The cosmic explosion that marks the end of a star’s life has long been a topic of fascination for astronomers. For the first time, scientists have captured visual evidence of a star meeting its end by detonating twice. The remains of supernova SNR 0509-67.5, studied with the European Southern Observatory’s Very Large Telescope (ESO’s VLT), show patterns that confirm its star suffered a pair of explosive blasts.

The explosions of white dwarfs play a crucial role in astronomy. Much of our knowledge of how the Universe expands rests on Type Ia supernovae, and they are also the primary source of iron on our planet, including the iron in our blood. However, despite their importance, the exact mechanism triggering these explosions remains unsolved.

All models that explain Type Ia supernovae begin with a white dwarf in a pair of stars. If it orbits close enough to the other star in this pair, the dwarf can steal material from its partner. In the most established theory behind Type Ia supernovae, the white dwarf accumulates matter from its companion until it reaches a critical mass, at which point it undergoes a single explosion.

However, recent studies have hinted that at least some Type Ia supernovae could be better explained by a double explosion triggered before the star reached this critical mass. This alternative model suggests that the white dwarf forms a blanket of stolen helium around itself, which can become unstable and ignite. This first explosion generates a shockwave that travels around the white dwarf and inwards, triggering a second detonation in the core of the star — ultimately creating the supernova.

Until now, there had been no clear, visual evidence of a white dwarf undergoing a double detonation. Recently, astronomers have predicted that this process would create a distinctive pattern or fingerprint in the supernova’s still-glowing remains, visible long after the initial explosion. Research suggests that remnants of such a supernova would contain two separate shells of calcium.

Astronomers have now found this fingerprint in a supernova’s remains. Ivo Seitenzahl, who led the observations and was at Germany’s Heidelberg Institute for Theoretical Studies when the study was conducted, says these results show “a clear indication that white dwarfs can explode well before they reach the famous Chandrasekhar mass limit, and that the ‘double-detonation’ mechanism does indeed occur in nature.”

The team were able to detect these calcium layers (in blue in the image) in the supernova remnant SNR 0509-67.5 by observing it with the Multi Unit Spectroscopic Explorer (MUSE) on ESO’s VLT. This provides strong evidence that a Type Ia supernova can occur before its parent white dwarf reaches a critical mass.

Type Ia supernovae are key to our understanding of the Universe. They behave in very consistent ways, and their brightness allows them to be seen from vast distances. By studying these cosmic events, scientists gain insights into the life cycles of stars and the evolution of the cosmos itself.

The discovery of a double-detonation mechanism in Type Ia supernovae has significant implications for our understanding of the Universe. It suggests that these explosions can occur at different stages of a star’s life, potentially leading to new observations and a deeper understanding of the cosmic web.

As scientists continue to study the remnants of supernova SNR 0509-67.5, they may uncover more secrets about the double-detonation mechanism and its role in shaping the Universe. The findings of this research have far-reaching implications for our understanding of the cosmos and the life cycles of stars.

The article highlights the groundbreaking discovery made by citizen scientists participating in the Kilonova Seekers project. This initiative allows members of the public to analyze near-real-time data collected from the Gravitational-wave Optical Transient Observer (GOTO) project, which involves two arrays of telescopes located on opposite sides of the planet.

The team, led by Dr. Tom Killestein and Dr. Lisa Kelsey, was able to identify a bright exploding star, dubbed GOTO0650, after public volunteers flagged it as an object of interest within 3.5 hours of the image being taken. The quick response enabled the team to gather an unusually complete dataset on the star, including spectroscopy, X-ray, and UV measurements.

The discovery was made possible by the involvement of citizen scientists from around the world, who were able to analyze images and data in real-time. One volunteer, Svetoslav Alexandrov, recalled his excitement when he saw that he would be a co-author on the research paper, while another, Cledison Marcos da Silva, credited the project with distracting him from a serious health problem.

The article concludes by emphasizing the importance of citizen science in making novel serendipitous discoveries in vast datasets. The Kilonova Seekers project is approaching its two-year anniversary and has provided over 3,500 members of the public with the opportunity to discover supernovae and variable stars using real data.

In summary, the article showcases the power of collaborative efforts between scientists and citizens, highlighting the potential for groundbreaking discoveries in real-time. The image prompt complements the article by visually representing the excitement and wonder of uncovering a rare exploding star, surrounded by the diverse group of scientists working together to understand this phenomenon.

The universe’s transition from darkness to light was a pivotal moment in its development, known as the Cosmic Dawn. However, despite the most powerful telescopes, we cannot directly observe these earliest stars. This makes determining their properties one of the biggest challenges in astronomy.

An international team of astronomers led by the University of Cambridge has made significant progress in understanding how the first stars and their remnants affected a specific radio signal – the 21-centimeter signal – created by hydrogen atoms filling the gaps between star-forming regions, just a hundred million years after the Big Bang.

By studying this signal, researchers have shown that future radio telescopes will be able to learn about the masses of the earliest stars. Their results were reported in the journal Nature Astronomy.

“This is a unique opportunity to learn how the universe’s first light emerged from the darkness,” said Professor Anastasia Fialkov from Cambridge’s Institute of Astronomy. “The transition from a cold, dark universe to one filled with stars is a story we’re only beginning to understand.”

The 21-centimeter signal provides a rare window into the universe’s infancy. It is influenced by the radiation from early stars and black holes. Researchers have found that this signal is sensitive to the masses of first stars.

Fialkov leads the theory group of REACH (the Radio Experiment for the Analysis of Cosmic Hydrogen). REACH is a radio antenna still in its calibration stage but promises to reveal data about the early universe. The Square Kilometre Array (SKA), under construction, will map fluctuations in cosmic signals across vast regions of the sky.

Both projects are vital in probing the masses, luminosities, and distribution of the universe’s earliest stars. In this study, Fialkov and her collaborators developed a model that makes predictions for the 21-centimeter signal for both REACH and SKA. They found that the signal is sensitive to the masses of first stars.

“We are the first group to consistently model the dependence of the 21-centimeter signal on the masses of the first stars, including the impact of ultraviolet starlight and X-ray emissions from X-ray binaries produced when the first stars die,” said Fialkov. “These insights are derived from simulations that integrate the primordial conditions of the universe, such as the hydrogen-helium composition produced by the Big Bang.”

Radio astronomy relies on statistical analysis of faint signals, unlike optical telescopes like the James Webb Space Telescope, which capture vivid images. REACH and SKA will not be able to image individual stars but will provide information about entire populations of stars, X-ray binary systems, and galaxies.

“It takes a bit of imagination to connect radio data to the story of the first stars, but the implications are profound,” said Fialkov.

The predictions made in this study have huge implications for understanding the nature of the very first stars in the universe. Researchers show evidence that their radio telescopes can tell us details about the mass of those first stars and how these early lights may have been very different from today’s stars.

Radio telescopes like REACH are promising to unlock the mysteries of the infant Universe, and these predictions are essential to guide the radio observations being done from the Karoo in South Africa. The research was supported in part by the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI).