Sky & Telescope - March 2025 - 9

METEORITE: JÉRÔME GATTACCECA / CNRS / CEREGE; V404 CYGNI: JORGE LUGO
SOLAR SYSTEM
Sources of Most Meteorites
Identified
TWO TEAMS PUBLISHING in the
October 17th Nature have traced 70%
of meteorite falls to specific collisions in
the main asteroid belt.
The origins of even the most common
meteorites, known as H chondrites
and L chondrites (which together make
up some 70% of meteorite falls), has
long remained elusive. To track down
their sources, a team led by Miroslav
Brož (Charles University, Czech Republic)
gathered data on major main-belt
asteroid families, members that were
once part of a larger body. After a collision
splits a body apart, the fragments'
initially similar orbits spread out over
time. The researchers simulated the
evolution of those orbital motions,
including the effects of exposure to
solar heating, cosmic rays, gravity, and
other forces.
Brož's team found that H and
L chondrite meteorites originate primarily
from three families produced in
BLACK HOLES
Newfound Stellar
Companion May Explain
Black Hole System
THE SYSTEM V404 CYGNI is an old
favorite: Its 9-solar-mass black hole is
slurping gas from a nearby star slightly
less massive than the Sun. The hot,
swirling gas creates an X-ray beacon,
making this system a canonical lowmass
X-ray binary (here, " low mass "
refers to the companion star).
But it turns out the binary at the
heart of V404 Cygni isn't alone. Even
back in the early 1990s, astronomers
noticed another star almost on top of
the binary as seen from our perspective,
though they generally assumed it
to be an interloper. But as Kevin Burdge
(MIT) and colleagues report in the
November 14th Nature, this star is part
of the V404 Cygni system after all.
The team determined from a suite
of observations that the star moves
recent collisions: Two of these occurred
7.6 million and 5.8 million years ago,
respectively, and a third happened
within the last 40 million years.
In an accompanying study in the
same issue of Nature, a group led by
Michaël Marsset (European Southern
Observatory) traced an additional
source of L chondrite meteorites back
to a collision that occurred some 470
million years ago. (That one might even
have left Earth with a ring of debris;
S&T: Feb. 2025, p. 10.) The more ancient
event might have supplied almost all
of the meteorites at that time and still
provides some 20% of falls.
through space with the binary and has
probably been part of the system from
the get-go. The tertiary star is a shirttail
relation, however: It lies more than
3,500 astronomical units from the
inner binary, or roughly 90 times farther
out than Pluto lies from the Sun.
Its current distance may help astronomers
clinch how a black hole can form
while still somehow retaining a small
stellar companion in a tight orbit.
In 2016, Smadar Naoz (University
of California, Los Angeles) and her colleagues
suggested that a third, distant
companion star could play a role in
these systems' formation. The distant
star's gravitational interactions with the
inner binary - as well as the evolution
of the star that will soon become
a black hole - would create a complex
interplay of changes that would ultimately
lead the inner binary's orbit to
shrink dramatically.
The tertiary's orbit in V404 Cygni
matches what Naoz's team predicted.
pThis image, 3 mm wide, shows transmitted
polarized light from an ordinary H chondrite,
called San Juan 029.
" The models are very elegant and
manage to explain several key observables
with a single model, " says Mikael
Granvik (University of Helsinki,
Finland), who was not involved in the
research. " I think that is a great feat,
and one that will push the field forward
by a great leap. " The details still need
to be worked out, though, he adds. " It
will be very interesting to see how tests
of their hypotheses will play out in the
years to come. "
¢JEFF HECHT
pAn artist's concept of V404 Cygni depicts a
black hole stealing gas from a nearby star (center
left), while another star orbits much farther
away (upper right).
" I'm very excited by this discovery, "
she says. She's now collaborating with
Burdge to investigate the system's history
in more detail.
Curiously, the black hole seems to
have had a quiet death. For V404 Cygni's
tertiary to hang on to the inner
binary, the black hole must have formed
without the messy violence expected to
send it reeling. The star might even have
imploded without fanfare.
¢CAMILLE M. CARLISLE
sk yand tele scope .o r g * MARCH 2025
9
http://skyandtelescope.org
Sky & Telescope - March 2025

Table of Contents for the Digital Edition of Sky & Telescope - March 2025
