Sky & Telescope - August 2021 - 11

APS; ATOMIC HYDROGEN DISTRIBUTION:
HEASARC / LAMBDA / NASA / GFSC
COSMIC RAYS
Tibetan Observatory Sees
Galactic PeVatrons
MOVE OVER, CERN. Unknown sources
in the Milky Way dubbed " PeVatrons "
accelerate protons to energies of a few
peta-electron-volts (PeV) - dozens
of times higher than the yield of the
Large Hadron Collider. Now, data from
a high-altitude experiment in Tibet
confi rm that these very-high-energy
accelerators exist inside our galaxy.
Galactic magnetic fi elds bend the
paths of cosmic rays, so they do not
" point back " to their origin. But cosmic
rays occasionally slam into cosmic
microwave background photons, and
the ensuing reaction imparts about 10%
of the cosmic ray's energy into gamma
The Tibet AS Collaboration found
dozens of very-high-energy gamma rays
(yellow points) concentrated along the
Milky Way. (The gray shaded areas are
outside the detectors' fi eld of view.)
rays. And unlike charged particles,
gamma rays maintain their direction.
The recently upgraded, 31-year-old
Tibet AS experiment registers the
secondary particles that rain down
when energetic gamma rays smash into
Earth's atmosphere. Some 700 scintillators
at an altitude of 4,300 meters
(14,000 feet) in Tibet detect these air
showers, revealing both the energy and
direction of the original gamma ray.
Between 2014 and 2017, the Tibet
AS Collaboration found a few dozen
very-high-energy gamma rays not
associated with other celestial sources;
one of them is the most energetic
gamma ray ever detected. They're
concentrated along the band of the
Milky Way, providing strong evidence
for particle accelerators not only within
our galaxy but spread over its disk, the
team reports in the April 9th Physical
Review Letters. Exactly what accelerates
particles to such high energies remains
unknown; possible sources include pulsars
and star-forming regions.
GOVERT SCHILLING
IN BRIEF
2022 NASA Budget Proposal
The Biden administration has revealed its
discretionary funding request for fi scal year
2022, including $10.2 billion for the National
Science Foundation and $24.7 billion for
NASA. The request represents 20% and
6.3% increases, respectively, relative to the
enacted 2021 budget. The NASA budget
would, among other things, fund the Artemis
initiative to return humans to the Moon, missions
to Europa and Titan (expected to launch
in 2024 and 2027, respectively), the fi rst-ever
sample return from Mars, and the continuation
of crewed missions to the International
Space Station (ISS). The Artemis program,
in particular, would receive $6.9 billion, $325
million more than in FY2021. For now, NASA
will continue to rely on SpaceX and Orbital
Sciences to bring crew and cargo to the
ISS. The FY2022 proposal also continues
development of the Nancy Grace Roman
Space Telescope, which was threatened with
termination in 2020 before being reinstated.
The new request would also return NASA
and NSF to advancing research in climate
science, which took a deep cut under the
previous administration (S&T: June 2020, p.
12), and increase funding for outreach initiatives.
However, the request makes no mention
of the Stratospheric Observatory, which the
previous administration had also highlighted
for termination in 2020.
DAVID DICKINSON
See the request at https://is.gd/FY2022.
AI Hunt for Quasar Lenses
New applications of machine learning (S&T:
Dec. 2017, p. 20) have enabled astronomers
to discover 12 quadruply lensed quasars. In
each case, a foreground galaxy splits the light
from a background quasar into four separate
images. Astronomers can utilize these beautiful
cosmic coincidences to obtain an independent
measure of the universe's current expansion
rate, a value that astronomers are still
debating (S&T: June 2019, p. 22). It has taken
four decades to fi nd 56 of these rare alignments.
Now, a project that subjects data from
the European Space Agency's Gaia satellite
to multiple machine-learning methods has
picked out another dozen in one fell swoop.
The team, led by Daniel Stern (JPL-Caltech),
used multiple ground-based observatories
to confi rm the fi nds; the results will appear in
the Astrophysical Journal. Not every machineselected
target turned out to be a quadruple
lens: Foreground stars sometimes fooled the
algorithms, masquerading as one or more distant
quasar images. This " ground truth " offers
the team a chance to revise their methods
before applying them to the newest Gaia data
release (S&T: Apr. 2021, p. 8). " Machine learning
was key to our study, but it is not meant
to replace human decisions, " explains team
member Alberto Krone-Martins (University
of California, Irvine). " We continuously train
and update the models in an ongoing learning
loop, such that humans and the human
expertise are an essential part of the loop. "
MONICA YOUNG
Read more at https://is.gd/AIquasars.
Puzzling Far-out Gas Giant
Astronomers have imaged a super-Jupiter
circling a young star 360 light-years away in
the southern constellation Musca, the Fly. It's
on a surprisingly wide orbit, about 115 times
farther out than Earth is from the Sun - a
distance that defi es traditional ideas about
planet formation. Alexander Bohn (Leiden
University, The Netherlands) and colleagues
were using the Spectro-Polarimetric Highcontrast
Exoplanet Research instrument on
the European Southern Observatory's Very
Large Telescope in Chile for the Young Suns
Exoplanet Survey, directly imaging planets
around infant stars, when they discovered the
planet YSES 2b. The six-Jupiter-mass planet
is still glowing with the heat of its formation
in a system just 14 million years old. Astronomers
think giant planets usually form closer to
their star via a process called core accretion.
But in the case of YSES 2b, there wouldn't
be enough material so far from the star. The
planet might instead have formed via gravitational
instability, but Bohn says computer simulations
of this process typically create much
more massive brown dwarfs. However, Ken
Rice (University of Edinburgh, UK), who was
not involved in the study, says smaller masses
could be possible. In the study, to appear in
Astronomy & Astrophysics, the researchers
suggest follow-up observations, such as of
the planet's atmosphere, could help decide
between scenarios.
JULIE FREYDLIN
Read more about YSES 2b at https://
is.gd/faroutgasgiant.
sk yandtelescope.org * AUGUST 2021 11
https://www.is.gd/faroutgasgiant https://www.is.gd/FY2022 https://www.is.gd/AIquasars https://www.is.gd/faroutgasgiant http://www.skyandtelescope.org
Sky & Telescope - August 2021

Table of Contents for the Digital Edition of Sky & Telescope - August 2021
