SDSS J0928+2031, a huge group of galaxies in the constellation of Leo, is so massive that its strong gravity bends light like a giant lens.
This Hubble image shows a giant cluster of galaxies called SDSS J0928+2031. The image is made up of observations from Hubble’s Wide Field Camera 3 (WFC3) in the infrared and optical parts of the spectrum. It is based on data obtained through four filters. The color results from assigning different hues to each monochromatic image associated with an individual filter. The image was made as part of the Sloan Giant Arcs Survey Program. Image credit: NASA / ESA / Hubble / M. Gladders et al / Judy Schmidt, www.geckzilla.com.
Galaxy clusters contain thousands of galaxies of all ages, shapes and sizes.
Typically, they have a mass of about one million billion times the mass of the Sun and form over billions of years as smaller groups of galaxies slowly come together.
At one point in time they were believed to be the largest structures in the Universe — until they were usurped in the 1980s by the discovery of superclusters, which typically contain dozens of galaxy clusters and groups and span hundreds of millions of light-years.
However, clusters do have one thing to cling on to; superclusters are not held together by gravity, so galaxy clusters still retain the title of the biggest structures in the Universe bound by gravity.
Albert Einstein predicted in his theory of general relativity that massive objects will deform the fabric of space itself.
When light passes one of these objects, such as a huge group of galaxies, its path is changed slightly.
This effect, called gravitational lensing, is only visible in rare cases and only the best telescopes can observe the related phenomena.
In the new Hubble image, we see two dominant elliptical galaxies of the massive galaxy cluster SDSS J0928+2031.
The gravity from the cluster is acting as the aforementioned gravitational lens, allowing us to view the more distant galaxies sitting behind them.
We see the effects of this lensing as narrow, curved streaks of light surrounding both of the large elliptical galaxies.
