Astronomers Find First Complete Galactic Gravitational Lens, Predicted By Relativity Theory

A team of British astronomers using the UK's MERLIN radio array and the Hubble Space Telescope have found an ``Einstein Ring'' - a gravitational effect predicted by Albert Einstein over 60 years ago as a consequence of his General Theory of Relativity. The Hubble picture is a beautiful demonstration of Einstein's ideas since, for the first time, it shows a complete ring surrounding the galaxy that created it.

The effect is a cosmic mirage caused by the gravity of a massive galaxy bending the light from an object behind it and acting as a ``gravitational lens''. On the rare occasions when the distant object, the lens galaxy and the telescope are exactly aligned an ``Einstein ring'' is created.

Dr. Ian Browne of the University of Manchester admits ``At first sight it looks artificial and we thought it was some sort of defect in the image but then we realised we were actually looking at a perfect Einstein ring!''.

Commenting later on the pictures Bristol University astronomer Professor Mark Birkinshaw said ``MERLIN and the Hubble have scored a bulls-eye!''.

The size of the ring on the sky is tiny - roughly a second of arc or about the size of a penny viewed from a distance of over two miles - even though the lens consists of an entire galaxy. The blurring effect of the atmosphere makes such fine detail hard for astronomers to spot using optical telescopes on the Earth.

The British team found it by using the 135 mile-wide MERLIN radio telescope to image distant radio sources. MERLIN is a network of six radio telescopes spread out across England and operated as a national facility by the University of Manchester's Jodrell Bank observatory. MERLIN's resolution is the same as that of the Hubble Space Telescope but at a completely different wavelength - the two make perfect astronomical partners. The Hubble, orbiting above the atmosphere, took a detailed picture of the object and this revealed the spectacular bulls-eye. This is only one of over 20 galaxy lenses now known.

In an ironic twist, counting the number of gravitational lenses in the sky, including the rare Einstein rings, is the best way of seeing whether Einstein really made his ``greatest blunder''. When he applied his General Theory of Relativity to the Universe as it was known 80 years ago, Einstein had to invent a repulsive force which overcomes gravity at very large distances. This new force was soon dismissed by other astronomers but many modern cosmologists now think that Einstein may have been right first time - the lens searches will soon tell us where the truth lies.

Editor's note: The original news release, with related links and images, can be found at http://www.jb.man.ac.uk/merlin/press/PR9801/press.html