Introduction

NANOGrav stands for North American Nanohertz Observatory for Gravitational Waves. As the name implies, NANOGrav members are drawn from across the United States and Canada and our goal is to study the Universe using gravitational waves. Gravitational waves are ripples in the fabric of space and time that cause objects to shrink and stretch by very, very small amounts. NANOGrav uses the Galaxy itself to detect gravitational waves with the help of objects called pulsars — exotic, dead stars that send out pulses of radio waves with extraordinary regularity. This is known as a Pulsar Timing Array, or PTA. NANOGrav scientists make use of some of the world's best telescopes and most advanced technology, drawing on physics, computer science, signal processing, and electrical engineering. Our short term goal is to detect gravitational waves within the next decade, an event which may be the first direct detection ever. But detection is only the first step towards studying our Universe in a completely new and revolutionary way, and we are sure to make unexpected discoveries in the process.

NANOGrav cooperates with similar experiments in Australia (the Parkes Pulsar Timing Array) and Europe (the European Pulsar Timing Array). Together, we make up the International Pulsar Timing Array, or IPTA. By sharing our resources and knowledge, we hope to usher in the era of gravitational wave astronomy more quickly and with greater impact.

NANOGrav was founded in October 2007 and has since grown to over 60 members at over a dozen institutions. NANOGrav members have been awarded over $10M in competitive scientific grants and awards to perform NANOGrav-related research at their institutions.

This figure illustrates the range of gravitational wave astronomy. Gravitational waves (GWs) span many orders of magnitude in frequency, from the Hubble-length primordial waves that leave their imprint on the cosmic microwave background (CMB), to the gravitational waves with periods of years detectable by pulsar timing arrays (PTAs) like NANOGrav, the hour-long period waves detectable by space-based instruments such as eLISA, and the millisecond period waves detectable by ground-based interferometers like LIGO and Virgo. Each of these experiments probes different time-scales and hence a wide range of objects and phenomena in the universe.

We show the range of amplitudes (measured by the gravitational wave strain h) and frequencies. The four essential techniques are shown, at the approximate locations for the amplitudes and frequencies that they probe. For each technique also shown is the expected kinds of sources that should produce gravitational waves at this range of amplitudes and frequencies.

The goal of NANOGrav and other PTAs in this enterprise is the detection of very low frequency (VLF) gravitational waves associated with supermassive binary black holes (SMBBHs), whose observations can be used to probe the innermost regions of merging galaxies and perhaps reveal the presence of other exotic phenomena.


This material is based in part on work supported by the National Science Foundation under Grant Number 968296. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.