10 AUSTRALIAN SKY & TELESCOPE APRIL 2016China’sdarkmatter
probe in orbit
A
stronomers have now found
dozens of stars zipping through
spaceat30kilometrespersecond
(108,000 kph) or faster relative to their
surroundings. These speedsters, called
runaway stars,tendtobeinisolated
regionsofthegalaxy,thoughtheir
paths often lead directly away from
stellar clusters or even our galaxy’s
central black hole.
Astronomers had previously
discoveredabout20ofthesestars,
throughpureluck.Butnowtheyhavea
new technique: searching for the
bowshocksthestarscreatein
interstellar gas and dust as they whiz
throughthismaterial.
ThestarZeta(ζ)Ophiuchi inspired
thenewapproach.It’sahot,massive
Ostarwitharelativemotionfast
enough—roughly24km/s—tobe
‘supersonic’. As this massive star
plows through space, astronomers
discovered, its strong outflowing wind
causes interstellar gas and dust to stack
upinfrontofit,liketheshockfront
ofairthatpilesupaheadofahigh-
performance jet. This arc-shaped gas
compresses, heats up, and shines with
infrared light, emission that revealsboth the mass and velocity of the star.
With Zeta Ophiuchi’s example in
hand, Grace Olivier (Case Western
Reserve University) and colleagues
decided to look for bow shocks in
ordertosearchforrunawaystars.
They turned to archival infrared data
fromtheSpitzerandWISEspace
observatories and found more than
200imagesoffuzzyredarcs.They
then used the Wyoming Infrared
Observatory’s 2.3-metre telescope to
lookfortheculpritsbehind80ofthem.
Theteamwassurprisedtofindthat
“morethan95%ofthesebowshocks
have a hot, massive, runaway candidate
at their centre,” team member William
Chick(UniversityofWyoming)said
during a press conference January 5
at the American Astronomical Society
meeting in Kissimmee, Florida. “It may
be that our Milky Way is swarming
with these hot runaway stars.”
The team plans to extend its search
to include the entire galactic plane.
With more runaways spotted, the
researchers will be able to trace the
stars’ motions backward in order to find
the source of their accelerating kicks.
■SHANNON HALLNASA/JPL
-CALTECH/UCLA
ZetaOphiuchi(bluestarinthecentreoftheimage)anditsaccompanyingbowshock,
as seen at infrared wavelengths by the WISE space telescope.On December 17, China launched its
first astrophysics payload. The Dark
Matter Particle Explorer (DAMPE)
will detect energetic particles known
as cosmic rays, as well as gamma-ray
photonsfromsupernovae, pulsars and
other astrophysical sources — including,
perhaps, elusive dark matter.
DAMPE is a collaboration among
universities in Switzerland and Italy and
the Chinese Academy of Sciences. (NASA
is restricted from trading technology with
China due to the 1976 International Trade
in Arms Regulations, a key reason why
China isn’t a partner on the International
Space Station.)
DAMPE joins the Alpha Magnetic
Spectrometer and the Calorimetric Electron
Telescope, both aboard the International
SpaceStation,intakingthe dark matter
hunt to space. It’s the first of a five-mission
series,withthenexttwopayloads — a
quantum-communications satellite and an
X-ray telescope — set to launch this year.
■DAVID DICKINSONNews Notes
Runaways’ shocking behaviour
Magnetic fields mear
the event horizon
Astronomers have detected magnetic fields
dancingintheskirtsoftheMilkyWay’s
central black hole. The work is part of the
Event Horizon Telescope, a planet-spanning
network of radio antennas aiming to ‘see’
asupermassiveblackhole—or,rather,its
telltale silhouette amid the glow of hot gas
surroundingitlikeasuperheatedtutu.
Michael Johnson (Harvard-Smithsonian
Center for Astrophysics) and other
membersoftheEHTcollaborationused
telescopes in Hawai‘i, California and
Arizona to peer into the inner sanctum
ofourgalaxy’sblackhole,SagittariusA*.
Withonlythreesitesandafewnights’
worthofobservations,theycouldn’t
reconstructacompleteimage—instead
of seeing the whole elephant, they’re only
seeing an ear and a bit of trunk.
But those bits are good enough for