A New Type of Supernova Unlocks Stellar Mysteries a Thousand Years Ago


Around July 4, 1054, Chinese astronomers recorded a “guest star” that shone so brightly, that it was visible in broad daylight for 23 days. The remnants of that supernova of long ago now form the Crab Nebula, which has long been of great interest to astronomers. Some have hypothesized that SN 1054 (as it is known today) was a rare new type of supernova first described by a physicist about 40 years ago. A team of astronomers has now identified a second recent supernova – called SN 2018zd – that meets all the criteria for this new type, according to a new letter published in the journal Nature Astronomy, thus providing a vital link missing in our knowledge of stellar evolution.

“The term ‘Rosetta Stone’ is used too often as an analogy when we find a new astrophysical object, but in this case I think it’s appropriate.” said co-author Andrew Howell of the Las Cumbres Observatory (LCO). “This supernova literally helps us decode records of thousands of cultures around the world. And it helps us associate something we don’t fully understand, the Crab Nebula, with something else that we have incredible modern records about, this supernova.” “In the process he teaches us about fundamental physics: how neutron stars are made, how extreme stars live and die, and how the elements of which we are made are created and spread around the universe.”

There are two types of acquaintances supernova, depending on the mass of the original star. An iron core collapse supernova presents itself with massive stars (more than 10 solar masses), which collapse so violently that it causes a huge catastrophic explosion. Temperatures and pressures become so high that the carbon in the star’s core begins to melt. This stops the collapse of the heart, at least temporarily, and this process continues, over and over again, with progressively heavier atomic nuclei. (Most of the heavy elements in the periodic table were born in the intense furnaces of exploding supernovae that were once massive stars.) When the fuel runs out entirely, the iron core (since then) collapses into a black hole. or a neutron star. .


Then there is a thermonuclear supernova. The smaller stars (up to about eight solar masses) gradually cool to become dense nuclei of ash called white dwarfs. If a white dwarf that ends up without nuclear fuel is part of a binary system, it can siphon matter from its mate, adding its mass until its core reaches temperatures high enough for carbon fusion.

In 1980, Japanese physicist Ken’ichi Nomoto of the University of Tokyo theorized that there may be a third intermediate type: a so-called “electron capture” supernova, in which a star is not heavy enough to produce. an iron core — collapsing the supernova, and yet it’s not light enough to prevent its core from collapsing entirely. However, such stars stop the fusion process when their nuclei are composed of oxygen, neon and magnesium. In this scenario, electrons are ingested by neon and magnesium in the heart, causing the heart to buckle under its weight. The end result is a supernova.

Since Nomoto first proposed electron-capturing supernovae, theorists have built on their work to identify six key features: stars should have a lot of mass; they should lose much of that mass before they explode; that the mass should have an unusual chemical composition; the resulting supernova should be weak; they should have little radioactive cascade; and the core should contain neutron-rich elements.

SN 2018zd was first detected in March 2018, just 31 million light-years away in a galaxy known as NGC2146. The team was able to identify the probable progenitor star by scanning archival images taken by the Hubble Space Telescope and the Spitzer Space Telescope. They will continue to collect data on SN 2018zd for the coming years. UC Davis astronomers contributed to the spectral analysis which was a key test that was, in effect, an electron capture supernova.

When they combed the published data on supernovae to date, the team noticed a handful that met some of the predicted criteria. But only SN 2018zd scored all six boxes. Because of this discovery, astronomers are even more certain that the 1054 supernova that gave birth to the Crab Nebula was also an electron-capturing supernova, although it happened far too long ago to make a definitive confirmation. . This would also explain why SN 1054 shone so brightly: It is likely that the matter ejected from the explosion will collide with the material shed by its parent star – the same thing that happened with SN 2018zd.

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