HubbleSupernova
Hubble used gravitational lensing to observe a very distant supernova.Credit: NASA, ESA, S. Rodney (John Hopkins University, USA) and the FrontierSN team; T. Treu (University of California Los Angeles, USA), P. Kelly (University of California Berkeley, USA) and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI) NASA/ESA/FrontierSN/Frontier Fields/CLASH/GLASS

Sometimes, even the most powerful telescopes need a little help from the cosmos. The Hubble Space Telescope observed a distant supernova whose light took 9 billion years to reach our part of the universe thanks to a galaxy whose light took 5 billion years to reach us. The process, known as gravitational lensing, bends light in such a way that lets Hubble peer further into the early universe.

Hubble was trained on MACS J1149+2223, a galaxy cluster in the distant universe. The massive cluster causes light from a more distant source to bend around the object. This gravitational lens and was predicted by Albert Einstein as part of his general theory of relativity. In Hubble's photo, light from a distant supernova is seen in four different point around the galaxy cluster, an alignment known as Einstein's Cross.

Hubble has used gravitational lensing as part of Frontier Fields, which is observing "Pandora's Cluster," to explore the cluster and distant objects in the early universe. MACS J1149+2223 previously was used by Hubble and NASA's Spitzer Space Telescope to observe a 13.2 billion-year-old galaxy.

"The supernova appears about 20 times brighter than its natural brightness,”co-author Jens Hjorth, from the Dark Cosmology Centre in Copenhagen, said in a statement. “This is due to the combined effects of two overlapping lenses. The massive galaxy cluster focuses the supernova light along at least three separate paths, and then when one of those light paths happens to be precisely aligned with a single elliptical galaxy within the cluster, a secondary lensing effect occurs."

In addition to being a cool trick, gravitational lensing also helps astronomers figure out how much dark matter can be found within the galaxy cluster. As the light of the supernova fades, it will travel along different paths that will arrive at different times. The delays in these "reruns" can be timed and the amount of dark matter in the cluster can be measured by comparing it to predictions based on existing models.

Gravitational Lens
This illustration shows how four different images of the same supernova were created when its light was distorted and magnified by the huge galaxy cluster MACS J1149+2223 in front of it. NASA and ESA

The astronomers believe an image of the supernova originally appeared in 1995 within the cluster and there's a chance to observe the supernova in the near future. "It is expected to reappear once more in the next one to five years — and at that time we hope to catch it in action," Steve Rodney, of Johns Hopkins University and Frontier Fields Supernova team leader, said in a statement.