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Clumped galaxies give general relativity its toughest test yet

Last Updated on Wednesday, 25 June 2014 13:59
Published on Wednesday, 25 June 2014 01:01

Nearly 100 years since Albert Einstein developed general relativity, the theory has passed its toughest test yet in explaining the properties of observable Universe. The most precise measurements to date of the strength of gravitational interactions between distant galaxies show perfect consistency with general relativity’s predictions. The results will be presented by Dr Lado Samushia at the National Astronomy Meeting 2014 in Portsmouth on Wednesday 25 June.

Samushia2Each point on the left panel represents a galaxy, while a right panel is an actually image of one of the patches of the sky observed by SDSS. Credit: SDSS.Samushia and his colleagues analysed more than 600,000 galaxies from the Sloan Digital Sky Survey III (SDSS-III) Baryon Oscillations Spectroscopic Survey (BOSS) catalogue to come up with a measurement of how much galaxies clump together within the vast volume that they occupy.

"Whilst the Cosmological Principle tells us that the Universe should have same properties in every direction, observations do not match this picture," explains Samushia, of the Institute of Cosmology and Gravitation at the University of Portsmouth. "Because galaxies are themselves parts of larger structures that are growing, they tend to 'infall' towards each other. This infall gives an apparent effect that we only see in the direction towards us, because of the way in which we observe the galaxies."

Using the observed distortions in galaxy positions, the team were able to measure the strength of gravity with a precision of 6 per cent, the strongest constraint of its kind as yet. The measurements turned out to be perfectly consistent with the predictions of Einstein’s general relativity theory.

SamushiaMore than 600 000 galaxies from the BOSS survey were utilized to measure the strength of gravitational interactions of galaxies extremely far away from each other. This is a visual representation of that measurement; the amount that the circles are distorted, or squashed from perfect concentric rings, indicates the velocity that galaxies are falling towards each other and hence the strength of the gravitational interactions. Credit: BOSS/U. Portsmouth"Gravity is the main driving force behind the growth of structure in the Universe. According to general relativity, gravity is a manifestation of the space-time curvature – massive objects curve the space-time around them, which affects the movement of other objects around them. It’s a very elegant theory that has been successful in explaining the outcomes of many experiments, however it is not the only theory of gravity," explained Samushia. "Theoretical physicists have proposed many alternative theories and modifications of general relativity and the challenge for observational physicists is to test the alternative theories with ever increasing precision."

 

Images and captions

http://www.ras.org.uk/images/stories/NAM/2014/Samushia.png
More than 600 000 galaxies from the BOSS survey were utilized to measure the strength of gravitational interactions of galaxies extremely far away from each other. This is a visual representation of that measurement; the amount that the circles are distorted, or squashed from perfect concentric rings, indicates the velocity that galaxies are falling towards each other and hence the strength of the gravitational interactions. Credit: BOSS/U. Portsmouth

http://www.sdss.org/news/releases/galaxies.jpg
Each point on the left panel represents a galaxy, while a right panel is an actually image of one of the patches of the sky observed by SDSS. Credit: SDSS.

 

Media contacts

NAM 2014 press office landlines: +44 (0) 02392 845176, +44 (0)2392 845177, +44 (0)2392 845178

Dr Robert Massey
Mob: +44 (0)794 124 8035
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Anita Heward
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Science Contact

Dr Lado Samushia
Institute of Cosmology and Gravitation
University of Portsmouth
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Further Information

The research has been published in Samushia et al, "The Clustering of Galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS): measuring growth rate and geometry", Monthly Notices of the Royal Astronomical Society vol. 439, p. 3504, 2014. A preprint of the paper is available.

Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/.

SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, University of Cambridge, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.

 

Notes for editors

The RAS National Astronomy Meeting (NAM 2014) will bring together more than 600 astronomers, space scientists and solar physicists for a conference running from 23 to 26 June in Portsmouth. NAM 2014, the largest regular professional astronomy event in the UK, will be held in conjunction with the UK Solar Physics (UKSP), Magnetosphere Ionosphere Solar-Terrestrial physics (MIST) and UK Cosmology (UKCosmo) meetings. The conference is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and the University of Portsmouth. Meeting arrangements and a full and up to date schedule of the scientific programme can be found on the official website and via Twitter.

The University of Portsmouth is a top-ranking university in a student-friendly waterfront city. It's in the top 50 universities in the UK, in The Guardian University Guide League Table 2014 and is ranked in the top 400 universities in the world, in the most recent Times Higher Education World University Rankings 2013. Research at the University of Portsmouth is varied and wide ranging, from pure science – such as the evolution of galaxies and the study of stem cells – to the most technologically applied subjects – such as computer games design. Our researchers collaborate with colleagues worldwide, and with the public, to develop new insights and make a difference to people's lives. Follow the University of Portsmouth on Twitter.

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter.

The Science and Technology Facilities Council (STFC) is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar. It enables UK researchers to access leading international science facilities for example in the area of astronomy, the European Southern Observatory. Follow STFC on Twitter.