Sky & Telescope - April 2021 - 9

GAMMA-RAY BURSTS

Gamma Rays Herald
Birth of a Magnetar

NEU TRON-STA R COLLISION: N ASA / ESA / D. PL AY ER (STSCI);
LMC A ND SMC: ESA / G AIA / DPAC / CC BY-SA 3.0 IGO;
ACK NOWLEDG EMEN T: L. CHEMIN; X . LURI E T A L (2020)

TWO NEUTRON STARS don't always
make a black hole, new observations
appear to show.
Neutron-star collisions are likely at
the heart of " short " gamma-ray bursts
(GRBs), flashes of gamma radiation less
than two seconds long. Simple math
suggests such mergers ought to add up
to a black hole, provided material isn't
lost in the process.
But the fading afterglow of one such
burst, GRB 200522A, suggests that a
highly magnetized neutron star, or magnetar, has survived one of these violent
collisions. The report by Wen-fai Fong
(Northwestern University) and her
colleagues will appear in an issue of the
Astrophysical Journal.
NASA's Neil Gehrels Swift Observatory first detected this burst after
the radiation had traveled 5.47 billion
light-years to Earth. Fong's team followed up with observations at multiple
wavelengths using the Hubble Space
Telescope, the Karl G. Jansky Very Large
Array, and other observatories. The later
observations traced the afterglow of
longer-wavelength emission that follows
the initial burst of gamma rays.
When compared to the source's
emission at other wavelengths, the
near-infrared afterglow was up to

S Two neutron stars collide in these stills from an artist's animation, forming a stable magnetar.

10 times brighter than expected, if
the astronomers assumed the emission came from a kilonova. This type of
explosion results when neutron stars
collide to form a black hole and was
thought to be the source of short GRBs.
If the remnant was not a black hole
but a magnetar, it would explain the
excess. What's more, within a few years
it would produce observable radio emission, Fong and her colleagues write.
" If detected, this would not only
break the degeneracy between the two

possible explanations in this specific
case, " says Maria Grazia Bernardini
(Brera Astronomical Observatory and
National Institute for Astrophysics,
Italy), a GRB expert not involved in the
study. " It would provide the long-sought
smoking gun of the magnetar scenario
[for producing short GRBs], and the
first direct evidence of a stable magnetar associated with a GRB. "
„ MONICA YOUNG

Watch the simulation at https://is.gd/
magnetarbirth.

still be missing). The new data paint a
more precise picture, for example, of
how the Milky Way's tidal gravitational
forces are slowly dispersing the stars in
the nearby Hyades cluster.
" Almost every field is benefitting
from this mission, " says Amina Helmi
(University of Groningen, The Netherlands). " Gaia is transformational. It is
revolutionizing astronomy. "
„ GOVERT SCHILLING
X This image based on Gaia data shows the
stellar density of the Large and Small Magellanic
Clouds. Red, green, and blue trace mostly the
older, intermediate-age, and younger stars.
sk yandtelescope.org * APRIL 2 021

9


https://is.gd/magnetarbirth https://is.gd/magnetarbirth http://www.skyandtelescope.org

Sky & Telescope - April 2021

Table of Contents for the Digital Edition of Sky & Telescope - April 2021

Contents
Sky & Telescope - April 2021 - Cover1
Sky & Telescope - April 2021 - Cover2
Sky & Telescope - April 2021 - 1
Sky & Telescope - April 2021 - Contents
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