22 ASTRONOMY • FEBRUARY 2018
But as the years passed, other astrono-
mers discovered FRBs, first at Parkes and
then using radio telescopes around the
world. Evidence that FRBs were, in fact,
from deep space began to mount. And sci-
entific skepticism grew into excitement
upon realizing that FRBs were very real,
and perhaps one of the greatest new dis-
coveries in astronomy in decades.
It’s been 10 years since the first FRB dis-
covery. It’s generated so much buzz that in
2017, a few dozen astronomers held the first
conference on FRBs, and millions of dollars
in funding have been devoted to finding
more. But as more bursts come in, the mys-
tery has only deepened. To travel the dis-
tance between galaxies, FRBs must have an
insane amount of energy — in the few brief
milliseconds it shines, an FRB can generate
more energy than the Sun does in a day.
And yet despite the tremendous energy, no
one has a clue about where they come from.What we know
So far, we’ve seen 33 bursts, and they last
a few milliseconds at most. We know they
are, for that brief period, one of the bright-
est radio sources in our sky, and they have
been identified in all areas of the sky, rath-
er than originating in a single direction.
But astronomers are cautious about draw-
ing many conclusions from such a small
sample as we have now.
We know FRBs come from beyond the
galaxy. This distance information is based
on a radio astronomy trick relying on the
fact that space is not a perfect vacuum —
while it is better than any vacuum on
Earth, even the void between galaxies has a
few hydrogen atoms per cubic meter. Radio
waves traveling through space from a sin-
gle source will interact with those few
atoms’ electrons they pass, causing a slight
delay in the waves depending on their fre-
quency. Measuring this exact delay, known
as the dispersion measure (DM), can tell
you how much material the signal has
passed through. A higher DM means a sig-
nal has traveled a greater distance, and the
FRB DMs are decidedly extragalactic.
But things get weirder from there. So far,
only one FRB repeats, despite many hours
of follow-up observations. This exception is
FRB 121102, the “repeater,” as astronomers
colloquially call it. Arecibo Observatory in
Puerto Rico first detected it November 2,
2012 (hence its name). Since then, astrono-
mers have observed periods of calm where
nothing is seen for months at a time from
this source, and periods of outburst where
it gives off over two dozen bursts in two
hours, with no distinguishable pattern. No
one knows whether the repeater is a type of
FRB different from the others, or if all FRBs
repeat and the Arecibo Observatory’s
1,000-foot (305 meters) radio dish is the
only telescope sensitive enough to easily
find repeating bursts.
The repeater has been crucial in provid-
ing the first clues on where FRBs come
from. Radio waves differ greatly from vis-
ible light. The wavelength of light varies
from 400 nanometers (violet) to 700 nm
(red); a nanometer is one-billionth of a
meter, or 40-billionths of an inch. But
radio waves can vary from a millimeter to
hundreds of meters in length.
This has important applications for the
telescopes astronomers use because the
angular resolution of a telescope on the sky
— that is, the level of detail the telescope
can see — depends on the wavelength of
light observed and the diameter of the tele-
scope. Point a 1-meter optical telescope onThe Parkes Observatory in New South Wales, Australia, is home to the 210-foot (64 meters) Parkes
radio telescope. This telescope not only discovered the first recorded fast radio burst, FRB 010724,
but also most of the currently known pool of 30-odd FRBs as well. CSIRO/DAVID MCCLENAGHAN
Arecibo Observatory in Puerto Rico contains the world’s second-largest radio dish, measuring
1,000 feet (305 m) in diameter. In 2012, Arecibo became the first telescope other than the Parkes dish
to detect an FRB: FRB 121102, later known as the “repeater.” NAIC — ARECIBO OBSERVATORY, A FACILITY OF THE NSF