72 Scientific American, December 2019FLYING JET
EARLY IN ITS TENURE Chandra observed the quasar
PKS 0637-752, a supermassive black hole in the nucleus
of a distant galaxy and one that I had studied a decade
before, using data from nasa’s Einstein Observatory.
The black hole is pulling in massive amounts of material
from its host galaxy. As the material falls, it becomes so
hot that it outshines the galaxy’s 100 billion stars.
The extended light on the west (right-hand) side was
a surprise and initially had the Chandra staff concerned
that something had gone wrong with the telescope optics.
Instead Chandra had discovered x-ray emission from a jet
of plasma flying out of the infalling matter. This jet had
previously been sighted in radio light, but the x-rays were
unexpected. Chandra’s ability to see the jet as well has
resulted in major advances in our understanding of jets
emanating from the poles of supermassive black holes.
NASA, CXC AND SAO
SMOKING GUN
AMONG CHANDRA’S most famous results is this com-
posite image of the Bullet Cluster—a pileup of two galaxy
clusters smashing together. The picture combines data
from Chandra, Magellan and the Hubble Space Telescope.
Here hot gas appears in x-ray light ( shown in pink ), where-
as galaxies can be seen in visible light ( white ) from Magel-
lan. From the visible-light image scientists infer the
distribution of dark matter ( blue ) from the distortion
of the galaxy images caused by gravity (a process called
gravitational lensing).
The separation between hot gas and dark matter pro-
vided the first direct evidence for the presence of dark
matter. It demonstrates that this mysterious stuff does
not interact with either itself or regular matter, because
it moves with the galaxies, not “seeing” the other matter
around it. In contrast, the hot gas interacts and slows
down, forming the bullet shape that gives the combined
clusters their name.
X-RAY: NASA, CXC, CFA AND M. MARKEVITCH ET AL.; OPTICAL: NASA, STSCI, MAGELLAN, UNIV. ARIZONA AND
D. CLOWE ET AL.; LENSING MAP: NASA, STSCI, ESO WFI, MAGELLAN, UNIV. ARIZONA AND D. CLOWE ET AL.
© 2019 Scientific American