Astronomers using NASA’s Hubble Space Telescope have discovered what they say is the most distant gravitational lens yet.
Light is affected by gravity, and light passing a distant galaxy will be deflected as a result. Since the first find in 1979, numerous such gravitational lenses have been discovered. In addition to providing tests of Einstein’s theory of general relativity, these objects have proved to be valuable tools – they magnify the background light source, acting as a natural telescope that allows astronomers a more detailed look at distant galaxies than is normally possible.
Gravitational lenses consist of two parts: one is further away and supplies the light, and the other, the lensing mass or gravitational lens, which sits between us and the distant light source, and whose gravity deflects the light.
Now, Dr Arjen Van der Wel from the Max Planck Institute for Astronomy in Heidelberg, Germany, with colleagues has discovered a quadruple gravitational lens dubbed J1000+0221 – the most distant gravitational lens ever seen.
“The discovery was completely by chance. I had been reviewing observations from an earlier project when I noticed a galaxy that was decidedly odd. It looked like an extremely young galaxy, but it seemed to be at a much larger distance than expected. It shouldn’t even have been part of our observing programme!” said Dr Van der Wel, who is a lead author of the paper, accepted for publication in the Astrophysical Journal Letters (arXiv.org).
The lensing mass is so distant that the light, after deflection, has traveled 9.4 billion years to reach Earth. The previous record holder, found thirty years ago, took less than 8 billion light-years for its light to reach us.
Not only is this a new record, the object also serves an important purpose: the amount of distortion caused by the lensing galaxy allows a direct measurement of its mass.
The discovery also poses a puzzle. Gravitational lenses are the result of a chance alignment. In this case, the alignment is very precise. To make matters worse, the magnified object is a starbursting dwarf galaxy: a comparatively light galaxy – it has only about 100 million solar masses in the form of stars, but extremely young and producing new stars at an enormous rate. The chances that such a peculiar galaxy would be gravitationally lensed are very small.
“This has been a weird and interesting discovery. It was a completely serendipitous find, but it has the potential to start a new chapter in our description of galaxy evolution in the early Universe,” Dr Van der Wel concluded.
Bibliographic information: A. van der Wel et al. 2013. Discovery of a Quadruple Lens in CANDELS with a Record Lens Redshift z=1.53. ApJ Letters, accepted for publication; arXiv: 1309.2826