An international team of scientists, led by astrophysicists from Northwestern University, has made a groundbreaking discovery in the field of astronomy. They have detected a new type of supernova, named SN2021yfj, which is rich in elements such as silicon, sulfur, and argon. This discovery challenges existing theories about the composition of exploding stars and offers unprecedented insight into the final moments of massive stars.
Typically, when massive stars explode, they exhibit strong signatures of lighter elements like hydrogen and helium. However, SN2021yfj has revealed a startlingly different chemical signature, suggesting that the star lost its outer layers of hydrogen, helium, and carbon before its explosion. This phenomenon provides direct evidence of the theorized layered structure of massive stars, akin to an onion, and offers a rare glimpse into the star’s deep interior just before its explosive death.
Revealing the Inner Workings of Massive Stars
Astronomers have long theorized that massive stars possess a layered structure, with the outermost layers composed of the lightest elements. As one moves inward, the elements become progressively heavier, culminating in an iron core. The observations of SN2021yfj suggest that this particular star somehow lost its outer layers, exposing the silicon and sulfur-rich layers beneath.
The study, which will be published in the journal Nature, represents a significant advancement in our understanding of stellar evolution. “This is the first time we have seen a star that was essentially stripped to the bone,” said Steve Schulze, the study’s lead author. “It shows us how stars are structured and proves that stars can lose a lot of material before they explode.”
A Hot, Burning Onion: The Life Cycle of Massive Stars
Massive stars, weighing between 10 to 100 times more than our sun, are powered by nuclear fusion. This process involves intense pressure and extreme heat in the stellar core, causing lighter elements to fuse and form heavier ones. As the star evolves, heavier elements are burned in the core, while lighter elements are burned in surrounding shells. Eventually, this process leads to an iron core, whose collapse triggers a supernova or forms a black hole.
While massive stars typically shed layers before exploding, SN2021yfj ejected far more material than previously observed. Other stripped stars have revealed layers of helium, carbon, and oxygen, but SN2021yfj’s exposure of deeper layers hints at an extraordinary and violent process.
Chasing Down a Cosmic Oddity
The discovery of SN2021yfj was made in September 2021 using Northwestern’s access to the Zwicky Transient Facility (ZTF) in California. ZTF scans the night sky for transient astronomical phenomena, such as supernovae. Schulze and his team identified an extremely luminous object in a star-forming region 2.2 billion light-years from Earth.
To further understand this mysterious object, the team sought its spectrum, which breaks down light into component colors, each representing different elements. Despite initial setbacks in obtaining the spectrum due to telescope availability and weather conditions, a colleague from UC Berkeley provided the crucial data using instruments at the W.M. Keck Observatory in Hawai’i.
“We thought we had fully lost our opportunity to obtain these observations,” said Adam Miller, a senior author of the study. “But the next morning, a colleague unexpectedly provided a spectrum. Without that spectrum, we may have never realized that this was a strange and unusual explosion.”
Exploring the Unknown: Theories and Implications
The spectrum of SN2021yfj was dominated by silicon, sulfur, and argon, rather than the typical elements found in other stripped supernovae. This suggests that nuclear fusion produced these heavier elements within the star’s deep interior during its final stages.
While the exact cause of this phenomenon remains uncertain, Schulze and Miller propose several scenarios, including interactions with a companion star, a massive pre-supernova eruption, or unusually strong stellar winds. Most likely, they suggest, the supernova resulted from the star literally tearing itself apart due to intense gravitational forces and nuclear fusion.
“One of the most recent shell ejections collided with a pre-existing shell, which produced the brilliant emission that we saw as SN2021yfj,” Schulze explained.
Despite having a theory for this explosion, Miller cautions, “I wouldn’t bet my life that it’s correct, because we still only have one discovered example. This star really underscores the need to uncover more of these rare supernovae to better understand their nature and how they form.”
The study, titled “Extremely stripped supernova reveals a silicon and sulphur formation site,” was supported by the National Science Foundation and benefited from CIERA’s access to ZTF telescope data. As astronomers continue to explore the universe, discoveries like SN2021yfj pave the way for a deeper understanding of the cosmic forces that shape our galaxy.
