Sky and Telescope - April 2016 - 12

News Notes

GALAXIES I Aussie Amateur Finds Dwarf

MICHAEL SIDONIO

In October 2012 Australian amateur
Michael Sidonio (a former captain of the
country's "strongman" team) used his
12-inch reﬂector and FLI Proline 16803
CCD camera to record frames of the
Sculptor Galaxy, NGC 253. All Sidonio
wanted was a pretty image of this intermediate spiral galaxy, which lies about
11½ million light-years away.
But later he noticed a small, elongated
smudge oﬀ to one side that wasn't plotted
on any of his reference charts. His chance
discovery triggered a succession of
observations with ever-larger professional
telescopes - culminating with Japan's
8.2-meter Subaru Telescope.
That little smudge, now designated
NGC 253-dw2, turns out to be a dwarf
spheroidal galaxy that the much bigger
spiral galaxy is in the process of gobbling
up via tidal disruption (as implied by its
elongated shape). This straggler lies about
160,000 light-years from NGC 253, about
Michael Sidonio's black-and-white discovery
image of the dwarf galaxy NGC 253-dw2
(circled) reveals a small concentration of stars
near the spiral NGC 253 (color image overlaid).

STELLAR I Two Types of Binary
A new radio survey suggests that binary
star systems come in two basic sizes:
tight and loose.
John Tobin (Leiden Observatory, The
Netherlands) and others used the Very
Large Array's 27 antennas to study newborn stars in a nearby molecular cloud
in the direction of Perseus. The team
noticed that most of the young binary star
systems in the cloud fall into two categories: they're either separated by less than
300 astronomical units or by a distance
greater than 1,000 a.u.
"We think this is evidence that they
form from distinct routes," Tobin said
during a January 5th press conference
at the American Astronomical Society's
January meeting.
Stars are born in enormous clouds of
gas and dust that collapse into clumps
under the pull of gravity. As the clumps
12

April 2016 sky & telescope

shrink, their outer regions ﬂatten out into
pancake-shaped disks. Meanwhile, deep
inside, conditions eventually become hot
and dense enough to ignite fusion, and a
star is born.
But astronomers aren't sure how this
process works with binaries. Tobin's
team suggests that in the closer-packed
systems, one star likely forms in its birth
cloud's dense central core, while companion stars coalesce within the large
gas disk encircling the forming primary
star, much as planets do. But for the
widely separated systems, each star might
come together on its own, as part of the
turbulent fragmentation of its parent
cloud. Since most of the widely separated
systems the team found are relatively
young, the researchers speculate that
these binaries drift apart over time.
■ SHANNON HALL

as far as the Large Magellanic Cloud is
from us and easily close enough to be held
within NGC 253's gravitational death grip.
Cosmologists have often assumed
that spiral galaxies grow and evolve by
consuming lots of galactic small fry in
their vicinity. But this big-ﬁsh-eats-smallﬁsh paradigm, a key prediction of the
standard cosmological framework, is in
some distress (S&T: Sept. 2015, p. 16). For
example, dwarf galaxies are scarce in the
Milky Way's immediate neighborhood.
Thus, NGC 253-dw2 is an important
ﬁnd, as Aaron Romanowsky (San Jose State
University) and nine coauthors - including Sidonio - detail in a forthcoming
issue of Monthly Notices Letters of the Royal
Astronomical Society. It provides a crucial
observational test for the distribution of
dark matter around the host spiral galaxy.
Another team has independently
reported ﬁnding the dwarf galaxy in
question. Elisa Toloba (Texas Tech University) and other observers spotted it in
images taken between November 2011
and October 2014 with the Magellan Clay
6.5-m telescope in Chile.
■ J. KELLY BEATTY

IN BRIEF
InSight Launch Postponed Until 2018.
NASA's next Mars-bound mission, InSight
(short for Interior Exploration using Seismic Investigations, Geodesy and Heat
Transport), will not be launched this spring
as planned. A vacuum seal in the lander's
French-built seismometer developed a leak
during a ﬁnal round of thermal testing at
Vandenberg Air Force Base in California.
Mission managers decided that there
wasn't enough time to make the needed
repairs before the launch. Since the opportunities to send spacecraft to Mars occur
during favorable orbital geometries that
occur every 26 months, InSight won't get
another chance to leave Earth until 2018.
■ J. KELLY BEATTY

Astronomers Predict a Supernova. Last
year, Patrick Kelly (University of California,
Berkeley) and colleagues announced the
Sky and Telescope - April 2016

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