Sky & Telescope - May 2020 - 9

STARS

IN BRIEF

Nearby Stellar Nurseries
Ride a Giant Wave
A NEW MAP OF THE MILKY WAY shows
a gigantic "wave" of stellar nurseries
riding just outside the Sun's orbit within
the spiral disk of our galaxy.
The Milky Way isn't ﬂat like a pancake: Its stars, and the gas clouds they
form in, all move in a large gas disk that
has warps and crinkles. Astronomers
have now discovered a new warp that's
only about 500 light-years away at its
closest point to the Sun. And it's huge
- so far, its mapped expanse stretches
some 9,000 light-years.
João Alves (University of Vienna),
Catherine Zucker (Harvard), and colleagues suspected that a connection
existed between nearby star-forming
clouds as they were mapping out the
clouds' precise locations. But it wasn't
until Alves, Zucker, and Alyssa Goodman (also at Harvard) plotted the
clouds using the WorldWide Telescope,
an open-source visualization software,
that they saw the shape and extent of
the structure.
Many nearby stellar nurseries trace a
giant wave that lines up with the Local
Arm, the section of spiral that our Sun
inhabits in the Milky Way, Goodman
explained at the winter American Astronomical Society meeting in Honolulu.

Second Planet Around
Proxima Centauri

p In this illustration, the locations of star-forming clouds (red dots) are overlaid on an image of
the Milky Way Galaxy.

The team's study also appeared January
7th in Nature.
The wave looks like a straight line
from above; it's only when seen from
the side that the crests and troughs
appear, rising some 500 light-years
above and below the disk's midplane.
The wave includes major star-forming
clouds familiar to skygazers - Orion,
Perseus, and the North America Nebula.
Astronomers don't yet know how old
this structure is or how it formed. However, the stars that formed in the gas
clouds are just a few million years old,
and the team can use them to track the
structure's movements, Zucker explains.
Based on these data, the researchers
think the wave is oscillating, circling
the galaxy like a sea monster on an orbit
that intersected with the Sun's some
13 million years ago.
■ CAMILLE M. CARLISLE

Interact with visuals showing the discovery at https://is.gd/stellarwave.

Astronomers announced the discovery
of Proxima Centauri c in the January 15th Science Advances. It's the
second planet around the cool, red
star 4.2 light-years away; the first,
Proxima Cen b, was found in 2016. The
new super-Earth has at least six times
Earth's mass. To find it, Mario Damasso
(Astrophysical Observatory of Torino,
Italy) and colleagues analyzed data
collected between 2000 and 2017 by
the UVES and HARPS spectrographs
at the Very Large Telescope and the
La Silla Observatory, respectively. The
astronomers found a periodic, 5.2year "wobble" in Proximas Centauri's
spectrum indicating a planet, but they
caution that follow-up observations are
needed to confirm the planetary nature
of the signal. Since Proxima Cen c orbits about 1.5 astronomical units from
its cool star - about 30 times farther
out than b - the planet would be too
cold to host life as we know it. Moreover, Proxima Cen c appears to orbit
far beyond the system's snowlines, the
regions where gaseous compounds
such as water, carbon monoxide, or
ammonia solidify into ices. The planet's
orbit would thus challenge planetformation theories, which suggest that
these regions should be sweetspots
where super-Earths come together.
■ JULIE FREYDLIN

R A DCLIFFE WAV E: WORLDWIDE TELESCOPE,
COURTESY OF A LYSSA GOODM A N; Q UASA RS: N ASA /
ESA / S. H. SU Y U / K . C. WONG

t A selection
of gravitationally lensed
quasars

Planck Institute for Astrophysics,
Germany), also used Hubble images of
lensed quasars, this time focusing on
how their light ﬂickers. This study will
also appear in the Monthly Notices of the
Royal Astronomical Society.
Each quasar image represents a
different path the light takes to the
observer. When the quasar ﬂickers, light
traveling a longer path will arrive later,
so astronomers will see the same ﬂicker

multiple times. They can then measure
the time delays to paint a 3D picture of
the gravitational lens.
From this picture, astronomers can
estimate the distances to the quasar
and the lensing galaxy in a way completely independent from other distance
measures. Based on these distances, the
team estimated that the universe is currently expanding at a rate between 71.5
and 75 km/s/megaparsec.

This ﬁnding conﬁrms other results
based on relatively nearby objects,
which show a similarly fast expansion
rate. But calculations based on the
cosmic microwave background emitted
shortly after the Big Bang suggest that
the current expansion rate ought to be
slower. The gravitational-lensing study
therefore deepens the ongoing controversy (S&T: June 2019, p. 22).
■ GOVERT SCHILLING
s k y a n d t e l e s c o p e . o r g * M AY 2 0 2 0

https://www.is.gd/stellarwave http://www.skyandtelescope.org

Sky & Telescope - May 2020

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