Sky and Telescope - March 2018 - 12

NEWS NOTES
STELLAR
t Ten of the 11 protostar outflows are marked
on the ALMA image of the area around the
Milky Way's central black hole (star).

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11
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Infant Stars Huddle Near Black Hole
A TEAM OF ASTRONOMERS has found
signs of low-mass stars forming within
a few light-years of the Milky Way's
central black hole.
Theoretically, the black hole's violent
gravitational effects, coupled with the
high-powered radiation pumped out by
nearby massive stars, should make star
formation here about as easy as cooking a perfect omelet on a storm-tossed
dinghy. Clouds in the galactic center
need to be at least 10 times denser than

normal in order to coalesce into stars.
Yet clearly that's not stopping them.
Astronomers have seen hints of current
starbirth here before, such as lopsided
gas concentrations that resemble the
disks around forming suns (S&T: June
2015, p. 16). However, these observations haven't been deﬁnitive.
Farhad Yusef-Zadeh (Northwestern
University) and colleagues report in
the December 1st Astrophysical Journal
Letters that they've now uncovered

strong evidence of small stars that
began forming near the black hole very
recently. Using ALMA to peer through
the dust toward the galactic center, the
team found 11 gaseous outﬂows tucked
within a bigger ring of molecular gas
that surrounds the black hole (spanning 6 to 15-20 light-years out from it).
The dumbbell-shaped objects look a lot
like the two-lobed outﬂows created by
protostars. Making some assumptions
about the masses involved, the team
estimates that the outﬂows come from
stars between 3,000 and 15,000 years
old. That's roughly comparable to previous protostar suspects.
The ALMA observations only include
the innermost few light-years, so it
remains unclear if there are more of
these outﬂows peppering the gas ring,
Yusef-Zadeh says. The team will need
to create a larger map in order to know
how common current star formation in
the galactic center really is.
■ CAMILLE M. CARLISLE

EXOPLANETS

A NEW ANALYSIS has settled one of
the many questions about the puzzling
planet 55 Cancri e: It's not an airless
hellscape after all. Instead, it appears to
have a substantial atmosphere.
This super-Earth - eight times
Earth's mass and almost twice its radius
- is in a scorchingly close orbit around
a star 40 light-years away. In 2015
Brice-Olivier Demory (then at Cavendish Laboratory, UK) and colleagues
published Spitzer Space Telescope
observations of the planet as it circled
its star. The infrared telescope acted like
night-vision goggles, enabling astronomers to see how much heat the planet
was emitting throughout its orbit.
The team's interpretation of the data
led to two contradictory results. The
temperature difference between dayside
and nightside was so extreme that it

M A RCH 2 018 * SK Y & TELESCOPE

precluded an atmosphere, which ought
to circulate heat from the dayside to the
nightside. Yet a shift of the hottest spot
on the planet of at least 30 degrees from
the center of the dayside hemisphere
suggested that something was recirculating the heat there - if not an atmosphere, then what? To solve the discrepancy, Demory's team suggested lava
ﬂows carry heat away from the center of
the dayside hemisphere, but as Demory
notes, "we always felt uncomfortable
with this explanation."
Now, theorists Isabel Angelo and
Renyu Hu (both at JPL-Caltech) have
compared those same Spitzer observations to their computer model of the
planet's atmosphere, publishing the
results in the December 2017 Astronomical Journal. The model describes
how well the atmosphere transports

p Artist's impression of 55 Cancri e

the star's heat. The result is a smaller
temperature difference between day and
night - one that's compatible with an
atmosphere surrounding the planet.
In addition to eliminating the
lava-ﬂow scenario, Angelo and Hu also
constrain the atmospheric makeup,
which could be based on nitrogen or
carbon monoxide but not water or carbon dioxide. Whatever constitutes the
atmosphere, though, it must be thick to
survive so close to the star.
■ MONICA YOUNG

PROTOSTA RS: A LM A (ESO / N AOJ / NR AO), F. Y USEF-Z A DEH E T A L., B. SA X TON (NR AO / AUI / NSF );
55 CA NCRI E: N ASA / JPL- CA LTECH

55 Cancri e Has an Atmosphere

Sky and Telescope - March 2018

Table of Contents for the Digital Edition of Sky and Telescope - March 2018