- 4212 - FAST RADIO & GAMMA RAY BURSTS? - Fast Radio Bursts are intense bursts of radio energy lasting anywhere from a fraction of a millisecond to a few seconds, typically with a frequency of around 1,400 MHz, and we still don’t know what causes them.
--------------------- 4212 - FAST RADIO & GAMMA RAY BURSTS?
- FRBs were first
detected in 2007 but were initially so rare and short-lived that it was
difficult to confirm they weren’t terrestrial in origin. With the inauguration
of the “CHIME telescope” and other wide-field radio observatories, astronomers
started observing lots of them, which confirmed they were both astrophysical
and mostly coming from outside our galaxy. Now one has been observed from a
galaxy 8 billion light years away, and it could help us solve a cosmological
mystery.
-
- The dominant
theory for “Fast Radio Bursts” (FRBs) is that they are caused by
“magnetars”. “Neutron stars” with an
extremely strong magnetic field. Just as the Sun’s magnetic field can trigger
solar flares, magnetars could experience magnetic flares that emit flashes of
radio light. We know they are extragalactic because they occur all over the
sky, not just along the galactic plane of the Milky Way.
-
- Since FRBs emit a
radio pulse at a uniform frequency, we can use what is known as a “Dispersion
Measure” (DM) to determine distance. When the radio pulse passes through
ionized intergalactic gas, higher frequencies pass through it a bit faster than
lower frequencies.
-
- This is similar to
the way visible light is refracted by a piece of glass. Violet is refracted the
most and red the least because violet light takes a bit longer to pass through
the glass than red light.
-
- What this means is
that rather than seeing the FRB light all at once, we see the lower frequencies
a bit later than the higher ones. The more distant the FRB, the more
intergalactic plasma it passes through to reach us, and the greater the
dispersion.
-
- To use this for
distance, you’d need to know the distribution of intergalactic plasma. If there
are clumps of plasma between close galaxies, the FRB would have a dispersion
measure similar to that of distant galaxies with little intergalactic plasma
between them. Unfortunately, we don’t have a good mapping of intergalactic
plasma. It’s a missing part of the “total mass” of the Universe.
-
- This new discovery
could help change that. Known as “FRB 20220610A”, it was observed by the
“Australian Square Kilometre Array Pathfinder” (ASKAP) radio telescope in 2022.
The ASKAP data was precise enough that astronomers could pinpoint its location
in the sky accurately enough to pin its origin to a particular galaxy. -
- Follow-up
observations by the Very Large Telescope (VLT) in Chile to confirm it likely
came from a small cluster of merging galaxies. The VLT observations then
determined the redshift of the cluster to find the distance.
-
- The light of the
FRB 20220610A traveled 8 billion light years to reach us, making it the most
distant fast radio burst ever observed, and likely at the distance limit for
FRBs we can currently detect. Knowing its distance, we can compare this to the
dispersion measure to calculate the amount of ionized gas between galaxies.
-
- If we can
pinpoint lots more fast radio bursts, we will be able to build a distribution
map of intergalactic gas. From that we can get a handle on the overall mass
between galaxies and help pinpoint the total mass of the cosmos. Basically
using one mystery to solve another.
-
- Fast Radio Bursts
are intense bursts of radio energy lasting anywhere from a fraction of a
millisecond to a few seconds, typically with a frequency of around 1,400 MHz,
and we still don’t know what causes them.
-
- Just as the Sun’s
magnetic field can trigger solar flares, magnetars could experience magnetic
flares that emit flashes of radio light. We know they are extragalactic because
they occur all over the sky, not just along the galactic plane of the Milky
Way.
-
- If we can pinpoint
lots more fast radio bursts, we will be able to build a distribution map of
intergalactic gas. From that we can get a handle on the overall mass between
galaxies and help pinpoint the total mass of the cosmos. Basically using one
mystery to solve another, which is a pretty cool trick.
-
-
November 7, 2023 FAST RADIO
& GAMMA RAY BURSTS
4212
------------------------------------------------------------------------------------------
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--------------------- ---
Tuesday, November 7, 2023 ---------------------------------
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