Sky & Telescope - August 2019 - 20

X-ray Explorers

Curse of the Calorimeter
One instrument that could explore the X-ray spectrum -
but hasn't yet - is a microcalorimeter. By recording the minute changes in heat due to incoming
X-ray photons, this instrument would
act as an extremely sensitive and
high-resolution spectrometer unlike
any ﬂown so far.
A microcalorimeter could help
astronomers understand what sustains galaxy clusters against collapse
or dissolution, and it could measure
the elements and energy supernovae
p UNEXPECTED JET
distribute
throughout the universe. It
Chandra revealed a
jet extending sevcould also help solve a key cosmological
eral hundred thousand mystery: the case of the missing matter.
light-years from the
Dark matter aside, astronomers can't
distant quasar PKS
even account for all normal matter in
0637-752.
their observations of stars, dust, and
gas. Tentative ﬁndings from Chandra and XMM-Newton
suggest that this missing mass might lurk as hot, tenuous gas
between galaxies. But the needed measurements are exceedingly difﬁcult to make with current instruments.
A microcalorimeter originally intended to accompany
Chandra into space was bumped to another mission, which
was later cancelled. In 2000 a more advanced version of that
instrument ﬂew on the Japanese Astro E mission, but the

p TYCHO Einstein could resolve turbulent structures, such as in the remains of a Type Ia supernova that appeared in Cassiopeia in 1572 (inset).
Chandra later captured far finer detail within the Tycho remnant.

rocket carrying it exploded shortly after launch. A replacement was ﬂown on Astro E2, later christened Suzaku, but
that too failed: A mistake in communication led to a design
ﬂaw that boiled away the cryogen required to keep the instrument cool, rendering it useless before the instrument could
take a single observation.
The next project, called Hitomi (Japanese for "pupil of
the eye"), integrated a lot of changes, including advances
to the instrument itself and improvements in communications. "They decided to be paranoid," says Ann Hornschemeier (NASA Goddard Space Flight Center). Before all the
instruments were deployed or even the (transparent) shutter
opened, the Hitomi team
took promising observations of hot gas drifting in
the Perseus galaxy cluster.
"But I don't think anybody would have guessed
that that would be the end
of the mission," Hornschemeier adds.
On March 26, 2016,
a series of minor errors
u PULSAR IN ANDROMEDA
XMM-Newton spotted the first
known pulsar spinning in our
sister galaxy.

JE T: N ASA / CXC / SAO; T YCHO BY CH A NDR A: X-R AY: N ASA / CXC / GSFC / B. WILLIA MS E T A L., OPTICA L: DSS; T YCHO BY EINSTEIN: N ASA; PULSA R: A NDRO MEDA: ESA / HERSCHEL / PACS / SPIRE / J.
FRIT Z, U. G EN T / X M M-NE W TON / EPIC / W. PIE TSCH, MPE

the aspect operations scientist, who looked up the source and
discovered that a radio image showed an extension in the
same direction. Chandra was simply imaging the powerful jet
emanating from near the black hole.
"We went to point at another source . . . and it also had
a jet!" Tananbaum says, laughing. The widespread existence
of X-ray-emitting jets highlights Chandra's capabilities, Elvis
notes: "Einstein showed that everything is an X-ray source;
Chandra showed that pretty much everything is extended."
Meanwhile, the three X-ray telescopes onboard XMMNewton have collected an abundance of photons from hundreds of thousands of sources, providing energy information
that's crucial to interpreting the science. Together, Chandra
and XMM-Newton have revolutionized the ﬁeld once more.

XMM-Newton
Chandra
ARGOS
BeppoSAX
IRS P3
RXTE
Alexis
ASCA
AGILE
Suzaku (Astro E2)
Neil Gehrels Swift Observatory

Shenzhou 2
Orbital Module
Kvant

Integral
High Energy Transient Explorer (HETE) 2

2000

2001

2002

AUGU S T 2 019 * SK Y & TELESCOPE

2003

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Sky & Telescope - August 2019

Table of Contents for the Digital Edition of Sky & Telescope - August 2019