The collision of two extremely dense collapsed stars in the distant universe has provided potential clues to axions, a dark matter candidate first proposed half a century ago.
Stellar remnants are neutron stars, the corpses left behind after a massive star collapsed on itself. These dead stars are so dense that their electrons collapse onto protons – hence the name “neutron stars.”Their extreme density also makes them the site of bizarre physics: specifically, they have Proposed as an axion sourcea hypothetical particle that may contribute to the dark matter content of the universe.
new research, publish Earlier this month in Physical Review Letters, constraints were drawn on how axion-like particles couple with photons, based on spectral and temporal data from a neutron star merger about 130 million light-years away.
Axion-like particles (or ALPs) are a class of hypothetical dark matter candidates that are more common than axions, and scientists believe their properties can be revealed by studying photons and limiting the particle’s mass range. The team writes in their paper that axion-like particles produced in neutron star mergers escape the remnants and decay back into two photons, producing an electromagnetic signal that can be detected by telescopes. The data were collected from 2017 observations of the collision by the Fermi Large Area Telescope (Fermi-LAT).
“For neutron star mergers, there is a unique opportunity to get a photon signal,” said Bhupal Dev, a physicist at Washington University in St. Louis and the study’s lead author, in a phone call with Gizmodo. “We can use this multi-messenger study and these data to explore some new physics beyond the Standard Model.”
dark matter Appears to make up 27% of the universebut its interaction with ordinary matter is very weak, and scientists can only Detect it by its gravitational effect about Us able look. Hot dark matter candidates (that is, the theoretical parties responsible for the surface presence of dark matter) are Weakly Interacting Massive Particles (WIMPs), hidden (or dark) photons, Massive Compact Halo Objects (MACHOs), and of course axions.
Axion, named after a brand of laundry detergent, is a hypothetical particle proposed in the 1970s as a solution to physics. Strong CP problemwhich describes the fact that even if particles are replaced by their mirror images, quarks’ compliance with the laws of physics remains the same.
Neutron stars are among the densest objects in the universe, second only to black holes. Unlike black holes, light can escape neutron stars, allowing them to be observed across the electromagnetic spectrum.
Dev explains that if axions do couple with photons, then neutron star mergers could produce axions in a variety of ways. Through photon coalescence, axions will be produced from photons that gather and fuse in extremely hot astrophysical environments. Another way axions are produced is through the Primakov process, where photons interact with a bath of electrons to create axions.
As proposed, the axion is so small that it sometimes behaves more like a wave than a particle, meaning it can escape a crime scene relatively easily. But protons are (relatively) massive, so it takes a while for the particles to emerge from this hotbed of interactions. Specifically, it took 1.7 seconds: the amount of delay the researchers observed between the gravitational wave signal produced by the neutron star merger and the electromagnetic signal produced by the neutron star merger.
“We get a lot of photons from the sky. So how do we really know that this photon signal comes from axions?” Dave said. “This comes from the decay of particles, not the astrophysical process of photons disappearing due to scattering. So there is a difference in the spectrum. We can analyze the timing information, and we can also analyze the spectral characteristics. This is how we can combine these new physical signals Separate from standard astrophysical processes.”
Experiments on Earth are also working to narrow down the potential mass range of axions. Lux-Zeppelin, Xenon 1T,as well as Alpine II experimentIt will begin operations in May 2023 and is designed to search for axions deep underground.But there are other projects like ADMX and Dark Matter Radio Pathfinder, works to constrain the mass range of hidden (or dark) photons, another class of dark matter candidates. Future generations of dark matter radio will search for axions.
The new study “puts some new constraints on axion-like particles, because so far we haven’t seen any axion signals,” Dave said. “It also gives us hope that, in the future, we can learn more about axion-like particles using these astrophysical observations. This will complement ongoing laboratory searches.“
Looking for axions is a lot like using a metal detector on a really, really big beach. Often, physicists and astronomers find nothing. But searching for axions and axion-like particles across the entire range of potential masses is the best way to ultimately track them down.
more: What is dark matter? Why hasn’t anyone discovered it yet?