27th March 1998

A Bull's Eye for MERLIN and the Hubble


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.

Background information on gravitational lenses is available by clicking HERE.

Gravitation Lens Figure 1
Hubble and MERLIN
image of 1938+666

A postscript version
is available for
Figure 1
Diagram Figure 2
Diagram demonstrating
the principle of a
gravitational lens

A postscript version
is available for
Figure 2
      Click on these images
for full size versions

Background information
is available HERE

For further information contact any of the following team members:

The results of this work will be published in Letters section of the April 1 Issue of the Monthly Notices of the Royal Astronomical Society.

L.J. King et al. ``A complete infrared Einstein ring in the gravitational lens sytem B1938+666''

The MERLIN radio array is a UK National Facility operated by the University of Manchester on behalf of the Particle Physics and Astronomy Research Council. The Very Large Array is a US National Facility operated by the National Radio Astronomy Observatory on behalf of Associcated Universities Inc.

The astronomers involved work at the following institutes: University of Manchester; University of Oxford; California Institute of Technology (Pasadena); Netherlands Foundation for Radio Astronomy; University of Groningen; Institut d'Astrophysique de Paris.