Scientists are using pulsars to detect the gravitational wave 'hum' created from supermassive black hole mergers.
Credit: National Science Foundation (NSF)
Credit: National Science Foundation (NSF)
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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
00:59 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.
01:27 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.
01:44 Nanograv is an NSF-funded collaboration of astronomers and astrophysicists.
01:49 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
02:16 stars known as millisecond pulsars.
02:21 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.
02:31 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.
02:44 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
02:54 trace ripples in space-time.
02:57 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.
03:09 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
03:21 symphony, revealing unique insights into the evolution of galaxies and the history of the
03:26 cosmos.
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