32 AUSTRALIAN SKY & TELESCOPE April 2018
J. D. SOLER ET AL. /ASTRONOMY & ASTROPHYSICS2017 (603:A64)dust grains that line up perpendicular to a magnetic field will
emit polarised light. We use this polarisation to chart our
galaxy’s magnetic field. Launching BLAST-Pol in 2012, we
made the most detailed map to date of magnetic fields in a
massive star-forming cloud.
Strong enough magnetic fields can actually slow down
the rate at which stars form by stopping gas from moving
across field lines. BLAST-Pol’s map of a giant gas cloud in the
constellation Vela revealed that the magnetic field direction is
almost always related with the cloud structure we see: Faint,
wispy cloud features tend to run parallel to the field, while
denser regions, where we expect the stars to form, are more
often perpendicular to the field. This result suggests that the
magnetic field is strong enough to have shaped the formation
of the cloud. It may even partially explain why the observed
rate of star formation in our galaxy is only a few percent of
what we predict using simple assumptions.
As balloon telescopes become more powerful, the amount
of science data they can collect is growing accordingly. My
collaborators and I hope to launch a new, upgraded version of
BLAST-Pol, known as BLAST-TNG (for ‘the next generation’)
above Antarctica in late 2018. We are using the newest
version to test arrays of microwave kinetic inductance detectors,
a new type of superconducting detector that enables us to
build large, inexpensive pixel arrays for faster survey imaging.
BLAST-TNG will also carry a cryogenic system to keep those
detectors cold throughout the flight’s duration. By testing
new detector technologies in the upper stratosphere, we candemonstrate their operation in space-like conditions — an
important step for making these advances available for future
satellite telescopes.
We expect BLAST-TNG to map 20 times the area of sky
surveyed by BLAST-Pol during its first flight in 2010. We’re also
inviting other astronomers to submit their ideas for how to use
our telescope, making BLAST-TNG the first ever balloon-borne
observatory to accept proposals from the community.Science takes to the skies
Hundreds of balloons launched over the decades have tackled
questions across astronomy. For example, some of these
stratospheric observatories enable us to observe our universe’s
infancy by mapping its oldest detectable light, radiation
known as the cosmic microwave background (CMB). This
snapshot of our universe, released 370,000 years after the Big
Bang, contains the seeds of all the large-scale structure we see
around us today. By 2000 balloon telescopes Boomerang and
Maxima had measured tiny fluctuations in this radiation,
clearly showing that our universe’s shape is flat (see ‘How
Shape Determines Fate’ below).
Today, many different balloon telescopes (such as Spider,
EBEX and PIPER) are looking for an even fainter signal
buried in the CMB: specific patterns in polarisation that are
expected to be a billion times fainter than the total CMB
signal. If detected, this polarisation pattern would enable
astronomers to probe a much earlier era, a mere 10−35 second
after the Big Bang, when the universe was rapidly expanding.
Astronomers also use balloons to measure the energy and
composition of cosmic ray particles. One of the most successful
of these experiments is the Cosmic Ray Energetics And Mass
(CREAM) experiment. It logged a record-breaking 161 total
days of science operation over six separate Antarctic flights
from 2004 to 2011. The data it collected showed many more
high-energy cosmic rays than predicted, which has prompted
astronomers to rethink ideas about cosmic-ray origins.
After the instrument’s success on a balloon platform,
the CREAM team adapted their experiment for even higher
altitudes: onboard the International Space Station. The new
experiment is called ISS-CREAM (and yes, that’s pronounced
‘ice cream’).The next generation
What are the limits for balloon astronomy? Can we ever hope
to do the equivalent of space-based astronomy (read: Hubble-STHROUGH THE VEIL BLAST-Pol measured the polarisation of
submillimetre-wavelength radiation from the star-forming Vela C region.
From the polarised light, the team inferred the cloud’s magnetic fields
(white lines), finding that the field tended to cross dense cloud structures.
The Herschel satellite provided the far-infrared background image.THE SHAPE OF THE UNIVERSE
Density determines the universe’s geometry: A jam-packed
universe would be closed, like the surface of a sphere to use
a 2D analogy, whereas a sparse universe would be open, like
the surface of a saddle. Balloon-borne observations showed
that our universe is remarkably flat, with just enough density
to lie almost exactly between these two extremes.BALLOON ASTRONOMY