Fermi Large Area Telescope (IMAGE)
Caption
Orbiting 500 km above the earth, the Fermi Large Area Telescope collects gamma rays from millisecond pulsars. As these high-energy photons travel across the Milky Way, they encounter a sea of low-frequency gravitational waves produced by pairs of supermassive black holes coalescing in the centers of merged galaxies. The spacetime ripples, with wavelengths extending beyond 100 trillion kilometers, cause each photon to arrive slightly earlier or slightly later than expected. Monitoring the gamma rays from many of these millisecond pulsars---an experiment known as a pulsar timing array---can reveal this telltale signature. Pulsar timing arrays have previously only used sensitive radio telescopes. Now, data from Fermi are enabling a gamma-ray based pulsar timing array and giving a new, clear view of these gravitational waves.
Credit
Daniëlle Futselaar/MPIfR (artsource.nl)
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