Sky & Telescope - December 2020 - 10

NEWS NOTES

GALAXIES

"Dead Ringer" for the
Milky Way Found in the
Early Universe
ASTRONOMERS HAVE USED a gravita-

tional lens to investigate a surprisingly
Milky Way-like galaxy that existed
1.4 billion years after the Big Bang.
The gravity of a massive foreground
galaxy bends the light of the more distant galaxy, referred to as SPT0418-47,
distorting its shape into a near-perfect
Einstein ring. Francesca Rizzo (Max
Planck Institute for Astrophysics, Germany) and colleagues used the Atacama
Large Millimeter/submillimeter Array
(ALMA) in Chile to image the glow of
this galaxy's cool dust, as well as emission associated with its star-forming

gas. They then reconstructed the galaxy
to show what it would look like without
the distortions, publishing the results in
the August 13th Nature.
The digitally restored galaxy is
roughly 10 times smaller than the
Milky Way and furiously forming stars
more than 100 times the rate in our
own galaxy. But the young galaxy is
surprisingly modern in its shape and
behavior. Like our own, it's a rotating
disk with a central bulge. And it's less
chaotic than expected.
Cosmological simulations have
taught astronomers to expect ﬂuffy
disks in the early universe, with forces
other than rotation also contributing
to the movement of gas. But in this
galaxy, rotation dominates over random
motions by about 10:1, similar to modern-day galaxies like the Milky Way.
However, Marcel Neeleman (Max
Planck Institute for Astronomy,
Germany) cautions that comparing
observations with cosmological simulations isn't so simple. Most simulations,
including the one quoted in this study,
do not model the cold gas that ALMA

W This mosaic of radar images from Cassini's
Titan flybys shows the various lakes and seas
on Saturn's largest moon.

MOONS

Waves on Titan's Seas
SUNLIGHT GLITTERING OFF rough
patches of a methane-ethane sea on
Titan has provided the ﬁrst solid evidence for abundant (albeit tiny) waves
on Saturn's largest moon.
NASA's Cassini spacecraft previ-

10

DECEMBER 2 02 0 * SK Y & TELESCOPE

ously detected the glare of sunlight
reﬂecting off the smooth surfaces of
the moon's lakes and seas, and in early
years, scientists saw no signs of waves.
But calculations suggested that winds
would begin to rise as the northern
hemisphere entered spring in 2010 and
surface temperatures increased slightly.
Subsequent observations found hints of
a few, isolated instances of waves in two
seas (S&T: Oct. 2014, p. 18).
Michael Heslar (University of Idaho)
and colleagues have now dived into
Cassini's data and found evidence of
widespread wave activity on Titan's largest sea, Kraken Mare.
The team took advantage of highresolution observations gathered during

sees. That said, Neeleman thinks the
implications could be profound if additional observations can replicate these
ﬁndings in other early galaxies.
Cosmological simulations used to
form too many stars early on, Neeleman explains. Current models solve
that problem by including feedback,
such as the blowback from newborn
stars and supernovae or black hole jets.
Feedback hinders gas from settling into
stars - but it also produces turbulence.
If astronomers ﬁnd that other young
galaxies also lack turbulence, Neeleman says, then they'll have to rethink
the role, or at least the mechanisms of
feedback in galaxy evolution.
■ MONICA YOUNG

S These images show motions within the galaxy as observed (left) and in the reconstructed
version (right); blue and red represent gas
moving toward and away from the observer,
respectively. The galaxy is a rotating disk with a
central bulge.

Cassini's later Titan ﬂybys to look for
sun glitter, when sunlight reﬂects off
rougher seas. Sun glitter is weaker than
the glare of direct reﬂection. Combining
imaging and spectral data with radar
surface maps, the team found several
instances of sun glitter on Kraken
Mare's surface, especially in and around
two narrow straits, Bayta Fretum and
Seldon Fretum. The sun glitter may
indicate consistently agitated seas in
the straits - unsurprising for coastal
areas, the team notes in the September
Planetary Science Journal.
Calculations and lab experiments
suggest that weak winds and tides lead
to waves up to 20 cm (8 inches) high -
hardly a surfer's dream. But wave height
is difﬁcult to gauge without better
knowledge of the seaﬂoors.
■ CAMILLE M. CARLISLE

DISTA N T G A L A X Y: A LM A / ESO / N AOJ / NR AO / RIZ ZO E T A L. / N AT URE
AUG. 12, 2020 (2); TITA N: N ASA / JPL- CA LTECH / ASI / USGS

W The ALMA radio observatory reveals a
distant galaxy gravitationally lensed into a nearperfect ring of light.
Sky & Telescope - December 2020

Table of Contents for the Digital Edition of Sky & Telescope - December 2020
