Neutron star mergers are a treasure trove for brand new physics signals, with implications for determining the true nature of dark matter, in response to research from Washington University in St. Louis.
On Aug. 17, 2017, the Laser Interferometer Gravitational-wave Observatory (LIGO), in the USA, and Virgo, a detector in Italy, detected gravitational waves from the collision of two neutron stars. For the primary time, this astronomical event was not only heard in gravitational waves but additionally seen in light by dozens of telescopes on the bottom and in space.
Physicist Bhupal Dev in Arts & Sciences used observations from this neutron star merger — an event identified in astronomical circles as GW170817 — to derive latest constraints on axion-like particles. These hypothetical particles haven’t been directly observed, but they seem in lots of extensions of the usual model of physics.
Axions and axion-like particles are leading candidates to compose part or all the “missing” matter, or dark matter, of the universe that scientists haven’t been in a position to account for yet. On the very least, these feebly-interacting particles can function a sort of portal, connecting the visible sector that humans know much about to the unknown dark sector of the universe.
“We have now good reason to suspect that latest physics beyond the usual model is likely to be lurking just across the corner,” said Dev, first writer of the study in Physical Review Letters and a school fellow of the university’s McDonnell Center for the Space Sciences.
When two neutron stars merge, a hot, dense remnant is formed for a temporary time frame. This remnant is an excellent breeding ground for exotic particle production, Dev said. “The remnant gets much hotter than the person stars for a couple of second before settling down into a much bigger neutron star or a black hole, depending on the initial masses,” he said.
These latest particles quietly escape the debris of the collision and, distant from their source, can decay into known particles, typically photons. Dev and his team — including WashU alum Steven Harris (now NP3M fellow at Indiana University), in addition to Jean-Francois Fortin, Kuver Sinha and Yongchao Zhang — showed that these escaped particles give rise to unique electromagnetic signals that will be detected by gamma-ray telescopes, comparable to NASA’s Fermi-LAT.
The research team analyzed spectral and temporal information from these electromagnetic signals and determined that they may distinguish the signals from the known astrophysical background. Then they used Fermi-LAT data on GW170817 to derive latest constraints on the axion-photon coupling as a function of the axion mass. These astrophysical constraints are complementary to those coming from laboratory experiments, comparable to ADMX, which probe a distinct region of the axion parameter space.
In the longer term, scientists could use existing gamma-ray space telescopes, just like the Fermi-LAT, or proposed gamma-ray missions, just like the WashU-led Advanced Particle-astrophysics Telescope (APT), to take other measurements during neutron star collisions and help improve upon their understanding of axion-like particles.
“Extreme astrophysical environments, like neutron star mergers, provide a brand new window of opportunity in our quest for dark sector particles like axions, which could hold the important thing to understanding the missing 85% of all of the matter within the universe,” Dev said.
This work was supported by the Department of Energy’s Office of Science.
