Guest Post: Evalyn Gates on Cosmic Magnification (or — Invasion of the Giant Blue Space Amoebas)
Scientists like to argue, contra Walt Whitman, that understanding something increases our appreciation of its beauty, rather than detracting from it. The image below, as Evalyn Gates explains, is a perfect example. Evalyn is an astronomer at the University of Chicago, and the author of a great new book on the science of gravitational lensing, Einstein’s Telescope: The Hunt for Dark Matter and Dark Energy in the Universe (Amazon, Barnes & Noble, Powell’s). This post is an introduction to how gravitational lensing gives us some of the most visually arresting and scientifically informative images in all of astronomy.
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I had the pleasure of meeting up with Sean and some other old friends at the World Science Festival in NYC last month, and over champagne at the opening night reception (science has its benefits) Sean graciously invited me to write a guest post on gravitational lensing. It’s a broad topic, mainly because lensing is proving to be such an incredibly useful tool for many areas of cosmology and astronomy, but I have to admit that the visual beauty of the images produced by lensing is part of the appeal for me.
I’m also enamored of the visceral connection between these images and lensing phenomena that all of us encounter in daily life – and the access into a complex theory that this connection affords. The giant arcs, Einstein Rings, and multiple copies of a single distant galaxy or quasar that have now been observed in hundreds of images are concrete visualizations of otherwise abstract concepts of general relativity – they effectively trace out the warps in spacetime created by massive objects, revealing the outline of the cosmos much as the technique of “rubbing” can reveal the writing on an ancient gravestone.
This image, from a recent paper by Adi Zitrin and Tom Broadhurst is both scientifically and visually irresistible:
First, the image itself is really cool. The bright white/yellow galaxies are members of a cluster known as MACS J1149.5+2223, while the blue amoeba-like objects that appear to be invading the cluster are actually five images of a single distant (z ~ 1) spiral galaxy.
This galaxy has been lensed by the warp in spacetime created by the cluster. Light from the galaxy, which lies almost directly behind the center of the cluster but much farther away from us, travels along several curved paths through the cluster lens, producing multiple magnified images of the galaxy. The inset box shows a computer generated model of the unlensed source galaxy, enlarged by a factor of four so that the details, including the spiral arm structure, are visible. Without the lensing power of the cluster, we would see this galaxy as a single small blue smudge.
In general, lensing will both magnify and distort (shear) images of a background source. This lens is fairly unique in that we see large but relatively intact images of the spiral galaxy, which implies that the mass distribution in the central region of the cluster must be nearly uniform. The images in the upper left (#1) and lower right (#2) are especially striking. #1 is magnified but very minimally distorted, while #2, the largest image with a magnification of over 80, seems to be curling its tentacles about one of the galaxies in the cluster.
A close look also reveals the negative parity (mirror symmetry) of the remaining three images – the spiral arms appear to circle in the opposite direction – as expected from lensing. The total magnification of the distant galaxy (the sum of all five images) is about 200, the largest known to date – supporting the authors’s claim that this is “the more powerful lens yet discovered.”
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