In March 2013, researchers at the CERN laboratory made
history when they announced the discovery of the Higgs Boson. Though its
existence had been hypothesized for over half a century, confirming its
existence was a major boon for scientists. In discovering this one particle,
the researchers were also able to confirm the Standard Model of particle
physics. Much the same is true of our current cosmological model.
For decades, scientists been going by the theory that
the Universe is made of 70% dark energy, 25% dark matter and 5% “luminous
matter” – i.e. the matter we can see. But even when all the visible matter is
added up, there is a discrepancy where much of it is still considered
“missing”. But thanks to the efforts of a team from the Commonwealth
Scientific and Industrial Research Organization (CSIRO), scientists now know that we have it
right.
This began on April 18th, 2015, when the CSIRO’s Parkes Observatory in
Australia detected a fast radio burst (FRB) coming from space. An international
alert was immediately issued, and within a few hours, telescopes all around the
world were looking for the signal. The CSIRO team began tracking it as well
with the Australian Telescope Compact Array (ATCA) located at the Paul Wild Observatory
(north of Parkes).
Image showing the field of view of the Parkes radio
telescope (left) and zoom-ins on the area where the signal came from (left).
Credit: D. Kaplan (UWM), E. F. Keane (SKAO).
With the help of the National Astronomical Observatory
of Japan’s (NAOJ) Subaru telescope in Hawaii, they were able to pinpoint where
the signal was coming from. As the CSIRO team described in a paper submitted to Nature, they identified the source, which was an elliptical
galaxy located 6 billion light years from Earth.
This was an historic accomplishment, since pinpointing
the source of FRBs have never before been possible. Not only do the signals
last mere milliseconds, but they are also subject to dispersion – i.e. a delay
caused by how much material they pass through. And while FRBs have been
detected in the past, the teams tracking them have only been able to obtain measurements
of the dispersion, but never the signal’s redshift.
Redshift occurs as a result of an object moving away
at relativistic speeds (a portion of the speed of light). For decades,
scientists have been using it to determine how fast other galaxies are moving
away from our own, and hence the rate of expansion of the Universe. Relying on
optical data obtained by the Subaru telescope, the CSIRO team was able to
obtain both the dispersion and the redshift data from this
signal.
As stated in their paper, this information yielded a
“direct measurement of the cosmic density of ionized baryons in the
intergalactic medium”. Or, as Dr. Simon Johnston – of the CSIRO’s Astronomy and
Space Science division and the co-author of the study – explains, the team was
not only to locate the source of the signal, but also obtain measurements which
confirmed the distribution of matter in the Universe.
“Until now, the dispersion measure is all we had,” he
said. “By also having a distance we can now measure how dense
the material is between the point of origin and Earth, and compare that
with the current model of the distribution of matter in the Universe.
Essentially this lets us weigh the Universe, or at least the normal matter
it contains.”
Dr. Evan Keane of the SKA Organization, and lead author on the paper, was similarly enthused
about the team’s discovery. “[W]e have found the missing matter,” he said.
“It’s the first time a fast radio burst has been used to conduct a cosmological
measurement.”
As already noted, FRB signals are quite rare, and only
16 have been detected in the past. Most of these were found by sifting through
data months or years after the signal was detected, by which time it would be
impossible for any follow-up observations. To address this, Dr. Keane and his
team developed a system to detect FRBs and immediately alert other telescopes,
so that the source could be pinpointed.
Artists impression of the SKA-mid dishes in Africa
shows how they may eventually look when completed. Credit: skatelescope.org
It is known as the Square Kilometer Array (SKA), an international effort led by the SKA
Organization to build the world’s largest radio telescope. Combining extreme
sensitivity, resolution and a wide field of view, the SKA is expected to trace
many FRBs to their host galaxies. In so doing, it is hoped the array will
provide more measurements confirming the distribution of matter in the
Universe, as well as more information on dark energy.
In the end, these and other discoveries by the SKA
could have far-reaching consequences. Knowing the distribution of matter in the
universe, and improving our understanding of dark matter (and perhaps even dark
energy) could go a long way towards developing a Theory Of Everything (TOE).
And knowing how all the fundamental forces of our universe interact will go a
long way to finally knowing with certainty how it came to be.
These are exciting time indeed. With every step, we
are peeling back the layers of our universe!
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