Astronomers have finally managed to detect a mysterious burst of radio
waves in real-time - but are we ever going to be able to work out where
they're coming from?
This article was written by Emily Petroff, a PhD candidate in Astro Physics at Swinburne University of Technology in Melbourne, Australia. It was originally published on the Conversation.
Astronomers
are trying to improve their hunt for rapid bursts of radio emission in
the universe called Fast Radio Bursts (FRBs) so they can better observe
these mysterious events, which are thought to occur thousands of times a
day. Only nine have so far been detected.
The most recent burst was spotted in the early hours of the morning on May 15 last year when the Parkes radio telescope, in New South Wales, was observing a patch of sky in the direction of the Aquarius constellation.
This
region was of interest to our team of astronomers because a Fast Radio
Burst had been detected emanating from that direction back in 2011. We
suspected these bursts might repeat themselves, even years later, so we
visited the spot again.
While we didn’t see a repeat of the old
burst we did find something interesting. A new burst of radio waves lit
up the receiver at preciesly 3:14am.
Within
10 seconds the detector systems working through the data identified the
burst and sent an automated email to the scientists with the below
subject line.
Subject: New Detection: FRB 140514.
The
Parkes team sprang into action within minutes of getting the message
and began emailing collaborators around the world. Coordinates were
sent, telescopes were pointed, and the first multi-wavelength follow-up
of a Fast Radio Burst discovery was underway.
In the days, weeks
and months that followed, the location of FRB 140514 was observed with
telescopes around the world and in space looking for any changes in the
field that might give away where exactly the burst came from.
Unfortunately, these telescopes found nothing that could pinpoint the source or shed definitive light on its origin.
Clearly
astronomers need to respond as quickly as possible when a radio burst
is found if we are to better understand these curious phenomena and
their causes.
Fast Radio Burst origins
Fast Radio Bursts first attracted the attention of the astronomical community when the first event was discovered in 2007 (in archival data recorded in 2001).
Since then, only nine more bursts have been found including the one picked up last year by the CSIRO’s Parkes radio telescope.
At the moment we don’t know for certain what is causing these mysterious bursts that we’re so eager to find.
Since
these flashes occur on millisecond timescales, whatever it is has to be
very bright, and very short-lived. Current contenders are things like
giant flares from energetic stars called magnetars or the collapse of a neutron star to form a black hole.
In either case, the sources are believed to be billions of light years away, in galaxies spread out across the universe.
How
do we know they originate so far away from us? Astronomers have been
using radio pulses to study the space between stars for years. The
vacuum of space is not quite empty and contains a small number of
particles per cubic metre.
Radio pulses travelling through this
medium encode information about how many particles they have encountered
on their way from a source to our telescope. This gives us a measure of
the average density of the space between stars, or the interstellar
medium.
Fast Radio Bursts appear to have travelled through about
ten times more particles than we expect from the Milky Way. To account
for all those particles, the burst must have also travelled through the
intergalactic medium as well, putting their sources billions of light
years distant.
If the exact distance to a burst could be measured
with an optical telescope, the information from these bursts could be
used to determine the “weight” of the universe in a particular
direction, something that has never before been possible.
While
the Parkes telescope is good at finding these radio bursts, telescopes
at other wavelengths will ultimately be the next important step in
pinning down their origin and natures.
If they give off light at
other wavelengths, like X-rays or visible light, picking up important
new clues will require a fast response from other telescopes when a
radio detection is made.
In the case of FRB 140514, the first
multi-wavelength observation didn’t occur until eight hours after the
radio burst, preventing us from saying anything definitive about the
source.
Rapid response
Part of the problem in observing
these Fast Radio Bursts is that they only last for a few milliseconds,
and the universe is a very big place to look for them.
So finding
where they come from means we need to think about more real-time
observations and developing a speedier and more collaborative approach
to observing any new bursts. The next big breakthrough in the puzzle
will come from a faster response to observing and a multi-wavelength
effort.
Doing this requires many people. No single individual can
watch for bursts 24 hours a day, and no single person can operate dozens
of telescopes simultaneously to get the necessary data. Collaborative
teams are becoming more important than ever.
The most comprehensive effort currently underway is the Survey for Pulsars and Extragalactic Radio Bursts (SUPERB) at Swinburne University.
The
aims of the survey, besides finding new Fast Radio Bursts, are to
foster international collaboration and develop a robust and fast method
for alerting other telescopes with the next real-time discovery.
Ultimately,
all we can do is wait for the next burst. Finding a needle in a
haystack requires being in the right place at just the right time.
But
with more eyes prepared to look and a speedier response we might have a
better chance of finding where Fast Radio Bursts really come from.
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