Science reports that :
Turning networks of dead stars into galaxy-size gravitational wave detectors allows astronomers to tune in to the slowly undulating swells in spacetime arising from pairs of supermassive black holes (SMBHs) that are about to collide.
A BILLION SECONDS IS A LONG TIME:
NANOHERTZ GRAVITY WAVES TAKE GENERATIONS TO RISE AND FALL
NANOGrav investigators now feel they have strong evidence for nanohertz gravity waves in a 15-year data set of 67 pulsars located up to 20,000 light-years away. They identified anomalies of one part in a quadrillion—comparable to measuring the distance between Earth and the Moon to a micron.
The results were published in The Astrophysical Journal Letters. The signal is very different from what ground-based detectors such as the Laser Interferometer Gravitational-wave Observatory (LIGO) pick up. The background signal could include other, more exotic sources. Primordial gravitational waves might have been generated shortly after the big bang if the universe experienced convulsions from a still-hypothetical breakneck expansion in size known as inflation. Some theorists also posit that the violent emergence of one of the fundamental forces at the dawn of time left defects in spacetime called cosmic strings, which would now stretch across the universe, vibrating like piano wires and emitting gravitational waves in the range that PTAs are sensitive to.
A gravitational wave spectrum
Pulsar timing arrays have now brought long-period gravitational waves into focus. Ground-based interferometers detected the first short-period gravitational waves in 2015. Future detectors in space could probe the wavelengths in between.
| DETECTOR TYPE | PERIOD | SOURCES |
|---|---|---|
| Pulsar timing arrays | Years to decades | Merging supermassive black holes (SMBHs), big bang ripples, exotic new physics |
| Space-based interferometers | Hours to seconds | Midsize SMBHs, stellar-size black hole mergers, white dwarf mergers |
| Ground-based interferometers | Milliseconds | Stellar black hole mergers, merging neutron stars, supernovae |
