a galaxy’s distance has been established
with Cepheids, astronomers can use the
same galaxy to calibrate the next rung
on the ladder: stellar explosions called
type Ia supernovae. Supernovae are
brighter than Cepheids and can be seen
at greater distances, allowing astrono-
mers to measure distance, speed, and
the Hubble constant based on farther
galaxies. The process then continues,
using new distance indicators each time
the previous one becomes too dim.
NEW SH0ES
Because uncertainty in any rung of the
ladder propagates into every other step,
minimizing the uncertainty in measur-
ing distances to Cepheid variables is
key to the entire process. Based on their
new work, Riess’ team reduced the
uncertainty in the distance to Cepheid
variables in the LMC from 2.5 percent
to 1.3 percent.
Using their new calibrations, the
team confirmed that earlier measure-
ments of the Hubble constant in the
nearby universe were spot-on. This also
confirms the disagreement with the
expansion rate calculated using condi-
tions in the early universe, making it
more likely than ever that the two rates
are different.
“This is not just two experiments
disagreeing,” Riess said in a press
release. “We are measuring something
fundamentally different. One is a
measurement of how fast the universe is
expanding today, as we see it. The other
is a prediction [of the current expansion
rate] based on the physics of the early
universe and on measurements of how
fast it ought to be expanding. If these
values don’t agree, there becomes a very
strong likelihood that we’re missing
something in the cosmological model
that connects the two eras.”
Riess said their next goal is to reduce
the uncertainty in Cepheid distance
measurements to 1 percent. The team
hopes that by further shrinking the
uncertainty, astronomers will be better
able to determine why the two rates
differ — which remains a hotly debated
issue. — KOREY HAYNES, A.K.ASTROBEES
The International Space Station
recently received two small cube-
shaped robots named Honey and
Bumble, which will aid astronauts
with mundane tasks like checking
and moving inventory.WI-FI IN THE SKY
SpaceX has launched its first
batch of 60 Starlink satellites,
which Elon Musk hopes will
become a network of 12,
orbiting devices providing cheap,
global internet coverage.ICE BLANKET
New research suggests gases like
methane trapped in a thin layer of
ice may keep Pluto’s suspected
underground ocean from
completely freezing over.SHAKY SPIN
Astronomers witnessed a black
hole’s jets wobbling like a top,
thanks to a misalignment between
the black hole’s axis of spin and
the disk of material around it,
which feeds the jets.TRIP TO MARS
NASA is offering to send your
name to the Red Planet aboard the
Mars 2020 rover. Sign up by
September 30 and receive a
souvenir boarding pass at
https://mars.nasa.gov/participate/
send-your-name/mars2020/LUNAR IMPACT
The meteorite that struck the
Moon during January’s total lunar
eclipse hit the surface at about
38,000 mph (61,000 km/h),
producing a crater 33 to 50 feet
(10 to 15 meters) wide.DUAL PERSONALITY
Researchers used positrons —
the antimatter equivalent of
electrons — to re-create the
classic double-slit experiment,
showing that antimatter acts as
both a particle and a wave, just
like normal matter. — JAKE PARKSQUICK
TAKE S
WWW.ASTRONOMY.COM 11
Unlike most galaxies, M90 appears headed toward,
not away from, our location. Its orbit around the center
of the Virgo Cluster of galaxies, of which it is a mem-
ber, is carrying the galaxy away from the cluster in our
direction, making it appear to approach at a fast pace.
Eventually, M90 may even escape the
cluster; if not, it will move back toward
the center and appear to recede from
Earth instead. This colorful image
of M90, taken with
the Wide Field and
Planetary Camera 2
on the Hubble Space
Telescope, includes
visible, infrared,
and ultraviolet light.
The camera, which
operated from 1994
until 2009, pro-
duced images with
a distinct staircase
shape. — A.K.
A distant galaxy speeds closer
ESA/
HUBBLE
&
N
ASA,^W.
SARGENT^ ET^ AL.