Shortly after midsummer, an
enormous helium-filled balloon will be launched from the
Esrange Space Centre near Kiruna with the PoGOLite
(Polarised Gamma-ray Observer) telescope dangling under it.
The PoGOLite telescope will study the high energy light
(known as X-rays) emitted by heavenly bodies such as neutron
stars, pulsars and black hole systems. When fully inflated,
the balloon has a volume of about 1 million cubic metres
which is twice the volume of the Globen Arena in Stockholm.
The balloon has to be so large because PoGOLite is not so
light - it weighs about 2 Tonnes. It is important to lift
PoGOLite as high as possible since X-rays are absorbed by
the Earth's atmosphere.
After launch, PoGOLite will drift Westwards on stratospheric
winds passing over Sweden, Norway, Iceland, Greenland and
Canada. We are hoping to be able to continue the flight over
Alaska and onwards over Russia, returning to Sweden some 20
days later.
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X-ray emission from the Crab pulsar (artist's
impression).
http://www.astro.uu.nl/~jleeuwen/presentations/nrao_outreach_2007/
How polarised sunglasses help remove
glare reflected from water.
http://www.sunglasstent.com/images/PolarizedSunglassesDiagram.gif
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One of the observation
targets for PoGOLite are neutron stars. A neutron star is
formed when a star of a certain size has expended all its
fuel and collapses in on itself releasing huge amounts of
energy in a so-called supernova explosion. The conditions
during the collapse are so extreme that the atoms in the
star are pressed together converting protons and electrons
into neutrons. A neutron star is very small, only 15 km in
diameter, but weighs an astonishing one and a half times as
much as the Sun. A teaspoon of neutron star material would
weigh a billion tonnes!
A neutron star which rotates is called a pulsar. A pulsar in
the constellation of Taurus called ‘The Crab’ rotates 30
times a second and sends out flashes of X-rays, like a
cosmic lighthouse. The supernova explosion which gave rise
to the Crab was recorded by Chinese and Arab astronomers in
year 1054. We plan to intercept Crab X-rays with PoGOLite
and measure their polarisation in order to learn more about
how X-rays are produced in the pulsar.
X-rays are a form of electromagnetic radiation, just like
visible light or radio waves. The polarisation of a wave
describes how the oscillation of the wave is oriented with
respect to the wave’s motion. Now that it’s summer, check
your sunglasses - they may be polarised. If you’re near
water on a sunny day you’ll notice a glare on the water as
sunlight is reflected towards your eyes. You can remove much
of this glare by putting on your polarised sunglasses. This
is because the reflected light waves become polarised as
they ‘bounce off’ the surface of the water and your
sunglasses are designed to block these polarised waves. In a
similar fashion X-rays can become polarised as they leave a
pulsar.
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