Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2023 June 29
The illustration shows the beams from pulsars around the image and a pair
of merging black holes on the upper left. A grid depicting the warping
of spacetime by passing gravitational waves spreads across the image center.
Please see the explanation for more detailed information.

A Message from the Gravitational Universe
Illustration Credit: NANOGrav Physics Frontier Center; Text: Natalia Lewandowska (SUNY Oswego)

Explanation: Monitoring 68 pulsars with very large radio telescopes, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has uncovered evidence for the gravitational wave (GW) background by carefully measuring slight shifts in the arrival times of pulses. These shifts are correlated between different pulsars in a way that indicates that they are caused by GWs. This GW background is likely due to hundreds of thousands or even millions of supermassive black hole binaries. Teams in Europe, Asia and Australia have also independently reported their results today. Previously, the LIGO and Virgo detectors have detected higher-frequency GWs from the merging of individual pairs of massive orbiting objects, such as stellar-mass black holes. The featured illustration highlights this spacetime-shaking result by depicting two orbiting supermassive black holes and several of the pulsars that would appear to have slight timing shifts. The imprint these GWs make on spacetime itself is illustrated by a distorted grid.

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