Synopsis: Homing in on Primordial Gravitational Waves

An analysis of data spanning 29 orders of magnitude in gravitational-wave frequency provides insights into the physics of the early cosmos.

Gravitational waves—the distortions in spacetime first spotted by the LIGO Scientific Collaboration in September 2015—are fundamentally distinct from electromagnetic waves. But like their electromagnetic counterparts, they can come in a broad range of frequencies. Different experiments to detect them target specific frequency bands, each of which links to particular wave sources, such as the two colliding black holes that generated the signal detected by LIGO. In a study that combines data across an unprecedented swath of gravitational-wave frequencies, Paul Lasky from Monash University, Australia, and colleagues now put stringent bounds on a source that should produce a signal in all experiments: quantum fluctuations in the early cosmos.

Researchers believe that a fraction of a second after the big bang, quantum fluctuations of the gravitational field were magnified by a rapid expansion of space called inflation, generating a primordial background of gravitational waves. Lasky and co-workers pulled together data from several experiments that should carry direct or indirect imprints of this background. Spanning 29 orders of magnitude in gravitational-wave frequency, these data included observations of the cosmic microwave background radiation obtained by the Planck satellite and the BICEP2 experiment, of the arrival times of pulses from rotating neutron stars, and of mirror displacements in ground-based interferometers such as LIGO. The combined data allowed the authors to put stringent bounds on the slope of the background’s energy spectrum, which quantifies how the energy density of the waves varies with frequency. From these bounds, they were able to rule out exotic models of inflation that produce large slopes.

This research is published in Physical Review X.

–Ana Lopes


Features

More Features »

Announcements

More Announcements »

Subject Areas

CosmologyAstrophysicsGravitation

Previous Synopsis

Materials Science

Topological Origami

Read More »

Next Synopsis

Condensed Matter Physics

Electron–Phonon Affair Comes to Light

Read More »

Related Articles

Synopsis: Persistence of Gravitational-Wave Memory
Gravitation

Synopsis: Persistence of Gravitational-Wave Memory

Researchers predict the existence of three new long-lived signatures of gravitational waves, as part of a unified mathematical framework for identifying such effects.   Read More »

Synopsis: Inflation Goes Up Against the Clock
Cosmology

Synopsis: Inflation Goes Up Against the Clock

A proposed cosmological signature, called a clock signal, could provide a way to study the first ticks of cosmic time. Read More »

Synopsis: Black Hole Test for Gravity
Gravitation

Synopsis: Black Hole Test for Gravity

Researchers test a key element of the theory of gravity in the strongest gravitational field to date—that produced by the supermassive black hole at the center of the Milky Way. Read More »

More Articles