When it comes to telescopes, bigger is always better. Galileo's first telescope was tiny; in the 400 years since astronomers have used larger lenses to peer deeper into the sky, revealing more stars and more distant galaxies. In the quest for largesse, we've even moved beyond glass lenses, with radio telescope arrays that measure their effective diameter in miles, not feet. Now the “bigger is better” motto is being taken to a new extreme: Astronomers are using entire galaxies as telescope lenses.
Galaxies can be used as lenses through a process called gravitational lensing, a strange effect first predicted by Einstein’s Theory of General Relativity. The theory says that the presence of matter can curve space-time, deflecting light on its path from, say, a distant galaxy to a telescope on Earth. Starlight is bent and magnified as it curves around the galaxy, somehwat like an ordinary lens, only this one is much, much bigger.
This past January, at the 2014 American Astronomical Society meeting, an international team of astronomers led by the Instituto de Astrofísica de Canarias and La Laguna University revealed a lens 500,000 light years wide: A cluster of galaxies known as Abell 2744. Through gravitational lensing, Abell 2744 is allowing astronomers to see further into space than ever before.
Hubble’s image of Abell 2744 (cropped above) shows almost 3,000 distant galaxies magnified as much as 10 to 20 times larger than they would normally appear, galaxies that would be completely invisible to our orbiting telescopes without the magnifying effects of gravitational lensing.
This video gives good background on how gravitational lensing works.
The investigation is part of the Frontier Fields program, a cooperative effort that has thee of NASA’s space-based observatories using Abell 2744 to see further back in time than ever before. By combining data from the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory, researchers are able to use three sets of eyes in the sky that each has a slightly different way of looking at things—Hubble is tuned for visible light images, Spitzer for infrared light, and Chandra for X-rays.
The goal of Frontier Fields is to combine all that data to image the earliest galaxies possible. It’s “an experiment to explore the first billion years of the Universe’s history,” Matt Mountain, of the Space Telescope Science Institute in Baltimore, Maryland, said in a release. The immediate question is whether astronomers can combine Hubble’s incredible imaging abilities with Einstein’s theory of relativity to search for and find the very first galaxies that formed after the Big Bang.
So far, it's worked. The collaborative effort has already gathered some of the furthest views of the universe, views that contain images of thousands of the faintest and youngest galaxies astronomers have ever detected. Astronomers are seeing galaxies as they were more than 12 billion years ago, not too long after the Big Bang.
Among the Abell 2744 results presented at the AAS meeting is one of the most distant galaxies ever seen—a star system 30 times smaller but 10 times more active than our own Milky Way galaxy. This far off galaxy is bursting with young stars, giving astronomers a rare glimpse of an extremely young galaxy.
Abell 2744 is just the first galaxy astronomers are planning to use as a space-based lens. The Frontier Fields program is targeting six different galaxy clusters as lenses. Like arrays on Earth, these galaxies will function like a telescope array in space, ultimately revealing details of the sky we would never be able to see otherwise.