A gravitational lens is a cosmic phenomenon in which gravity bends light, magnifying it in a manner similar to an optical lens. One such lens observed last year revealed a distant supernova, later named Winny.
The
Postdoctoral Researcher Stefan Schuldt detected Winny’s light passing through a gravitational lens. Further observations were carried out using the Nordic Optical Telescope, maintained by Finland and the other Nordic countries. It was confirmed that the object is a rare supernova more than 10 billion light-years from Earth.
This is an exceptionally large distance for an observed supernova. Astronomers measure such distances by observing how the light has been stretched and redshifted over its journey due to the universe’s expansion. Using this method, the galaxy has a redshift of 2.01.
A gravitational lens occurs when light from a distant object, such as a supernova, passes near another galaxy on its journey to Earth. The nearer galaxy’s gravitational field acts as a lens, bending and magnifying the light from the more distant object. In Winny’s case, this has produced five distinct images.
Gravitational lenses are extremely rare. Prior to last year’s observation, only two cases were known in which a single galaxy produced a lens – and neither was suitable for cosmological studies.
Winny presents a different case.
“A gravitational lens bent the light from Winny’s explosion on its way to Earth along five different paths. Each of them is also of a slightly different length,” explains Schuldt, who works as a Postdoctoral Researcher at the Finnish Centre for Astronomy with ESO and the University of Helsinki. He is also involved in HOLISMOKES collaboration. “The temporal differences between the paths allow us to measure the universe’s expansion rate,” he adds.
Early observations of Winny produced four images, with a fifth appearing later. This is crucial because multiple paths give additional data, enabling more accurate measurements of the universe’s expansion rate. This rate is measured by the Hubble constant, although its precise value remains disputed.
Schuldt believes that the five images of Winny created by the gravitational lens can shed further light on the matter.
Additional study of this remarkable system is ongoing, with the goal of obtaining, perhaps before the end of the year, a new, independent value for the Hubble constant.