around July 4 In 1054, Chinese astronomers recorded a “guest star” that shone brightly and was visible in broad daylight for 23 days. Form the remnants of that supernova long ago now Crab Nebula, which has always been of great interest to astronomers. Some have hypothesized that SN 1054 (as it is now known) was a rare new type of supernova first described by the physicist about 40 years ago. A team of astronomers has now identified a new, second supernova – called SN 2018zd – that meets all the criteria for this new type, according to new paper Published in the magazine natural astronomy, thus providing a vital link missing in our knowledge of stellar evolution.
“The term ‘Rosetta Stone’ is used quite often as an analogy when we find a new astrophysical object, but in this case I think it is appropriate,” Co-author Andrew Howell said: From the Las Cumbres Observatory (LCO). “This supernova is literally helping us decipher thousands of years old records from cultures all over the world. It helps us connect something we don’t fully understand, the Crab Nebula, with something else we have amazing recent records about, this supernova. In the process it teaches us about physics Fundamental: how some neutron stars form, how extreme stars live and die, and how the elements we form are formed and spread throughout the universe.”
There are two types of known Supernova, depending on the mass of the original star. An iron core supernova occurs with massive stars (larger than 10 solar masses), which collapse so violently that they cause a massive and catastrophic explosion. The temperatures and pressures become so high that the carbon in the star’s core begins to fuse. This stops the breakdown of the nucleus, at least temporarily, and this process continues, over and over, with progressively heavier atomic nuclei. (Most of the heavy elements in the periodic table were born in the intense furnaces of supernova explosions that were once massive stars.) And when it finally runs out of fuel completely, the iron core (by then) collapses into a black hole or neutron star.
Then there is a thermonuclear supernova. Smaller stars (up to eight solar masses) gradually cool down to become dense ash cores known as white dwarfs. If a white dwarf that has run out of nuclear fuel is part of a binary system, it can pull matter from its partner, adding mass until its core reaches temperatures high enough for carbon fusion to occur.
In 1980, Japanese physicist Kenichi Nomoto of the University of Tokyo theorized that there could be a third intermediate type: a so-called “electron capture” supernova, in which a star is not heavy enough to produce an iron core. A supernova collapse, however, is not light enough to prevent its core from collapsing completely. Instead, these stars stop the fusion process when their cores are made of oxygen, neon, and magnesium. In this scenario, the electrons gobble up the neon and magnesium in the core, causing the nucleus to bend under its own weight. The end result is a supernova.
Since Nomoto first proposed electron-capturing supernovae, theorists have built on his work to identify six major features: stars must have a large mass; They should lose a lot of that mass before they explode; This mass should have an unusual chemical composition; The resulting supernova must be weak; There should be little radiation precipitation; And the core must contain elements rich in neutrons.
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 likely star by searching archival images taken by the Hubble Space Telescope and the Spitzer Space Telescope. They continued to collect data on SN 2018zd for the next two years. Astronomers from the University of California, Davis contributed spectroscopy which proved to be key evidence that this was indeed an electron-capturing supernova.
When they combed through the published data on supernovae so far, the team noticed a handful that met some of the expected criteria. But only SN 2018zd ticked all six boxes. Because of this discovery, astronomers have become more confident that the supernova in 1054 that gave birth to the Crab Nebula was also an electron-capturing supernova, although it happened too long ago to conclusively confirm this. This would also explain why SN 1054 shines so brightly: the material ejected from the explosion likely collided with material shed by its former star – the same thing that happened with SN 2018zd.