The powerful vision of the NASA/ESA Hubble Space Telescope has allowed astronomers to analyze for the first time the multiple images of a gravitationally lensed Type Ia supernova.
Hubble’s view on iPTF16geu. Image credit: NASA / ESA / Hubble.
Type Ia supernovae always have the same intrinsic brightness, so by measuring how bright they appear astronomers can determine how far away they are.
Known as standard candles, these supernovae have been used for decades to measure distances across the Universe, and were also used to discover its accelerated expansion and infer the existence of dark energy.
“Resolving, for the first time, multiple images of a strongly lensed standard candle supernova is a major breakthrough,” said Prof. Ariel Goobar, from the Oskar Klein Centre at Stockholm University in Sweden.
“We can measure the light-focusing power of gravity more accurately than ever before, and probe physical scales that may have seemed out of reach until now.”
The newly-discovered supernova, called iPTF16geu, was first detected on September 5, 2016 by the intermediate Palomar Transient Factory (iPTF) collaboration with the Palomar Observatory.
Also known as SN 2016geu, the supernova exploded at a distance corresponding to a time 4.3 billion years ago.
It could only be detected because a foreground galaxy — SDSS J210415.89-062024.7, which is 2.5 billion light-years away — lensed the light of the explosion, making it 52 times brighter for observers on Earth.
It also caused iPTF16geu to appear in four distinct places on the sky, surrounding the lensing galaxy in the foreground.
The four images lie on a circle with a radius of only 3,000 light-years around the galaxy, making it one of the smallest extragalactic gravitational lenses discovered so far.
This composite image shows iPTF16geu, as seen with different telescopes. The background image shows a wide-field view of the night sky as seen with the Palomar Observatory. The leftmost image shows observations made with the Sloan Digital Sky Survey. The central image was taken by Hubble and shows the lensing galaxy. The rightmost image was also taken with Hubble and depicts the four lensed images of iPTF16geu, surrounding the lensing galaxy. Image credit: NASA / ESA / Hubble / Sloan Digital Sky Survey / Palomar Observatory / California Institute of Technology.
“The discovery of iPTF16geu is truly like finding a somewhat weird needle in a haystack,” said Dr. Rahman Amanullah, also from Stockholm University.
“It reveals to us a bit more about the Universe, but mostly triggers a wealth of new scientific questions.”
Currently the astronomers are in the process of accurately measuring how long it took for the light to reach us from each of the four images of the supernova.
The differences in the times of arrival can then be used to calculate the Hubble constant — the expansion rate of the Universe — with high precision.
This research was presented in a paper published in the journal Science (arXiv.org preprint) on April 21, 2017.
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A. Goobar et al. iPTF16geu: A multiply-imaged gravitationally lensed Type Ia supernova. Science 356 (6335): 291-295; doi: 10.1126/science.aal2729
