A flash in the constellation of Scorpio, seen by medieval Korean astrologers in 1437, helped confirm the theory of the nature of new stars. Thanks to their records, modern scientists have found a corresponding astronomical object and found much less bright flares, as they should be according to models. An article with the results was published in the journal Nature.
A new star is a thermonuclear explosion of hydrogen on the surface of a white dwarf in a binary star system. When a companion star expands during evolution, material from its outer shells can be captured by a compact white dwarf. Upon reaching the critical mass, hydrogen undergoes an explosive thermonuclear combustion, as a result of which the brightness of the system can increase 300,000 times. According to modern theories, after such an event, the system does not change dramatically, but it can take thousands of years to accumulate enough hydrogen for the next nova, during which the brightness remains low, but dwarf novae can form.
“This is the first nova to have been reliably detected from Chinese, Korean or Japanese astronomical observations spanning 2,500 years,” says lead author Michael Shara. He and his colleagues tried for many years to establish the system in which the outbreak of the new year 1437 occurred. They recently discovered a discarded shell of a classic nova. To confirm that the shell belonged to this particular explosion, they used other historical information - a photographic plate of 1923.
“With this record, we were able to figure out how much the star has moved over the century,” explained Shara. "Then we extrapolated the data six centuries ago and hit exactly the center of the previously discovered shell." Other photographic plates of the 20th century helped to prove that dwarf novae occur in this system, that is, it is a cataclysmic variable. Thus, the theory about the general nature of new, nova-like and cataclysmic stars was confirmed: after an outburst, a new one becomes nova-like, then a dwarf nova, and then, after a possible period of calm, moves in the opposite direction with intensification of flares.
“Just as the egg, caterpillar, pupa and butterfly are life stages of the same organism, we now have strong indications that different active binaries are also different phases,” Shara sums up. "The main difficulty in understanding the evolution of such objects lies in the long time that the evolutionary cycle takes: unlike a butterfly, it can be thousands of years."