about 8 degrees. But SPI cannot distiguish between a point-source and a source of 2 degrees in extension (due to the limited angular resolution). IBIS, which is more sensitive to point-source emission with an angular resolution of about 12 arcmin, has seen nothing. This implies that the emission is not coming from a small number of point sources (which would have been seen by IBIS), but either from a large number of sources (which are individually below the IBIS detection limit) or from an intrinsically diffuse source.
Positrons can indeed be produced in a pair jet, but it is not clear how many of the positrons can indeed escape the jet (they have to escape since the line we see is very narrow, indicating annihilation in a warm, 8000 K partly ionized interstellar medium). But positrons can also be produced by radioactive decay, called beta+ decays. And Type Ia supernovae are a good source for such positrons.
Since positrons need electrons for annihilation, one could indeed expect that the 511 keV signature should follow the matter distribution, in the case that positron diffusion is important. Yet simulations indicate that positrons can&#39;t move far from their sources, since they are tied by magnetic fields. So if they stay close to the sources (say a few 10 kpc), one would expect that 511 keV emission follows more the source distribution. This is coroborated by the observations : the galactic bulge is matter poor, so if positron diffusion would be important we would expect a strong signal for example from the molecular ring structure at about 4 kpc from the galactic centre - yet we do not see any signal from this area. This means that positrons do not travel far away from their sources ...

Best regards,
Jürgen

wstevenbrown
2005-Jun-09, 03:46 PM
First, let me convey my apology for wasting your time, Jurgen. The answer to all of my concerns above was: read the source article&#33; The article is very clear and thoro, addressing a very wide range of concerns about the data and their interpretation. On first reading of the UT article, I missed the hot link to the paper itself. Who&#39;d have thunk it-- as a result of the telescope&#39;s location, the &#39;scope itself becomes a source of noise&#33;
I am reduced to a layman&#39;s curiosity question. In Sec. 4.2.3, the positronium fraction P-sub-s is discussed. What distinction is being made here about the fate of the other 7% of the positrons? Are they perhaps undergoing some other decay after entering excited states from gamma interactions? (I can&#39;t think of another decay mode for unexcited positrons.) Thanks for your kind indulgence-- Steve

Nereid
2005-Jun-09, 04:59 PM
Originally posted by wstevenbrown@Jun 9 2005, 03:46 PM
First, let me convey my apology for wasting your time, Jurgen. The answer to all of my concerns above was: read the source article&#33; The article is very clear and thoro, addressing a very wide range of concerns about the data and their interpretation. On first reading of the UT article, I missed the hot link to the paper itself. Who&#39;d have thunk it-- as a result of the telescope&#39;s location, the &#39;scope itself becomes a source of noise&#33;
I am reduced to a layman&#39;s curiosity question. In Sec. 4.2.3, the positronium fraction P-sub-s is discussed. What distinction is being made here about the fate of the other 7% of the positrons? Are they perhaps undergoing some other decay after entering excited states from gamma interactions? (I can&#39;t think of another decay mode for unexcited positrons.) Thanks for your kind indulgence-- Steve
Steve,

93% of the positrons are annihilated via the positronium channel; the other 7% presumably annihilate directly (i.e. no formation of Ps first). All this is spelt out clearly in the paper Knödlseder et al. cite (Kinzer, R. L., Milne, P. A., Kurfess, J. D., et al. 2001, ApJ, 559, 282), which comes from work done analysing the results from the OSSE instrument on COMPTON.

Now, a question for you, if I may: how could the author of the UT story have done a better job? Some constructive criticism, please&#33; :P

ASEI
2005-Jun-09, 07:14 PM
Note - their&#39;s no way to tell which galaxies are composed of matter and which of antimatter based solely on light emmissions. I&#39;ve often wondered if antimatter might actually be present in large quantities, and our only evidence of it might be when ultra-diffuse gas has chance collisions in the intergalactic medium.

lswinford
2005-Jun-09, 07:41 PM
ASEI, I seem to recall that some antimatter discussions indicate that due to the normal matter sources, such as the isotope decays discussed earlier by others, antimatter isn&#39;t merely a mirror image counterpart to regular matter. There are sort of mechanical distinctions, the characteristic kinds of things that we note when we catagorize, say, quarks with convenient handles of "color" and "strangeness". I think the dust sort of settled on this about 20-ish years ago that antimatter was pretty well constrained to simple particles and very short lifetimes. But then, I have been wrong about more than a few things and will probably get an earful over this, right? :unsure:

Jürgen
2005-Jun-09, 10:49 PM
Originally posted by ASEI@Jun 9 2005, 07:14 PM
Note - their&#39;s no way to tell which galaxies are composed of matter and which of antimatter based solely on light emmissions. I&#39;ve often wondered if antimatter might actually be present in large quantities, and our only evidence of it might be when ultra-diffuse gas has chance collisions in the intergalactic medium.
It&#39;s really difficult to imagine antimatter galaxies or antimatter worlds ... since even if the space (and in particular) the intergalactic medium seems empty, it&#39;s not completely empty ... you see the point : there must be an interface between our normal world and the antimatter world. And even if there are few atoms per kubicmeter there, it&#39;s still enough to create violate annihilation at this interface. This signature should be detectable by our instruments ... but we have no hint for such a global antimatter annihilation in the Universe.

Jürgen

Greg
2005-Jun-10, 04:46 AM
First, I would like to thank the author of the article for visiting this forum and taking time to answer questions. Secondly, I did take the time to read trhough the article, although I must admit I skipped through the methods section as usual. I was most impressed with the detail, comprehensiveness and thoughtfullness of the article. My understanding of cosmology is merely introductory so I probably understood 80 percent of it. My intellect is keen, but my knowledge base is broad rather than deep in this field. Thirdly, I apologize for the sloppiness of part of my earlier post regarding point sources and the Compton. I got caught up posting conclusions of the earlier article about point sources without referencing the current article. Enough said on that.
You are correct in stating that I was driving at the SMBH as being a source of diffuse positron emission. I did not intend to mean that it was currently active in producing them. I am aware that positrons are driven by and associated with magnetic field lines. What I had in mind was that the SMBH may have been releasing an enormous amount of antimatter, abruptly ending 350 years ago. Over tiime of course this would rapidly dissipate, but perhaps a significant amount could be caught in "antimatter traps" where magnetic fields from the SMBH and other objects with strong magnetic fields intersect and be slowly diffusing from these traps until the present day. As far as why emissions cannot be detected in gas surrounding the bulge, I would argue by asking why does the buldge end where it does? Presumably the buldge is the approximate boundary constraining where the effects of the dramatic outbursts from the SMBH generally end. If the positrons in question are preserved in a deterministic fashoin by the effects of the SMBH and its magnetic field effects, then I would expect their effects to not exeed that boundary. In other words, the buldge-disc boundary could be the limit to which positrons preserved by the effects of the SMBH magnetic field can reach.
I see that in retrospect, the above idea would seem to be an exceptional way to produce such 511 kev emission lines, and even if actual probably would account for a miniscule percentage of those detected.
I think it does show I am thinking, which leads me to my next and most interesting point. What happens to the whole picture when the SMBH becomes active again? My guess would be that I would hope this doesn&#39;t happen before you complete your research and track down the source of the existing 511 kev emissions. In your conclusions, I do like the case for low-mass star x-ray binaries as the most likely source. I also like IA supernovae, but I would expect a clumpy distribution of emissions from the disc, unless our galaxy has had an extraordinary drought of disc Ia explosions.
Once again, thanks for your feedback, it has forced me to learn a great deal more about the subject and spurred an interest in it.

GOURDHEAD
2005-Jun-10, 01:34 PM
The article cites a huge tonnage per second of positron/electron annihilations. Since this process consumes a like number of electrons, is the universe becoming "plasmised"? Do conditions exist that allow the production of anti-particle pairs from energies above 511kev with the extra energy partitioned into the kinetic energy of the resulting particles. Can gammas with energies slightly below 511kev interact with "environments" with velocities with large fractions of that of light thus "acquiring" enough energy to produce positronium? Under what conditions will the oscillation between pair formation and gamma ray production persist indefinitely?