Sky and Telescope - July 2016 - 28

COLLISION IMMINENT
Simulations, such as the
frame depicted here,
show that inspiraling
neutron stars merge their
magnetic fields to create
a single jet and a sudden
clap of radiation. That
makes inspiraling neutron
stars one of the promising
potential sources of FRBs.

But first, astronomers need to catch an FRB in real
time rather than in archived data - not an easy feat.
In 2013 Parkes began sending all of its observations to
"Green II," a supercomputer at Swinburne University of
Technology. Within 30 seconds of a flash, the supercomputer pings 30 astronomers at 10 different institutions
and alerts them to the burst's location so they can obtain
follow-up observations.
The first several searches came up empty. But on April
18, 2015, the ATCA caught a slowly fading radio signal
in an elliptical galaxy 5 billion light-years away. Initially,
astronomers thought this signal was surely associated
with an FRB that had occurred two hours earlier. If true,
it would have proved that this FRB originated at a vast
distance. It would even have hinted at a progenitor.
The study, however, was quickly disputed. Follow-up
observations show the radio source is still there and has
in fact brightened since the initial observations. It may
be related to a supermassive black hole gobbling gas at
the galaxy's center, but astronomers remain in limbo.
Nevertheless, with the field now poised to catch FRBs

EXTRAGALACTIC EVIDENCE Plotting the 17 fast radio bursts
known to date with respect to the plane of the Milky Way shows
that the bursts can appear pretty much anywhere on the sky.
Many researchers take FRBs' scattered distribution as a hint that
these sources, whatever they are, lie far outside our galaxy.
S&T: LEAH TISCIONE; SOURCE: PETROFF ET AL. 2016; BACKGROUND IMAGE: 2MASS / J.
CARPENTER, T. H. JARRETT, & R. HURT

28

July 2016 sky & telescope

in action, and with the help of radio arrays that can
image sources with much higher precision, it won't be
long before astronomers pinpoint a source's location.

When Theorists Come Out to Play
Even as astronomers continue to hunt for more definitive
observations, they can still speculate about what creates
FRBs. There are three solid clues: the bursts are brief,
bright, and probably far away.
To astronomers, a brief signal points to a small
source. In the case of a pulse only a millisecond long, the
source must be small enough that a beam of light could
cross it within that time - several hundred kilometers
across, or roughly the length of Maine's coastline. And if
these sources are placed at cosmological distances, they
would have to be extremely powerful. What source that
small could pack so much power?
Theorists' favorite answer is neutron stars. These
crushed stellar corpses pack the mass of half a million
Earths into a sphere only tens of kilometers across. And
they offer plenty of opportunities that could produce the
right energetics, Lorimer says: "comets crashing into
neutron stars, neutron stars inspiraling, neutron stars
collapsing into black holes." The list goes on.
The FRB Masui detected with the Green Bank
Telescope might narrow the range of possibilities. That
FRB's radio waves rotated in a corkscrew motion as
they traveled through space. It's a signature caused by
a powerful magnetic field, quite possibly originating
from the source itself. So magnetars - neutron stars
with powerful magnetic fields - might be the culprit,
producing flares when starquakes break the magnetar's
brittle crust. Alternatively, collapsing stars may generate
jets of electrons that race along magnetic field lines.
A more exotic idea that Lorimer finds particularly
tantalizing is cosmic strings: these large defects in the
structure of spacetime could distort, releasing bursts of
energy. He admits the idea is highly speculative. But "we
should still keep an open mind and not just closet our-

L. REZZOLLA (AEI) & M. KOPPITZ (AEI & ZUSE INSTITUTE BERLIN)

Faraway Flashes



Sky and Telescope - July 2016

Table of Contents for the Digital Edition of Sky and Telescope - July 2016

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Sky and Telescope - July 2016 - A
Sky and Telescope - July 2016 - B
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