Supernova Encore: NASA Webb spots a second lensed supernova in the galaxy MACS J0138.0-2155 during observations.

 

The NASA James Webb Space Telescope recently detected a multiply-imaged supernova in the distant galaxy MRG-M0138. Captured by the Webb NIRCam, two supernova images are visible, with an anticipation of a third appearing by 2035. The image uses color-coding: blue for 1.15 and 1.5 microns, green for 2.0 and 2.77 microns, and red for 3.56 and 4.44 microns. Credit goes to NASA, ESA, CSA, STScI, Justin Pierel, and Andrew Newman. In November 2023, the telescope also observed the gravitational lensing effect in the massive galaxy cluster MACS J0138.0-2155, distorting and magnifying the appearance of the distant galaxy MRG-M0138 into five distinct images.

Astronomers announced in 2019 that a supernova occurred within the galaxy MRG-M0138, as revealed by NASA's Hubble Space Telescope images from 2016. Astonishingly, when another group analyzed the 2023 Webb images, they found a second supernova in the same galaxy, seven years later. This revelation, shared by Justin Pierel (NASA Einstein Fellow at the Space Telescope Science Institute) and Andrew Newman (staff astronomer at the Observatories of the Carnegie Institution for Science), marks the first instance of two gravitationally lensed supernovae observed in the same galaxy.

In explaining the phenomenon, Justin Pierel and Andrew Newman liken the observation of a supernova behind a gravitational lens to trains leaving a station simultaneously but taking varied routes, arriving at different times. This analogy extends to the appearance of gravitationally lensed supernova images to astronomers over varying durations—days, weeks, or even years. The unique timing discrepancies in these multiple images provide a means to measure the expansion history of the universe, specifically the Hubble constant, a significant cosmological challenge. Notably, the rarity of these multiply-imaged supernovae, with fewer than a dozen detected to date, adds complexity to this cosmological pursuit.

Among this exclusive group, the 2016 supernova in MRG-M0138, known as Requiem, stands out for several compelling reasons. Firstly, it resides an impressive 10 billion light-years away. Secondly, Requiem is likely of the same type (Ia) commonly used as a 'standard candle' for gauging cosmic distances. Thirdly, model predictions indicate that one of the supernova images experiences significant delay due to its trajectory through the intense gravitational field of the cluster, rendering it invisible until the mid-2030s. Unfortunately, Requiem, discovered only in 2019 after it had already faded, missed the opportunity for data collection to measure the Hubble constant at that time.

Hubble and Webb examine the galaxy cluster MACS J0138.

In 2016, NASA's Hubble Space Telescope captured a stunning sight—a multiply imaged supernova dubbed Supernova Requiem—in a distant galaxy distorted by the gravitational lensing effect of the intervening galaxy cluster MACS J0138. Displaying three visible images, with a fourth anticipated in 2035, this near-infrared image portrays light at 1.05 microns in blue and 1.60 microns in orange. Fast forward to November 2023, NASA's James Webb Space Telescope, equipped with the NIRCam instrument, identified a second multiply imaged supernova in the same galaxy. This marks the inaugural instance of a system producing more than one multiply-imaged supernova.

The discovery of a second gravitationally lensed supernova within the same galaxy as Requiem, aptly named Supernova Encore, marks a serendipitous find. Actively monitored through a time-critical director's discretionary program, Encore, confirmed as a standard candle or type Ia supernova, is now a focal point for measuring and confirming the Hubble constant using Webb images. Notably, Encore and Requiem constitute the most distant pair of standard-candle supernova 'siblings' ever identified, offering a unique opportunity for cosmological exploration.

In a departure from the usual unpredictability of supernovae, the final appearances of Requiem and Encore are anticipated, providing a unique opportunity for precise observations. By focusing on infrared observations around 2035, astronomers expect to witness the concluding moments of these celestial events and obtain a new, accurate measurement of the Hubble constant. These observations are conducted under the Webb Director's Discretionary Time program 6549, emphasizing the strategic and time-sensitive nature of this cosmological study.

The authors behind this astronomical exploration bring diverse expertise to the field.

Justin Pierel, based at the Space Telescope Science Institute in Baltimore, Maryland, serves as a NASA Einstein Fellow. Additionally, he holds the role of co-principal investigator for the Webb Director's Discretionary Time program 6549, contributing significantly to the current research endeavors.

Andrew Newman, a staff astronomer stationed at the Observatories of the Carnegie Institution for Science in Pasadena, California, plays a pivotal role in advancing our understanding of the cosmos. As the principal investigator of Webb General Observer program 2345, which led to the discovery of Supernova Encore, and as co-principal investigator of the Webb Director's Discretionary Time program 6549, Newman contributes extensively to the ongoing exploration of distant supernovae and the measurement of the Hubble constant.