Astronomy

ASTRONEWS

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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.

AR sandbox helps users visualize gravity

Extrasolar

systems are

neater than ours

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

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.

New model links three types of energetic particles

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.

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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

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

TIM SCHOON

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.

The number of graphics processing units in the new ARTS super-

computer, which aims to discover one fast radio burst per week.