Sky & Telescope - May 2024 - 9

ARTIST'S CONCEPT OF 55 CANCRI E: ESA / HUBBLE / M. KORNMESSER; NGC 1851: NASA / ESA / G. PIOTTO
(UNIVERSITÀ DEGLI STUDI DI PADOVA), PROCESSING: GLADYS KOBER (NASA / CATHOLIC UNIVERSITY OF AMERICA)
EXOPLANETS
Does the " Lava World " 55 Cancri e Have an Atmosphere?
To look for answers, Renyu Hu
(NASA / JPL) and colleagues asked
Webb to observe the planet as it orbited
its star, taking a spectrum of the heat
radiated from both sides.
Hu acknowledged that understanddensity,
as well as its measured day- and
nightside temperatures, supported a
lava-world scenario, in which magma
flows on 55 Cancri e, and only a wisp of
rock vapor stands between the surface
and the stars (S&T: July 2016, p. 11).
At the same time, an infrared map
of the planet's dayside showed that the
planet's brightest point is offset in the
east-west direction, instead of pointing
directly at the host star. If true,
then something (perhaps the same lava
flows) must be redistributing the heat.
BLACK HOLES
Mystery Objects Uncovered
in Globular Clusters
TWO GLOBULAR CLUSTERS - NGC
1851, in the southern constellation
Columba, and 47 Tucanae, the second
brightest globular in the sky - host an
enigmatic object. But astronomers are
still working out what these objects are.
The first mystery object is the unseen
companion of a pulsar, which turned
up during a survey of globular clusters
conducted with the MeerKAT radio
telescope array in South Africa. Ewan
Barr (Max Planck Institute for Radio
Astronomy, Germany) and others
combined 24 MeerKAT observations
with archival data from the Green Bank
Telescope in West Virginia to determine
that the pulsar and its invisible
companion together have 3.887 Suns'
worth of mass. Subtracting the pulsar's
likely contribution, the team infers
that the companion must have 2.09 to
2.71 solar masses.
pEither the most massive neutron star or the
least massive black hole known lurks in the
globular cluster NGC 1851, shown here.
The largest pulsars have less than
2.1 solar masses, and only a smattering
of black holes have popped up
with fewer than 5 solar masses. However,
the researchers conclude in the
January 19th Science that they cannot
determine whether the pulsar's companion
is a neutron star or a black hole.
Regardless, the discovery has " fascinating
the data was difficult, in part
because the 6th-magnitude host star
easily overwhelms Webb's sensitive
instruments. His team persisted, finding
that the JWST spectra indicate a
shroud of gases surrounds the planet,
made either of carbon monoxide,
carbon dioxide, or a mixture of the two
gases along with nitrogen.
The new data don't negate the idea
of lava flows. Hu and colleagues carried
out detailed simulations showing that a
magma ocean could in fact sustain this
thick atmosphere despite the planet's
proximity to its star.
The immense data challenges made
some astronomers in the audience cautious
about embracing the results.
THE HOT SUPER-EARTH 55 Cancri e,
which whizzes around its yellow star
every 17 hours, has intrigued astronomers
ever since its discovery in 2004.
Now, data from the James Webb Space
Telescope presented to the 243rd meeting
of the American Astronomical
Society is putting early speculation to
the test, providing evidence for a thick
atmosphere enveloping this rocky world.
Previous observations of the planet's
An artist's depiction of 55 Cancri e
" It certainly seems really interesting
to see that carbon-dioxide absorption
feature in the Near-Infrared Camera
data, and that's really exciting if it
holds, " says Kevin Stevenson (Johns
Hopkins University Applied Physics
Laboratory). " But I would love to see
independent data reductions.
" These types of claims, " he adds,
" require extraordinary evidence. "
¢MONICA YOUNG
ing implications, " writes Maya Fishbach
(University of Toronto) in an accompanying
perspective piece.
The second mystery object is in
47 Tucanae. Alessandro Paduano (Curtin
University, Australia) and colleagues
undertook a radio survey using the Very
Large Array and the Australia Telescope
Compact Array, looking for the lit-up
gas around feeding black holes. One of
the candidates they identified could be a
weakly accreting black hole with a mass
somewhere between 50 and 6,000 Suns.
Just as plausibly, the team writes in the
January 20th Astrophysical Journal, the
object could be a rapidly rotating pulsar.
Philip Kaaret (NASA's Marshall
Space Flight Center), who wasn't
involved with the study, points out that
previous studies of stars' motions inside
47 Tuc limit an unseen mass to less
than 600 Suns. That still leaves room
for the suggested black hole. Improved
observations of the cluster's stellar
orbits could help decide the matter.
¢CAMILLE M. CARLISLE
sk yand tele scope .o r g * MAY 2024
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