Artist’s impression of the pulsar PSR J0348+0432 and its white dwarf companion
Artist’s impression of the pulsar PSR J0348+0432 and its white dwarf companion
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Artist’s impression of the pulsar PSR J0348+0432 and its white dwarf companion
Record-breaking pulsar takes tests of general relativity into new territory
Astronomers have used ESO’s Very Large
Telescope, along with radio telescopes around the world, to find and
study a bizarre stellar pair consisting of the most massive neutron star
confirmed so far, orbited by a white dwarf star. This strange new
binary allows tests of Einstein’s theory of gravity — general relativity
— in ways that were not possible up to now. So far the new observations
exactly agree with the predictions from general relativity and are
inconsistent with some alternative theories. The results will appear in
the journal Science on 26 April 2013.
An international team has discovered an exotic double object that
consists of a tiny, but unusually heavy neutron star that spins 25 times
each second, orbited every two and a half hours by a white dwarf star.
The neutron star is a pulsar that is giving off radio waves that can be
picked up on Earth by radio telescopes. Although this unusual pair is
very interesting in its own right it is also a unique laboratory for
testing the limits of physical theories.
This pulsar is named PSR J0348+0432 and is the remains of a supernova
explosion. It is twice as heavy as the Sun, but just 20 kilometres
across. The gravity at its surface is more than 300 billion times
stronger than that on Earth and at its centre every sugar-cubed-sized
volume has more than one billion tonnes of matter squeezed into it. Its
companion white dwarf star is only slightly less exotic; it is the
glowing remains of a much lighter star that has lost its atmosphere and
is slowly cooling.
“I was observing the system with ESO’s Very Large Telescope,
looking for changes in the light emitted from the white dwarf caused by
its motion around the pulsar,” says John Antoniadis, a PhD student
at the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn and lead
author of the paper. “A quick on-the-spot analysis made me realise
that the pulsar was quite a heavyweight. It is twice the mass of the
Sun, making it the most massive neutron star that we know of and also an
excellent laboratory for fundamental physics.”
Einstein’s general theory of relativity, which explains gravity as a
consequence of the curvature of spacetime created by the presence of
mass and energy, has withstood all tests since it was first published
almost a century ago. But it cannot be the final explanation and must
ultimately break down [1].
Physicists have devised other theories of gravity that make different
predictions from general relativity. For some of these alternatives,
these differences would only show up in extremely strong gravitational
fields that cannot be found in the Solar System. In terms of gravity,
PSR J0348+0432 is a truly extreme object, even compared to the other
pulsars that have been used in high precision tests of Einstein’s
general relativity [2].
In such strong gravitational fields small increases in the mass can
lead to large changes in the spacetime around such objects. Up to now
astronomers had no idea what would happen in the presence of such a
massive neutron star as PSR J0348+0432. It offers the unique opportunity
to push tests into new territory.
The team combined Very Large Telescope observations of the white
dwarf with very precise timing of the pulsar from radio telescopes [3].
Such a close binary radiates gravitational waves and loses energy. This
causes the orbital period to change very slightly and the predictions
for this change from general relativity and other competing theories are
different.
“Our radio observations were so precise that we have already been
able to measure a change in the orbital period of 8 millionths of a
second per year, exactly what Einstein’s theory predicts,” states Paulo Freire, another team member.
This is just the start of detailed studies of this unique object and
astronomers will be using it to test general relativity to ever greater
precision as time goes on.
Notes
[1] General relativity is not
consistent with the other great theory of twentieth century physics,
quantum mechanics. It also predicts singularities under some
circumstances, where some quantities tend to infinity, such as the
centre of a black hole.
[2] The first binary pulsar, PSR B1913+16, was
discovered by Joseph Hooton Taylor, Jr. and Russell Hulse, for which
they won the 1993 Nobel Prize in Physics. They accurately measured the
changes in the properties of this remarkable object and showed that they
were precisely consistent with the gravitational radiation energy
losses predicted by general relativity.
[3] This work made use of data from the Effelsberg,
Arecibo and Green Bank radio telescopes as well as the ESO Very Large
Telescope and the William Herschel Telescope optical telescopes.
More information
This research was presented in a paper “A Massive Pulsar in
a Compact Relativistic Orbit”, by John Antoniadis et al., to appear in
the journal Science on 26 April 2013.
The team is composed of John Antoniadis
(Max-Planck-Institut für Radioastronomie [MPIfR], Bonn, Germany), Paulo
C. C. Freire (MPIfR), Norbert Wex (MPIfR), Thomas M. Tauris (Argelander
Institut für Astronomie, Bonn, Germany; MPIfR), Ryan S. Lynch (McGill
University, Montreal, Canada), Marten H. van Kerkwijk (University of
Toronto, Canada), Michael Kramer (MPIfR; Jodrell Bank Centre for
Astrophysics, The University of Manchester, United Kingdom), Cees Bassa
(Jodrell Bank), Vik S. Dhillon (University of Sheffield, United
Kingdom), Thomas Driebe (Deutsches Zentrum für Luft- und Raumfahrt,
Bonn, Germany), Jason W. T. Hessels (ASTRON, the Netherlands Institute
for Radio Astronomy, Dwingeloo, The Netherlands; University of
Amsterdam, The Netherlands), Victoria M. Kaspi (McGill University),
Vladislav I. Kondratiev (ASTRON; Lebedev Physical Institute, Moscow,
Russia), Norbert Langer (Argelander Institut für Astronomie), Thomas R.
Marsh (University of Warwick, United Kingdom), Maura A. McLaughlin (West
Virginia University), Timothy T. Pennucci (Department of Astronomy,
University of Virginia) Scott M. Ransom (National Radio Astronomy
Observatory, Charlottesville, USA), Ingrid H. Stairs (University of
British Columbia, Vancouver, Canada), Joeri van Leeuwen (ASTRON;
University of Amsterdam), Joris P. W. Verbiest (MPIfR), David G. Whelan
(Department of Astronomy, University of Virginia).
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Links
Contacts
John AntoniadisMax-Planck-Institut für Radioastronomie
Bonn, Germany
Tel: +49-228-525-181
Email: jantoniadis@mpifr-bonn.mpg.de
Michael Kramer
Max-Planck-Institut für Radioastronomie
Bonn, Germany
Tel: +49-228-525-278
Email: mkramer@mpifr-bonn.mpg.de
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
