- 4429
- FAST RADIO
BURSTS - Fast radio-wave explosion ever found could
be used to weigh the universe.
Astronomers traced a mysterious radio source to three merging galaxies 8
billion light-years away. Studying it could help uncover the universe's missing
matter.
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------------------------- 4429
- FAST RADIO
BURSTS
-
- (
See Review 4428 about “Gamma Ray Bursts” ).
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- Much of the universe is made of of matter
that we can't see. Astronomers have
discovered the most ancient "heartbeat" radio signal, and they want
to use it to find the missing half of the universe's matter.
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- The mysterious signal — a fast radio burst
“FRB 20220610A” — was found 8 billion years into the universe's past, its light
rhythmically pulsing from the heart of three merging galaxies.
As the fast radio burst (FRB)
is 1.5 times more ancient and distant than the previous record holder, its
light could be used to find an approximate weight to the universe.
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- If we count up the amount of normal matter
in the Universe — the atoms that we are all made of — we find that more than
half of what should be there today is missing.
We think that the missing matter is hiding in the space between
galaxies, but it may just be so hot and diffuse that it's impossible to see
using normal techniques.
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- Currently, there are two ways to approximate
the matter contained within our universe. The first uses gravitational lensing
to see how much matter warps the path of light from distant galaxies through
space; and the second looks at the universe's first light from the cosmic
microwave background — remnant radiation from the Big Bang that can reveal
where matter clumped together at the dawn of the universe and how it evolved over time.
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- These methods disagree, creating a
discrepancy called the “Sigma-8 tension” that threatens to tear standard
theories of cosmology apart. Where the missing matter could be isn't certain,
but astronomers have a hunch it is floating in intergalactic space in vast,
diffuse clouds of gas and dust. But to measure these clouds, astronomers need
powerful sources of light.
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- Fast radio bursts are perfect for the job —
discharging more energy in a few milliseconds than the sun does in a year.
Astronomers have long puzzled over the source of these sudden, bright flashes.
But because FRBs erupt predominantly from galaxies millions — or even billions
— of light-years away, and flare quickly, scientists have struggled to pin them
down.
-
- One known source of FRBs is a radio pulsar
or a magnetar, a highly magnetized, rapidly-rotating husk of a dead star.
Equipped with unusually strong magnetic fields that are trillions of times more
powerful than Earth's, the dead stars spin in space, sweeping out beams of
intense radio waves from their poles like giant lighthouses.
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- As FRB pulses move through space, the matter
they move through separates out the light pulse’s different frequencies,
producing a lag between the arrival of the high and low frequencies in the
signal. From the length of this delay, astronomers can figure out how much
matter the burst has moved through.
-
- Until now, astronomers had only detected
bursts from a bit more than 5 billion years into the universe's past, too
recent to make this calculation. But the new fast radio burst, traced back 8
billion years into the universe's 13 billion year age.
-
- While we still don't know what causes these
massive bursts of energy, fast radio
bursts are common events in the cosmos and that we will be able to use them to
detect matter between galaxies, and better understand the structure of the
Universe.
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- The fascinating patterns of 35 repeating
fast radio bursts reveal new properties
of these mysterious blasts of deep-space radiation that appear and disappear in
milliseconds. Astronomers watched 35
explosive outbursts from a rare repeating "fast radio burst" as it
shifted in frequency like a "cosmic slide whistle," blinking in a
puzzling pattern never seen before.
-
- FRBs are millisecond-long flashes of light
from beyond the Milky Way that are capable of producing as much energy in a few
seconds as the sun does in a year. FRBs are believed to come from powerful
objects like neutron stars with intense magnetic fields, called magnetars, or
from cataclysmic events like stellar collisions or the collapse of neutron
stars to form black holes.
-
- Complicating the FRB picture, a few FRBs
are "repeaters" that flash from the same spot in the sky more than
once, while the majority burst once and then vanish. The SETI Institute's Allen Telescope Array
(ATA) was used to study the highly active repeating FRB known as “FRB
20220912A”. As they watched the FRB over 541 hours (nearly 23 days), the team
saw its bursts of radiation cover a wide range of frequencies in the radio wave
region of the electromagnetic spectrum, which eventually developed into a fascinating pattern that
astronomers had never seen before.
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- The new data could finally help unravel the
mystery of where deep-space FRBs come from and why a small minority of these
rapid and intense blasts of radiation repeat.
It provides both confirmation of known FRB properties and the discovery
of some new ones. We're narrowing down
the source of FRBs to extreme objects such as magnetars, but no existing model
can explain all of the properties that have been observed so far.
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- The bursts of radiation from FRB 20220912A
shifted down in frequency, and when converted to notes played on a xylophone,
this shift sounded like a slide whistle's descending toot — a behavior that
scientists had never seen before from an FRB. This also helped the team
identify that there is a cutoff point for the brightness of bursts from FRB
20220912A, revealing how much of the overall cosmic signal rate this FRB is
responsible for.
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- While there was a noticeable pattern in the
frequency of FRB 20220912A's bursts, there was no clear pattern to how long
these bursts lasted or how much time passed between them. This shows there is
an inherent unpredictability in repeating FRBs.
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-
April 11, 2023 FAST
RADIO BURSTS 4429
------------------------------------------------------------------------------------------
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------ “Jim Detrick” -----------
--------------------- --- Saturday, April 13,
2024
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