Moving Closer to a Detection of nHz-frequency Gravitational Waves with NANOGrav

Millisecond Pulsars (MSPs) have become reliable and
extremely stable workhorses of modern astronomy and physics.  The
North American Nanohertz Observatory for Gravitational Waves, or
NANOGrav, has been observing growing numbers of these systems for over
15 years, and the data look great.  High precision timing of almost 80
MSPs has provided unprecedented sensitivity to the gravitational wave
Universe at nHz-frequencies, where our upper limits are already
constraining the population of super-massive black hole binaries.  But
our sensitivity is increasing each year as we continue to add MSPs to
our timing array and develop new techniques to remove systematics due
to the interstellar medium and the uncertain solar system ephemerides.
Meanwhile, though, our observations provide a wide variety of
astrophysics, such as new neutron star mass measurements and
constraints of the dense matter equation of state.