Sky & Telescope - April 2023 - 15

INFRARED: NASA / SOFIA / USRA / FORCAST TEAM / JAMES DE BUIZER;
VISIBLE: ANTHONY WESLEY
aircraft. KAO flew for 20 years and made
several major discoveries at infrared
wavelengths, including the first sightings
of the rings of Uranus and a definitive
identification of an atmosphere on Pluto.
KAO retired in 1995 to make room for its
successor, SOFIA.
In many ways, these airborne observaA
NEW VIEW OF JUPITER Bands appear on
Jupiter at both visible (top) and infrared (bottom)
wavelengths, but this composite infrared image
from SOFIA's first-light flight in 2010 includes
wavelengths either difficult or impossible for
ground-based instruments to observe. The
white strip is a relatively transparent cloud band
through which Jupiter's interior heat shines.
tories have an edge over both their spaceand
ground-based counterparts.
Unlike space-based observatories, they
can land. That means instrumentation
can be repaired or updated with improving
technology. Satellites, on the other
hand, carry outdated equipment designed
long before launch and can't be fixed
should something go wrong. And unlike
ground-based counterparts, plane-based
telescopes can fly above most of the
atmosphere and to any location on Earth,
enabling them to observe objects in both
hemispheres and seek the best paths
across the globe for occultations. In 2015,
for example, SOFIA watched Pluto slide
across the face of a distant star - a rare
celestial alignment that allowed scientists
to collect crucial data on the dwarf planet's atmosphere.
But for all the upsides, stabilizing a telescope on such a
bumpy platform is a tough problem. " It's a crazy idea, " Schulz
says. " There's nothing less stable than an airplane. "
For SOFIA, engineers spent years finding ways to direct
airflow around the hole in the fuselage to prevent the telescope
from shaking uncontrollably. They also sat the telescope
on 24 air springs and three dampers, to absorb most of
the plane's vibrations. The bearing floats on a very thin film
of oil to offer soft support. And the telescope utilizes gyros
to measure its own movement, counteract that movement,
and steady itself. It's no wonder the original completion date
(which was supposed to be 2001) was pushed back to 2014.
The budget also ballooned from $265 million in 1997 to $1.1
billion by the time SOFIA finally became fully operational.
Fields at Play
SOFIA filled the gap left by Herschel's decommissioning in
2013, covering a range that subsequent high-profile observatories
like the James Webb Space Telescope and the Atacama
Large Millimeter/submillimeter Array (ALMA) in Chile don't.
And that gap is crucial.
When astronomers observe the energy output of starforming
galaxies, they find that roughly half is in the form
of mid- to far-infrared radiation. " So if you didn't study the
universe in the far-infrared, you would only get half the picture, "
says Naseem Rangwala (NASA Ames Research Center),
SOFIA's project scientist. " There's so much at this wavelength
range that's waiting to be discovered. "
Take the question of star formation.
To build a star, the universe needs two
major ingredients (gas and dust) plus a
blend of things like gravity and turbulence.
Astronomers know the basics of
how a star is born, but according to most
computer models, star formation should
occur at a much faster clip than the one
we observe. So what's slowing it down?
Researchers have long wondered if
magnetic fields - which are so mysterious
they were ignored in early computer
models - could be the culprit.
To find out, scientists built an instrument
for SOFIA called HAWC+, which
maps the alignment of incoming light
waves and can reveal crucial information
about magnetic fields. When
Thushara Pillai (Boston University) used HAWC+ to observe a
nearby cluster of roughly 50 young stars, she was able to pinpoint
the zone where gravity becomes the dominant player.
Here, magnetic fields suddenly change orientation: Instead of
supporting gas filaments against collapse, they succumb as
gravity takes over and drags the gas (and the magnetic fields
trapped inside) to become channels flowing into a central,
star-forming hub. It's gravity's conquest of magnetic fields
that allows stars to form.
The finding suggests that magnetic fields are a key player
in star formation. But one cloud alone cannot explain why
star formation is so slow. So Pillai started a SOFIA survey to
repeat this experiment on a much larger sample.
Meanwhile, her colleagues used the same instrument to
Airborne Telescopes
Planes aren't the only way instruments take to the
skies: Scientific balloons also have a long, successful
history (S&T: Feb. 2018, p. 16). These balloons typically
fly between 96,000 and 127,000 feet above sea level,
can carry the equivalent of three cars' weight in gear,
and stay aloft for anywhere from 2 hours to 2 months.
But they don't have their own propulsion; they must
follow the winds. This is not as prohibitive as it sounds:
Campaigns over Antarctica, for instance, utilize the
predictable patterns of seasonal stratospheric winds
to plan observing targets in advance.
sk yand tele scope .o r g * APRIL 2023 15
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Sky & Telescope - April 2023

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