The first observation of a neutron star merger in 2017 by the LIGO collaboration was a truly remarkable breakthrough for multi-messenger astronomy and astrophysics. One event that occurred more than 100 million years ago was observed simultaneously across the electromagnetic spectrum and in gravitational waves, the latter of which was demonstrated for the first time only two years prior. Suddenly a field of astronomical research that had been previously veiled in speculation not only had real data behind it, but that data came from multiple pathways.
In the wake of this discovery, many research groups around the world were understandably excited, including our groups, the GPS.DM and GNOME collaborations. These two teams are dedicated to probing astrophysics with networks of quantum sensors. GPS.DM uses the orbital network of atomic clocks that make up the global positioning system, while GNOME uses a global network of magnetometers. After the neutron star merger in 2017, one question was on our minds: How can we help?
Since gravitational wave astronomy is very much still in its infancy, many of the measurements that are estimated by LIGO have large error bars. For example, the total energy released in gravitational waves estimated by LIGO in a given event likely has an uncertainty close to one solar mass. This is an incredible amount of energy that could exist in channels other than gravitational waves or electromagnetic waves. Instead, some of that energy could go into a yet undiscovered field, detectable by GPS.DM, GNOME, or another network of detectors. We deem these Exotic Low-mass Fields (ELFs).
These fields would have some important properties in order to be detectable. They must travel close to the speed of light, and thus have a very low mass, in order to arrive close to the same time as the gravitational waves. It also must interact in some fashion with atomic clocks or magnetometers. With these conditions met, there is a characteristic ELF signal that would be imprinted on network sensor data.
We show in our work that if such fields exist, GPS.DM is currently sensitive enough to detect them, and planned future networks will soon be able to as well. In the absence of a detection, we could instead set useful limits on exotic physics theories. It is also important to note that our results quite general, and can be applied to any other network of detectors.
A discovery of ELFs would have immense scientific consequences. Astronomers would then have access to an additional messenger not only for future merger events, but for past ones as well. There is only one observation of a neutron star merger so far, but if we can show that ELFs are emitted from them, we could catalog ELF emission for the entire history of GPS.DM and GNOME data, which is an archive of 20 years for the case of GPS.DM.
In any case, astronomers and astrophysicists alike should be excited that they have a new tool to investigate the universe with.
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