Astronomers Crack 600-Year-Old Korean Nova Mystery

This photo of the recovered nova of March 11, 1437 and its ejected shell highlights the hot hydrogen gas of the shell. The now-quiet star that produced the nova shell is indicated with the red tick marks below the shell’s center. However, its motion across the sky places it at the red ‘+’ in 1437. Green and blue plus signs mark the center of the shell now and in 1437. The agreement of the 1437 positions of the shell center and of the old nova show that the nova of 1437 A.D. really is the source of the shell. Credit: K. Ilkiewicz and J. Mikolajewska

Long before Kim Jong-un, on a cold March night in Seoul almost 600 years ago, Korean astrologers spotted a bright new star in the tail of the constellation Scorpius. The date was March 11, 1437; two weeks later the “guest star” had faded from view. Based on its behavior, modern-day astronomers determined that the Royal Imperial Astrologers saw a nova explosion.

All novas, except the Chevy type, occur in close binary star systems, where a tiny, dense white dwarf — the dead remnant of a sun-like star — is paired up with a normal star similar to our sun. The dwarf cannibalizes the companion, stealing its tasty hydrogen gases and funneling them down to its surface. It takes about 100,000 years for the dwarf to build up a layer of hydrogen dense and hot enough to detonate in a colossal explosion. When it does, the blast blows the envelope off to produce a burst of light up to 300,000 times brighter than the sun.

This map shows the nova’s approximate location in the tail of Scorpius. Created with Stellarium

For years, Michael Shara, a curator in the American Museum of Natural History’s Department of Astrophysics and lead author of a new study published this week in the journal Nature, has tried to pinpoint the location of the binary star that produced the nova eruption. Recently, his team expanded the search field and found the ejected shell of still-hot hydrogen gas expanding into space.  They confirmed the finding with a photographic plate from 1923 taken at the Harvard Observatory station in Peru that showed the old nova undergoing yet another smaller burst called a dwarf nova eruption.

Finding old supernovas is difficult enough, but a smaller nova explosion is even more of a needle in a haystack. Shara and team did it by figuring out how much the star had moved in the century since the photo was taken and then extrapolating that motion back six centuries to what then would have been the center of the shell and site of the eruption.

This series of photographic plates taken over six weeks in 1942 shows the old nova of 1437 A.D. undergoing a dwarf nova eruption. Credit:Harvard DASCH

Shara’s study pinpoints the nova and shows that it now undergoes smaller-scale dwarf nova eruptions. This jibes with with the long-held idea that novas go through a long-term life cycle: erupting, fading to obscurity for thousands of years, and then re-erupting in smaller scale explosions called dwarf novae after grabbing fresh material from their companions.

“This is the first nova that’s ever been recovered with certainty based on the Chinese, Korean, and Japanese records of almost 2,500 years,” said Shara.

More plates from the 1940s helped confirm that the old nova is now a dwarf nova, proving that novae, so-called “nova-like” stars and dwarf novae fall along a continuum. After a nova eruption, a nova becomes “nova-like,” then a dwarf nova, and then, after a possible hibernation, returns to nova-hood. Over and over again up to 100,000 times over billions of years.

“In the same way that an egg, a caterpillar,  a pupa, and a butterfly are all life stages of the same organism, we now have strong support for the idea that these binaries are all the same thing seen in different phases of their lives,” Shara said. What a wonderful comparison. I suppose it’s no surprise to see that nature operates in similar ways whether it comes to remote stars or the butterflies that delight us on warm afternoons.

3 Responses

  1. Wow. Amazing those astute sky watchers so long ago in Korea noticed such a thing as different and, without telescopes, cameras and all our modern gear, recorded it all accurately. Bravo to the modern sleuths who put it all together. Fascinating

  2. Jerry Glazman

    Bob, enjoy your blog very much. I am always learning something new. It is one of the pages that is permanent on my web browser.

    Today I am writing in my role as “Jerry, the grammar nag”. The line “This jives with with the long-held idea that novas…” makes no sense. Jive means “glib, deceptive, or foolish talk” or “swing music or the dancing performed to it”. The word that should be used is “jibed” which means “to be in accord or agree with”.

    Sorry to be the nag but please see the following links:

    https://www.merriam-webster.com/dictionary/jibe

    https://www.merriam-webster.com/dictionary/jive

    Jerry

    1. astrobob

      Hi Jerry,

      Oh, you are so right! Thanks for pointing that out. I even knew the difference but got lazy (now corrected). I appreciate it, and I’m glad you enjoy the blog. Thanks for writing.

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