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Quasars put lens on dark energy

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Observations of distant quasars distorted by massive invisible objects have provided fresh evidence that the Universe is mostly made up of mysterious "dark energy".

The research indicates that around two thirds of the Universe consists of dark energy, a strange "anti-gravity" force affecting distant objects. This is consistent with previous studies, such as those on very distant supernovae explosions.

These indicate that the Universe is expanding at an increasing rate, because the supernovae are dimmer than would be expected for a Universe without dark energy.

Ian Browne, at the University of Manchester's Jodrell Bank Observatory in the UK, led the team that performed the observations. "The idea that the Universe is dominated by dark energy is pretty bizarre," Browne told New Scientist . "It deserves somebody going out and checking it."

Double vision

The researchers used powerful radio telescopes to study thousands of quasars. These are very distant compact sources of light and X-ray radiation thought to be fuelled by gas falling into black holes at the centre of galaxies.

They found their view of about one in every 700 was distorted by a massive intervening object that acts as a gravitational lens. Radio emissions from these are bent around the object by its gravity, resulting in two or more images of the quasar.

Kyu-Hyun Chae, also at Jodrell Bank Observatory, then calculated the number of lensed quasars that would be expected for different quantities of dark energy in the Universe, using parameters including the age of the Universe and the number possible sources of gravitational lensing.

The number of lensed quasars actually seen is roughly twice what would be expected if there was no dark energy at all. Chae calculated that two thirds of the Universe must be made of dark matter to explain the number observed.

Browne says the results neatly match earlier work: "It's a completely independent way of getting at the same parameters and to our surprise we came up with the same result."

The telescopes used for the research were the Very Large Array in New Mexico, US, MERLIN at Jodrell Bank in the UK and the Very Long Baseline Array across the US.

Journal reference: Physical Review Letters (DOI: 10.1103/PhysRevLett.89.151301)

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Dark Energy is cool 8)

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The strongest energy too..(mass)

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