00:28Supermassive Black
00:29Black holes lurk in the hearts of most galaxies, and galaxies grow by merging with other
00:35galaxies.
00:36When that happens, their black holes also merge and grow, becoming more and more massive
00:41over time.
00:43How exactly this happens is not fully understood, but the universe is telling us its secrets
00:49in gravitational whispers.
00:51We just have to listen.
00:54Just as sound waves are vibrations of air molecules, gravitational waves are vibrations
00:59in the fabric of space-time.
01:01When two massive black holes spiral toward each other, they produce gravitational waves
01:06that travel through the cosmos at the speed of light.
01:10If we imagine the universe as a grand symphony, these merging supermassive black holes are
01:15the bass players.
01:16As they orbit each other, these black holes play the deep bass notes that echo throughout
01:22the cosmic concert hall.
01:23But that's not all there is to the symphony.
01:26In the background is a faint but pervasive hum produced by the collective motion of massive
01:32objects throughout the universe, from the earliest moments of the Big Bang until now.
01:37This gravitational wave background is truly a harmony of space and time.
01:43Nanograv is an NSF-funded collaboration of astronomers and astrophysicists.
01:48Our goal is to solve some of the deepest mysteries of the universe by studying the gravitational
01:53waves produced by these dancing monster black holes.
01:58These waves are light years long and can only be detected by the most extraordinary instruments.
02:04To measure these giant but subtle ripples in spacetime, Nanograv created a galaxy-sized detector
02:11using some of the most incredible objects in the cosmos, rapidly rotating neutron stars known
02:17as millisecond pulsars.
02:20Pulsars are the ultra-dense remnants left behind when massive stars reach the end of their lives
02:25and explode as supernovae.
02:28These pulsars are also cosmic beacons.
02:30They spin extraordinarily rapidly and with startling regularity, releasing pulses of radio waves
02:37with each rotation.
02:39Astronomers detect those pulses using giant radio telescopes.
02:43By monitoring the radio pulses from these ultra-precise cosmic clocks, Nanograv can detect the slightest
02:49deviations in the regularity of their timekeeping, and these deviations trace ripples in spacetime.
02:55This galactic-scale detector is called a pulsar timing array.
03:01Nanograv has now observed an array of dozens of pulsars for more than 15 years, and the results
03:06are astounding.
03:08We are finally hearing the faint background hum likely coming from in-spiraling pairs of
03:14supermassive black holes.
03:15With time, astronomers expect to pick out the individual instruments in this cosmic symphony, revealing
03:22unique insights into the evolution of galaxies and the history of the cosmos.
03:26New heavens and the stars.
03:27New heavens and the stars.
03:41You
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