The discovery of a new type of supernova sheds light on a medieval mystery.

A global team led by UC Santa Barbara scientists at Las Cumbres Observatory has discovered the first convincing evidence for a new type of stellar explosion. That is, a supernova traps electrons. Even though they’ve been theorized for 40 years, real-world examples are elusive. It is thought to be caused by an explosion of a superassymtotic branching star (SAGB), with little evidence of that as well. The findings were published in natural astronomyIt also reveals the mystery of a millennial supernova from A.D. 1054 visible around the world in daylight. before eventually becoming the Crab Nebula.

Historically, supernovae have been divided into two main categories: thermonuclear and iron core collapse. A thermonuclear supernova is an explosion of a white dwarf after it hits matter in a binary star system. These white dwarfs are dense ash cores that remain after low-mass stars. (one as much as about 8 solar masses) to the end of life. An iron core collapse supernova occurs when a massive star, about 10 times more massive than the Sun, runs out of nuclear fuel and its iron core collapses. causing black holes or neutron stars Between the two main types of supernovae are electron-capturing supernovae. These stars stop merging when their cores contain oxygen. Neon and Magnesium They don’t have enough mass to make steel.

While gravity is always trying to crush the stars. What keeps most stars from collapsing is their continuous fusion. or in the core where the melting stops The fact that you couldn’t compress the atoms more tightly. In supernovae traps electrons. Some electrons in the oxygen-neon-magnesium core is knocked into the nucleus of an atom in a process known as electron capture. This removal of electrons causes the star’s core to collapse under its own weight and collapse. This results in a supernova that traps electrons.

If the star is slightly heavier Core elements could also be fused together to form heavier elements. and extend the life of the stars So it was a reverse Goldilocks scenario: the star wasn’t light enough to escape the core collapse. and not heavy enough to prolong life and die later by various means.

That’s a theory invented in 1980 by Ken’ichi Nomoto of the University of Tokyo and others. over the decades Theorists have established predictions of what to look for in electron-capturing supernovae and their SAGB star origins. Stars should be massive. Lose a lot before it explodes. And the mass near the dying star should have an unusual chemical composition. Then the electron-capturing supernova should be weak. There is little radioactivity. and there are neutron-rich elements in the core.

The new study was led by Daichi Hiramatsu, a graduate student at UC Santa Barbara and Las Cumbres Observatory (LCO). Hiramatsu is a core member of the Global Supernova Project, a global team of scientists using dozens of telescopes around the world. The team found that the supernova SN 2018zd has several unique characteristics. some of which were first seen in supernovae.

It brought supernovae closer—just 31 million light-years away—in galaxy NGC 2146, helping the team review archived images taken by the Hubble Space Telescope prior to the explosion and detect a “supernova”. A probable progenitor star before it exploded. This observation coincides with another recently discovered SAGB star. this in the Milky Way But it doesn’t correspond to the Red Super Giant model. which is the origin of the normal collapsed iron core supernova.

The authors looked at all published data on supernovae. and found that while some had some predicted indicators for electron-capturing supernovae, only SN 2018zd had a total of six: the apparent SAGB origin, the strong pre-supernova mass loss. and unusual stars chemical composition weak explosion little radioactivity and a neutron-rich core

“We started by asking, ‘What kind of weird thing is this?'” Hiramatsu said. “We then examined all aspects of SN 2018zd and realized that all of this could be explained in the electron capture scenario.”

The new discovery also sheds light on some of the mysteries of some of the most famous supernovas of the past. In 1054, a supernova occurred in the Milky Way galaxy. which according to the records of China and Japan It is so bright that it can be seen during the day for 23 days and at night for almost two years. The rest of the Crab Nebula has been studied in great detail.

The Crab Nebula was previously the best candidate for electron-trapping supernovae. But its status is uncertain, in part because the explosion happened almost a thousand years ago. This new result adds to the confidence that the historic SN 1054 was an electron-capturing supernova. It also explains why supernovae are relatively bright compared to other models: the luminosity of the supernova is likely artificially enhanced by the ejection of the supernova colliding with the material. where the progenitor star fell out, as seen in SN 2018zd

Ken Nomoto of the University of Tokyo’s Kavli IPMU expressed excitement that his theory has been confirmed. “I am very pleased that electron-trapping supernovae have finally been discovered. which my colleagues and I predicted to exist. “It’s very important and relevant to the Crab Nebula 40 years ago,” he said. This is a wonderful case of combining observation and theory.”

Hiramatsu added, “It was a ‘Eureka moment’ for all of us that we were able to participate in the 40-year-old theory closure, and for me personally because of my career in the field of ‘Eureka’. Astronomy started when I looked at the incredible images of A universe in a high school library. One of which is the iconic Crab Nebula photographed by the Hubble Space Telescope.”

Andrew Howell, a scientist at the Las Cumbres Observatory and an adjunct at UCSB, said: “The term rosettastone is often used as an analogy when we encounter astrophysical objects of the type. New.” Supernovas are helping us decipher millennia of records from cultures around the world, and they are helping us connect one thing we don’t fully understand, the Crab Nebula, with another that we have a fascinating modern record. Intrigued by this supernova in the process It’s teaching us basic physics: how to make some neutron stars. How do extreme stars live and die? and various components Howell is also the lead author of the Global Supernova project and Hiramatsu’s Ph.D., lead author, advisor.