Sky and Telescope - October 2016 - 13

on FIRE." Latte has the highest resolution
yet of any simulation of its kind, zooming
in to a mere few light-years as it follows
the development of a Milky Way-size
galaxy and its legion of dwarfs.
The team ran two versions of the
simulation: one with just dark matter, and
one with dark matter plus gas physics plus
stellar feedback. The researchers found
that the souped-up version produced about
700 dark-matter satellites lurking around
the big central galaxy, only a tenth as many
as in the dark-matter-only version. And of
these 700, only nine managed to form a
stars-and-gas dwarf galaxy inside it.
The big galaxy itself keeps dwarfs from
forming, Wetzel explains. As budding
satellites ﬂy through its hot halo of gas,
they're ripped clean of their own gas by
frictional drag, preventing star formation.
The Milky Way-like galaxy also destroys
the dark-matter clumps in which the
dwarfs would have formed: as the satellites orbit the large stellar disk - which is
completely absent in the dark-matter-only
simulation - the disk's tidal forces yank
on the satellites. If the satellites ﬂy within
two or three times the disk's radius, the
tides wrench them apart.
In addition to solving both problems,
Latte creates galaxies that look real enough
to fool colleagues, Hopkins boasts.
■ CAMILLE M. CARLISLE

ammonia and carbon dioxide can also
aﬀect spin when they go from frozen to
gaseous states in a process called sublimation as the comet nears the Sun.
Other periodic comets are known to
have a double-lobed shape. Of the seven
comets astronomers have seen at high
resolution, ﬁve are bi-lobed.
So could this be a common characteristic among periodic comets? "The
conclusion that the other comets are
necessarily bi-lobate is not so obvious as
with 67P," said Uwe Keller (Max Planck
Institute for Astronomy, Germany). He
says other comets that undergo sublimation also have elongated shapes, but that
not all elongated comets need to be of
bi-lobate origin.
■ ANA V. ACEVES

IN BRIEF
Baby Planets Leave Gas Footprints. A new analysis of ALMA radio data conﬁrms
that gaps in the disk around the young star HL Tauri likely have been carved out by
forming planets. Two years ago, astronomers used ALMA to capture a stunning image
of gaps in the star's dusty disk. The disk spans 235 astronomical units, and gaps
exist at around 32, 64, and 74 a.u. But ALMA's observations, taken at a wavelength
of 1.3 mm, recorded emission only from cool dust; they don't reveal if gas ﬁlls the
apparent gaps. If it does, then they're not carved out by forming planets and must
arise some other way. Now Hsi-Wei Yen (Academia Sinica Institute of Astronomy and
Astrophysics, Taiwan) and others report in the April 1st Astrophysical Journal Letters
that, when they summed up the gas emission in diﬀerent parts of the image, the gaps
appear to be real. But HL Tau is only a million years old, and along with a recently discovered planet around the 2 million-year-old star CI Tau, it deﬁes theorists' prediction
that these worlds should take at least 10 times longer to accumulate.
■ MONICA YOUNG

LISA Pathﬁnder Surpasses Expectations. The European Space Agency's technology testbed for its upcoming space-based gravitational-wave detector is working even
better than hoped, Michele Armano (ESA) and fellow team members report in the June
10th Physical Review Letters. LISA Pathﬁnder contains two test masses in freefall,
which, when scaled up in the full-size 2030s mission, will be inﬂuenced by only gravitational waves. The ﬁrst results exceeded engineers' goal by a factor of ﬁve, reaching
femtometer scales (a femtometer is a million-billionth of a meter). For comparison, the
charge radius of a proton is about 0.8 femtometer. Learn more and watch the press
conference at https://is.gd/lisapathexceeds.
■ DAVID DICKINSON

Rolf G. Meier (1953-2016). On June 26th amateur astronomy lost a dedicated
observer and successful visual comet hunter to brain cancer. As a teenager, Meier
joined the Royal Astronomical Society of Canada's Ottawa Centre. He discovered his
ﬁrst comet - the ﬁrst comet ever found from Canada - on the evening of April 26,
1978, after searching for only 50 hours. Comet Meier, initially designated 1978f and later
C/1978 H1, is one of the largest comets ever found. Meier went on to ﬁnd three more
in the 1970s and 1980s. An engineer by day, he also pursued planetary photography
with characteristic passion. He and his wife, Linda (herself an accomplished amateur
astronomer), often observed together and hosted meteor watches at their home.
■ DAVID H. LEVY

First Chiral Molecule Discovered in Space. Molecules come in two "handed," or
chiral, forms, one a mirror image of the other. All of life's chemistry seems to be based
on chiral molecules of a certain handedness: the amino acids in proteins are lefthanded, whereas the sugars that form the helical backbone of DNA are right-handed.
Scientists don't know why. One idea is that the molecules on Earth started out with
a preference for one chirality over the other, thanks to conditions in the cloud that
formed the solar system - say, if polarized radiation from stellar nurseries destroyed
slightly more molecules of one kind than the other. In the June 17th Science, Brett
McGuire (National Radio Astronomy Observatory) and others report the ﬁrst discovery of a chiral molecule in space, propylene oxide (CH3CHCH20). The molecule ﬂoats
(probably on icy dust grains) near protostars in the giant molecular cloud Sgr B2(N).
The team can't yet tell whether the propylene oxide is right- or left-handed, but they
hope future observations of polarized radio waves will reveal its chirality. ✦
■ MONICA YOUNG

SkyandTelescope.com October 2016

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Sky and Telescope - October 2016

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