High energy events, like supermassive black hole mergers, some supernovae, and the mergers of neutron stars all have the potential to give off massive amounts of energy via gravitational waves, while also sending out particles and light across many wavelengths. This triple feature of particles, light, and gravitational waves turns astronomy into a multi-messenger field, where we can start to look at things through a variety of instruments that probe radically different kinds of physics. This is all really new, and folks are still exploring all the ways they can leverage the combined information to understand our universe.

In a new paper in Science, led by Tim Dietrich, a team of astronomers examines how merging neutron stars may be used as standard candles, and what we can learn about the interiors of these weird stars from so many forms of data. So far, their estimates of neutron star sizes are in line with prior estimates made using pulsar data, and the error bars are such that it’s not yet possible to determine if neutron stars are solid neutrons or if their core is some denser, weirder substance that would allow them to have a smaller radius. It’s good to see consistency, and we can only hope to see the error bars coming down over time.

They also found, again with fairly hefty error bars, that the strength of detected gravitational waves can be combined with theoretical calculations about the initial energy in the waves, to sort out where the neutron star mergers were located. Essentially, if we know how much energy the wave should have contained at its origin, and we can measure how much energy it has as it passes through the Earth, we can calculate the distance. By combining thus calculated distances with measured redshifts of the galaxies containing the neutron stars, we can calculate how fast the universe is expanding. Preliminary results, with error bars, yield a value of 66 km/sec/Mpc and are consistent with measurements from all other techniques. While it’s frustrating that these results aren’t precise enough to say if the supernova-related expansion measurements or the Cosmic Mircowave Background-related measurements of the universe’s expansion are correct, again, things can only improve as more data is taken and techniques and instrumentation are perfected.

This is the start of a new area of astronomy. It’s exciting to see new techniques matching old results, and I can’t wait to see how multimessenger astronomy expands our understanding of the universe.

More Information

Los Alamos National Laboratory press release 

Scientific American article 

“Multimessenger constraints on the neutron-star equation of state and the Hubble constant,” Tim Dietrich et al., 2020 December 18, Science