Contributions to Cosmic Reionization from Dark Matter Annihilation and Decay

Image: A Schematic Outline of the Cosmic History - Credit: NASA/WMAP Science Team

The epoch of reionisation and the emergence of the universe from the cosmic dark ages is a subject of intense study in modern cosmology.

As baryonic matter began to collapse around initial fluctuations in the dark matter (DM) density seeded by inflation, the earliest galaxies in our universe began to form. These structures, perhaps accompanied by other sources, eventually began to emit ionising radiation, creating local patches of fully ionised hydrogen gas around them. These patches ultimately grew to encompass the entire universe, leading to the fully ionised intergalactic medium (IGM) that we observe today.

While the process of reionisation is broadly understood, the exact details of how and when reionisation occurred are still somewhat unclear.

Dark matter annihilation or decay could have a significant impact on the ionisation and thermal history of the universe.

In a recent paper (Liu et al. 2016) the authors study the potential contribution of dark matter annihilation (s-wave- or p-wave-dominated) or decay to cosmic reionisation, via the production of electrons, positrons and photons.

They map out the possible perturbations to the ionisation and thermal histories of the universe due to dark matter processes, over a broad range of velocity-averaged annihilation cross-sections/decay lifetimes and dark matter masses.

They find that for dark matter models that are consistent with experimental constraints, a contribution of more than 10% to the ionisation fraction at reionisation is disallowed for all annihilation scenarios.

Such a contribution is possible only for decays into electron/positron pairs, for light dark matter with mass m_χ ≲ 100 MeV, and a decay lifetime τ_χ ∼10²⁴−10²⁵ s.

Liu et al. 2016 (preprint) - The Darkest Hour Before Dawn: Contributions to Cosmic Reionisation from Dark Matter Annihilation and Decay - (arXiv)

Comments

A Sapphire Super-Earth

Twenty-one light years away, in the constellation Cassiopeia, a planet by the name of HD219134 b orbits its star with a year that is just three days long. With a mass almost five times that of Earth, it is what is known as a super-Earth. Unlike our planet, however, these super-Earths were formed at high temperatures close to their host star and contain high quantities of calcium, aluminum and their oxides – including sapphire and ruby. HD219134 b is one of three candidates likely to belong to a new, exotic class of exoplanets. These objects are completely different from the majority of Earth-like planets. They have 10 to 20 percent lower densities than Earth. Researchers looked at different scenarios to explain the observed densities. For example, a thick atmosphere could lead to a lower overall density. But two of the exoplanets studied, 55 Cancri e and WASP-47 e, orbit their star so closely that their surface temperature is almost 3,000 degrees and they would have lost this ...

Protoplanetary disks in the hostile environment of Carina

Image: Star-forming region in the Carina Nebula. Credit: NASA, ESA, N. Smith (University of California, Berkeley), and The Hubble Heritage Team (STScI/AURA) In a recent paper (Mesa-Delgado et al. 2016) [1] the authors report the first direct imaging of protoplanetary disks in the star-forming region of Carina, the most distant, massive cluster in which disks have been imaged.

Hubble observes energetic lightshow at Saturn’s north pole

This image is a composite of observations made of Saturn in early 2018 in the optical and of the auroras on Saturn’s north pole region, made in 2017. In contrast to the auroras on Earth the auroras on Saturn are only visible in the ultraviolet — a part of the electromagnetic spectrum blocked by Earth’s atmosphere — and therefore astronomers have to rely on space telescopes like the NASA/ESA Hubble Space Telescope to study them. Credit: ESA/Hubble, NASA, A. Simon (GSFC) and the OPAL Team, J. DePasquale (STScI), L. Lamy (Observatoire de Paris) In 2017, over a period of seven months, the NASA/ESA Hubble Space Telescope took images of auroras above Saturn’s north pole region using the Space Telescope Imaging Spectrograph. The observations were taken before and after the Saturnian northern summer solstice. These conditions provided the best achievable viewing of the northern auroral region for Hubble. On Earth, auroras are mainly created by particles or...

SpaceTime

Search This Blog