12 ASTRONOMY • JANUARY 2020
QUANTUM GRAVITY
To celebrate the Spitzer Space
Telescope’s 16th bir thday last
August, NASA highlighted 16
of the most amazing images
created with the help of Spitzer
data — four of which are shown
here. At top left is a vibrant
image of the Orion Nebula
(M42), an active star-forming
region located 1,500 light-years
away. The image at top right
shows ring-shaped ripples
within the Cartwheel Galaxy,
created when a smaller galaxy
tore through it some 100 million
years ago. At bottom left is the
Helix Nebula (NGC 7293), a
planetary nebula that formed
when a Sun-like star shed its
outer layers near the end of
its life. And shining bright blue
at bottom right is the gigantic
star Zeta (ζ) Ophiuchi. Visible
beside the star is the enormous
shock wave generated by its
strong stellar winds. Although
Spitzer has continued to chug
along for more than a decade
after its primary mission
concluded, the space telescope
is finally scheduled to retire on
January 30, 2020. — J.P.Spitzer’s
scrapbook
2.
The mass, in solar
masses, of the
heaviest neutron
star discovered to
date. Based on its
size, this stellar
remnant is near
the theoretical
limit of how
massive such an
object can grow
before collapsing
into a black hole.A DIM GALAXY RICH
IN DARK MATTER
Some 30 million light-years from Earth, a faint mon-
ster lurks in the constellation Cetus the Whale. It’s a
galaxy fainter than even the background brightness
of our planet’s atmosphere, which makes it tough to
see with Earth-based telescopes. Astronomers took
this image of the ghostly galaxy, dubbed UGC 695,
using the Hubble Space Telescope. So-called low-
surface-brightness galaxies like UGC 695 get their signature dimness from the fact that
they’re loaded with huge clouds of gas and dust, plus abundant dark matter, while con-
taining relatively few stars spread over a large area. Astronomers still aren’t sure how these
galaxies form, which makes views like this one from Hubble all the more valuable. — ERIC BETZCLOCKWISETOP^ L
EFT:^ NASA/JPL- CA
LTECH
/STSCI
;^ NASA/JPL- CA
LTECH
/STSCI
/CXC;^ NASA/JP
L-CALTECH;^ N
ASA/JPL- CA
LTECHESA/NASA/HUBBLE/D.^ CA
LZETTI