Sky & Telescope - December 2023 - 9

HYADES: MAURICE TOET / WWW.MAURICETOET.NL;
LUNAR TRACKS: INDIA SPACE RESEARCH ORGANIZATION
BLACK HOLES
The Hyades Might Harbor
Black Holes
THE NEAREST BLACK HOLES might be
hiding around the corner, astronomically
speaking - lurking in the Hyades,
a 650 million-year-old open star cluster
155 light-years away in Taurus, the Bull.
If that's true, it would shatter the previous
record for nearest black hole by a
factor of 10 (S&T: Aug. 2021, p. 8).
Gravitational interactions between
stars in the Hyades would have caused
more massive objects, including black
holes, to sink toward the center. Less
massive stars would in turn gain kinetic
energy and end up on wider orbits,
effectively spreading out the cluster.
Working with the latest astrometry
data from the European Space Agency's
Gaia mission, Stefano Torniamenti
(University of Padova, Italy) and colleagues
conclude that the Hyades is
about 30% larger than expected if the
cluster had never possessed black holes.
Computer simulations with two or
three black holes residing in the cluster
SPACE
Chandrayaan 3 Lands on
the Moon; Luna 25 Crashes
INDIA'S CHANDRAYAAN 3 successfully
touched down near the Moon's south
pole on August 23rd. Prime Minister
Narendra Modi called the day " historic "
for the nation, as India is now the
fourth nation to conduct a controlled
landing on the Moon. Russia's Luna 25,
on the other hand, crashed on the lunar
surface just four days before.
Chandrayaan 3 landed near the
Manzinus U Crater in the south polar
region on the lunar nearside, making
it the first probe to explore the lunar
south pole. The Vikram lander then
deployed the six-wheeled Pragyan rover,
to explore the surrounding terrain.
Both lander and rover are equipped with
scientific instruments to collect data on
the plasma density above the surface,
surface composition, and seismic activity.
The solar-powered rover entered
sleep mode for the two-week lunar
night on September 2nd.
Russia almost beat India to the lunar
south pole, but a failed orbital maneuver
on August 19th caused the Luna 25
lander to crash instead, falling into the
Pontécoulant G Crater. Luna 25 had
been scheduled to land on August 21st.
That crash followed several recent failures,
including ispace's Hakuto-R lander
earlier this year as well as the Israeli
Beresheet lander and India's Chandrayaan
2 lander, both of which crashed on
the Moon in 2019. Chandrayaan 3 built
off of lessons learned from Chandrayaan
2's collision, including several
changes to the lander configuration.
¢DAVID DICKINSON
sk yand tele scope .o r g * DECEMBER 2023
9
pThe Hyades star cluster, a group of thousands
of stars 155 light-years away in Taurus
for hundreds of millions of years better
match the observations, the team writes
in the September Monthly Notices of the
Royal Astronomical Society. (There is,
however, no guarantee the black holes
didn't leave the cluster more recently.)
Black holes in the Hyades aren't
completely unexpected: They'd come
from the most massive stars, which
would go supernova after just a few
million years. The surprising thing,
according to team member Mark Gieles
(University of Barcelona, Spain), is that
the long-term presence of a couple of
black holes has had such a strong effect
on the cluster's structure and motions.
Finding black holes in the Hyades
would have implications beyond breaking
proximity records. It would also
suggest that whatever " kick " newborn
black holes receive, it can't be very
much for at least some of them or
they'd all have escaped the cluster.
At the same time, Pavel Kroupa (University
of Bonn, Germany), who wasn't
involved with the research, notes that
under an alternative theory of gravity,
known as modified Newtonian dynamics,
the same data would be consistent
with no black holes.
Independent confirmation is vital,
but that might be easier said than done.
According to team member Zephyr
Penoyre (University of Cambridge, UK),
direct evidence of those black holes
will be difficult to find. Their search for
binary systems with one massive companion
has so far turned up empty.
¢GOVERT SCHILLING
The Pragyan rover made
tracks as it explored the
lunar south pole.
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Sky & Telescope - December 2023

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