ASTRONEWS
DIM DETECTIONS. By using Hubble to peer deep into the Orion Nebula, astronomers discovered the
largest population of brown dwarfs yet, identifying 20 small, failed stars.
New model links three types of energetic particles
Energetic cosmic rays, gamma
rays, and neutrinos emitted
from sources far across the
universe act as cosmic mes-
sengers, carrying information
to Earth about extreme objects
from beyond our galaxy.
Although the origins of these
particles remain mysterious,
their comparable energies have
led astronomers to wonder for
decades if they might all come
from a similar source.
Astronomers have posited
that active galactic nuclei (AGN)
— supermassive black holes
feeding at the centers of galax-
ies — may be responsible for
these three types of high-
energy emissions, but have
struggled to explain exactly
how or why. A new model
based on highly detailed
numerical calculations and
published January 22 in Nature
Physics bolsters the case for
exactly this origin.
The work, by Ke Fang at the
Pennsylvania State University
and Kohta Murase at the
University of Maryland, shows
how all three particles can
result when cosmic rays are
accelerated within the powerful
jets emitted from the region
around active supermassive
black holes.
According to the model,
such acceleration boosts the
energy of these cosmic rays
into the “ultrahigh” range,
above about 10 17 electron volts.
When these cosmic rays collide
with the gas that permeates the
galaxy clusters where many
AGN reside, they produce the
PACKED IN. The Kepler-11 system has six
planets of similar mass orbiting their sun with
relatively even spacing. The entire system could
fit inside the orbit of Venus. NASA/TIM PYLE
high-energy neutrinos and
gamma rays we observe.
“This model paves a way to
further attempts to establish a
grand-unified model of how all
three of these cosmic messen-
gers are physically connected
to each other by the same class
of astrophysical sources,”
Murase said in a press release.
Both authors hope their model
will prompt further studies of
active galaxies in clusters and
groups to confirm or disprove
their predictions. — A.K.
Extrasolar
systems are
neater than ours
The number of graphics processing units in the new ARTS super-
computer, which aims to discover one fast radio burst per week.
200
TRIPLE PLAY. The supermassive black hole in the center of the Cygnus A
galaxy produces bright jets. Astronomers believe such jets could generate
energetic cosmic rays, gamma rays, and neutrinos. COURTESY OF NRAO/AUI
AR sandbox helps users visualize gravity
GRASPING GRAVITY. Undergraduates at the University of Iowa designed and built an augmented reality (AR)
sandbox, dubbed Gravbox, that helps users visualize how variations in gravity influence an object’s motion. Although
similar AR sandboxes exist, Gravbox is the first to simulate the effects of gravity in real time. How does it work? The
user sculpts an environment from sand, then a computer projects a moving particle onto the terrain. The projection
simulates how an object, such as a comet or space probe, would travel through the imagined landscape. — J.P.
As our catalog of extrasolar systems
grows, so does astronomers’ ability to
pick out patterns that reveal the secrets
of planet formation. One such pattern
presents further evidence that our solar
system may be an outlier: Extrasolar
planets in other systems often share
similar masses and circle their suns in
regularly spaced orbits.
The finding, published January 3 in
The Astronomical Journal, is based on 909
planets in 355 systems discovered by the
Kepler telescope. Two major patterns
arose when astronomers examined the
data statistically. First, neighboring exo-
planets tend to have similar masses.
Second, their orbits are regularly spaced
from one planet to the next. By compari-
son, our solar system’s inner planets have
mismatched sizes and are widely spaced.
“These patterns would not occur if the
planet sizes or spacings were drawn at
random,” said study leader Lauren Weiss
of the Université de Montréal in a press
release. That indicates the planets in the
systems surveyed — and possibly most
extrasolar systems — remain relatively
undisturbed since their formation from a
disk of debris around their young star.
Based on current models of planet for-
mation, planets should easily form in such
a disk with a compact configuration that
leaves them similarly sized and at regular
intervals. Astronomers believe our solar
system appears different because Jupiter
and Saturn moved inward to disrupt any
existing structure before retreating to
their current positions.
Additional data on more planetary
systems will help pin down how common
it is for either disruption or undisturbed
planet formation to occur. Weiss is now
working on a study to look for extrasolar
systems with planets like Jupiter to learn
more about its role in our own solar sys-
tem’s history. — A.K.
W W W.ASTR ONOMY.COM
15