APEC Seminar (Astronomy - Particle Physics - Experimental Physics - Cosmology)

Speaker: Chris Belczynski (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences)
Title: Binary neutron star formation and the origin of GW170817
Date: Tue, Jan 15, 2019, 12:00 - 13:00
Place: Seminar Room A
Related File: 2231.pdf
Abstract: The first neutron star-neutron star merger (NS-NS: GW170817) was
detected in gravitational waves by LIGO/Virgo in a galaxy in which the
majority of star formation was taking place a long time ago (~11
Gyr). Based on this single event, LIGO/Virgo estimated that local
cosmic NS-NS merger rate is 110-3840 Gpc^-3 yr^-1. Only some extreme
evolutionary models can generate NS-NS merger rates in old host
galaxies consistent with the LIGO/Virgo estimate. However, we show
that these models generate rates exceeding empirical Galactic NS-NS
merger rates based on the large population of Milky Way NS-NS
binaries.
Typically, current evolutionary models produce NS-NS merger rates
that are consistent with the Milky Way empirical rates (~10-200
Myr^-1). However, these models generate local (z=0) cosmic NS-NS
merger rate in old host galaxies (1-70 Gpc^-3 yr^-1) that are below
the LIGO/Virgo estimate. The reason behind this tension is the
predicted delay time distribution between star formation and NS-NS
mergers that favors short delays.
This study highlights the tension between the current evolutionary
predictions and the observation of the first NS-NS merger in an old
host galaxy. It is crucial to understand that models need to explain
not only the LIGO/Virgo rate estimate, but also the merger site.