The particles are antielectrons, also known as positrons, and could be a sign of dark matter — the exotic and unidentified culprit that makes up the bulk of the universe’s mass. But more mundane explanations are also plausible: Positrons might be spewed from nearby pulsars, the spinning remnants of exploded stars, for example. But researchers with the High-Altitude Water Cherenkov Observatory, or HAWC, now have called the pulsar hypothesis into question in a paper published in the Nov. 17 Science.
Although the new observations don’t directly support the dark matter explanation, “if you have a few alternatives and cast doubt on one of them, then the other becomes more likely," says HAWC scientist Jordan Goodman of the University of Maryland in College Park.
Earth is constantly bathed in cosmic rays, particles from space that include protons, atomic nuclei, electrons and positrons. Several experiments designed to detect the showers of spacefaring particles have found more high-energy positrons than expected (SN: 5/4/13, p. 14), and astrophysicists have debated the excess positrons’ source ever since. Dark matter particles annihilating one another could theoretically produce pairs of electrons and positrons, but so can other sources, such as pulsars.
It was uncertain, though, whether pulsars’ positrons would make it to Earth in numbers significant enough to explain the excess. HAWC researchers tested how positrons travel through space by measuring gamma rays, or high-energy light, from two nearby pulsars — Geminga and Monogem — around 900 light-years away. Those gamma rays are produced when energetic positrons and electrons slam into low-energy light particles, producing higher-energy radiation.
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1 e, a spin of 1/2 (same as electron), and has the same mass as an electron.
When a positron collides with an electron, annihilation occurs. If this collision occurs at low energies, it results in the production of two or more gamma ray photons (see electron–positron annihilation).
Positrons may be generated by positron emission radioactive decay (through weak interactions), or by pair production from a sufficiently energetic photon which is interacting with an atom in a material.
https://en.wikipedia.org/wiki/Positron
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Antimatter
In modern physics, antimatter is defined as a material composed of the antiparticle (or “partners”) to the corresponding particles of ordinary matter.
In theory, a particle and its anti-particle have the same mass as one another, but opposite electric charge, and other differences in quantum numbers. For example, a proton has positive charge while an antiproton has negative charge.
A collision between any particle and its anti-particle partner is known to lead to their mutual annihilation, giving rise to various proportions of intense photons (gamma rays), neutrinos, and sometimes less-massive particle–antiparticle pairs.
Annihilation usually results in a release of energy that becomes available for heat or work. The amount of the released energy is usually proportional to the total mass of the collided matter and antimatter, in accord with the mass–energy equivalence equation, E = mc2.[1]
Antimatter particles bind with one another to form antimatter, just as ordinary particles bind to form normal matter.
For example, a positron (the antiparticle of the electron) and an antiproton (the antiparticle of the proton) can form an antihydrogen atom. Physical principles indicate that complex antimatter atomic nuclei are possible, as well as anti-atoms corresponding to the known chemical elements.
There is considerable speculation as to why the observable universe is composed almost entirely of ordinary matter, as opposed to an equal mixture of matter and antimatter. This asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics.[2]
The process by which this inequality between matter and antimatter particles developed is called baryogenesis.
Antimatter in the form of anti-atoms is one of the most difficult materials to produce.
Individual antimatter particles, however, are commonly produced by particle accelerators and in some types of radioactive decay.
The nuclei of antihelium have been artificially produced with difficulty. These are the most complex anti-nuclei so far observed.[3]
https://en.wikipedia.org/wiki/Antimatter
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Composition of dark matter: baryonic vs. nonbaryonic
Baryonic matter
Baryons (protons and neutrons) make up ordinary stars and planets. However, baryonic matter also encompasses less common black holes, neutron stars, faint old white dwarfs and brown dwarfs, collectively known as massive compact halo objects (MACHOs).[74] This ordinary, but hard to see, matter could explain dark matter.
However multiple lines of evidence suggest the majority of dark matter is not made of baryons:
Sufficient diffuse, baryonic gas or dust would be visible when backlit by stars.
The theory of Big Bang nucleosynthesis predicts the observed abundance of the chemical elements.
If there are more baryons, then there should also be more helium, lithium and heavier elements synthesized during the Big Bang.[75][76]
Agreement with observed abundances requires that baryonic matter makes up between 4–5% of the universe’s critical density. In contrast, large-scale structure and other observations indicate that the total matter density is about 30% of the critical density.[69]
Astronomical searches for gravitational microlensing in the Milky Way found that at most a small fraction of the dark matter may be in dark, compact, conventional objects (MACHOs, etc.); the excluded range of object masses is from half the Earth’s mass up to 30 solar masses, which covers nearly all the plausible candidates.[77][78][79][80][81][82]
Detailed analysis of the small irregularities (anisotropies) in the cosmic microwave background.[83] Observations by WMAP and Planck indicate that around five-sixths of the total matter is in a form that interacts significantly with ordinary matter or photons only through gravitational effects.
Non-baryonic matter
Candidates for nonbaryonic dark matter are hypothetical particles such as axions, sterile neutrinos or WIMPs (e.g. supersymmetric particles).
The three neutrino types already observed are indeed abundant, and “dark”, and matter, but because their individual masses – however uncertain they may be – are almost certainly tiny, they can only supply a small fraction of dark matter, due to limits derived from large-scale structure and high-redshift galaxies.[84]
Unlike baryonic matter, nonbaryonic matter did not contribute to the formation of the elements in the early universe (”Big Bang nucleosynthesis”)[14] and so its presence is revealed only via its gravitational effects.
In addition, if the particles of which it is composed are supersymmetric, they can undergo annihilation interactions with themselves, possibly resulting in observable by-products such as gamma rays and neutrinos (”indirect detection”).[84]
https://en.wikipedia.org/wiki/Dark_matter#Composition_of_dark_matter:_baryonic_vs._nonbaryonic
Sorry for the repeat of the excerpt in the first comment section. Just about falling asleep as I’m typing. Not sure how I did that.
My money says it’s the Russians.
Interesting
Assuming there is an attraction to do so............
I find much of this fascinating but it also tells me that our understanding of the universe is about as solid as an ant in a flower box, in a window in the Bronx, has of the world.
Great post