Sky and Telescope - March 2018 - 11

EXOPLANETS

Ross 128b Orbits Quiet
Nearby Star
A LIKELY ROCKY PLANET orbits a
red dwarf star 11 light-years away,
astronomers announced in Astronomy
& Astrophysics.
Xavier Bonﬁls (University Grenoble
Alpes, France) and colleagues turned
the HARPS spectrograph at the La Silla
Observatory in Chile on Ross 128, the
15th-closest star to the Sun. The star's
motions reveal a planet, Ross 128b, that
circles it every 9.9 days. The tight orbit
puts Ross 128b 20 times closer to its
host star than Earth is to the Sun, but
the planet receives just 40% more light

GALAXIES

Deeper View of Hubble's
Deep Field
ASTRONOMERS HAVE upgraded the

ROSS 128B: ESO / M. KOR NMESSER; HUDF: ESO

Hubble Ultra Deep Field (HUDF).
Hubble imaged a tiny, now-famous
square of sky in Fornax for almost
12 days in 2003, revealing thousands of
faraway galaxies. Now, the Multi Unit
Spectroscopic Explorer (MUSE) on the
European Southern Observatory's Very
Large Telescope in Chile has taken a

than our own. The star is small and
cool, so that light would also be much
redder than our Sun's. With a mass at
least 1.35 times that of Earth, Ross 128b
is the second-closest, potentially Earthsize planet within the habitable zone of
its star, after Proxima Centauri b.
The star itself, unlike many low-mass
stars, is relatively well-behaved. Most
low-mass stars are cauldrons of magnetic activity, unleashing ﬂares typically
an order of magnitude more powerful than the Sun's. Such ﬂares could
severely limit the development of life in
these star systems.
However, even though Ross 128 is
technically classiﬁed as a ﬂare star,
it's old and doesn't ﬂare as often as its

visible spectrum of virtually every pixel
in the 10-square-arcminute ﬁeld of view
using a technique known as integral
ﬁeld spectroscopy. Ten papers in a special
issue of Astronomy & Astrophysics discuss the data and their implications.
Previously, astronomers had only
measured precise distances, via spectroscopic redshift, for 161 galaxies in
the HUDF. Distances to the rest of the
roughly 10,000 galaxies in the ﬁeld were
less well known. MUSE's pixel-by-pixel
spectra increased the number of precise

p Artist's impression of a temperate Ross 128b

younger counterparts, such as Proxima Centauri and Trappist-1. Expect
Ross 128b to be a target of future atmospheric studies.
■ JOHN BOCHANSKI

redshift measurements by an order of
magnitude, to 1,338 galaxies.
These new measurements have farreaching effects. Emmy Ventou (University of Toulouse, France) and colleagues,
for example, used the data to identify
close pairs of galaxies across cosmic
time, showing that the rate of galaxy
mergers peaked roughly 2 billion years
after the Big Bang - in tandem with the
early universe's star-formation activity.
MUSE also revealed 160 previously
uncataloged distant galaxies, known
as Lyman-alpha emitters, including 72
undetected in Hubble images. The faint,
low-mass galaxies are teeming with
newborn stars that excite abundant
neutral hydrogen gas. As a result, the
galaxies emit most of their radiation at
a single wavelength, making them difﬁcult to detect. The MUSE team sliced
apart the data by wavelength to search
speciﬁcally for these objects, catching
692 of them in all.
Alyssa Drake (then at University of
Lyon, France) and colleagues show that
these diminutive galaxies, as prevalent
as dust bunnies during early times,
could have single-handedly lit up the
young universe during what is known as
the epoch of reionization.
■ MONICA YOUNG

p The medusa-like MUSE instrument

Read the full story and ﬁnd original
papers at https://is.gd/muse_hudf.
sk yandtelescope.com * M A RCH 2 018

https://www.is.gd/muse_hudf http://www.skyandtelescope.com

Sky and Telescope - March 2018

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