Gravitational Waves Create A 'Cosmic Symphony' That Scientists Are Tuning Into

Space.com

Scientists are using pulsars to detect the gravitational wave 'hum' created from supermassive black hole mergers.   Credit: National Science Foundation (NSF)

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00:00 [Music]

00:29 Supermassive black holes lurk in the hearts of most galaxies, and galaxies grow by merging

00:34 with other galaxies.

00:36 When that happens, their black holes also merge and grow, becoming more and more massive

00:41 over time.

00:43 How exactly this happens is not fully understood, but the universe is telling us its secrets

00:49 in gravitational whispers.

00:51 We just have to listen.

00:54 Just as sound waves are vibrations of air molecules, gravitational waves are vibrations

00:58 in the fabric of space-time.

01:01 When two massive black holes spiral toward each other, they produce gravitational waves

01:06 that travel through the cosmos at the speed of light.

01:10 If we imagine the universe as a grand symphony, these merging supermassive black holes are

01:15 the bass players.

01:17 As they orbit each other, these black holes play the deep bass notes that echo throughout

01:22 the cosmic concert hall.

01:24 But that's not all there is to the symphony.

01:26 In the background is a faint but pervasive hum produced by the collective motion of massive

01:32 objects throughout the universe, from the earliest moments of the Big Bang until now.

01:38 This gravitational wave background is truly a harmony of space and time.

01:43 Nanograv is an NSF-funded collaboration of astronomers and astrophysicists.

01:48 Our goal is to solve some of the deepest mysteries of the universe by studying the gravitational

01:53 waves produced by these dancing monster black holes.

01:58 These waves are light-years long and can only be detected by the most extraordinary instruments.

02:05 To measure these giant but subtle ripples in space-time, Nanograv created a galaxy-sized

02:10 detector using some of the most incredible objects in the cosmos, rapidly rotating neutron

02:15 stars known as millisecond pulsars.

02:20 Pulsars are the ultra-dense remnants left behind when massive stars reach the end of

02:24 their lives and explode as supernovae.

02:28 These pulsars are also cosmic beacons.

02:30 They spin extraordinarily rapidly and with startling regularity, releasing pulses of

02:36 radio waves with each rotation.

02:39 Astronomers detect those pulses using giant radio telescopes.

02:43 By monitoring the radio pulses from these ultra-precise cosmic clocks, Nanograv can

02:48 detect the slightest deviations in the regularity of their timekeeping, and these deviations

02:53 trace ripples in space-time.

02:56 This galactic-scale detector is called a Pulsar Timing Array.

03:01 Nanograv has now observed an array of dozens of pulsars for more than 15 years and the

03:06 results are astounding.

03:08 We are finally hearing the faint background hum likely coming from in-spiraling pairs

03:13 of supermassive black holes.

03:16 With time, astronomers expect to pick out the individual instruments in this cosmic

03:20 symphony, revealing unique insights into the evolution of galaxies and the history of the

03:26 cosmos.

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