An international team of astronomers has captured four separate high-resolution images of a gravitationally lensed supernova, a discovery that enables obtaining a very precise measurement of the universe’s expansion rate.
Gravitational lensing is a technique proposed a century ago by Albert Einstein and involves using the gravity of a foreground object to bend and magnify the light from a more distant object, often bending it into several separate images.
In this case, scientists studied the light of a Type 1a supernova dubbed iPTF16geu, whose light, which traveled 4.3 billion years, was magnified 50 times by a foreground galaxy.
The supernova was first seen by the intermediate Palomar Transient Factory (iPTF), which conducts wide-field real-time surveys of the sky to catch rapidly changing events like supernovae.
Once iPTF16geu was detected, scientists looked at it with some of the world’s most powerful telescopes, including the Hubble Space Telescope, the European Southern Observatory (ESO) Very Large Telescope in Chile, and the W.M. Keck Observatory’s OSIRIS and NIRC2.
Both of the Keck instruments use laser-guided adaptive optics to observe in near-infrared wavelengths.
Adaptive optics remove distortions caused by Earth’s atmosphere.
While thousands of supernovae are found every year, very few are discovered through gravitational lensing.
“The discovery of iPTF16geu is truly like finding a somewhat weird needle in a haystack,” noted Stockholm University research scientist Rahman Amanullah, lead author of a paper on the findings published in the journal Science.
“It reveals to us a bit more about the universe, but mostly triggers a wealth of new scientific questions.”
Supernovae are difficult to observe because they stay bright for only a limited time.
Type 1a supernovae can be used as “standard candles” to calculate great cosmic distances because they are produced by explosions of dying massive stars, explosions that always have the same absolute brightness.
Knowing an object’s true brightness or luminosity, astronomers can determine its distance from Earth.
“Resolving for the first time, multiple images of a strongly lensed supernova is a major breakthrough,” said Ariel Groobar of the Oskar Klein Centre at Stockholm University.
“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.”
Using the four gravitationally lensed images of the supernova, the researchers measured the travel time each image took to reach Earth, which varies because of differences in the way light is bent in the individual images.
They then were able to use the differences in the light’s arrival time to calculate the Hubble constant, or rate at which the universe is expanding.