Webb sees supernova explosion in gravimetrically lensed galaxy for second time

Nature, in her infinite creativity, provides natural astronomical lenses that allow us to see objects beyond the normal range of our telescopes. They’re called gravitational lenses, and a few years ago the Hubble Space Telescope used one of them to spot supernova explosions in distant galaxies.

Now, using the same lens, JWST has discovered another supernova in the same galaxy.

A gravitational lens is a massive object such as a galaxy or galaxy cluster. The mass of an object causes space-time to curve. When light from an object behind the lens passes through the cluster, it is magnified. Most gravitational lenses are discovered by chance, but recently, dedicated searches have uncovered many more, and they have become important tools in astronomy.

In 2019, astronomers discovered a supernova in an image of a galaxy called MRG-M0138 taken by the Hubble Space Telescope in 2016. The images were formed by gravitational lensing of a galaxy cluster called MACS J0138.0-2155.

Now, JWST has looked at the same galaxy through the same lens and discovered another supernova, which exploded just seven years after the previous one. This is noteworthy and is the first time astronomers have discovered two supernovae in the same galaxy.

Gravity lenses do more than just magnify background objects. They also create multiple images of objects. But the images don’t arrive at the same time, and their temporal separation is another astronomical tool.

In a NASA blog post, Justin Pierel of NASA’s Space Telescope Science Institute (STScI) and Andrew Newman of the Carnegie Institution for Science Observatory explained the discovery.

“When a supernova explodes behind a gravitational lens, its light takes several different paths to reach Earth,” the duo explained. “We can compare these paths to several trains leaving the station at the same time, all traveling at the same speed and heading to the same location. Each train travels a different route, and due to differences in trip length and terrain, the trains They will arrive at their destination at the same time.”

Therefore, images of a single supernova can arrive at our telescopes at different times, sometimes several years apart. This arrangement, although it may seem confusing, is actually another useful tool. Studying these images can help scientists measure the Hubble constant, the history of the universe’s expansion rate. “The problem is that these multiple-image supernovae are extremely rare: fewer than a dozen have been detected so far,” the pair explain.

“In this small club, the 2016 supernova in MRG-M0138, titled Requiem, stands out for a number of reasons,” Pierre and Newman explain. First, supernovae are 10 billion light-years away. Secondly, it is also a Type 1a supernova. Type 1a supernovae serve as standard candles, objects with a known luminosity that can be used to measure distances on the cosmic distance ladder. The third reason is that one of the images will be delayed and will not arrive until the mid-2030s.

“Unfortunately, because Requiem was not discovered until 2019, long after it had disappeared from view, it was impossible to collect enough data to measure the Hubble constant at that time,” the scientists explained.

But now Webb has observed a second supernova, called an Encore star.

“Encore was discovered by accident, and we are now actively tracking supernovae in progress through a time-critical Director’s Discretionary Program,” the scientists wrote. “Using these Webb images, we will measure and confirm Hubble’s detection of supernovae based on multiple imaging Constant. Encore was confirmed to be a standard candle supernova, or Type Ia supernova, making Encore and Encore the most distant pair of standard candle supernova ‘siblings’ ever discovered.”

Measuring the Hubble constant is an ongoing challenge in cosmology. The expansion of the universe is the main evidence supporting the Big Bang. So getting the constants right is an important part of understanding the universe. The Hubble constant measures how galaxies move away from us at a rate proportional to their distance. It is expressed in kilometers per second of a galaxy at 1 megaparsec, and different researchers have come up with different numbers over the decades. The latest measured value of the Hubble constant is 68.3 (km/s)/Mpc.

Shortly after the Big Bang, the universe expanded due to inflation. About three billion years ago, a mysterious force we call dark energy took hold. The power of dark energy has not diminished as the universe expanded, and it is still driving the expansion of the universe. In fact, this expansion is accelerating, but we don’t know why. But somehow, a precise measurement of the Hubble constant is part of the explanation. Measuring the same supernova several years apart will yield accurate measurements.

The pursuit of the most accurate measurements is the pursuit of a better understanding of the universe. Finding two standard candle supernovae in the same galaxy is a unique opportunity to measure the Hubble constant more accurately than ever before. “Given the rarity of finding multiple Type Ia supernovae in the same host galaxy, coupled with the extreme rarity of lenticular supernovae, this finding is indeed surprising,” the scientists wrote in their proposal for the observation.

Supernovae in distant galaxies do not give us any advance indication that they are about to explode. We know which types of stars explode and eventually go supernova, but we can’t measure when that happens. But this case is unique. We know when the next image will appear, or rather, when the next image of the same image will appear.

“Supernovae are usually unpredictable, but in this case we know when and where to watch the final appearance of the Requiem and Encore. Infrared observations around 2035 will have a final hurray, and a new precise measurement of the Hubble constant,” the scientists wrote.