The Hubble Space Telescope has taken an awe-inspiring image that must rank as one of its most incredible pictures ever. The orbiting observatory, operated jointly by NASA and ESA, looked nearly halfway back to the beginning of the Universe to capture countless galaxies clustered together in the constellation of Cetus, the whale.
The cluster, known as Abell 370, lies six billion light-years away, so that we are seeing it as it was six billion years ago. But it is the stunning detail revealed by Hubble that makes the picture so extraordinary.
What can usually only be dimly seen through the biggest telescopes becomes a rich and brilliant field of countless galaxies, held together in a gravitational embrace. They are among the most massive structures in the Universe.
It is astonishing to think that each galaxy is made up of many billions of stars. And it is impossible to imagine how many planets might be orbiting those stars. One can only wonder how many support life, and whether some may host intelligent aliens.
Look more closely at the image and you will see something else that is odd in one of Hubble’s best photos. There are many bright streaks, including a number of arcs which appear to be sections of circular rings. These are not blemishes, or artefacts in the image.
One in the lower left of the image is particularly luminous and has been recognised since it was first noted in high-resolution images from telescopes on Earth in the 1980s.
They are the magnified and distorted light from other galaxies that lie far beyond even those in the cluster. That is because the mass of all the galaxies in the foreground are acting as what scientists call a gravitational lens.
The cluster is warping the shape of spacetime around it, like a vast telescope in space, revealing what lies in the far reaches beyond. The light is magnifies has come from some of the earliest galaxies as they were just a few hundred million years after the Big Bang.
Hubble took the photo as part of its Frontier Fields programme that looked at six clusters of galaxies to learn more about the mysteries of dark matter and the very early Universe. They are no snapshots because the project’s images were built up from 630 hours of precious Hubble observing time. How’s that for some long exposures!
The photos were produced by combining images taken by two cameras on Hubble, the Wide Field Camera 3 (WFC3) which observes in infrared light, and the Advanced Camera for Surveys (ACS) which pictures visible light.
Now that the Frontier Fields programme is completed with Abell 370, astronomers hope to learn more about how the first galaxies switched after the early Universe’s dark ages, and how normal matter exists alongside mysterious dark matter.