Gravitational lensing always gets my attention not only because of its growing use in astronomy but because of its potential for deep space missions like FOCAL, Claudio Maccone’s concept for a deep space probe that would be sent beyond the Sun’s 550 AU gravitational lensing distance to make observations of astronomical targets. FOCAL is an interstellar precursor mission that could give us detailed information about any system to which we might send a future probe. And, as Maccone has shown, lensing could also be used to create the kind of robust communications relay that would function with little data loss over huge distances.

But we don’t have to wait for FOCAL to exploit the potential of lensing for studying distant exoplanets. As Centauri Dreams readers know, gravitational microlensing has developed into a potent tool. A foreground star distorts the light from a background object when the alignment is right, and that magnification is likewise affected by planets orbiting the foreground star. Given the right configuration of star and background object, microlensing can be used to discover planets in a wide range of sizes and distances from their stars. Yes, it does depend on chance alignments, but the same can be said for the transit methods of Kepler.

In exoplanet work, we’re interested in the foreground star and its planets, but on a galactic scale, it’s often the more distant object that provides the scientific windfall. As the image below reminds us, gravitational lensing can be caused by any massive foreground object — from a star to an entire galactic cluster — moving in front of a more distant background object. Here the light from a distant galaxy is magnified and distorted by the effect of a foreground galactic cluster. We’re looking at a Hubble image of the cluster RCS2 032727-132623. Arcing around it almost 90 degrees is the light from a background galaxy that would otherwise be too faint to be studied in any detail.

Image: In this image the light from a distant galaxy, nearly 10 billion light-years away, has been warped into a nearly 90-degree arc of light in the galaxy cluster RCS2 032727-132623. The galaxy cluster lies 5 billion light-years away. The background galaxy’s image is over three times brighter than typically lensed galaxies. The natural-color image was taken in March 2011 with the Hubble Space Telescope’s Wide Field Camera 3. Credit: NASA, ESA, J. Rigby (NASA Goddard Space Flight Center), K. Sharon (Kavli Institute for Cosmological Physics, University of Chicago), and M. Gladders and E. Wuyts (University of Chicago).

What lensing delivers is the chance to study a galaxy that was in a process of intense star formation at a time when the universe was only a third of its present age. Researchers are calling this the brightest ‘magnified’ galaxy ever discovered. You can see from the image that interpreting the distorted light is an art in itself, but it’s one we’re learning as we use lensing to study star formation in galaxies that would otherwise be beyond the range of Hubble’s vision. In this case, the galaxy’s distorted image actually repeats several times, so that interpreting the results becomes a matter of straightening out and reconfiguring this arc of information.

Take a look at the image again, this time enhanced to highlight the arc and display the position of the background galaxy if it were directly visible. Note the reconstructed galaxy at bottom left:

Image: A reconstruction (at lower left) of the brightest galaxy whose image has been distorted by the gravity of a distant galaxy cluster. The small rectangle in the center shows the location of the background galaxy on the sky if the intervening galaxy cluster were not there. The rounded outlines show distinct, distorted images of the background galaxy resulting from lensing by the mass in the cluster. The image at lower left is a reconstruction of what the lensed galaxy would look like in the absence of the cluster, based on a model of the cluster’s mass distribution derived from studying the distorted galaxy images. Credit: NASA, ESA, and Z. Levay (STScI).

The paper on this work notes that the source galaxy is actually lensed into five images, but they are by no means complete copies of each other. Imagine the job in straightening this out:

Due to the location of the galaxy in the source plane with respect to the lensing caustics, parts of the source are multiply-imaged five times, while other parts are multiply-imaged only three times in a merging-pair configuration. In particular, we find that the brightest parts of the giant arc, which were targeted for rest-frame optical spectroscopy by R11, are lensed images of a small region of the source galaxy (~ 10% of the spatial size of the galaxy).

Using imaging data from Hubble’s Wide Field Camera 3, the researchers were able to construct the lens model needed to extract a ‘de-lensed’ image of the background galaxy. In future work, Keren Sharon (University of Chicago) and colleagues intend to map the spectral energy distribution and star formation rate in this galaxy, using further spectroscopy to tighten up their model. The paper is Sharon et al., “Source Plane Reconstruction of the Bright Lensed Galaxy RCSGA 032727-132609,” in press at the Astrophysical Journal (preprint).