46 Scientific American, June 2022
N
obody noticed when an australian radio telescope captured
a fleeting explosion coming from far beyond the Milky Way in 2001.
Records of the powerful flare sat unseen for more than half a decade
until a group of scientists sifting through archival data spotted the
eruption—a so-called fast radio burst (FRB). According to one of those
scientists, astrophysicist Duncan Lorimer of West Virginia University,
the burst produced as much energy in a few thousandths of a second as the sun does in a month.
Today researchers know that these explosions happen at least
800 times a day all over the sky, and they are one of the most
active topics in astrophysics. Although much about FRBs
remains unknown, in just the past year a clearer picture has
started to emerge. “I think we’re closer to understanding what
some FRBs are,” says Ziggy Pleunis, an astrophysicist at the Uni-
versity of Toronto. “But as we’ve been going on this quest, new
discoveries have led to new questions.”
The study of FRBs is now at an inflection point. A torrent of
new detections and deeper studies have elevated certain mod-
els of their inner workings while eliminating others, and several
upcoming projects should help further narrow the possibilities.
Meanwhile scientists have learned that the bright light of an FRB
carries within it a record of the contents of the intergalactic
depths it traversed along its way to Earth, providing informa-
tion about galaxies and the material between them that no other
mechanism can.
MAGNETIC MOMENTS
in april 2020 three separate research teams detected an enormous
blast of radio energy coming from a magnetar located in the Milky
Way. Magnetars are an extreme kind of neutron star, a city-sized
remnant left behind when a massive star dies in a supernova. A
magnetar’s magnetic field can be so strong that approaching
within 1,000 kilometers of one would disrupt your body’s atomic
nuclei and electrons, causing you to effectively dissolve.
Magnetars were already a leading candidate for the source of
FRBs. But the few dozen known magnetars in our galaxy had
never been observed to produce eruptions that might resemble
the phenomena. The discovery of a short and formidable radio
burst from a galactic magnetar called SGR 1935+2154 was exactly
what researchers had been missing. If the same burst had come
from another galaxy, its signature would have been indistin-
guishable from a typical FRB. “That was a huge moment for the
field,” says Kenzie Nimmo, an astronomer at the University of
Amsterdam. “It alleviated all doubt that at least some FRBs come
from magnetars.”
How, exactly, a magnetar can produce an FRB is still the sub-
ject of debate. Most theories involve some kind of jarring star-
quake or an explosion caused when a magnetar’s twisting mag-
netic field lines snap and reconnect. Events such as these could
directly generate an FRB’s flash, or they might make a shock
wave that heats up surrounding material, incinerating dust and
turning gas into plasma to produce light as it travels outward.
Several telescopes saw an x-ray flash arriving just after SGR
1935+2154’s radio signal, suggesting that whatever released the
radio energy also generated more complicated side effects. Many
details are still unclear. “Did this happen on the surface of the
star, or in the magnetosphere, or in the material around the mag-
netar?” asks Emily Petroff, an astrophysicist also at the Univer-
sity of Amsterdam. “We still don’t really agree on that.”
COSMIC CURIOSITIES
because Frbs can vary in brightness, duration and other proper-
ties, it is unlikely that any single observation can explain them all.
In the summer of 2021 the Canadian Hydrogen Intensity Mapping
Experiment (CHIME), a dedicated FRB-hunting telescope in Brit-
ish Columbia, released a catalog of 536 FRBs that it had detected
during the first year of its operation, quadrupling the number
known. The bursts were already known to come in two distinct
flavors—those that repeatedly flash their signals and those that
are one-off events. CHIME’s data showed that nonrepeaters
Adam Mann is a journalist specializing in astronomy
and physics. His work has appeared in National Geographic,
the Wall Street Journal, Wired, and elsewhere.
