THE SPEKTRUM-RÖNTGEN-GAMMA
(SPEKTR-RG) satellite, a long-delayed
and much-modifi ed X-ray astronomy
package, launched successfully from the
Baikonur Cosmodrome in Kazakhstan
on July 13th.
Once Spektr-RG reaches a stable
solar orbit 1.5 million kilometers
(1 million miles) from Earth, at
Lagrangian point L 2 , two telescopes
onboard will commence mapping the
X-ray sky. The fi rst is the German space
agency’s Extended Röntgen Survey with
an Imaging Telescope Array (EROSITA);
the second is the Russian-built Astro-
nomical Röntgen Telescope – X-ray Con-
centrator (ART-XC).
Each telescope contains multiple
modules of concentric mirror pairs.
X-rays will skip off these mirrors at
grazing incidence angles, like smooth
pebbles off a pond, before coming to aX-RAYS
German-Russian Satellite to Map X-ray Skyfocus on the detectors. EROSITA’s vision
is the sharper, with 18-arcsecond reso-
lution, and its wide fi eld of view enables
it to survey the full sky eight times over
four years. With 25 times the sensitiv-
ity of the last all-sky survey, conducted
with ROSAT in the 1990s, EROSITA will
discover millions of new sources.
ART-XC will focus higher X-ray
energies, from 5,000 to 30,000 elec-
tron volts (eV), complementing the
lower-energy photons that EROSITA
is sensitive to (200 to 10,000 eV). The
tradeoff for access to higher energies is
fuzzier images: The resolution of ART-
XC images will be 45 arcseconds.
One of the aims of the joint mission
is to better characterize dark energy,
the unknown force that determines the
universe’s expansion rate and ultimateAL
L-S
KY
VI
EW
:^ T.
DA
US
ER
/^ R
EM
EIS
- O
BS
ER
VA
TO
RY
/^
FA
U^ /EROSITATEAM;^ EROSITA^ MIRRORM
ODULES
:^P.^
FRIEDRICH^ /MPE^tNative Hawaiian activists at the base of
Maunakea protest the start of Thirty Meter
Telescope construction.uEROSITA’s seven mirror modules on displaytThis simulated image shows what EROSITA
will see in its all-sky survey in galactic coordi-
nates. The two bright spots are artifacts due to
increased exposure time at the poles.skyandtelescope.com • NOVEMBER 2019 9continuing at press time, but on August
8th, the observatories announced that
they would resume normal operations.
Opposition to the TMT began build-
ing in 2009, when the Maunakea site
was selected for construction; active
protests have continued off and on
since 2014. The mountain is sacred to
Native Hawaiians, but wrapped in with
this devotion is the sovereignty of the
Hawaiian people.“They’re utilizing the funds of the
people, to protect the rights of foreign
investors over the rights of the people of
this place,” activist Kaho‘okahi Kanuha
told the news outlet Big Island Now.
Rich Matsuda, chief of operations at
the W. M. Keck Observatory, says that
the ongoing tensions are painful for
all involved. More than 500 employees
work at the observatories, with about 50
to 75 of them at the summit on a typi-
cal day. “Observatory workers have been
part of the communities of this island
for fi ve decades,” Matsuda notes. “We’refate. Via its all-sky surveys, EROSITA
will detect the tenuous gas swirling in
some 100,000 galaxy clusters, catalog-
ing clusters back to when the universe
was half its current age. By measuring
changes in large-scale structure over
cosmic time, astronomers will be able
to study the nature of the mysterious
repulsive force.
As of early August, both telescopes
are undergoing commissioning and
working as expected. “It will be exciting
to see the sky slowly covered,” says prin-
cipal investigator Peter Predehl (Max
Planck Institute for Extraterrestrial
Physics, Germany).
■ MONICA YOUNGvery embedded into the community.
Those conversations are happening at
the family level.... It’s very diffi cult.”
The TMT collaboration has applied
for a building permit at the secondary
site in Spain’s Canary Islands, but only
to keep options open; for now, TMT
offi cials remain committed to building
in Hawai‘i. Meanwhile, work on the 574
hexagonal mirror segments continues at
other locations.
■ MONICA YOUNG- Read the latest updates at
https://is.gd/TMTprotest.