Weizmann Institute of Science scientists won a front row seat to the closest supernova to Earth in decades
A supernova - an exploding star - is a phenomenon that has intrigued humanity for thousands of years, long before the invention of the telescope. But while we now understand that these explosions burning with the power of a hundred million suns are the source of the building blocks of life in our world, the conditions that cause a star to destroy itself are still not clear enough. The main reason for this is that a supernova cannot be predicted in advance, so scientists have no choice but to study it in retrospect. The scientists of the Weizmann Institute of Science recently took a significant step towards a deeper understanding of those exploding stars, when they managed to "arrive" at the scene of the explosion while it was happening, and thus successfully map it at an unprecedented level of detail. The mapping they performed included data not only from the course of the explosion but also from the last years of the star - a rare achievement that may shed light on the processes leading to the explosion of stars. The new findings are published today in the scientific journal Nature.
Supernovas used to be considered a rare phenomenon: the last supernova observed in our galaxy exploded about four hundred years ago, and one can only imagine its effect on our ancestors, who suddenly and without any explanation recognized a new bright sparkle in the sky. Innovations in telescopic means allow us, today, to witness explosions not only in our galaxy but also in distant galaxies, and to collect data that until recently could not be imagined at all. And yet - the main problem in the study of supernovae remains: astrophysicists are forced to play space archaeologists who arrive at the scene of the explosion after the fact and dig for remains from the ruins. "This is part of what makes the supernova we witnessed special," says doctoral student Erez Zimmerman, from the group of Prof. Avishai Gal-Yam In the Department of Particle Physics and Astrophysics. "This is the first time that we observe, in ultraviolet radiation - where most of the light is emitted - the collision between the material emitted in the supernova and the material from which the star's envelope was composed."
""Stars behave unpredictably at the end of their lives. This research is a rare opportunity to better understand the mechanisms that lead to the end of a star's life and the formation of a completely new thing."
The institute's scientists are the first to admit that they were lucky: Prof. Gal-Yam's group submitted a request for research time on the Hubble Space Telescope - one of the largest and most sophisticated space telescopes available to NASA, the American space agency - in the hope that they might have the opportunity to witness a supernova and collect data about the ultraviolet radiation that will erupt from the explosion and the material scattered around it. To their delight, it turned out that they had a front-row seat to the closest supernova to Earth in decades: a red supergiant type star that exploded in the Vane Galaxy (also called "Monsieur 101") neighboring the Milky Way.
While the goddess of fortune provided the opportunity and NASA the means - The scientists were still required to act quickly and with a lot of resourcefulness to collect the precious data in real time. The indication of a supernova was received on Saturday evening, and the scientists knew that if they waited until Monday - the beginning of the week in the United States - valuable information would be lost. If that wasn't enough, to heighten the drama, Sunday was the wedding date of Zimmerman who led the research alongside doctoral student Ido Irani, also from Prof. Gal-Yam's group. The scientists successfully raced against the clock, made telescopic measurements, measured and calculated the required information and delivered the data, within hours, to their colleagues at NASA, which allowed the Hubble Space Telescope - a powerful instrument that is usually carried very heavily - to look away at the explosion while Happening. "It is rare in scientific work that there is research that is so time-dependent," says Prof. Gal-Yam. "Most scientific projects don't happen on a Friday night, but the opportunity arose, and we had no choice but to respond to the challenge and meet it."
Not only were the researchers able to provide the measurements to NASA in time, thus allowing Hubble to collect the necessary data, due to its relative proximity to the explosion site, it turned out that Hubble had observed this galaxy many times before. The members of the group, in collaboration with their colleagues in other research groups, turned to the NASA archives and retrieved from there photographs of the star before the explosion - when it was "just" a red supergiant on its deathbed. All of this allowed scientists to create the most detailed portrait ever of a supernova, combining the last years of its life and its death.
Analyzing the ultraviolet light data received from Hubble, and confirmed with the help of additional satellites, allowed scientists to measure the amount of material ejected from the star in the explosion. An unusual hypothesis emerged from the measurement: "When we compare the mass of the star after the explosion, which we measured from the explosion itself, to the mass of the star at the beginning of its life, a significant residue remains," says Irani. "The gap makes it possible to determine, with a very high probability, that the supernova left behind a black hole - into which the rest of the missing mass was apparently swallowed."
"Stars behave unpredictably at the end of their lives. They become unstable, and usually we cannot be sure what complex processes took place in their core, because we only start investigating them after death - when most of the information has already been lost," says Prof. Gal-Yam. "Because of the proximity of the star and the quality of the data collected, this research is a rare opportunity to better understand the mechanisms that lead to the end of a star's life and the formation of a completely new thing," adds Zimmerman.
What will happen to the material that made up that former red supergiant? We may never know, but the supernova in question is still in its final stages, and new data continues to be collected, so it is possible that, in the end, this study - and future studies - will help us answer one of the central questions about our existence: How, in fact, did we get here?
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