Sky and Telescope - December 2016 - 14

News Notes

GALAXIES I Giant "Frankenstein" Spiral

■ ANA V. ACEVES

NASA / JPL / CALTECH / SDSS / NRAO / L. HAGEN & M. SEIBERT

using spare parts - like Victor Frankenstein's creation. The researchers think
the best explanation is that a group of
dwarf galaxies fell into orbit around a
lens-shaped galaxy a few billion years
ago, eventually becoming its spiral arms
and providing gas for star formation in
the interior. This process would make
the center of UGC 1382 younger than the
spiral disk surrounding it.
But Lynn Matthews (MIT Haystack
Observatory) says one has to be cautious
with this scenario. It's diﬃcult to ﬁnd the
precise age of a galaxy because stars form
at diﬀerent times, and that process doesn't
always occur at a constant rate. Measuring
the stars' heavy-element content, which is
normally higher for younger stars, would
help conﬁrm the stars' ages.

New observations reveal that dark
streaks are surprisingly common on Mars.
These streaks, called recurring slope lineae
(RSL), appear and fade year after year. Last
September, Lujendra Ojha (Georgia Institute of Technology) and others conﬁrmed
that these warm-season features contain
water-soaked salts (S&T: Jan. 2016, p. 14).
But scientists didn't know where the water
was coming from.
Matthew Chojnacki (University of
Arizona) and other members of Ojha's
team investigated thousands of streaks in
41 sites of the Valles Marineris region, the
largest canyon complex in the solar system. The team found that pretty much all
of the canyon walls, including the sides of
isolated peaks, had RSL.
Because the streaks appear on steep
slopes, underground pools can't be
responsible. Instead, it's more likely that
the salts are pulling water from the atmosphere in a process called deliquescence.
Chojnacki's team estimates that
about 10 to 40 Olympic-sized swimming
pools of water are required to make the
streaks. Based on orbiter estimates,
there's enough water vapor ﬂoating above
Valles Marineris for that to happen, but
researchers can't think of an eﬃcient way
for the surface to extract that much water
from the atmosphere. Or perhaps we've
underestimated how much water is there,
and some places are unexpectedly humid.
Chojnacki's study appears in the July 7th
Journal of Geophysical Research: Planets.

In optical light (left), UGC 1382 appears to be a simple elliptical galaxy. But when astronomers
observed it using ultraviolet and deep optical data (middle), spiral arms emerged. When those
were combined with a view of low-density hydrogen gas (seen in green at right), scientists discovered UGC 1382 is bigger than they thought.

Astronomers have taken a second look
at the isolated galaxy UGC 1382 and
discovered everything they thought they
knew about its size, age, and formation is
probably wrong.
UGC 1382 lies about 250 million
light-years away in a quiet and unremarkable neighborhood, with few neighbors
to bother it. Several surveys in the 2000s
looked for structural features like star
rings and bars but didn't ﬁnd anything
other than a typical elliptical galaxy. Then
Lea Hagen (Penn State) noticed something interesting in ultraviolet images
taken with NASA's Galaxy Evolution
Explorer (GALEX): UGC 1382 actually
has very extended spiral arms.
Further multiwavelength investigation showed the galaxy is roughly 10
times bigger than previously thought. At
about 520,000 light-years across, UGC
1382's spiral disk is ﬁve times wider than
the Milky Way's and makes it one of the
largest such galaxies known. The system
is so delicate that even a small nudge
from a neighboring galaxy would make it
disintegrate, says coauthor Mark Seibert
(Observatories of the Carnegie Institution
for Science).
Reporting in the August 1st Astrophysical Journal, the team also found
that, unlike in most galaxies, UGC 1382's
innermost stars appear to be younger
than the stars on the outskirts. It's
almost as if the galaxy had been built
14

December 2016 sky & telescope

MARS I Too Much Water?

IN BRIEF
Possible Replacement for Hitomi. The
Japanese Space Agency (JAXA) and NASA
are considering replacing the failed Hitomi
X-ray observatory. Launched in February
and originally slated for a three-year mission, Hitomi lasted just over a month, torn
to pieces by an out-of-control tumble (S&T:
July 2016, p. 11). X-ray astronomers had
long awaited the chance to use this craft's
instruments, especially its calorimeter,

which recorded the energy of each incoming photon with unprecedented precision.
Because Hitomi was an essential link
between current and future X-ray observatories, JAXA and NASA are now discussing
building and launching a successor, potentially a copy of the original, with a launch
around 2020. Otherwise, the next chance is
Europe's Athena, launching in 2028.
■ DAVID DICKINSON

Sky and Telescope - December 2016

Table of Contents for the Digital Edition of Sky and Telescope - December 2016