Graviational-wave standard sirens and cosmology

Daniel Holz (LANL)

We discuss the use of gravitational wave sources as probes of
cosmology. The inspiral and merger of a binary system, such as a pair
of black holes or neutron stars, is extraordinarily bright in
gravitational waves. By observing such systems it is possible to
directly measure an absolute distance to the sources out to very high
redshift. When coupled with independent measures of the redshift, these
"standard sirens" enable precision estimates of cosmological
parameters. We review proposed GW standard sirens for the LIGO and LISA
gravitational wave observatories. Percent-level measurements of the
Hubble constant and the dark energy equation-of-state may be feasible
with these instruments.