New supernova solves the mystery of millennium stars


Around July 4th, In 1054, Chinese astronomers recorded a “guest star” whose light is so bright that it can be seen for 23 days in broad daylight.The remnants of that long ago supernova are now formed Crab NebulaFor a long time, astronomers have been very interested in this. Some people hypothesized that SN 1054 (as it is now known) is a new and rare type of supernova, first described by a physicist about 40 years ago.A group of astronomers have now identified the second most recent supernova-called SN 2018zd-which meets all the criteria for this new type, according to A new paper Published in the journal Natural astronomy, Thus providing an important missing link for our knowledge of stellar evolution.

“When we discover a new astrophysical object, the term’Rosetta stele’ is often used as an analogy, but in this case, I think it is appropriate,” Co-author Andrew Howell says Las Cumbres Observatory (LCO). “This supernova really helped us decode the thousand-year record of cultures from all over the world. It helped us connect something we don’t fully understand, the Crab Nebula, with another thing we have an incredible modern record. This supernova. In this process, it taught us basic physics: how some neutron stars are formed, how extreme stars survive and die, and how the elements we make are created and dispersed in the universe .”

There are two known Supernova, Depends on the mass of the original star. Iron-core collapse supernovae occur together with massive stars (greater than 10 solar masses), which collapse so violently that they cause a huge catastrophic explosion. The temperature and pressure became so high that the carbon in the star’s core began to fuse. This prevents the core from collapsing, at least temporarily, and the process continues over and over again, with the nucleus gradually becoming heavier. (Most of the heavy elements in the periodic table were born in the intense melting pot of explosive supernovas that were once massive stars.) When the fuel is finally completely exhausted, (by then) the iron core will collapse into a black hole or neutron star.

Then there are thermonuclear supernovae. Smaller stars (up to about 8 solar masses) gradually cool down and become dense gray cores called white dwarfs. If a white dwarf star running out of nuclear fuel is part of a binary star system, it can suck material from its partner and increase its mass until its core reaches a high enough temperature for carbon fusion to occur.

In 1980, Ken’ichi Nomoto, a physicist at the University of Tokyo in Japan, speculated that there may be a third intermediate type: the so-called “electron capture” supernova, in which a star is not heavy enough to produce an iron core-collapse supernova, but not enough. Prevent its core from collapsing completely. Conversely, when the cores of these stars are composed of oxygen, neon, and magnesium, they stop the fusion process. In this case, electrons will be swallowed by neon and magnesium in the core, causing the core to bend under its own weight. The end result is a supernova.

Since Nomoto first proposed electron capture supernovae, theorists have determined six key characteristics based on his work: stars should have a lot of mass; they should lose most of their mass before they explode; Ordinary chemical composition; the resulting supernova should be weak; there should be almost no radioactive fallout; and the core should contain neutron-rich elements.

SN 2018zd was first discovered in March 2018, only 31 million light-years away, in a galaxy called NGC2146. The team was able to identify possible ancestors by searching archive images taken by the Hubble Space Telescope and Spitzer Space Telescope. In the next few years, they continued to collect data on SN 2018zd. Astronomers at the University of California, Davis provided spectroscopic analysis to prove that this is the key evidence that this is indeed an electron trapping supernova.

When they combed through the supernova data released so far, the team noticed that a few met some prediction criteria. But only SN 2018zd checked all six boxes. Because of this discovery, astronomers are even more convinced that the supernova that gave birth to the Crab Nebula in 1054 was also an electron-capturing supernova, although it took too long to make a definite confirmation. This can also explain why SN 1054 emits such a bright light: the material ejected from the explosion is likely to collide with the material shed from its predecessor star-this is the same thing that happened with SN 2018zd.

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