- 3840 - FAST RADIO BURSTS - what can they tell us? Since 2010, fast radio bursts (FRBs) have been puzzling scientists. These ultra-short-lived, bright flashes of radio waves across the sky happen all day, but no one yet knows what causes them.
--------- 3840 - FAST RADIO BURSTS - what can they tell us?
- (
Also see Review 3838 about FAST
RADIO BURSTS - what can
radio waves teach us? And ,
3839 - RADIO
ASTRONOMY - )
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- Although FRBs are still a mystery, new
observations of this strange phenomenon may actually help astronomers learn
more about our own galactic neighborhood.
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- The “Deep Synoptic Array” (DSA) is a
collection of 110 radio antennas in the Owens Valley of Central California on
the ancestral lands of the Big Pine Paiute Tribe used to make more precise
measurements of FRBs.
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- The DSA goal is to pinpoint the location on
the sky of each FRB observed, to help figure out where these flashes originate.
This task requires highly detailed resolution, the equivalent of spotting a
dime on the surface of the moon.
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- At the same time, the array must survey a
large chunk of the sky to have any hope of spotting the extremely short bursts.
Surveying a large amount of sky means processing a lot of data, so the array's
computers are processing 24 gigabytes per second.
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- In the long run, astronomers hope to build
an even more advanced FRB observatory, nicknamed DSA-2000 in the Nevada
desert. In 2022, its first year of
operations of DSA-110 helped astronomers discover 30 FRBs with precise
locations, more than matching the 21 scientists had previously traced in the
years since the first FRB was detected in 2007.
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- And not only are these observations giving astronomers
clues into the mystery of FRBs, they also reveal invisible matter all around
us. More than 80% of baryonic matter,
not dark matter, but actually matter like you and me, is invisible in the nearby universe. This
hidden matter is really spread out, making it hard for our telescopes to see.
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- As the radio waves travel from distant
galaxies to our antennas on Earth, certain frequencies of the waves will be
delayed whis is an indicator of how much stuff there is between the observer
and the FRB. Data from the DSA revealed that our Milky Way has far less regular
matter than astronomers expected.
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- Most of the universe is made of around 16%
regular matter and 84% dark matter, our Milky Way is less than 10% regular
matter and over 90% dark matter.
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- These results strongly support scenarios
predicted by galaxy-formation simulations where feedback processes expel matter
from the halos of galaxies.
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- This is only the first year of observations
with the newly-christened DSA, which began commissioning in February 2022, and
the observatory is still ramping up, with only 63 of the 110 dishes involved in
the new research. -
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- Astronomers have detected a radio signal from the most distant galaxy
yet. The signal was detected at a special and significant wavelength known as
the "21-centimeter line" or the "hydrogen line," which is
emitted by neutral hydrogen atoms. The detection of the hydrogen line from such
a galaxy so far away, and therefore so early in the universe, by the Giant
Metrewave Radio Telescope in India could mean astronomers are ready to begin
investigating the formation of the earliest stars and galaxies.
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- The signal from the star-forming galaxy
“SDSSJ0826+5630” was emitted when our 13.8 billion-year-old galaxy was just 4.9
billion years old. The signal allowed the astronomers to measure the galaxy's
gas content and find that its mass is double that of the early galaxy's visible
stars.
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- Galaxies emit electromagnetic radiation, or
light, across a wide range of radio wavelengths, but thus far 21-cm-wavelength
radio waves have only been seen from nearby and thus more recent galactic
sources. It's the equivalent to a
look-back in time of 8.8 billion years.
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- The difficulty in spotting these
wavelengths from more distant galaxies is due to the fact that as
electromagnetic radiation from early galaxies travels vast distances to Earth,
the expansion of the universe stretches its wavelength and causes its energy to
reduce. That means telescopes here on Earth need a natural boost to see
long-wavelength, low-energy radio waves like the hydrogen line signal.
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- General Relativity suggests that objects
with mass warp spacetime similar to how a ball placed on a stretched rubber
sheet would weigh it down in the center, and just like in that analogy, the
greater the mass, the more extreme the curvature.
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- That means a tremendously massive object
like a black hole or galaxy causes extreme curvature in spacetime just as a
bowling ball would cause the extreme curvature of the rubber sheet in the
analogy.
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- This curving of spacetime causes light to
bend as well as it passes by objects of tremendous mass. A phenomenon known as
“gravitational lensing” occurs when a foreground or lensing object of
tremendous mass sits between an observer and a background source, causing the
light from the background object to curve and take different paths through and
around the lensing object. This can not only make a single object appear at
multiple points in the sky, but it can also have the effect of magnifying this
light.
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- In the case of SDSSJ0826+5630, the radio
wave signal was magnified by another galaxy between the early galaxy acting as
a lensing body. This effectively results
in the magnification of the signal by a factor of 30, allowing the telescope to
pick it up.
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- This could in turn open up a new way of
using long-wavelength radio telescopes to probe the evolution of stars and
galaxies and how the early universe evolved into the cosmos we see around us in
its current era.
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January 24, 2022 FAST RADIO
BURSTS - what can they tell us? 3840
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--------------------- --- Friday, January 27, 2023 ---------------------------
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