How To Discover Mirror Stars? (Cosmology / Astronomy)

Curtin and Setford examine the visible signatures of Mirror Stars in observations for the first time.

Friends, many studies suggested that visible sector interact with dark sector through some kind of channels (like fields, symmetries etc.). Chacko and colleagues also suggested that there are many similarities between standard model (SM) matter and mirror matter which makes it clear that the mirror matter could cool and clump in our galaxy, leading to the formation of Mirror Stars (MS) that fuse mirror nuclei and shine in mirror photons.

The possibility that some fraction of DM could form Mirror Stars is both extremely intriguing and quite general for a complex dark sector, requiring only a massless dark photon. The idea of Mirror Stars has been discussed in the context of Mirror-DM models but their more general nature and non-gravitational observational consequences were never carefully explored.

FIG. 1: Important interactions between mirror and visible matter. Left: nucleus-nucleus scattering. Right: Thomson conversion of a mirror photon to a SM photon © Curtin and Setford

Now, Curtin and Setford in their recent paper, examined the visible signatures of mirror stars in observations for the first time. They demonstrated that, mirror stars lead to spectacular astrophysical signals if the standard model/visible and dark photons have a small kinetic mixing.

They found that when Mirror Stars capture SM matter in their cores. This “SM nugget” gets heated up to T ∼ 10⁴ K by ϵ² -suppressed interactions with the mirror matter, giving rise to an optical signal similar to but much fainter than standard white dwarfs. They also showed for the first time that “mirror Thomson conversion” allows thermal dark photons from the Mirror Star core to be converted to visible X-rays that escape the nugget, providing a direct window into the MS interior.

“This robust and highly distinctive signature is a smoking gun of mirror stars and could be discovered in optical and X-ray searches”

— told Curtin, first author of the study

FIG. 2: A Hertzsprung-Russell diagram showing the dual signatures of their Mirror Star benchmarks estimated in their paper. Each MS is represented by two points connected by a line. The solid lines show the approximate distances up to which such objects could be observed in Gaia or Chandra. © Curtin and Setford

In addition, they suggested that this could be discovered in full-sky surveys like Gaia out to the distances indicated by blue lines in fig 2. (which also provides a parallax measurement to determine absolute luminosity). The discovery of such faint Mirror Star candidates would prompt extremely detailed study with an X-ray observatory: Chandra could see the X-ray signal roughly out to distances indicated by green lines (in fig. 2 above) with an exposure equal to the Hubble Deep Field North. Detection of this black-body-like X-ray signal would be a true smoking gun of Mirror Stars and provide a direct window into their interior, allowing measurement of the core temperature and perhaps even aspects of mirror nuclear physics via detailed study of spectral features. This is also true for higher ϵ ≳ 10¯10, where Mirror Stars might appear similar to white dwarfs, providing additional motivation to study them with X-ray observations.

“We have shown that Mirror Star signals are highly distinctive and robust. They arise in well-motivated theories that may not show up in collider measurements. This makes dedicated searches for Mirror Stars a new frontier in DM detection with completely untapped discovery potential, and an opportunity we cannot afford to miss.”

— concluded authors of the study

Reference: David Curtin, Jack Setford, “How to discover Mirror Stars”, Physics Letters B, Volume 804, 2020, 135391, ISSN 0370-2693, https://doi.org/10.1016/j.physletb.2020.135391.
(https://www.sciencedirect.com/science/article/pii/S0370269320301957)


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