Astronomy

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One of the most mysterious

signals encountered in modern

astrophysics is a blast of radio

waves lasting only milliseconds.

The first of these fast radio

bursts (FRBs) was discovered

about a decade ago, but several

years elapsed before astronomers

detected another. Now, they know

of around 20 FRBs, and yet these

bizarre signals remained mysteri-

ous because astronomers couldn’t

figure out precisely where any of

them were originating.

What scientists needed was to

pinpoint a signal’s location on

the sky with enough precision to

find out how far away the source

was. In the past year and a half,

the universe has obliged.

It all hinged on a discovery

made a few years ago. Scientists

found an FRB that actually

seemed to repeat, though not

with any noticeable pattern. Now

they knew a rough location in the

sky. A coordinated effort of sev-

eral radio telescopes across the

globe followed. Using the Very

Large Array (VLA) to take 83

hours of observations in 2015

and 2016, astronomers figured

out roughly where the blast

— called FRB 121102 — is located

on the sky. The VLA captured

the repeating signal nine times.

“The FRB was extremely gen-

erous to us,” said Casey Law of

University of California,

Berkeley, during a January 4,

2017, press conference announc-

ing the observations. The scien-

tists found a varying source of

radio waves at that rough loca-

tion. Was that source connected

to the FRB signals?

Astronomers used additional

radio instruments to zoom in on

the suspected sky site. The

European Very-Long-Baseline

Interferometry Network, which

connects 21 radio telescopes scat-

tered mostly across Europe, iso-

lated the location further. The

FRB signal was originating just

130 light-years away from

another source of both radio

waves and optical light. It looked

like the two might be related.

Next, scientists used an optical

telescope to identify where in

three-dimensional space the signal

was coming from. They learned

that a small, faint galaxy hosts this

FRB. This dwarf galaxy has 1,000

times less mass than the Milky

Way and is physically 10 times

smaller than our home galaxy. It

lies so far away that the radio

waves traveled some 2.4 billion

light-years to reach our telescopes.

Now that astronomers have

pinpointed the precise location,

the next step is to figure out what

process is producing this repeat-

ing radio signal. For that, astron-

omers may need the universe to

cooperate again.

Totality crosses

America

One of nature’s greatest spectacles
arrived at the Oregon shore at
10:16 A.M. PDT on August 21. The
midmorning light turned to dark-
ness as the Moon blocked the Sun’s
disk from view. The Sun’s million-
degree outer atmosphere, the solar
corona, then took center stage. And
for the millions of people in that
70-mile-wide (115 km) shadow, the
corona looked like fire sprouting
from a gray disk. The shadow then
continued across 13 more states before the South
Carolina coast ushered it into the Atlantic Ocean.
There was nothing surprising about the August 21
solar eclipse. Astronomers understand eclipse geom-
etry very well, and they can predict these events
millennia in advance. But this eclipse was historic for
other reasons. It crossed the entire continental United
States, the first eclipse to do so in almost a century.
More than 12 million people lived along the
path of the 2017 eclipse. An additional 20 million
people traveled to get a better view, according to
the University of Minnesota’s Jon Miller. Talk of traffic
nightmares, like gridlock on interstates, began cir-
cling months beforehand. Some hotels and camping
sites were booked several years in advance. Twenty-
one national park units and seven scenic national
trails lay in the path of totality — including Grand
Teton in Wyoming and Great Smoky Mountains in
Tennessee and North Carolina — and some of them
experienced full capacity that August day.
Whether people made their observing plans years
out or waited until the day before, August 21, 2017,
presented an act of beautiful celestial geometry to
those along the Moon’s umbral path. It’s likely no
other astronomical observing event in history has
garnered so much attention.

The case of the

mysterious radio waves

August 21 marked

the first time a total

solar eclipse crossed

the continental

United States in

nearly 100 years.

As millions of people

watched the Moon

blot out the disk

of the Sun, the

brilliant solar corona

appeared. NASA/AUBREY

GEMIGNANI

The fast radio burst FRB 121102 is the only known repeating FRB. Astronomers

used this property to track down the burst’s host galaxy: an unassuming

dwarf galaxy nearly 3 billion light-years away. GEMINI OBSERVATORY/AURA/NRC/NSF/NRAO

FRB 121102