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Intergalactic magnifying glasses could help astronomers map galaxy centres

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Posted July 2, 2013
Images of a quasar from the Sloan Digital Sky Survey in 2005 and then made with the Liverpool Telescope in 2012. The quasar has brightened dramatically as a result of microlensing. Credit: A. Lawrence and the Liverpool Telescope

Images of a quasar from the Sloan Digital Sky Survey in 2005 and then made with the Liverpool Telescope in 2012. The quasar has brightened dramatically as a result of microlensing. Credit: A. Lawrence and the Liverpool Telescope

An international team of astronomers may have found a new way to map quasars, the energetic and luminous central regions typically found in distant galaxies. Team leader Prof. Andy Lawrence of the Royal Observatory Edinburgh presents the new results on Monday 1 July at the RAS National Astronomy Meeting in St Andrews, Scotland.

If a star passes too close to a giant black hole found in the centre of a galaxy, it will be shredded by the strong gravitational field. This should produce a flare-up in the brightness of an otherwise normal looking galaxy that then fades over a few months. In a large scale survey Prof. Lawrence and his team studied galaxies to search for this effect, finding flare-ups but with very different behaviour to predictions.

Instead of seeing a fade over months, the objects they found look like ‘normal’ quasars, regions in the centre of galaxies where material is swirling around a giant black hole in a disk. The quasars in the survey were not seen a decade ago, so must be at least ten times brighter than before. They are also changing slowly, fading over a timescale of years rather than months.

Illustration of the effect of gravitational microlensing on a distant quasar. Credit : Jason Cowan, Astronomy Technology Centre; adapted from a figure made by NASA

Illustration of the effect of gravitational microlensing on a distant quasar. Credit : Jason Cowan, Astronomy Technology Centre; adapted from a figure made by NASA

The biggest surprise however was that the quasars seemed to be at the wrong distance. Measuring the characteristic shift in lines found in the spectrum of the quasars allows astronomers to measure the speed at which they are moving away from the Earth. Knowing the way in which the universe is expanding enables scientists to deduce the distance to each object.

Read more at: Phys.org

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