- 4250 - FAST RADIO BURSTS - These Fast Radio Burst took 8 billion years to reach us. What was the universe like 8,000,000,000 years ago? 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.
------------------------- 4250 - FAST RADIO 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
this 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 this dispersion.
-
- Of course, 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. We know it’s there, we just aren’t sure how much of it is there.
-
- This new discovery
could help change that. Known as “FRB 20220610A”, it was observed by the
Australian Square Kilometer 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. -
- The team then used
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.
-
-
November 30, 2023
FAST RADIO BURSTS 4250
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