Sky & Telescope - December 2022 - 9

ILLUSTRATION OF BLACK WIDOW PULSAR: NASA GODDARD SPACE FLIGHT CENTER / CRUZ
DEWILDE; WEBB IMAGE OF GALAXY: NASA / ESA / CSA / JUDY SCHMIDT
NEUTRON STARS
Black Widow Pulsar Sets
Mass Record
THE PULSAR PSR J0952−0607 already
holds the title of second-fastest-known
rotator, spinning around its axis 707
times per second. Now, it has also
broken the record for the most massive
neutron star known.
Discovered in December 2016, PSR
J0952 is 20,000 light-years away in
Sextans and rotates every 1.41 milliseconds,
just shy of the 1.40-millisecond
record holder, PSR J1748−2446ad. The
surfaces of these objects whip around at
some 20% of the speed of light.
These millisecond pulsars spin so fast
because they're accreting material from
an orbiting companion star. This slow
devouring has also earned them the
nickname " black widows. "
Roger Romani (Stanford University)
and colleagues have now succeeded in
Thin Red Lines
taking spectra of the pulsar's extremely
faint (23rd-magnitude) companion
using the Keck telescope on Mauna
Kea, Hawai'i. In a study to appear in
Astrophysical Journal Letters, the team
reports that the companion, which has
the mass of a few tens of Jupiters, orbits
the pulsar at 380 km/s (850,000 mph).
Combined with brightness measurements
over the orbital period of 6.42
hours, this yields a mass estimate for
the neutron star of 2.35 solar masses.
No one knows how matter behaves
under the extreme conditions present
in neutron star interiors. But gauging
how massive a neutron star can become
before collapsing further into a black
hole helps narrow down what types of
matter might exist there.
The mass estimate of J0952 is still
quite uncertain, with a possible error
of ±0.17 solar masses. More precise
measurements, Romani and colleagues
write, await the 30-meter telescope era.
pAn artist illustrates a black widow pulsar with
its small companion.
" I think this result sends a warning
to modelers of ultra-dense matter that
neutron stars may be capable of having
pretty high masses, " says Victoria
Kaspi (McGill University, Canada), who
wasn't involved in the current study.
" If I were a theorist wedded to a model
that permitted only lower-mass neutron
stars, I'd start scratching my head about
now, though I wouldn't yet be in full
panic mode. "
¢GOVERT SCHILLING
There's no such thing as the birth
of a single star. Star formation is a
global phenomenon, and its grand
scale becomes clear in the James
Webb Space Telescope's sharp image
of NGC 7496. The galaxy is one of
those being surveyed as part of the
Physics at High Angular Resolution in
Nearby Galaxies (PHANGS) project.
" In the [Webb image], we can see
through the dust - for the first time
with this detail - to see the bright
clusters and bubbles that signify the
early stages of star formation, " says
PHANGS principal investigator Janice
Lee (NSF's NOIRLab). The web-like
pattern is a result of the interdependent,
regulating effects that govern
star formation over vast regions of
space. Glowing dust outlining the
star-blown bubbles reveals evidence
of both positive feedback, which
compresses clouds of gas and dust
to create new stars, and negative
feedback, which disperses molecular
clouds and interrupts star formation.
The PHANGS collaboration will be
using Webb to examine another 18
nearby galaxies to see star formation
in unprecedented detail.
¢ ARWEN RIMMER
sk yand tele scope .o r g * DECEMBER 2022
9
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Sky & Telescope - December 2022

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