Mysterious X-Ray Signals Have Astronomers Excited About Dark Matter

Dark matter is one of the biggest mysteries in our universe. We think it makes up about 85 percent of all matter, but because it doesn’t emit or absorb light like ordinary matter, we can’t see or measure it. But now, astronomers might (emphasis: might) have found traces of this enigmatic matter: a mysterious X-ray signal seen in a study of galaxy clusters. NASA reports that the signal could be from the decay of a type of particle astronomers have considered as a candidate for dark matter.

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Experimental results show that all produced and observed neutrinos have left-handed helicities (spins antiparallel to momenta), and all antineutrinos have right-handed helicities, within the margin of error. In the massless limit, it means that only one of two possible chiralities is observed for either particle. These are the only helicities (and chiralities) included in the Standard Model of particle interactions.
http://en.wikipedia.org/wiki/Sterile_neutrino

Recent experiments such as neutrino oscillation, however, have shown that neutrinos have a non-zero mass, which is not predicted by the Standard Model and suggests new, unknown physics. This unexpected mass explains neutrinos with right-handed helicity and antineutrinos with left-handed helicity: since they do not move at the speed of light, their helicity is not relativistic invariant (it is possible to move faster than them and observe the opposite helicity). Yet all neutrinos have been observed with left-handed chirality, and all antineutrinos right-handed. Chirality is a fundamental property of particles and is relativistic invariant: it is the same regardless of the particle’s speed and mass in every reference frame. The question, thus, remains: can neutrinos and antineutrinos be differentiated only by chirality? Or do right-handed neutrinos and left-handed antineutrinos exist as separate particles?

> astronomers might (emphasis: might) have found traces of this enigmatic matter: a mysterious X-ray signal seen in a study of galaxy clusters. NASA reports that the signal could be from the decay of a type of particle astronomers have considered as a candidate for dark matter.

“An intriguing possibility is the decay of sterile neutrino, a long-sought dark matter particle candidate. Assuming that all dark matter is in sterile neutrinos with m _s = 2E = 7.1 keV, our detection in the full sample corresponds to a neutrino decay mixing angle sin ² (2theta) = 7e-11, below the previous upper limits. However, based on the cluster masses and distances, the line in Perseus is much brighter than expected in this model.”

Is this the same frequency as has been seen from the core of the Milky Way?

Only one way to find out. The New Study detects an emission line at 3.56 keV. The paper also say that this line may be due to anomalous emission from Argon, there’s an Argon emission line next door at 3.62 keV.

The earlier Milky Way study gives the mass of dark matter particles as much heavier. “If this is the case and the glimmer of gamma-rays from the inner galaxy is the afterglow from annihilating dark matter particles then their detected energy levels indicate that they most likely originate from dark matter particles with a mass range from 31 to 40 GeV.”

Quite different.

> Experimental results show that all produced and observed neutrinos have left-handed helicities (spins antiparallel to momenta), and all antineutrinos have right-handed helicities, within the margin of error. In the massless limit, it means that only one of two possible chiralities is observed for either particle. These are the only helicities (and chiralities) included in the Standard Model of particle interactions. http://en.wikipedia.org/wiki/Sterile_neutrino

Aha. That confirms what I thought, the Neutrino is a Dirac particle, not a Majorana particle.

Some days I really wish I hadn’t named my daughter “Neutrino”.

mollwollfumble said:

> astronomers might (emphasis: might) have found traces of this enigmatic matter: a mysterious X-ray signal seen in a study of galaxy clusters. NASA reports that the signal could be from the decay of a type of particle astronomers have considered as a candidate for dark matter.

“An intriguing possibility is the decay of sterile neutrino, a long-sought dark matter particle candidate. Assuming that all dark matter is in sterile neutrinos with m _s = 2E = 7.1 keV, our detection in the full sample corresponds to a neutrino decay mixing angle sin ² (2theta) = 7e-11, below the previous upper limits. However, based on the cluster masses and distances, the line in Perseus is much brighter than expected in this model.”

Is this the same frequency as has been seen from the core of the Milky Way?

Only one way to find out. The New Study detects an emission line at 3.56 keV. The paper also say that this line may be due to anomalous emission from Argon, there’s an Argon emission line next door at 3.62 keV.

The earlier Milky Way study gives the mass of dark matter particles as much heavier. “If this is the case and the glimmer of gamma-rays from the inner galaxy is the afterglow from annihilating dark matter particles then their detected energy levels indicate that they most likely originate from dark matter particles with a mass range from 31 to 40 GeV.”

Quite different.

> Experimental results show that all produced and observed neutrinos have left-handed helicities (spins antiparallel to momenta), and all antineutrinos have right-handed helicities, within the margin of error. In the massless limit, it means that only one of two possible chiralities is observed for either particle. These are the only helicities (and chiralities) included in the Standard Model of particle interactions. http://en.wikipedia.org/wiki/Sterile_neutrino

Aha. That confirms what I thought, the Neutrino is a Dirac particle, not a Majorana particle.

Some days I really wish I hadn’t named my daughter “Neutrino”.

molly, what are her thoughts on her name?