- 4356 - FAST RADIO BURSTS - The biggest 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.
------------------- 4356 - FAST RADIO BURSTS - biggest ever?
- 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.
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- 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 for the universe.
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- If we count up the amount of normal matter
in the Universe 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, it may just be so hot and
diffuse that it's impossible to see using normal techniques.
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- 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 which is a 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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- The problem is that 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, 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
because they are 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 of
light-years away, and flare quickly, scientists have struggled to pin them
down.
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- 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.
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- 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, gives fresh hope for the
calculation.
-
- While we still don't know what causes these
massive bursts of energy fast radio bursts are common events in the cosmos and
we will be able to use them to detect matter between galaxies, and better
understand the structure of the Universe.
-
- The fascinating patterns of 35 repeating
fast radio bursts (FRBs) 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, magnetars, or from cataclysmic events like stellar
collisions or the collapse of neutron stars to form black holes.
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- 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.
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- While studying the highly active repeating
FRB known as “FRB 20220912A”astronomers watched over 541 hours (nearly 23
days). They 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.
-
- 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.
-
- “SETI's ATA”
is a telescope designed to hunt for radio signals from potential alien
intelligence but has an important contribution to make to the study of FRBs and some of the universe's most extreme
events and objects.
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- The most powerful events in the known
universe are gamma-ray bursts (GRBs).
They are short-lived outbursts of the highest-energy light. They can
erupt with a quintillion (a 10 followed by 18 zeros) times the luminosity of
our sun. Now thought to announce the births of new black holes, they were
discovered by accident.
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- The backstory takes us to 1963, when the
U.S. Air Force launched the Vela satellites to detect gamma rays from banned
nuclear weapons tests. The United States had just signed a treaty with the
United Kingdom and the Soviet Union to prohibit tests within Earth's
atmosphere, and the Vela satellites ensured all parties' compliance. Instead,
the satellites stumbled upon 16 gamma-ray events.
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- By 1973, scientists could rule out that
both Earth and the sun were the sources of these brilliant eruptions. That's
when astronomers at Los Alamos National Laboratory published the first paper
announcing these bursts originate beyond our solar system.
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- Scientists at NASA's Goddard Space Flight
Center quickly confirmed the results through an X-ray detector on the IMP 6 satellite.
It would take another two decades and contributions from the Italian Space
Agency's BeppoSax and NASA's Compton Gamma-Ray Observatory to show that these
outbursts occur far beyond our Milky Way galaxy, are evenly distributed across
the sky, and are extraordinarily powerful. The closest GRB on record occurred
more than 100 million light-years away.
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- Though discovered by chance, GRBs have
proven invaluable for today's researchers. These flashes of light are rich with
insight on phenomena like the end of life of very massive stars or the
formation of black holes in distant galaxies.
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- In 2017, GRBs were first linked to
gravitational waves, ripples in the fabric of space-time, steering us toward a
better understanding of the how these events work.
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- Astronomers separate GRBs into two main
classes: short (where the initial burst of gamma rays lasts less than two
seconds) and long events (lasting two seconds or longer). Shorter bursts also produce fewer gamma rays
overall, which lead researchers to hypothesize that the two classes originated
from different progenitor systems.
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- Astronomers now associate short bursts with
the collision of either two neutron stars or a neutron star and a black hole,
resulting in a black hole and a short-lived explosion. Short GRBs are sometimes
followed by “kilonovae”, light produced by the radioactive decay of chemical
elements. That decay generates even heavier elements, like gold, silver, and
platinum.
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- Long bursts are linked to the explosive
deaths of massive stars. When a high-mass star runs out of nuclear fuel, its
core collapses and then rebounds, driving a shock wave outward through the
star. Astronomers see this explosion as a supernova. The core may form a either
a neutron star or a black hole.
-
- In both classes, the newly born black hole
beams jets in opposite directions. The jets, made of particles accelerated to
near the speed of light, pierce through and eventually interact with the
surrounding material, emitting gamma rays when they do.
-
- In August, 2020, NASA's Fermi Gamma-ray
Space Telescope tracked down a second-long burst named “GRB 200826A”, more than
6 billion light-years away. It should have fallen within the short-burst class,
triggered by mergers of compact objects.
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- However, other characteristics of this
event, like the supernova it created, suggested it originated from the collapse
of a massive star. Astronomers think this burst may have fizzled out before it
could reach the duration typical of long bursts.
-
- Fermi and NASA's Neil Gehrels Swift
Observatory captured its opposite number, “GRB 211211A” in December 2021.
Located a billion light-years away, the burst lasted for about a minute. While
this makes it a long GRB, it was followed by a kilonova, which suggests it was
triggered by a merger. Some researchers attribute this burst's oddities to a
neutron star merging with a black hole partner.
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- As astronomers discover more bursts lasting
several hours, there may still be a new class in the making: Ultra-long GRBs.
The energy created by the death of a high-mass star likely can't sustain a
burst for this long, so scientists must look to different origins.
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- Some think ultra-long bursts occur from
newborn magnetars, neutron stars with rapid rotation rates and magnetic fields
a thousand times stronger than average. Others say this new class calls for the
power of the universe's largest stellar residents, blue supergiants.
Researchers continue to explore ultra-long GRBs.
-
- While gamma rays are the most energetic form
of light, they certainly aren't the easiest to spot. Our eyes see only a narrow
band of the electromagnetic spectrum. Studying any light outside that range,
like gamma rays, hinges tightly on the instruments our scientists and engineers
develop. This need for technology, alongside GRBs' already fleeting nature,
made bursts more difficult to study in early years.
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- Afterglows emit radio, infrared, optical,
UV, X-ray, as well as gamma-ray light, which provides more data about the
original burst. Afterglows also linger for hours to days (or even years) longer
than their initial explosion, creating more opportunities for discovery.
-
- Studying afterglows became key to deducing
the driving forces behind different bursts. In long bursts, as the afterglow
dims, scientists eventually see the source brighten again as the underlying
supernova becomes detectable.
-
- Although light is the universe's fastest
traveler, it can't reach us instantaneously. By the time we detect a burst, millions
to billions of years may have passed, allowing us to probe some of the early
universe through distant afterglows.
-
- Despite the expansive research conducted so
far, our understanding of GRBs is far from complete. Each new discovery adds
new facets to scientists' gamma-ray burst models.
-
- Fermi and Swift discovered one of these
revolutionary events in 2022 with “GRB 221009A”, a burst so bright it
temporarily blinded most space-based gamma-ray instruments. A GRB of this
magnitude is predicted to occur once every 10,000 years, making it likely the
highest-luminosity event witnessed by human civilization. Astronomers
accordingly dubbed it the brightest of all time, or the “BOAT”.
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- This is one of the nearest long burst ever
seen at the time of its discovery, offering scientists a closer look at the
inner workings of not only GRBs, but also the structure of the Milky Way. By
peering into the BOAT, they've discovered radio waves missing in other models
and traced X-ray reflections to map out our galaxy's hidden dust clouds.
-
- GRBs also connect us to one of the
universe's most sought-after messengers. Gravitational waves are invisible
distortions of space-time, born from cataclysmic events like neutron-star
collisions. Think of space-time as the universe's all-encompassing blanket,
with gravitational waves as ripples wafting through the material.
-
- In 2017, Fermi spotted the gamma-ray flash
of a neutron-star merger just 1.7 seconds after gravitational waves were
detected from the same source. After traveling 130 million light-years, the
gravitational waves reached Earth narrowly before the gamma rays, proving
gravitational waves travel at the speed of light.
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- Scientists had never detected light and
gravitational waves' joint journey all the way to Earth. These messengers
combined to paint a more vivid picture of merging neutron stars.
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- With continued research, our ever-evolving
knowledge of GRBs could unravel the unseen fabric of our universe. But the
actual burst is just the tip of the iceberg. An endless bounty of information
looms just beneath the surface, ready for the harvest.
-
-
February 15, 2024 FAST RADIO BURSTS 4356
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--------------------- --- Thursday, February 15,
2024
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