Astronomers discover the secrets of 'string of pearls' supernova relic and the zombie star at its heart

Scientists are still unraveling the mysteries of a cosmic phenomenon known as the "string of pearls," a unique supernova relic that humanity witnessed around 850 years ago. This discovery is thanks to the most detailed observation of the dandelion-shaped chains of gas and supernova debris that make up Pa 30, the only known supernova remnant of its type in the Milky Way. What sets Pa 30 apart is the presence of a rare zombie star at its core.

Type Ia supernovas, which create Pa 30, are triggered when a dead white dwarf star, known as a white dwarf, overfeeds on a companion star. This overfeeding initiates a runaway nuclear explosion that typically destroys the white dwarf. However, in rare cases, the supernova doesn't entirely obliterate the star, leaving behind a shattered stellar body known as a zombie star. These occurrences are referred to as Type Iax supernovas.

Pa 30 was first spotted in 2013 by a citizen scientist, but scientists soon connected it to a cosmic explosion recorded independently in 1181 in Japanese, Chinese, and Arabic historical records. This makes Pa 30 one of only five supernovas observed before the invention of the telescope. Ancient historical records of stellar explosions extend back only about a thousand years. There may well be similar remnants hidden in our galaxy that we have yet to discover.

The proximity of Pa 30 to Earth, approximately 7,500 light-years away, makes it an ideal laboratory for studying supernovas. Its proximity allows scientists to see unprecedented detail in the cosmic strings of gas and debris surrounding the star. Using the Gemini North telescope, researchers discovered knots along the strands of gas radiating from the site of the cosmic explosion, akin to pearls on a string. Each knot is vast enough to span the orbit of Neptune, approximately ten times, leaving ample space.

The uniformity of these knots is striking, and scientists are eager to model them. Additionally, the zombie star sits almost perfectly at the heart of Pa 30, suggesting that the explosion was roughly symmetrical and the resulting kick was relatively light. This is significant because explosions conserve momentum, so if the explosion was perfectly symmetric, the surviving star should not receive a substantial kick.

While there are still many unanswered questions surrounding Pa 30 and its zombie occupant, the research could potentially help identify the wreckage of other Type Iax supernovas in our galaxy. These events are challenging to observe in distant galaxies as point sources of light, but they are only observable in our own galaxy and a few nearby ones.

The team plans to utilize Pa 30's distinctive properties to search the Milky Way and nearby galaxies for similar objects. Their research was published in The Astrophysical Journal.