March 2010 - Swinburne University of Technology

March 2010 swinburne
Photo: Paul Jones
scrutinise the results. The surveys, dubbed
the ‘High Time Resolution Universe Legacy
Surveys’, are part of an international
project between Swinburne, CSIRO and the
universities of Manchester and Cagliari.
Finding the elusive gravitational waves
is not simply an end in itself, says Professor
Matthew Bailes, director of Swinburne’s
Centre for Astrophysics and Supercomputing.
Unlike many other forms of observation,
such as optical light, radio and gamma rays,
it offers a new window through which to
observe the largest events in the universe
and so improve our understanding of how
galaxies and the cosmos itself evolve.
Swinburne students have been engaged in
pulsar surveys since 1998, compiling a mass
of data that is being reinvestigated using new
techniques. The current effort is much more
comprehensive than previous efforts due to
the telescope effectively wearing “a better set
of glasses”, Professor Bailes explains. During
the past year the team has added a further 21
pulsars to the world’s list of known objects
by sifting through 200,000 gigabytes of data,
and is revealing them as vastly more diverse
and curious objects than previously imagined.
Sarah Burke-Spolaor, who came to
Swinburne from the US for her PhD, is one
of the doctoral students engaged in the quest,
searching for elusive one-off radio flashes –
single pulses of radiation emitted by a new
class of pulsar called rotating radio transients
(RRATs). “Some pulsars are on all the time
and flash constantly, others turn on and off
for part of the time, while others flash at rare
and unpredictable intervals,” she explains.
“We don’t yet know why, but one theory is
that we are seeing parts of the ageing process
in neutron stars. Another view is that they
are being bombarded by the debris from
surrounding asteroid belts.”
The highlight for Ms Burke-Spolaor was
the discovery of an entirely new class of
star, PSR J0941-39. When first detected it
was thought to be a form of RRAT, but on
subsequent visits it was found to fluctuate
between its RRAT state and being a bright
pulsar switched on and emitting constantly
for about 90 per cent of the time, making it
the ‘Jekyll and Hyde’ of pulsars.
“When we are observing we may see
hundreds of pulses for many minutes, then
at other times just a few in the same period.”
The current thinking among the astronomers
is that it may be a neutron star having a
sort of ‘mid-life crisis’ as it progresses
from a high-energy youthful state to a more
sedentary, aged condition. “It’s very exciting.
It seems like almost every time we look we
find something new,” Ms Burke-Spolaor says.
Her Swinburne colleague, PhD student
Lina Levin, originally from Sweden, finds
exploring the cosmos at this scale equally aweinspiring,
especially when she was involved
in the discovery of the first-ever magnetar
found in the radio band – a neutron star with
a very strong magnetic field. First spotted by
University of Manchester PhD student Sam
Bates, the magnetar “boomed in” and was a
complete shock to the team who thought it
was so bright it might not be real. Ms Levin’s
follow-up observations showed that not only
was it a real pulsar, it was unique.
Of the 15 found so far by astronomers
worldwide, all were discovered via the
emission of x-rays or gamma rays – not
radio signals. Ms Levin’s magnetar emits a
radio pulse every 4.3 seconds and its signal
Key points
Using signals from a range
of fast-twirling pulsars,
astronomers are hoping to
discover the most elusive
waves in the universe –
Einstein’s gravitational
waves
With equipment that
includes customised circuit
boards, 20 billion samples a
second are digitised on the
giant telescope at Parkes
This information is
pre-processed on a
supercomputer before
being sent on a dedicated
1250-kilometre fibre link to
Swinburne’s supercomputer
Finding these elusive
waves offers a new window
through which to observe
the largest events in the
universe and improve our
understanding of how
galaxies evolve
strength varies widely, as does the shape
and number of components in its radio
beams. Finally, the rate of spin appears to be
slowing, indicating an enormous magnetic
field, the highest ever seen in a pulsar. It
appears to be undergoing a momentous
transformation. “We expect that eventually
it will disappear,” she says. Why the pulsar
has such a strong magnetic field is unknown.
However, it forms an important new link
between radio pulsars and the other types
of magnetar, suggesting some sort of
evolutionary pattern.
“It’s really weird – it changes so much,”
Ms Levin says. “It’s quite bright and regular
now, but when our collaborator Dr Marta
Burgay, of the Cagliari Observatory in Italy,
examined the historical data from the Parkes
Radio Telescope she found it was turning on
and off every few years.” Dr Simon Johnston’s
team at the Australia Telescope has mapped
the area in the vicinity of the magnetar and
found it is associated with a faint x-ray source,
which is probably the magnetar.
“Lina has also found four millisecond
pulsars that will be important in the search
for gravitational waves,” Professor Bailes
says. The plan is to pick out at least 20 of
the most reliable millisecond pulsars spread
across the southern sky and monitor their
signals in the hope of detecting the minute
fluctuations caused by interference from a
rare gravitational wave passing through.
With its CSIRO and California Institute
of Technology (Caltech) collaborators, the
team has been monitoring millisecond pulsars
for the past 16 years. The new millisecond
pulsars are among the most rapidly spinning
stars ever detected and sure to play a role in
gravitational wave detection as telescopes
such as the Square Kilometre Array come
online towards the end of this decade.
“We’re hoping to use them as a sort of
astronomical GPS system, to triangulate the
position of the source of the gravitational
wave, so we can see what caused it,”
Ms Burke-Spolaor says. “Because millisecond
pulsars are so reliable, if their signal arrives
a billionth of a second sooner or later than
expected, it could be due to the distortion in
space-time caused by a gravitational wave.”
Observing the same minute fluctuation
in the signals of several pulsars would help
characterise the source. If they can achieve
that, the collaboration will stand at the
threshold of a momentous new insight into
the universe we inhabit. ••
Contact. .
Swinburne University of Technology
1300 275 788
magazine@swinburne.edu.au
www.swinburne.edu.au/magazine
astronomy
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