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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00:00Supermassive Black Hole
00:29Supermassive black holes lurk in the hearts of most galaxies, and galaxies grow by merging
00:34with other galaxies. When that happens, their black holes also merge and grow, becoming
00:40more and more massive over time. How exactly this happens is not fully understood, but
00:47the universe is telling us its secrets in gravitational whispers. We just have to listen.
00:54Just as sound waves are vibrations of air molecules, gravitational waves are vibrations
00:59in the fabric of spacetime. When two massive black holes spiral toward each other, they
01:05produce gravitational waves that travel through the cosmos at the speed of light. If we imagine
01:10the universe as a grand symphony, these merging supermassive black holes are the bass players.
01:17As they orbit each other, these black holes play the deep bass notes that echo throughout
01:22the cosmic concert hall. But that's not all there is to the symphony. In the background
01:28is a faint but pervasive hum produced by the collective motion of massive objects throughout
01:33the universe, from the earliest moments of the Big Bang until now. This gravitational
01:38wave background is truly a harmony of space and time.
01:44Nanograv is an NSF-funded collaboration of astronomers and astrophysicists. Our goal
01:49is to solve some of the deepest mysteries of the universe by studying the gravitational
01:53waves produced by these dancing monster black holes. These waves are light-years long and
02:00can only be detected by the most extraordinary instruments. To measure these giant but subtle
02:07ripples in spacetime, Nanograv created a galaxy-sized detector using some of the most incredible
02:12objects in the cosmos, rapidly rotating neutron stars known as millisecond pulsars.
02:21Pulsars are the ultra-dense remnants left behind when massive stars reach the end of
02:24their lives and explode as supernovae. These pulsars are also cosmic beacons. They spin
02:31extraordinarily rapidly and with startling regularity, releasing pulses of radio waves
02:37with each rotation. Astronomers detect those pulses using giant radio telescopes.
02:44By monitoring the radio pulses from these ultra-precise cosmic clocks, Nanograv can
02:48detect the slightest deviations in the regularity of their timekeeping, and these deviations
02:54trace ripples in spacetime. This 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
03:06results are astounding. We are finally hearing the faint background hum likely coming from
03:12in-spiraling pairs of supermassive black holes. With time, astronomers expect to pick out
03:18the individual instruments in this cosmic symphony, revealing unique insights into the
03:23evolution of galaxies and the history of the cosmos.
03:36NASA Jet Propulsion Laboratory, California Institute of Technology