- 4146 - GRAVITATIONAL WAVES - changing our Universe? The James Webb Space Telescope is showing astronomers more of the Universe than we have ever seen before. Problem is what we see is not what the theories say we should be seeing. Maybe how the universe started is different than what we thought?
-------------- 4146 - GRAVITATIONAL WAVES - changing our Universe?
- Scientists are reporting the 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.
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- From 15 years' worth of observations made
by the “North American Nanohertz Observatory for Gravitational Waves”
(NANOGrav) used data from radio telescopes to monitor 68 dead stars, called
“pulsars”, in the sky. The pulsars acted like a network of buoys bobbing on a
slow-rolling sea of gravitational waves.
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- The effect of the gravitational waves on the
pulsars is extremely weak and hard to detect.
We have a new way of probing what happens as monstrous black holes at
the cores of galaxies begin a slow but inexorable death spiral.
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- 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. 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.
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- 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 lumber around each other slowly and have
millions of years to go before they merge.
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- NANOGrav is thought to have picked up a
collective hum of gravitational waves from many pairs of merging supermassive
black holes throughout the universe. 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.
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- 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 in some
cases.
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- 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.
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- To search for the background hum of
gravitational waves computers 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.
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- 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.
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- 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.
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- 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.
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September 8, 2023 GRAVITATIONAL
WAVES 4146
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