Sky & Telescope - January 2025 - 10

NEWS NOTES
COSMIC STRUCTURE
Black Hole's Colossal Jets
Pierce the Void
A NEWLY DISCOVERED pair of plasma
jets span far beyond their host galaxy,
potentially affecting the cosmic web
around it.
The jets, powered by a supermassive
black hole at the galaxy's center, span
23 million light-years from tip to tip -
almost 10 times the distance between
our Milky Way and the Andromeda
Galaxy. Astronomers have nicknamed
the record-breaking system " Porphyrion, "
after the king of the giants in
Greek mythology. And the giant is
indeed the king of many: A new catalog
of such radio-emitting giant jet pairs
tallies thousands of them.
" Giant jets were known before we
started the campaign, but we had no
idea that there would turn out to be so
many, " says Martin Hardcastle (University
of Hertfordshire, UK), coauthor
on two associated studies. Porphyrion's
SOLAR SYSTEM
Visiting Star Might Have Reshaped Outer Solar System
BILLIONS OF YEARS AGO, the close
pass of another star might have sculpted
our solar system's outermost regions.
On September 4th in Nature Astronomy,
astronomers suggest such a flyby could
explain some peculiarities of the solar
system's most distant worlds, known as
trans-Neptunian objects (TNOs).
The Nice model of solar system formation
holds that TNOs' orbital properties
resulted from a phase when the
four giant planets migrated about the
solar system. But the Nice model can't
easily explain distant TNOs beyond the
planets' reach.
Susanne Pfalzner, Amith Govind
(both at Jülich Research Center,
Germany) and Simon Portegies Zwart
(Leiden University, The Netherlands)
have now carried out simulations of a
close stellar encounter and its effects on
TNO dynamics. They find that the flyby
most likely happened in the first 10
million years of the Sun's history, when
it was still part of the cluster it was
born in. A star with 80% of the Sun's
mass passing within 110 au of the Sun
" gives a near-perfect match " to TNO
orbits, they write. It even reproduces the
recently discovered population of TNOs
with retrograde orbits.
However, Alessandro Morbidelli
(Observatory of Cô te d'Azur, France),
This snapshot from a simulation shows the
Sun at center and the visiting star at left, with
TNO populations represented as dots. Watch
the simulation at https://is.gd/starvisit.
10 JANUARY 2025 * SKY & TELESCOPE
definition: These jets' tip-to-tip length
as projected on the sky is more than
2.3 million light-years. (Porphyrion
spans 10 times that length.)
Rafaël Mostert (Leiden University,
The Netherlands) and colleagues combined
the power of citizen science with
machine learning to find more than
11,000 giant radio jets in LOFAR's Twometre
Sky Survey. The number suggests
this giant variety is fairly common.
Martijn Oei (also at Leiden) led
An artist's illustration of the longest black hole
jets ever observed, nicknamed Porphyrion
discovery is published in the Sept. 19th
Nature; the accompanying catalog will
appear in Astronomy & Astrophysics.
When astronomers looked for black
hole-powered jets in a radio survey by
the Low-Frequency Array (LOFAR),
based in the Netherlands, they were
surprised to find giant jets by the
thousands. " Giant " here has a technical
the study on Porphyrion, whose jets
penetrate a cosmic void of mostly empty
space. To power such long, straight
streams of gas, the supermassive black
hole's feeding rate and spin axis must
have been stable for about a billion
years, Hardcastle says.
The power carried by giant radio jets
like Porphyrion and its legion can heat
and expand filaments of the cosmic web
that feed growing galaxies - though
how much they do so remains a question
for future work.
¢MONICA YOUNG
one of the originators of the Nice
model, is " not impressed " by the new
results, arguing that even the distant
TNOs are easily explained as objects
scattered from the giant planet region
while the Sun was still embedded in
its birth cluster. " All the rest, " he adds,
" are consistent with the giant planet
instability scenario. "
Other recent results seem to bolster
the stellar-flyby scenario: The new
computer simulations predict that
distant TNOs are common, and, indeed,
Japan's Subaru Telescope on Mauna
Kea, Hawai'i, has uncovered more than
expected - a finding supported by readings
from the dust counter on NASA's
New Horizons mission.
According to Pfalzner, the future
Vera C. Rubin Observatory will provide
an observational test of the flyby theory.
Expected discoveries could determine,
for example, how common distant or
retrograde TNOs are. As the researchers
writes in their paper, " [the work] presented
here can only be a first step. "
¢GOVERT SCHILLING
ARTIST'S ILLO OF PORPHYRION JETS: E. WERNQUIST / D. NELSON (ILLUSTRISTNG
COLLABORATION) / M. OEI; STELLAR FLYBY SIMULATION: JÜLICH RESEARCH CENTER
https://www.is.gd/starvisit
Sky & Telescope - January 2025

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