I’m here to talk about short gamma-ray bursts (GRBs) that are linked to neutron star mergers and the associated kilonova that go with them. These detonations – in gamma-ray light – are very briefly the most luminous objects in the universe. For over a decade, people have been looking for ways to use these objects and other, longer GRBs as standard candles to measure distances to the farthest corners of our universe. Exploding white dwarfs all explode with the same mass (with some exceptions), and thus explode with the same luminosity (with some exceptions).

Neutron stars, however, have a variety of sizes and when they explode in pairs, they can explode in a variety of different ways, and there is no linear relationship between their luminosity and distance. Instead, however, it appears that where a line can’t fit the data, a plane maybe can.

A new paper to appear in The Astrophysical Journal with lead author Maria Fainotti describes a fundamental plane for neutron stars that allows their luminosity to be predicted based on the duration of the X-ray plateau phase and the luminosity of the gamma-ray peak. The work is still messy; by which I mean there is still a lot of noise due to a combination of these objects being rare and very rarely close enough to accurately measure.

For us to be able to accurately use kilonovae and their associated short GRBs as standard candles, we need to be able to calibrate them. To understand distances in the universe, we need overlapping methods that allow us to measure distances in more than one way. For the nearest stars, we use parallax, like a surveyor, to measure distances based on triangles. From there we use pulsating stars like RR Lyrae and Cepheid variables that are sometimes close enough for parallax measurements but can be seen as far away as nearby galaxies. These galaxies allow us to calibrate type 1a supernovae, and in a perfect universe, those type 1a supernovae will allow us to calibrate these short GRBs.

While there are other ways to measure distances, they haven’t allowed this potential plane to be well defined. There is a lot of noise, and we have a long way to go before we can use distant GRBs to measure parameters of the universe beyond what we measure with supernovae.

Here is to hoping we see GRBs in systems we’ve previously seen with Type 1a supernovae.

More Information

Space Science Institute press release 

“The X-Ray Fundamental Plane of the Platinum Sample, the Kilonovae, and the SNe Ib/c Associated with GRBs,” Maria Giovanna Dainotti et al., 2020, to appear in the Astrophysical Journal (preprint on arxiv.org)