Sky & Telescope - February 2023 - 40

MSA: S&T; STELLAR STREAMS IN THE HALO: S. PAYNEWARDENAAR
/ K. MALHAN, MPIA
Data Overload
halo should be home to countless invisible subhalos of dark
matter. If they incidentally passed through a stellar stream,
they could leave telltale " holes " and other gravitational
disturbances. No such signatures have been confirmed so
far. Moreover, studying the dynamics of stellar streams could
provide information on the overall mass distribution in the
Milky Way, which is thought to be dominated by dark matter.
Quiet Revolution
Over the next few years, many new results on a wide variety
of astronomical topics will be published on the basis of Gaia
DR3 data. But this release is only one third of Gaia's eventual
astrometric harvest. " Around 2025, we plan to release
the fourth batch of data, based not on 34 but on 66 months
of observations, " says Brown, who is the chair of the Data
Processing and Analysis Consortium. " With DR4, for the first
time, we will also publish all individual observations. Five
years later, the final data release of 126 months is expected. "
The spacecraft's micro-propulsion fuel is expected to run
out in early 2025. But scientists and engineers are already
drawing up plans for a successor to Gaia that operates at
near-infrared wavelengths. GaiaNIR, proposed as part of ESA's
Voyage 2050 scientific program, would be able to peer through
most of the absorbing dust in the plane of our Milky Way
and map stars in the galactic center and dusty spiral arms.
By revisiting stars from the Gaia catalog, the new mission
would also vastly improve on proper motion measurements.
The development of a Gaia-like drift scan detector for infrared
wavelengths is still a technological challenge, says Brown, but
once that's been solved, GaiaNIR could launch in the 2040s.
For now, astronomers are just wallowing in the wealth of
ultra-precise data from Europe's indefatigable star mapper. As
Frédéric Arenou (Paris Observatory) says: " Gaia is an all-inone
instrument. There are no fancy images, but Gaia is providing
material for an important fraction of the astrophysiGALACTIC
CRUMBS
Spread throughout the
Milky Way's halo are
stellar streams (colored
dots), globular clusters
(star symbols), and
dwarf galaxies (small
cubes). They're shown
here projected into
their 3D location in an
illustrated version of
the Milky Way. The ☉
symbol marks the Sun's
location.
Mine the Archive
The 1,548 charts of the 1997
Millennium Star Atlas (produced
by Sky & Telescope in close
collaboration with the European
Space Agency) were based
on data from ESA's Hipparcos
mission. There are currently no
plans to turn the Gaia measurements
into a hardcopy atlas,
given that there would be no
notable differences in the positions
of stars bright enough for
observers' use. " But all data
are freely available, so everyone can do it, " says Anthony
Brown, the chair of Gaia's Data Processing and Analysis
Consortium (DPAC).
For individual stars and other objects, you can access
the latest information through the Gaia Archive (https://
gea.esac.esa.int/archive) or through the SIMBAD
astronomical database (https://simbad.u-strasbg.fr/
simbad). Moreover, Gaia scientists produced an opensource
software package, Gaia Sky, advertised as a " 3D
universe simulator with support for more than a billion
objects. " You can download Gaia Sky from https://zah.
uni-heidelberg.de/gaia/outreach/gaiasky.
cal field for several years, if not decades. The most profound
revolutions are sometimes quiet. "
¢ Contributing Editor GOVERT SCHILLING's coordinates put
him in the Netherlands, and his proper motion is restricted to
the surface of a rocky planet orbiting a G2V star.
MSA The three-volume
Millennium Star Atlas used
Hipparcos data as well as
nebula outlines handtraced
from sky images.
It's now a collector's item.
40 FEBRUARY 2023 * SKY & TELESCOPE
http://gea.esac.esa.int/archive http://gea.esac.esa.int/archive https://simbad.u-strasbg.fr/simbad https://simbad.u-strasbg.fr/simbad http://www.zah.uni-heidelberg.de/gaia/outreach/gaiasky http://www.zah.uni-heidelberg.de/gaia/outreach/gaiasky
Sky & Telescope - February 2023

Table of Contents for the Digital Edition of Sky & Telescope - February 2023
