YSM Issue 97.1
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FEATURE<br />
Astronomy<br />
MASSIVE,<br />
MYSTERIOUS<br />
CIRCLES IN SPACE<br />
HOW DYING STARS EXPLAIN RADIO ODDITY<br />
BY DAVID GAETANO ART BY ALONDRA MORENO SANTANA<br />
Scientists believe they may have found<br />
a possible explanation for a puzzling,<br />
recently discovered cosmological<br />
phenomenon. First observed in 2019, odd<br />
radio circles (ORCs) are haloes of radio<br />
waves centered around certain galaxies.<br />
At first, these haloes were especially<br />
perplexing because they didn’t match<br />
the known signatures of any large-scale<br />
astronomical events. There was something<br />
more unique about this phenomenon,<br />
hence its namesake.<br />
Professor Alison Coil of the University of<br />
California San Diego and her team believe<br />
they discovered something particularly<br />
new and exciting about these ORCs.<br />
Unlike others before them, Coil’s team<br />
looked at the optical light signatures from<br />
one of the ORC galaxies instead of merely<br />
inspecting the glowing halo of signals in<br />
radio wavelengths. This turned out to be<br />
the right call, as their observations gave<br />
way to a deeper understanding of the<br />
haloes’ mysterious origins in an article<br />
recently published in Nature.<br />
The insight arose from their previous<br />
work. Before ORCs, Coil and her team had<br />
been studying the evolution of galaxies<br />
by assessing supermassive black holes<br />
and outflowing galactic winds, which are<br />
streams of high-speed gas particles expelled<br />
due to colossal events like supernovae—<br />
large star explosions that expel gaseous<br />
matter into the surroundings. They used<br />
observational data collected from some<br />
of the most advanced telescopes in the<br />
world to create a timeline of how certain<br />
galaxies evolved. In particular, their work<br />
was concerned with the formation of<br />
“starburst” galaxies, which experience<br />
rapid star formation over a relatively<br />
short timescale, resulting in a rapid series<br />
of supernovae.<br />
Coil and her team stumbled upon ORCs<br />
somewhat unexpectedly. During one of<br />
their scheduled research trips to the Keck<br />
Telescope in Hawaii, they capitalized<br />
on their time with the equipment and<br />
pointed the telescope at one of the special<br />
ORC galaxies. Other research had shown<br />
evidence that these ORCs behaved like<br />
three-dimensional expanding shells,<br />
which made Coil and her team wonder<br />
whether this phenomenon could be a latestage<br />
effect of the galactic winds they had<br />
been studying. They postulated that these<br />
radio signals could be made up of gas<br />
from galactic winds being rapidly pushed<br />
outward, originally stemming from<br />
starburst explosions. Based on their<br />
hypothesis, the team captured<br />
optical wavelength images of<br />
the galaxy, which allowed<br />
them to make some new<br />
and exciting discoveries.<br />
The most jarring<br />
observation that arose<br />
from these optical<br />
images was the presence<br />
of an abnormally large<br />
amount of shocked gas<br />
sitting within the galaxy<br />
at the heart of each ORC. This shocked<br />
gas is essentially an abundance of singly<br />
ionized oxygen gas, which is highly<br />
unusual in these types of galaxies.<br />
“Galaxies that are like that—ones that<br />
aren’t forming stars anymore—[usually]<br />
don’t have a ton of gas in them still,” Coil<br />
said. Typically, galaxies that have had<br />
many stars form and die have lost much<br />
of their gas because these colossal events<br />
push most of it out.<br />
Coil and her team hypothesized that<br />
this shocked gas could be the long-term<br />
result of the galactic winds decoupling,<br />
or separating, and collapsing back into<br />
the galaxy after<br />
the rapid<br />
30 Yale Scientific Magazine March 2024 www.yalescientific.org