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Ian
18th September 2003, 06:46 AM
Hi. I think that there might be a way to detect antimatter in the universe if you can detect the type of electromagnetic radiation that's released when antimatter collides with normal matter. If antimatter exists out there in the cosmos at all besides being artificailly created in partical accelerators. What kinds of energy could be released when antimatter and normal matter collide?

Walter Wayne
18th September 2003, 08:40 AM
Originally posted by Ian
What kinds of energy could be released when antimatter and normal matter collide? My undestanding, when one gets total annihilation any products whose energies sum to same value as the energy involved in the initial collision. Most of the products will be short lived and decay to other new things. My impression is the only radiation that reached earth from such a collision would be the long lived type stuff, so a few photons and garbage that could not be distinguished from background.

In particle accerators, collisions of anything other than fundamental matter-antimatter particles are inefficient. In a proton antiproton collision one doesn't necessarily get total annihilation because the two particle require a certain orientation of the quarks in order to collide with correct quark-antiquark contacting.

I don't know of any natural phenomenon that would yield a large amount antimatter-matter collisions, so while energy density might be high, total energy of most collision would be small. Once you spread that energy out over lightyears it would disappear into the background noise most likely.

Walt

Ian
18th September 2003, 08:46 AM
If one galaxy is made entirely of antimatter and another
galaxy collides with it, than the antimatter explosion should be visible for a short time, then whatever "short-lived" radiation could be detected by a very sensitive detector that could detect
it even though it would be extremely far away. Could whole
stars and planets and galaxies out there somewhere
be made of antimatter instead of normal matter?

Ziggurat
18th September 2003, 09:51 AM
Originally posted by Ian
If one galaxy is made entirely of antimatter and another
galaxy collides with it, than the antimatter explosion should be visible for a short time, then whatever "short-lived" radiation could be detected by a very sensitive detector that could detect
it even though it would be extremely far away.

Matter-antimatter anihilation will release photons - lots of them, and very high energy ones at that. If a matter galaxy collided with an antimatter galaxy, the collision would last a very long time (at least on a human scale), as in tens of thousands of years.


Could whole stars and planets and galaxies out there somewhere be made of antimatter instead of normal matter?


That does not appear to be the case. There apears to be a fundamental asymmetry between matter and antimatter (which is why the universe is mainly the former), and that shouldn't have allowed for such large regions of space to be dominated by antimatter while the rest of the universe tipped to the matter side. The idea suggests interesting possibilities for science fiction (and I recall even reading a story along those lines), of course, but we're fairly sure all the galaxies and stars out there are matter and not antimatter.

Correa Neto
18th September 2003, 10:01 AM
One of the most intrigant things about our universe is why matter dominates. One would expect a symmetry to exist, at least on some degree. Some cosmologists made hypothesis that there was at the very first moments of the big bang roughly the same ammounts of matter and antimatter, with a small (infinitesimal) extra ammount of "ordinary" matter. After matter/antimatter anihilation, what remained, that dx of mater became the universe as we know.

Matter/antimatter collisions result in massive release of energy, as gamma rays. Years ago, matter/antimatter reactions were ocasionally used as a possible explanation for gamma ray bursts.

I remember some years ago a group of astronomers claimed to have found a "cloud" of antimatter above our galaxy (no, I am not mixing reality with a Star Trek episode ;)).

Tez
18th September 2003, 10:07 AM
The problem ian is that all of those photons could have arisen from other processes involving only normal matter. Thus it takes more than simply observing a whole bunch of high energy radiation to conclude antimatter was involved...

The Bad Astronomer
18th September 2003, 11:39 AM
There is a fountain of antimatter erupting from the center of our own Galaxy. When the electrons and anti-electrons collide, they give off gamma rays at the signature energy of 511 keV. Evidently this is from a rash of star formation some time ago. High-mass stars went supernovae quite often, creating positrons, and the fountain is the result of a pressure blowout from the expanding gas.

Here is a press release about it (http://www.spacetoday.org/DeepSpace/Galaxies/MilkyWay/Antimatter.html). You can also read the journal paper (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...487L..57D&db_key=AST&high=3ccf23290021443).

Agammamon
22nd September 2003, 09:04 AM
Some research indicates that Charge, Parity, Time symmetry may be conserved only if you reverse all 3 (rather than 1 0r 2), meaning that for anti-matter some reactions may not be time-reversable the same way for matter reactions. If this is the case all you have to do is contact the aliens you r suspect galaxy, have them run some tests, and then send them to you to compare with the results expected for matter. Obviously this approach has many technical hurdles to overcome so I am set up to receive any donations you care to make to study the issue.

Otherwise photons is photons. Outside of throwing matter at whatever you think might be antimatter and looking for the explosion, AM galaxies would be indistinguishable from M galaxies.

a_unique_person
30th September 2003, 04:55 PM
If you stick your hand in some and your hand disappears, you have found some.