News & Analysis
Galactic-scale observatory planned
Physicists have drawn up ambitious
plans to detect very low-frequency
gravitational waves – ripples in the
fabric of space–time that general relativity predicts ought to pervade the
universe. But rather than looking for
them using existing facilities like the
LIGO detectors in the US, which are
designed to detect tiny changes in the
interference patterns of laser beams
sent down pairs of kilometre-long
pipes positioned at right angles to one
another, the idea is instead to use
radio telescopes on Earth. The telescopes would measure tiny variations
in the output of pulsars spread thousands of light-years apart.
The galactic observatory, proposed
by the North American Nanohertz
Observatory for Gravitational Waves
(NANOGrav), would rely on minute
changes in the relative timing of emissions from different pulsars – rapidly
rotating neutron stars that emit very
regular pulses of radio waves. A gravitational wave passing between a
pulsar and a radio telescope affects
the time it takes for the emissions to
arrive, and so an array of pulsars with
different lines of sight to the Earth
would reveal the presence of any wave
as well as its direction of propagation
and polarization.
This idea was first put forward in
the late 1970s but requires such high-precision measurements that it has
NRAO
Telescope in West Virginia, US, as
well as developing advanced software
to process the huge amounts of data
involved. It estimates this would cost
a few tens of millions of dollars over
the next 10 years, in addition to the
money spent by their European and
Australian collaborators.
This is small fry compared with the
hundreds of millions of dollars being
spent on gravitational-wave interferometers. Indeed, NANOGrav member Fredrick Jenet of the University
of Texas at Brownsville says it is possible that the pulsar network could detect gravitational waves before the
interferometers, although he points
out that having different approaches
not only expands the astrophysics that
can be studied, but also improves the
chances of detecting gravitational
waves in the first place.
Jim Hough, a gravitational-wave
researcher at the University of Glasgow and a member of the GEO-600
gravitational-wave observatory based
in Germany, says that pulsar timing
“looks a very good way” to search for
gravitational waves at extremely low
frequencies. He believes that by observing 20 pulsars with a timing precision of better than 100 ns for five
years, Jenet and colleagues “have a
very good possibility of observing
gravitational-wave signals”.
Edwin Cartlidge
not been technically feasible until
now. The NANOGrav team says that
it should be possible to correlate the
output of 40 pulsars, each with a timing precision better than 100ns,
within the next decade. This would
allow astronomers to observe gravitational waves with wavelengths of several light-years coming from sources
such as the black-hole binaries that
form when galaxies merge, as well as
early-universe phenomena such as
cosmic strings or inflation.
The NANOGrav consortium says
that this could be achieved by expanding the time currently devoted to
pulsar observations on existing facilities such as the Arecibo Observatory
in Puerto Rico and the Green Bank
Listening in
The Green Bank
Telescope in West
Virginia, US, could be
used to study the
emissions of pulsars
to detect signs of
gravitational waves.
Facilities
Scientists welcome world’s ‘quietest’ building
The University of Bristol in the UK
has opened what it claims is the
quietest building in the world. The
£ 11.5m Bristol Centre for Nanoscience and Quantum Information
(NSQI) will be a hub of interdisciplinary research involving groups from
the university’s biology, physics, chemistry and engineering departments.
Staff will use the new facility for a
range of experiments in condensed-matter physics to biochemistry.
Construction of the NSQI facility
has taken over two years to complete
and the site in Bristol is well suited to
hosting such a “quiet” lab since the
Michael Banks
ground under the building consists of
solid rock. Engineers excavated a one-storey deep hole in the rock and filled
it with concrete to make a solid foundation upon which the building was
constructed. “The centre is the right
building, in the right place,” says Fred
Hale, building manager of the NSQI.
The four-storey building has a
number of “quiet rooms” in the basement, where most of the experiments
are housed. Each experiment sits on
an additional 24 tonne block of concrete separated from the floor by
rubber bearings to dampen vibrations
that could interfere with sensitive
Quiet, please!
The Bristol Centre for
Nanoscience and
Quantum Information
features eight
low-noise labs.
measurements. Each lab in the basement also sits inside a Faraday cage,
and the temperature, air flow and
acoustic noise in the room can also be
strictly controlled.
The centre incorporates two cleanrooms, a wet lab, a sound-proof lab,
eight low-noise labs and two cell-cul-ture labs. The NSQI is also home to
one of the UK’s newly launched doctoral training centres. Funded by the
Engineering and Physical Sciences
Research Council, the centre for functional nanomaterials will train up to
10 PhD students every year.
Michael Banks
