Sky & Telescope - July 2022 - 11

DEBRIS CLOUD: NASA / JPL-CALTECH; PULSAR: X-RAY: NASA / CXC / STANFORD
UNIV. / M. DE VRIES; OPTICAL: NSF / AURA / GEMINI CONSORTIUM
PROTOPLANETS
Dusty Debris Transits Star
ASTRONOMERS HAVE WATCHED
protoplanetary rubble transit across the
face of a star, giving us our best view yet
of planetary formation in action.
For years, a group led by Kate Su
(University of Arizona) observed young
stars with NASA's Spitzer Space Telescope,
looking for the warm, infrared
signature of planet formation.
Debris disks around two young stars
showed signs of past planetesimal collisions.
But serendipity struck when they
witnessed a large cloud of rubble form,
then cross in front of the 10 millionyear-old
star HD 166191, 329 light-years
away in Sagittarius.
Su and colleagues reported in the
March 10th Astrophysical Journal that
the system's infrared emission started
brightening in early 2018, and it had
doubled by early 2020.
This artist's concept shows what the debris
cloud around the young star HD 166191
might have looked like up close.
During this overall brightening, the
star's light (visible and infrared) twice
plunged steeply before returning to previous
levels. The group concluded that
two bodies the size of the asteroid Vesta
had collided, producing a giant debris
cloud that passed twice in front of the
star. The second pass was 142 days after
the first, corresponding to a distance
from the star of 0.62 astronomical unit,
or slightly smaller than Venus's orbit
around the Sun.
On the first pass, the debris covered
an area up to hundreds of times
larger than that of the star. The cloud
appeared to expand further between the
two transits.
" [The researchers] have strong
evidence for ongoing collisions of the
kind thought to occur during the giant
impact epoch, " says Scott Kenyon
(Center for Astrophysics, Harvard &
Smithsonian), who was not involved in
the study. The observations thus provide
a sanity check on computer simulations
describing the violent early years of
planet formation.
¢JEFF HECHT
Pulsar Shoots Beam
7 Light-years Long
This image tells the story of a pulsar as
it speeds through space via a combination
of visible light (red, brown, and
black), collected by the Gemini telescope
through a hydrogen-alpha filter,
and high-energy photons detected by
the Chandra X-ray Observatory (blue).
PSR J2030+4415 is a city-size
stellar core that whirls around three
times every second, 1,630 light-years
away in Cygnus. When Martijn de Vries
and Roger Romani (both at Stanford
University) first observed its X-ray
emission, they saw not only the pulsar
and the glow of energetic particles
trapped within its magnetic field, but
also a thin, straight beam that trailed
off the edge of the discovery image
like a celestial version of Harold's
purple crayon. So de Vries and Romani
asked for additional observations
(more pages for Harold) to determine
the beam's true extent: 15 arcminutes
across the sky, or 7 light-years long.
The results will appear in the Astrophysical
Journal.
The beam formed a couple decades
ago, when the pulsar punched
through the bow shock that preceded
its journey through space. The breakthrough
briefly aligned the pulsar's
own magnetic field lines with those of
the galaxy, allowing a thin thread of
electrons and positrons to escape.
Events such as this one might help
astronomers explain how energetic
particles, including antimatter, spread
throughout the galaxy.
¢ MONICA YOUNG
See more images and details at
https://is.gd/phaserpulsar.
sk yand tele scope .o r g * JULY 2022 11
https://www.is.gd/phaserpulsar http://www.skyandtelescope.com
Sky & Telescope - July 2022

Table of Contents for the Digital Edition of Sky & Telescope - July 2022
