JWST finds a second "lensed" supernova in a distant galaxy
In a recent discovery, NASA’s James Webb Space Telescope has brought to light a second lensed supernova event within the distant galaxy MRG-M0138.
This discovery, stemming from observations of the galaxy cluster MACS J0138.0-2155, marks a significant milestone in astronomy.
Gravitational lensing of a supernova
Through a process called gravitational lensing – which was first predicted by Albert Einstein – the intense gravity of a massive object warps and magnifies the light from objects behind it.
In this case, the cluster MACS J0138.0-2155 acts as a cosmic lens, distorting and amplifying the light from the galaxy MRG-M0138, situated far behind it. This effect not only magnified the distant galaxy but also produced five separate images of it.
The story of MRG-M0138’s two supernovas began in 2019 when astronomers, using NASA’s Hubble Space Telescope images from 2016, identified a stellar explosion within the galaxy.
Fast forward to November 2023, and the James Webb Space Telescope captured yet another supernova in the same galaxy, a rare occurrence that offers a unique window into cosmic events.
Expert insights
Justin Pierel, NASA Einstein Fellow at the Space Telescope Science Institute, and Andrew Newman, a staff astronomer at the Observatories of the Carnegie Institution for Science, explained this phenomenon:
“When a supernova explodes behind a gravitational lens, its light reaches Earth by several different paths. We can compare these paths to several trains that leave a station at the same time, all traveling at the same speed and bound for the same location.”
“Each train takes a different route, and because of the differences in trip length and terrain, the trains do not arrive at their destination at the same time. Similarly, gravitationally lensed supernova images appear to astronomers over days, weeks, or even years.”
The Hubble constant
“By measuring differences in the times that the supernova images appear, we can measure the history of the expansion rate of the universe, known as the Hubble constant, which is a major challenge in cosmology today. The catch is that these multiply-imaged supernovae are extremely rare: fewer than a dozen have been detected until now.”
“Within this small club, the 2016 supernova in MRG-M0138, named Requiem, stood out for several reasons. First, it was 10 billion light-years distant. Second, the supernova was likely the same type that is used as a ‘standard candle’ to measure cosmic distances. Third, models predicted that one of the supernova images is so delayed by its path through the extreme gravity of the cluster that it will not appear to us until the mid-2030s.”
Second gravitationally lensed supernova
Pierel and Newman said that unfortunately, since Requiem was not discovered until long after it had faded from view, it was not possible to gather sufficient data to measure the Hubble constant then.
“Now we have found a second gravitationally lensed supernova within the same galaxy as Requiem, which we call Supernova Encore. Encore was discovered serendipitously, and we are now actively following the ongoing supernova with a time-critical director’s discretionary program.”
“Using these Webb images, we will measure and confirm the Hubble constant based on this multiply imaged supernova. Encore is confirmed to be a standard candle or type Ia supernova, making Encore and Requiem by far the most distant pair of standard-candle supernova ‘siblings’ ever discovered.”
“Supernovae are normally unpredictable, but in this case we know when and where to look to see the final appearances of Requiem and Encore. Infrared observations around 2035 will catch their last hurrah and deliver a new and precise measurement of the Hubble constant.”
More about gravitational lensing
As discussed above, gravitational lensing, a fascinating phenomenon in astrophysics, occurs when a massive object, like a galaxy or a cluster of galaxies, bends the light coming from a more distant object, such as a star, supernova or galaxy.
This bending effect is a consequence of Einstein’s theory of general relativity, which describes gravity not as a force, but as a curvature of spacetime caused by mass.
Mechanics of gravitational lensing
At its core, gravitational lensing acts like a natural telescope, magnifying and distorting the light from distant celestial bodies.
Astronomers use this effect to study objects otherwise too faint or too far away to observe directly. It has become a crucial tool in exploring the cosmos, aiding in the discovery of distant galaxies, the mapping of dark matter, and the study of the expansion rate of the universe.
Types of gravitational lensing
There are three types of gravitational lensing: strong, weak, and microlensing. Strong lensing creates multiple images, arcs, or even ring-like structures known as Einstein rings around the lensing object.
Weak lensing, while less visually dramatic, alters the shapes of background galaxies slightly, providing essential information about the distribution of dark matter.
Microlensing, on the other hand, occurs when a single star passes in front of another, causing a temporary increase in brightness.
Impact on astronomy and physics
Gravitational lensing also serves as a powerful test for Einstein’s theory, consistently supporting its predictions about how gravity affects light.
The Hubble Space Telescope and other ground-based observatories have captured stunning images of this phenomenon, offering not just scientific insights but also visually striking evidence of the intricate workings of our universe.
In summary, as technology advances, gravitational lensing continues to expand our understanding of the cosmos, unveiling secrets of dark matter, galaxy formation, and the very fabric of spacetime.
Image Credit: NASA, ESA, CSA, STScI, Justin Pierel (STScI) and Andrew Newman (Carnegie Institution for Science).
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