A variable signal aligned to the heart of the Milky Way is tantalizing scientists
From:
University of Sydney
October 12, 2021 -- The radio waves fit
no currently understood pattern of variable radio source and could suggest a
new class of stellar object.
"The strangest property of this new
signal is that it is has a very high polarization. This means its light
oscillates in only one direction, but that direction rotates with time,"
said Ziteng Wang, lead author of the new study and a PhD student in the School
of Physics at the University of Sydney.
"The brightness of the object also
varies dramatically, by a factor of 100, and the signal switches on and off
apparently at random. We've never seen anything like it."
Many types of star emit variable light
across the electromagnetic spectrum. With tremendous advances in radio
astronomy, the study of variable or transient objects in radio waves is a huge
field of study helping us to reveal the secrets of the Universe. Pulsars,
supernovae, flaring stars and fast radio bursts are all types of astronomical
objects whose brightness varies.
"At first we thought it could be a
pulsar -- a very dense type of spinning dead star -- or else a type of star
that emits huge solar flares. But the signals from this new source don't match
what we expect from these types of celestial objects," Mr. Wang said.
The discovery of the object has been
published today in the Astrophysical Journal.
Mr Wang and an international team,
including scientists from Australia's national science agency CSIRO, Germany,
the United States, Canada, South Africa, Spain and France discovered the object
using the CSIRO's ASKAP radio telescope in Western Australia. Follow-up
observations were with the South African Radio Astronomy Observatory's MeerKAT
telescope.
Mr Wang's PhD supervisor is Professor
Tara Murphy also from the Sydney Institute for Astronomy and the School of
Physics.
Professor Murphy said: "We have
been surveying the sky with ASKAP to find unusual new objects with a project
known as Variables and Slow Transients (VAST), throughout 2020 and 2021.
"Looking towards the center of the
Galaxy, we found ASKAP J173608.2-321635, named after its coordinates. This
object was unique in that it started out invisible, became bright, faded away
and then reappeared. This behavior was extraordinary."
After detecting six radio signals from
the source over nine months in 2020, the astronomers tried to find the object
in visual light. They found nothing.
They turned to the Parkes radio
telescope and again failed to detect the source.
Professor Murphy said: "We then
tried the more sensitive MeerKAT radio telescope in South Africa. Because the signal
was intermittent, we observed it for 15 minutes every few weeks, hoping that we
would see it again.
"Luckily, the signal returned, but
we found that the behavior of the source was dramatically different -- the
source disappeared in a single day, even though it had lasted for weeks in our
previous ASKAP observations."
However, this further discovery did not
reveal much more about the secrets of this transient radio source.
Mr. Wang's co-supervisor, Professor
David Kaplan from the University of Wisconsin-Milwaukee, said: "The
information we do have has some parallels with another emerging class of
mysterious objects known as Galactic Center Radio Transients, including one
dubbed the 'cosmic burper'.
"While our new object, ASKAP
J173608.2-321635, does share some properties with GCRTs there are also
differences. And we don't really understand those sources, anyway, so this adds
to the mystery."
The scientists plan to keep a close eye
on the object to look for more clues as to what it might be.
"Within the next decade, the
transcontinental Square Kilometer Array (SKA) radio telescope will come online.
It will be able to make sensitive maps of the sky every day," Professor
Murphy said. "We expect the power of this telescope will help us solve
mysteries such as this latest discovery, but it will also open vast new swathes
of the cosmos to exploration in the radio spectrum."
Video showing an artist's impression of
signals from space is available at: https://www.youtube.com/watch?v=J_eGd9Ps9fE&t=5s
https://www.sciencedaily.com/releases/2021/10/211012080039.htm
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