Aurore Simonnet’s concept of stars, black holes, and nebula in spacetime

Gravity waves are everywhere!

Scientists are reporting the first evidence that our Earth and the whole universe around us are awash in a quiet background of vibration called gravitational waves. Ripples in spacetime itself. These waves oscillate very slowly over years and even decades and are thought to originate from pairs of supermassive black holes leisurely spiraling together before they merge.

When they do merge the explosion of gravitational waves may be detected by LIGO (a Gravitational Observatory).

The results are reported by a team of scientists at the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) based at Caltech, as is LIGO. A team of radio telescopes.

NANOGrav is a network of observatories that carefully record the signals from 68 pulsars located throughout our galaxy. Pulsars are the remnants of stars that go supernova, leaving behind a neutron star that’s rapidly spinning. These compact objects are incredibly stable Cosmic clocks that can spin hundreds of times a second with no significant change for decades. As they spin they give off radio waves in regularly timed pulses, like a clock.

The pulsars act like a network of buoys bobbing on a sea of gravitational waves. The timing of the pulsar signals very gradually change as Gravity waves pass through them, making the pulsar and its signal move too. Slowly rocking the galaxy to and fro.

“To tease out the gravitational-wave background, we had to nail down a multitude of confusing effects, such as the motion of the pulsars, the perturbations due to the free electrons in our galaxy, the instabilities of the reference clocks at the radio observatories, and even the precise location of the center of the solar system, which we determined with help from NASA’s Juno and Cassini missions,” says Michele Vallisneri, a NANOgrav team member at JPL. The observations took 15 years.

This network of pulsars and radio telescopes is called a “pulsar timing array”. The vast distances between the pulsars allows for detection of very large, low frequency gravity waves. These are emitted by massive black holes as they gradually circle each other, usually near the center of a galaxy. LIGO detects higher frequency waves, as black holes and neutron stars merge.

Gravity waves were predicted by Einstein in 1915, and exactly a century later were discovered by LIGO in 2015, then awarded the Nobel Prize. So it’s an important part of physics.

It was long predicted that gravity waves would be everywhere, since any object in the universe that moves creates a gravity wave. NANOGrav is the first evidence that this is true, that the whole universe is bathed in a sea of gravity waves.Caltech’s Deep Synoptic Array-2000 will add 2000 more radio telescopes to the network in 2027. Learn more at https://nanograv.org.

It’s important to know this is an indirect detection of gravity waves by their effect on pulsar timing. LIGO detects gravitational waves directly, more on that in an upcoming article.

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