- 4073 - GRAVITY WAVES - detected using Pulsars? Scientists have been hunting for the gravitational wave background, a faint but persistent echo of gravitational waves thought to have been set off by events that took place soon after the Big Bang and the mergers of supermassive black holes throughout the universe.
------------------- 4073 - GRAVITY WAVES - detected using Pulsars?
- Astronomers have
detected low-frequency gravitational waves for the first time using a galaxy-sized antenna of millisecond
pulsars in the Milky Way.
-
- Signals of
gravitational waves that make up that background have been hard to detect due
to being faint, in addition to vibrating at decade-long timescales. Now, long-term
observations have finally confirmed their presence.
-
- Scientists
worldwide have reported the discovery of the "low pitch hum" of these
cosmic ripples flowing through the Milky Way.
-
- Astronomers don't
definitively know what's causing the hum, the detected signal is
"compelling evidence" and consistent with theoretical expectations of
gravitational waves emerging from copious pairs of the most massive black holes
in the entire universe weighing as much as billions of suns.
-
- These signals may
be coming from merging supermassive black holes that are caught in cosmic
dances, circling each other in orbits that shrink across millions of years.
During this process, they release energy in the form of gravitational waves
that reverberate throughout the universe.
These waves astronomers now say they have detected.
-
- The observed
background hum of gravitational waves has grown in significance over time,
providing tantalizing proof that there may be hundreds of thousands or even
millions of supermassive black holes about to merge in the next few hundred
thousand years, even though the gargantuan objects themselves haven't yet been
spotted.
-
- To detect the
gravitational wave background, astronomers studied fast-spinning stars called
millisecond pulsars, which are dead stars that spin up to 700 times per second
with astonishing regularity, blasting out beams of light from their magnetic
poles, which are seen as "pulses" when they flicker in Earth's
direction.
-
- Such cosmic lighthouses
can help spot gravitational waves from black holes that are supermassive,
millions to billions times larger than our sun. In comparison, the Laser
Interferometer Gravitational-Wave Observatory (LIGO) network can only detect
gravitational waves originating from smaller black holes that are up to 10
times as massive as the sun.
-
- If the stretch of
space between Earth and the pulsars were absolutely empty, then light from the
flashing cosmic clocks would take the same time to reach Earth every time they
pulse in our direction. In actuality, the timing of the pulses is influenced by
factors such as the gas and dust in the interstellar medium and motions of
pulsars as well as Earth in the Milky Way.
-
- Gravitational
waves, too, stretch and compress the space-time fabric between us and the
pulsars, distorting their otherwise regular pulses from anywhere between tens
of nanoseconds to five or more years, resulting in the light flashes arriving
earlier or later than normal.
-
- In the new research,
the "critical evidence" that betrays the source of the signals to be
supermassive black holes is a unique pattern found in the arrival times of
pulses from a galaxy-sized cosmic antenna of nearly 70 millisecond pulsars in
the Milky Way. Gravitational wave signals from black hole binaries overlap
"like voices in a crowd" and result in an incessant hum that embeds
as a unique pattern in the pulsar timing data.
-
- Scientists
extracted that pattern by observing lighthouse-like beams from pairs of pulsars. They collected data about the timing of those
pulses every month for 15 years. Then, they calculated the difference between
the pulses' actual arrival times and their predicted arrival times which they
could estimate within 1 microsecond, comparable to measuring the distance to
the moon to within a thousandth of a millimeter.
-
- The much
sought-after gravitational wave signals were embedded in those
differences. This is the first time that
scientists have found compelling evidence for such patterns of inconsistency
etched by a backdrop of gravitational waves, whose effects on pulsars' light
flashes were predicted by Einstein's theory of general relativity back in 1916.
-
- When black holes
merge, their gravity interacts with nearby stars, which drains the black holes'
orbital energies and nudges them increasingly closer to the point of becoming a
single black hole. After black holes get within 3.2 light-years of one another
other, they merge by radiating gravitational waves. However, other models have
suggested that black holes span timescales longer than the universe itself in
that they stall their merger when they reach that 3.2 light-years mark.
-
- At one point,
scientists were concerned that supermassive black holes in binaries would orbit
each other forever, never coming close enough together to generate a signal
like this.
-
- If the discovery
pans out and the signals being detected do end up being from binary black
holes, then they absolutely had to have passed the final parsec one way or
another.
-
-
June 31, 2023 GRAVITY
WAVES - detected using Pulsars? 4073
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