Gravitational Waves Conceptual Illustration

Supermassive binary black hole binary systems at the cores of galaxies produce ripples in spacetime called gravitational waves. Gravitational waves from all of the supermassive black hole binaries in the universe combine to form a stochastic background which we can detect using pulsar timing.  Illustration: Olena Shmahalo


Low-Frequency Gravitational Waves

When massive bodies like black holes accelerate, they give off energy in the form of gravitational waves. As gravitational waves travel through the universe, they stretch and squeeze spacetime, but the effect is tiny (only around one part in 1,000,000,000,000,000) which makes them very difficult to detect. Gravitational waves carry information about the sources that produced them, and are particularly useful for studying sources that cannot be seen using light.

As with light waves, gravitational waves are emitted over many orders of magnitude in frequency. Gravitational wave detectors operate by searching for changes in light travel time due to spacetime being stretched and squeezed by gravitational waves. Just like we need different types of telescopes to observe the entire electromagnetic spectrum, we need different types of gravitational wave detectors to observe the entire gravitational wave spectrum. Pulsar timing arrays are sensitive to low-frequency (i.e., long period) gravitational waves. These are gravitational waves with frequencies of order nanohertz, which corresponds to periods of months to decades. This is much lower in frequency than what can be seen by ground-based interferometers like LIGO or space-based interferometers like LISA. Hence, pulsar timing arrays are sensitive to completely different types of sources than other types of gravitational wave detectors. Pulsar timing arrays are therefore opening a new window on the gravitational wave universe.

More Topics

Radio Astronomy Conceptual Illustration

Radio Astronomy

We observe with the largest telescopes in the world in order to detect electromagnetic waves with the very longest wavelengths. Radio astronomy allows us to probe energetic processes which are invisible to optical telescopes.

Pulsar Conceptual Illustration

Pulsars as Cosmic Clocks

Neutron stars are the collapsed cores of massive stars which have ended their lives in cataclysmic supernova explosions. Pulsars are rapidly rotating, highly magnetic neutron stars which emit beamed radio emission, like cosmic lighthouses. They are unique laboratories for a variety of fundamental physics experiments.

Galactic Evolution Conceptual Illustration

Galaxies and Supermassive Black Holes

Galaxies have evolved through cosmic time through consecutive mergers with other galaxies. We will gain unique insights into this important process by detecting the gravitational waves produced by extremely massive pairs of black holes at the cores of merged galaxies.  

MMA  Conceptual Illustration

Multimessenger Astrophysics

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.