- 4159 - GRAVITATIONAL WAVES - finally detected! Gravitational waves were first proposed by Albert Einstein in 1916 but were not directly detected until about 100 years later when LIGO picked up the waves from a pair of distant colliding black holes.
-------------- 4159 - GRAVITATIONAL WAVES - finally detected!
- Scientists are
reporting the first evidence that our Earth and the universe around us are
awash in a background of spacetime undulations called gravitational waves. The
waves oscillate very slowly over years and even decades and are thought to
originate primarily from pairs of supermassive black holes spiraling together
before they merge.
-
- The effect of the
gravitational waves on the pulsars is extremely weak and hard to detect.
-
- LIGO detects
gravitational waves that are much higher in frequency than those registered by
NANOGrav. NANOGrav's name comes from the
fact that it detects lower-frequency gravitational waves in the nanohertz
range, one cycle every few years.
-
- Higher-frequency
gravitational waves come from smaller pairs of black holes zipping around each
other rapidly in the final seconds before they collide, while the
lower-frequency waves are thought to be generated by huge black holes at the
hearts of galaxies, up to billions of times the mass of our sun, that orbit
around each other slowly and have millions of years to go before they merge.
-
- NANOGrav's network
of pulsars is also known as a “pulsar-timing array”. The pulsars, which formed
from the explosions of massive stars, send out beacons of light that rapidly
spin around at very precise intervals.
These are like lighthouse beacons that sweep by at a regular rate. You
can predict the timing to a level of tens of nanoseconds. They have the same
level of precision of atomic clocks.
-
- When gravitational
waves travel across the cosmos, they stretch and squeeze the fabric of
spacetime very slightly. This stretching and squeezing can cause the distance
between Earth and a given pulsar to minutely change, which results in delays or
advances to the timing of the pulsars' flashes of light.
-
- To search for the
background hum of gravitational waves, they compare the timing of pairs of
pulsars in their network. Gravitational waves will shift this timing to
different degrees depending on how close the pulsars are on the sky. Imagine lots of ripples on an ocean from
pairs of supermassive black holes scattered throughout. Now, we're sitting here on Earth, which acts
like a buoy along with the pulsars, and we try to measure how the ripples are
changing and causing the other buoys to move toward and away from us.
-
- To tease out the
gravitational-wave background, they had to nail down a multitude of confusing
effects, such as the motion of the pulsars, the perturbations due to the free
electrons in our galaxy, the instabilities of the reference clocks at the radio
observatories, and even the precise location of the center of the solar system.
-
- The scientists hope
to answer mysteries about the nature of merging supermassive black holes, such
as how common they are, what brings them together, and what other factors
contribute to their coalescence.
-
- NANOGrav is an
international collaboration dedicated to exploring the low-frequency
gravitational-wave universe through radio pulsar timing. NANOGrav was founded
in October 2007 and has grown to more than 190 members at more than 70
institutions.
-
- Astrophysicists
around the globe have been busy chasing this gravitational-wave signal. Several
papers released today by collaborations using telescopes in Europe, India,
China, and Australia report hints of the same signal in their data. Through the
International Pulsar Timing Array consortium, the individual groups are working
together to combine their data to better characterize the signal and search for
new types of sources.
-
-
September 18, 2023 GRAVITATIONAL WAVES
- finally detected! 4159
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Tuesday, September 19, 2023 ---------------------------------
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