A 2 per cent Hubble constant measurement from standard sirens within 5
  years
  Gravitational wave coalescence events provide an entirely new way to
determine the Hubble constant, with the absolute distance calibration provided
by the theory of general relativity. This standard siren method was utilized to
measure the Hubble constant using LIGO-Virgo's detection of the binary
neutron-star merger GW170817, as well as optical identifications of the host
galaxy, NGC 4993. The novel and independent measurement is of particular
interest given the existing tension between the value of the Hubble constant
determined using Type Ia supernovae via the local distance ladder ($73.24 \pm
1.74$) and that from Cosmic Microwave Background observations ($66.93 \pm
0.62$) by $\sim 3$ sigma. Local distance ladder observations may achieve a
precision of $1\%$ within 5 years, but at present there are no indications that
further observations will substantially reduce the existing discrepancies. In
addition to clarifying the discrepancy between existing low and high-redshift
measurements, a precision measurement of the Hubble constant is of crucial
value in elucidating the nature of the dark energy. Here we show that LIGO and
Virgo can be expected to constrain the Hubble constant to a precision of
$\sim2\%$ within 5 years and $\sim1\%$ within a decade.
