Astronomers have told about mysterious nodules in the remnant of the supernova of 1181

In the constellation of Cassiopeia, astronomers have obtained the most detailed image of Pa 30, a nebula associated with a supernova outbreak observed on Earth in 1181. Its diverging threads resemble frozen fireworks, but new data has shown that they consist of chains of gas clots. What the mysterious nodules are and how the central star was able to survive the explosion is in the Izvestia material.

The star seen by medieval astronomers

In August 1181, Chinese and Japanese observers noticed a new bright dot in the sky. Such objects were then called "guest stars": they appeared among the usual luminaries, remained visible for a while, and then disappeared. Today, astronomers associate this event with supernova SN 1181.

According to historical evidence, the object could be observed with the naked eye for 185 days — about six months. It was comparable in brightness to Saturn. But after the flare went out, its trace was lost for a long time: scientists had to determine which of the modern nebulae remained from that event.

For a long time, 3C 58, a pulsar nebula with a rapidly rotating neutron star, was considered the main candidate. However, studies have called this connection into question: estimates of the age of the system turned out to be significantly longer than the time that has passed since 1181. It was necessary to find another object that would match both the location of the outbreak and its estimated age.

A suitable nebula was discovered only in 2013. American amateur astronomer Dana Patchick found it by viewing infrared data from the WISE Space Telescope as part of a citizen science project. The object was designated Pa 30. Subsequent observations revealed an unusual shell with outward-spreading filaments around its central star.

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In 2021, researchers presented arguments in favor of linking Pa 30 with a 12th-century supernova. The nebula's position was consistent with ancient descriptions, and its size and rate of expansion indicated an explosion about a thousand years ago. Estimates of the brightness of the historical flare also fit into the proposed explanation. So the medieval records became part of the modern reconstruction of the stellar catastrophe.

What the new image showed

The new images were obtained using the GMOS instrument on the Gemini North telescope located in Hawaii. The images revealed about an order of magnitude more filamentous structures than before. The main discovery was their internal structure: what looked like continuous streaks in less detailed images turned out to be sequences of individual bright gas clumps.

The observations were carried out in narrow radiation ranges of ionized sulfur and oxygen. This approach allows you to highlight the glow of a certain gas and consider the details that are lost in the overall image. In the new study, the scientists also confirmed that the previously detected weak oxygen glow is associated with the same filaments that are clearly visible in sulfur radiation.

The word "tiny" is relative to the found nodules. Their characteristic diameter is estimated at about four light—days - about 100 billion km. In other words, it takes light several days to cross one such cluster. Against the background of the entire nebula, these formations look like small beads strung on threads radiating from the center.

Why did the gas gather in chains?

The new image does not provide a definitive answer to the question of the origin of the nodules. It shows the structure that the physical models are now supposed to explain. One possibility is related to the heterogeneity of the surrounding matter. If the temperature or density of the gas around the exploded system varied from site to site, the expanding emissions could interact unevenly with this environment. According to the researchers, such differences could be involved in the formation of the observed chains.

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There is reason to take into account the influence of the central star. Back in 2023, scientists considered the interaction of its powerful stellar wind with clumps of ejected matter as a possible explanation for the unusual appearance of Pa 30. The stellar wind is a stream of matter that a star ejects into the surrounding space. When it collides with the nebula's gas, it is able to change its movement and structure. However, the specific mechanism of formation of long filaments and individual seals is still the subject of research.

The shape of the find itself is important for testing hypotheses. The model should explain why the substance has formed outward-pointing filaments and why these filaments break up into chains of clots. New observations have added details that can be used to determine how well the proposed scenario corresponds to a real object.

Why is there a star left after the supernova?

The event is classified as a suspected type Iax supernova. Unlike the usual type Ia supernova scenario with the complete destruction of a white dwarf, a less energetic explosion can leave a bound stellar remnant. In popular science publications, it is called a "zombie star": the object survived a catastrophe that could destroy it. Pa 30 is considered to be the only known Type Iax supernova remnant in the Milky Way.

What does the position of the star indicate?

The new data made it possible to clarify one more detail: the central star is located almost in the geometric center of the nebula. The researchers found no signs of a strong transverse thrust that would noticeably shift it relative to the shell.

This is important for restoring the mechanics of the explosion. If the substance is released unevenly, the preserved object may receive a recoil. In the case of the Pa 30, measurements limit the possible speed of such movement across the line of sight to about 100 km/s. It is precisely about limiting this component of the velocity, and not about proving the complete immobility of the star.

However, proximity to the center does not in itself mean that the entire shell is perfectly symmetrical. In a 2024 study, when astronomers built a three-dimensional map of Pa 30, they found signs of an asymmetry in the distribution of emissions and a large cavity inside the nebula. The position of the stellar remnant and the shape of the surrounding gas provide different, complementary information about what happened.