Merging white dwarfs may create most of our galaxy’s antimatter

Newsgroups	sci.physics
From	Yousuf Khan <bbbl67@spammenot.yahoo.com>
Subject	Merging white dwarfs may create most of our galaxy’s antimatter
Date	2017-06-02 14:57 -0400
Message-ID	<4MydnTMVTrS6KKzEnZ2dnUU7-InNnZ2d@giganews.com> (permalink)

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http://www.astronomy.com/news/2017/05/white-dwarfs-may-create-antimatter

More than four decades ago, astronomers discovered the first gamma-ray 
emission coming from outside the solar system. This high-energy signal 
is associated with the destruction of roughly 1043 positrons — a type of 
antimatter — each second. Despite extensive follow-up, astronomers today 
are still looking for the exact source (or sources) of this emission, 
which could run the gamut from mundane (natural processes in a star’s 
life) to exotic (dark matter) origins. Recently, a group of astronomers 
has determined that positrons resulting from white dwarf mergers could 
contribute significantly to the signal we see.

The emission associated with galactic positron annihilation occurs when 
a positron meets its counterpart, an electron, destroying both particles 
in the process. Thus, this emission requires a ready source of 
antimatter, which has remained mysterious ever since its initial detection.

Measurements suggest that the signal is nearly one and a half times 
higher in the bulge, or central regions of the Milky Way, than in the 
arms. This particular aspect of the emission has led to the development 
of several models that speculate an overabundance of positrons in this 
area could be due to processes related to dark matter or our galaxy’s 
central supermassive black hole. However, many astronomers are still 
searching for less exotic ways the positrons we’re seeing undergo 
annihilation could be produced.

In a paper published May 22 in Nature Astronomy, first author Roland M. 
Crocker of the Research School of Astronomy and Astrophysics at 
Australian National University and his co-authors examine a possible 
stellar source of galactic positrons that could be responsible for the 
signal: white dwarf mergers.

White dwarfs are the remnant cores of Sun-like stars, left behind after 
the star runs out of fuel and dies. If two low-mass stars (between about 
1.4 and 2 times the mass of our Sun) circle each other closely in a 
binary system, they can interact via a process called mass transfer, 
where gas from the stars is exchanged. The end result is two white 
dwarfs that may eventually merge, and that merger can result in the 
production of radioactive isotopes that decay into positrons.

There are several clues that have led Crocker and his co-authors to this 
conclusion. The ratio of the signal’s strength in the bulge and arms is 
similar to the ratio of the stellar mass (essentially the number of 
stars) in these two structures as well. This led the astronomers to 
consider that the positron production could be related to an older 
stellar population, such as white dwarfs. Additionally, by looking at 
the processes that produce positrons through radioactive decay, they 
determined that the decay of 44Ti into positrons is the most likely source.

However, this material is not produced in sufficient amounts in most 
core collapse supernovae, which occur when a massive star reaches the 
end of its life. While supernovae triggered by the merger of two white 
dwarfs are much rarer, these events should produce more 44Ti per merger, 
which would then decay and produce the number of positrons required to 
create the emission line from their subsequent annihilation.

The current resolution of instruments used to study this emission is not 
high enough to find point sources, such as individual supernova 
remnants, in the bulge. Thus, more precise measurements and computer 
simulations will be needed to determine the positron production rates 
from such events. The authors also state that white dwarf mergers are 
likely not the only source of antimatter in our galaxy, which still 
includes contributions from massive stars and black holes, even if dark 
matter is eventually ruled out as a viable source for this emission.

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Merging white dwarfs may create most of our galaxy’s antimatter Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2017-06-02 14:57 -0400
  Merging white dwarfs may create most of our galaxy’s antimatter john <johnsefton288@gmail.com> - 2017-06-02 15:05 -0700
    Merging white dwarfs may create most of our galaxy’s antimatter john <johnsefton288@gmail.com> - 2017-06-03 04:52 -0700
      Merging white dwarfs may create most of our galaxy’s antimatter john <johnsefton288@gmail.com> - 2017-06-03 06:29 -0700
        Merging white dwarfs may create most of our galaxy’s antimatter john <johnsefton288@gmail.com> - 2017-06-03 06:56 -0700
          Re: Merging white dwarfs may create most of our galaxy’s antimatter moroney@world.std.spaamtrap.com (Michael Moroney) - 2017-06-03 15:05 +0000
            Re: Merging white dwarfs may create most of our galaxy’s antimatter john <johnsefton288@gmail.com> - 2017-06-03 08:17 -0700
              Re: Re: Merging white dwarfs may create most of our galaxy’s antimatter moroney@world.std.spaamtrap.com (Michael Moroney) - 2017-06-03 16:11 +0000
                Re: Re: Merging white dwarfs may create most of our galaxy’s antimatter john <johnsefton288@gmail.com> - 2017-06-03 09:53 -0700
                Re: Re: Re: Merging white dwarfs may create most of our galaxy’s antimatter moroney@world.std.spaamtrap.com (Michael Moroney) - 2017-06-04 04:41 +0000
                Re: Re: Re: Merging white dwarfs may create most of our galaxy’s antimatter john <johnsefton288@gmail.com> - 2017-06-04 08:27 -0700
                Re: Re: Re: Re: Merging white dwarfs may create most of our galaxy’s antimatter moroney@world.std.spaamtrap.com (Michael Moroney) - 2017-06-04 16:43 +0000
                Re: Re: Re: Re: Merging white dwarfs may create most of our galaxy’s antimatter john <johnsefton288@gmail.com> - 2017-06-04 10:21 -0700
        Merging white dwarfs may create most of our galaxy’s antimatter john <johnsefton288@gmail.com> - 2017-06-03 07:00 -0700
          Re: Merging white dwarfs may create most of our galaxy’s antimatter moroney@world.std.spaamtrap.com (Michael Moroney) - 2017-06-03 15:16 +0000
      Re: Merging white dwarfs may create most of our galaxy’s antimatter Odd Bodkin <bodkinodd@gmail.com> - 2017-06-03 16:15 -0500
        Re: Merging white dwarfs may create most of our galaxy’s antimatter john <johnsefton288@gmail.com> - 2017-06-03 15:31 -0700
          Re: Merging white dwarfs may create most of our gala xy’s antimatter Odd Bodkin <bodkinodd@gmail.com> - 2017-06-04 21:21 +0000
            Re: Merging white dwarfs may create most of our gala xy’s antimatter john <johnsefton288@gmail.com> - 2017-06-04 14:53 -0700
              Re: Merging white dwarfs may create most of our gala xy’s antimatter Odd Bodkin <bodkinodd@gmail.com> - 2017-06-04 23:13 +0000
                Re: Merging white dwarfs may create most of our gala xy’s antimatter john <johnsefton288@gmail.com> - 2017-06-04 16:55 -0700
                Re: Merging white dwarfs may create most of our gala xy’s antimatter john <johnsefton288@gmail.com> - 2017-06-04 16:59 -0700
                Re: Merging white dwarfs may create most of our gala xy’s antimatter Odd Bodkin <bodkinodd@gmail.com> - 2017-06-05 09:41 -0500
                Re: Re: Merging white dwarfs may create most of our gala xy’s antimatter moroney@world.std.spaamtrap.com (Michael Moroney) - 2017-06-05 00:38 +0000
                Re: Re: Merging white dwarfs may create most of our gala xy’s antimatter john <johnsefton288@gmail.com> - 2017-06-04 19:48 -0700
                Re: Re: Re: Merging white dwarfs may create most of our gala xy’s antimatter moroney@world.std.spaamtrap.com (Michael Moroney) - 2017-06-05 04:18 +0000
                Re: Merging white dwarfs may create most of our gala xy’s antimatter Poutnik <poutnik4nntp@gmail.com> - 2017-06-05 08:32 +0200
                Re: Merging white dwarfs may create most of our gala xy’s antimatter Odd Bodkin <bodkinodd@gmail.com> - 2017-06-05 09:36 -0500
      Re: Merging white dwarfs may create most of our galaxy’s antimatter Edward Prochak <edprochak@gmail.com> - 2017-06-04 20:36 -0700

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