NANOGrav: Fluctuations in space captured in real-time

Heading into the holiday weekend, social media exploded with news that a massive discovery was going to be announced on Thursday June 29 by the NANOgrav collaboration. This network of North American observatories had been watching the sky in radio light for over 15 years and now they had something big to share.

For those who’d been following the team’s work, hopes were high. This team had been carefully monitoring the metronome-like ticking of radio pulsars to see if they could see alterations in the fabric of space-time that are caused by gravitational waves. That big news — we hoped — would be a description of our universe warping in observable ways.

“We can gain unique insights about our Universe through observations with the multiple messengers of gravitational waves and electromagnetic waves at radio to gamma-ray frequencies observed with telescopes on Earth and in space.” Credit: NANOGrav.org

Funded by the National Science Foundation in 2015, NANOGrav used the Arecibo and Greenbank radio dishes, as well as the CHIME and Very Large Array to monitor an ever increasing number of pulsars.

These spinning neutron stars blast our radio light like an over-caffeinated lighthouse spinning 1000 times a second. Neutron stars are the high-density remnants of massive stars that can no longer fuel nuclear reactions. Neutron stars are just what their name implies: giant balls of neutrons. Because these particles can get much closer together than a mix of protons and electrons, neutron stars can cram all their mass into a volume that could rest comfortably on Manhattan Island. That mass — it is 1.4 solar masses to something like 2.2 solar masses.

Pulsars blast out radio light like lighthouse as they rotate. Credit: NANOGrav.org

When that much mass crams into a space that small and spins extremely rapidly, that you end up with a nature-made top that doesn’t have a single wibble or wobble to its motion. A stand-alone pulsar is the ultimate clock, and when we find pulsars paired up in binary systems, their obits can be precisely measured by the shifting of their pulses.

Essentially, as the pulsar moves toward us in its orbit, each pulse has to travel a little less distance than the one before, so the ticking of the clock seems to speed up. As the pulsar moves away from us, each tick has to travel a little bit farther, and the beating seems to slow down.