What blazed in the sky almost 1,000 years ago could have been a strange supernova

In the year 1054, there was an explosion in the sky so bright that it was visible for almost two weeks in broad daylight and two years after dark. So what caused this sudden phenomenon?

It was probably a rare type of supernova known as an electron capture supernova. These supernovas, thought to be almost nonexistent, lie just between the extremes of thermonuclear and iron-core supernovas. It’s not the remnants of ghost stars dying again or huge hot young stars that live fast and die hard. An international team of scientists led by the Las Cumbres Observatory now has more convincing evidence than ever of their existence.

That, and the clues that they were looking at a completely different beast when observing the SN 2018zd supernova match descriptions from nearly a thousand years ago. The burst of light our ancestors saw was not the same supernova whose remains became the Crab Nebula, but it was the same type.

Researcher Daichi Hiramatsu from the University of California, Santa Barbara (UCSB) and the Las Cumbres Observatory, is a lead member of the Global Supernova Project, a group of international scientists who observe supernovas with telescopes everywhere. on the planet. It was while working with this team that Daichi realized what was happening with the SN 2018zd supernova. He recently led a study recently published in Nature astronomy.

“I think the first strange thing I realized was the particular ultraviolet evolution of SN 2018zd observed by the Swift satellite,” Daichi told SYFY WIRE. “Usually, core-collapsing supernovae will turn redder after the explosion as they expand and cool. SN 2018zd turned bluer right after the explosion, then turned redder, making it stand out.

Supernovas generally belong to one of the following two types. Thermonuclear or Type Ia supernovas occur when a white dwarf star in a binary star system, the undead core of what was once a much larger star, gains more and more stars until it expires. . These supernovas are cosmic zombies that only revive to die again. Supernovae with collapsed iron core occur when huge stars of at least ten solar masses use up all of their hydrogen after turning into helium through nuclear fusion. Their iron cores then collapse on themselves and form black holes. These supernovas are more like space Godzillas that stomp and roar until they are finally taken down.

Electron capture supernovas are neither, but share some characteristics of both. They are believed to be the corpses of super asymptotic or super-AGB giant stars. Such stars have sufficient mass and strength for nuclear fusion to create a core (mostly) of oxygen and carbon, with some neon and magnesium, but stop there because they are not large enough to merge their cores into iron, unlike transforming stars. in black holes after becoming a supernova.

These supernovas result from the crushing of electrons from the central elements of atoms in the nuclei of these atoms, causing the star to collapse under its own weight. They are too heavy for their core to remain intact, but too light to stay alive any longer.

“Electron-capture supernovas are inherently rare, as we estimated their rate to be only a small percentage of all core-collapsing supernovae,” Hiramatsu said. “Additionally, the explosion energy of electron capture supernovae is lower than that of typical nucleus collapse supernovae, so they could be weaker and harder to see. Finally, it requires in-depth observations to identify electron-capturing supernovae that meet the six required criteria. “

SN 2018ze observations revealed a super-AGB progenitor star, significant mass loss while this star was still alive, weak explosion, nucleus filled with neutrons, strange abundance of chemicals, low kinetic energy and little radioactivity. What makes electron-capturing supernovas so elusive? Hiramatsu believes there are a trio of reasons they have been so notoriously difficult to find and observe.

Whatever the formation of the Crab Nebula, it meets most of these criteria. No one who saw it at the time really knew what it was, except for a flash of light in the Milky Way that visibly lingered, especially at night. While the Crab Nebula was previously believed to be a remnant of an electron-capturing supernova, there were still uncertainties because it happened so long ago. However, Hiramatsu believes strange chemicals, low kinetic energy, and low ejecta mass, and ejecta enveloped in dense gas have revealed that this is more than likely all that is left of an air-capture supernova. electrons.

“SN 2018zd showed similar characteristics in our observations of the ancestor and the supernova,” he said, “so we hope to be able to fill our understanding of the electron-capture supernovae of the early explosion (SN 2018zd) to the late nebula (the Crab Nebula). ). ”

There might have been a lot of misconceptions about the universe in the ancient world, but sometimes the ancients were right.