Sky & Telescope - September 2024 - 10

DISTANT GALAXY MERGER: ESA / WEBB / NASA / CSA / J. DUNLOP, D. MAGEE, P. G. PÉREZ-GONZÁLEZ, H. ÜBLER & R.
MAIOLINO, ET. AL; EXOPLANET AROUND RED DWARF STAR: NASA / JPL-CALTECH / R. HURT (CALTECH-IPAC)
NEWS NOTES
GALAXIES
Webb Sees Most Distant
Galaxy Merger
THE JAMES WEBB SPACE TELESCOPE
(JWST) has spotted two galaxies
colliding 750 million years after the
Big Bang. In a study appearing in the
June Monthly Notices of the Royal Astronomical
Society, Hannah Übler (University
of Cambridge, UK) and colleagues
report the detection of the galaxies' two
supermassive black holes.
Using JWST's Near-Infrared Spectrograph,
the team observed a previously
discovered galaxy, dubbed ZS7, known
to host a supermassive black hole. The
spectra show narrow emission lines associated
with this obscured black hole at
the galaxy's center.
The real surprise came with the
discovery of a broad emission line. This
light is emitted by gas clouds whipping
around an unobscured black hole with
the mass of 50 million Suns - and that
black hole is offset from the galaxy's
center by about 2,000 light-years.
" That [offset], along with additional
EXOPLANETS
Earth-size Planet Discovered 40 Light-Years Away
its atmosphere, but the planet is close
enough to be a future target for the
James Webb Space Telescope (JWST).
Gliese 12b was initially detected
Artist's illustration of Gliese 12b
THE DISCOVERY OF Gliese 12b - the
closest transiting, temperate, Earthsize
planet found to date - promises to
help us understand terrestrial planets
outside the solar system.
Gliese 12b orbits a cool red dwarf
star 40 light-years away. With an orbital
period of 12.8 days, its surface might
be temperate enough for life (although
uncomfortable for humans), with an
equilibrium temperature of 107°F
(42°C). We don't yet know the status of
10 SEPTEMBER 2024 * SKY & TELESCOPE
using NASA's Transiting Exoplanet
Survey Satellite; follow-up observations
confirmed those transits were real and
helped characterize the planet. Two
groups of astronomers, led by Shishir
Dholakia (University of Southern
Queensland, Australia) and Masayuki
Kuzuhara (Astrobiology Center and
National Astronomical Observatory of
Japan, Japan), reported observations
simultaneously, in the June Monthly
Notices of the Royal Astronomical Society
and in the June 1st Astrophysical Journal
Letters, respectively.
So far, astronomers have studied
atmospheres in only one other system
of terrestrial planets: TRAPPIST-1. It
hosts no less than seven planets, three
ZS7
pThe galaxy ZS7 appears to be undergoing a merger in which two black holes emit both doubly
ionized oxygen (OIII, dark red) and ionized hydrogen (Hβ, orange). The source to the upper right of
the central orange blob marks the offset black hole.
imaging data, indicates a merger of two
systems with massive black holes at a
very early time, " Übler says.
Übler thinks that, because the black
holes are so close to each other and
their relative velocities are so small, the
two " will most likely merge within the
next few hundred million years. "
However, Fabio Pacucci (Center for
Astrophysics, Harvard & Smithsonian),
who was not involved with this study,
says it's difficult to tell whether distant
galaxies are actually merging.
" This is an exciting discovery that
tells us that black hole pairs may be
common in the high-redshift universe, "
he says. But he also considers another
scenario offered by the team to be
equally likely: Perhaps the two galaxies'
black holes already merged, their
coalescence kicking the merged black
hole away from the galaxy's center.
Regardless of whether the merger is
just beginning or already over, the discovery
joins a growing body of research
suggestin that in the early universe
black holes are merging and becoming
more massive faster than predicted
(S&T: May 2024, p. 20).
¢ARWEN RIMMER
of them " potentially temperate Earthsize
planets that are suitable for atmospheric
transmission spectroscopy, "
Kuzuhara says. However, the system's
two innermost planets studied so far
appear to be stripped of any significant
atmosphere (S&T: Aug. 2023, p.8 and
Nov. 2023, p. 9).
But unlike TRAPPIST-1, Gliese 12 is
a quiet star. While some red dwarf stars
flare regularly, stripping their planets of
their atmospheres, X-ray observations
have found Gliese 12 to be an inactive
host, and that bodes well for any planetary
atmosphere.
Kuzuhara and colleagues plan to
ask for observations of Gliese 12b with
JWST. Meanwhile, Dholakia hopes to
obtain radial velocity measurements.
The gravitational tug of Gliese 12b pulls
on its host star, so observations of the
star's wobble enable measurement of
the planet's mass, which can in turn
narrow down its interior structure.
¢ARIELLE FROMMER

Sky & Telescope - September 2024

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