Sky & Telescope - March 2019 - 9

GALAXIES

Dwarf Galaxy Found
by Amateur
IN AN ERA OF GIANT telescopes, one

could be forgiven for thinking there
wasn't much left for an enthusiastic
hobbyist to discover. But with patience
and the right equipment, even an amateur astronomer can stumble onto an
undiscovered galaxy.
Beneath the dark skies of Pollino National Park in southern Italy,
Giuseppe Donatiello had been investigating the Andromeda Galaxy with
his home-built telescope. In images
acquired late in 2010 and 2013, he
noticed an unidentiﬁed smudge of
light. That smudge turned out to be a
dwarf spheroidal galaxy - now dubbed
Donatiello I - lurking on the farside of
Andromeda. "I literally jumped for joy,"
says Donatiello.
As far as galaxies go, Donatiello I is a

runt. Assuming an estimated distance of about
10 million light-years,
it appears to be roughly
several thousand lightyears across. The dwarf
galaxy is faint, too. With
a surface brightness of
just 26.5 magnitudes per
square arcsecond, it's
barely visible against the
night sky.
Astronomer David
Martínez-Delgado
(Heidelberg University, Germany) came
across the discovery on Facebook, where
Donatiello had posted his discovery
image. Martínez-Delgado reached out
and offered to collaborate on a paper, to
appear in Astronomy & Astrophysics. The
pros took a closer look with much larger
telescopes. The dwarf galaxy appears
to be old and on its own, just outside
our Local Group of galaxies. Martínez-

EXOPLANETS

Chilly Super-Earth May Orbit Barnard's Star

DWA RF G A L A X Y: G. DON ATIELLO; PL A NE T: M. KOR NMESSER / ESO

IN THE CONSTELLATION OPHIUCHUS

lies Barnard's Star, one of the closest
and most well studied red dwarf stars
in the galaxy. Now, after more than
two decades of searches, astronomers
have found signs of an exoplanet hiding in its light.
Led by Ignasi Ribas (Institute of
Space Sciences, Spain), this latest investigation combines new and archival
observations spanning 20 years from
seven different facilities across the
globe. The data, which record the star's
speed toward and away from Earth,
suggest that a planet at least 3.2 times
as massive as Earth orbits Barnard's Star
every 233 days at a distance of 0.4 a.u.
(60 million km). The team reports their
ﬁnd in the November 15th Nature.
The putative planet is a bit farther
out from its star than Mercury's average
distance from the Sun. But given the
star's weak luminosity - less than 4%
that of the Sun - this orbit puts the
planet close to the system's snow line,
where water exists only in its frozen

form, making habitability unlikely.
At just under 6 light-years away,
Barnard's Star is the fourth-closest star
to the Sun (after the three stars of the
Alpha Centauri system). This proximity
means the separation between planet
and star on the sky is large enough to

t The amateur-discovered
dwarf galaxy Donatiello I
is just a fuzzy blob in this
composite image obtained
with the discoverer's 127-mm
refractor in Italy.

Delgado and colleagues
hope to get a better look
with the Hubble Space
Telescope, which should
provide them with
precise measurements
for the galaxy's distance,
size, and mass.
Donatiello, meanwhile, plans to
keep searching. "I have always had a
great interest in dwarf galaxies, so I
will continue in this direction," he
says. "But more generally, I am interested in galactic archeology, so at the
same time I will dedicate myself to the
search for stellar streams around Milky
Way-like galaxies."
■ CHRISTOPHER CROCKETT

make Barnard's planet an ideal candidate for direct imaging with nextgeneration observatories. The researchers say that the European Gaia satellite
and even the Hubble Space Telescope
might be able to directly measure the
star's planet-induced wobble on the sky,
which could help astronomers zero in
on the planet's true mass.
■ SUMMER ASH

q A ruddy glow bathes the imagined surface of a putative rocky planet orbiting the red-hued Barnard's Star, in this artist's illustration.

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Sky & Telescope - March 2019

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