People watched this star explode in 1181, and it is still expanding

About 845 years ago a new light appeared in the night sky, stayed for half a year and faded away. Astronomers think they have found what it left behind, and it is not what an exploded star is supposed to leave.

This article contains affiliate links. If you buy through them, we may earn a small commission at no extra cost to you.

Early in August 1181, a new light joined the Moon and the stars in the night sky. People looking up saw a star that had not been there before. Sky watchers in China and Japan wrote it down. So did Arabic astronomers, according to the Center for Astrophysics, Harvard and Smithsonian. They called it a "guest star". The telescope had not been invented yet. All they had was their eyes.

The guest stayed for 185 days. That is about half a year, long enough for the Moon to turn full six times. Then it faded and was gone. For people on Earth, that was the end of the story for a very long time.

NASA's Chandra page says the guest star was about as bright as the planet Saturn. Eight separate old texts describe it. That is more than you can count on one hand.

Why does this matter to you? You can still read what those people saw. "Their descriptions began the story," says the astronomer Tim Cunningham, "and our observations are allowing us to continue it across nearly nine centuries."

In the same part of the sky, in the star pattern called Cassiopeia, there is a faint glowing cloud named Pa 30. It looks like a firework caught in the middle of its burst. Thin bright threads run straight out from one point in every direction.

Astronomers call Pa 30 "the likely remnant" of the guest star. A remnant is what is left after a star blows up. Notice the word likely. Pa 30 is the top candidate, because its age and its brightness fit. A NASA page from 2024 calls it a "contender". Nobody says it is proven.

The best clue is speed. In 2024 a team measured how fast the threads are flying outward. The answer was about 1,000 kilometers every second. At that speed you could travel from your home to the Moon in about six and a half minutes.

The threads are not slowing down either. The team found that the material has neither slowed nor sped up since the explosion. So you can run the film backward and see when it all started. "From the measured velocities, looking back in time, you can pinpoint the explosion to almost exactly the year 1181," Cunningham said.

This is what the title means. The explosion itself happened once. What goes on is the flying apart. In about 845 years, which is about 34 generations of parents and children, something moving that fast covers about 2.8 light years. The Keck Observatory describes the threads as about three light years long. Light is the fastest thing there is, and even light would need almost three years for that trip. It is about two thirds of the way from the Sun to the nearest other star.

The sharpest picture so far comes from Gemini North, a telescope on the mountain Maunakea in Hawaii. It stands more than 4,200 meters up, about half as high as Mount Everest. The news site The Brighter Side reports that the team watched Pa 30 on six nights between 26 July and 5 August 2025. Six nights is almost a week's worth of nights.

Why does this matter to you? Something that people watched begin, with their own eyes, has not finished. You are living in the middle of that story.

When a star blows up in the usual version of this kind of explosion, nothing of the star is left. It is destroyed completely.

But in the middle of Pa 30, almost exactly at its center, a star is still shining.

The researchers conclude that the explosion of 1181 was a very rare, weak kind. It was a blast that did not finish the job. Part of the star was left behind. NASA's Chandra page says such an explosion can leave a "zombie" star.

It is not a quiet survivor. Its temperature is about 200,000 degrees Celsius, about 36 times hotter than the surface of the Sun. It blows out a wind of about 16,000 kilometers every second. That is 16 times faster than the flying threads. A wind like that could go all the way around the Earth in two and a half seconds.

According to the researchers, Pa 30 is the only known remnant of this rare kind in our whole galaxy, the Milky Way. And the guest star of 1181 is one of only five exploding stars in the Milky Way that people saw before telescopes existed. That is one for each finger of a hand.

There is a second surprise, and it is about who found the cloud. Astronomers had searched for the remains of the guest star for centuries. In 2013 it turned up in pictures from a space telescope called WISE. The person who spotted it was Dana Patchick, an American amateur astronomer who was helping in a project for volunteers. Pa 30 was the 30th nebula he had found. A nebula is a glowing cloud in space. He found it 832 years after the guest star appeared.

Why does this matter to you? You do not have to be a professional to find something the professionals have been looking for. You have to look carefully at pictures that already exist.

The Gemini North picture, released in October 2026, showed something nobody had seen. The threads are not smooth lines. "Instead of simple streaks, we see chains of bright knots extending outward from the center," Cunningham said in the announcement. The picture shows about ten times more thread detail than earlier ones.

Each knot is about 4 light days wide, according to NASA's caption for the picture. Light needs four days to cross one knot. Sunlight reaches you in about eight minutes.

Here is another way to see it. One knot is about ten times as wide as the whole path that the planet Neptune follows around the Sun. Ilaria Caiazzo, who led the work together with Cunningham, puts it like this: "The planetary region of our solar system could fit in each knot about ten times with room to spare."

So every tiny bead in that picture could hold our solar system, out to Neptune, ten times over.

How can a telescope see beads at all? "We can see this much detail because of Pa 30's proximity to Earth," Caiazzo said. Proximity means closeness.

Why does this matter to you? The dots in a photo can fool you. A speck that looks like a grain of sugar can be bigger than everything from the Sun to Neptune.

Caiazzo calls Pa 30 close. But how close? Here the sources do not agree.

The Institute of Science and Technology Austria, where Caiazzo works, says about 7,500 light years. The Brighter Side gives the same number. NASA's Chandra page says about 10,100 light years. The second number is about a third bigger than the first. It is like two maps that put the same town 75 kilometers away and 101 kilometers away.

This article does not pick a winner. It matters, though, because a size measured on a photograph depends on how far away the thing is. That is why the 2.8 light years above come from speed and time, and not from a ruler held against a picture.

Why does this matter to you? Even for a famous object, a basic number can be unsettled. When two good sources disagree, the honest thing is to show both.

This is the part nobody can explain yet.

"The knots are quite strikingly uniform. We are excited to try to model them," Caiazzo said. Uniform means they are all nearly alike.

The announcement offers one idea. The knots could have something to do with differences in heat or in thickness in the gas around the star. It is only an idea. The earlier team also said it did not know how or when the threads themselves formed.

So a star blew up about 845 years ago, part of it survived, and its wreckage is still racing outward as rows of beads. What made the beads come out so nearly the same size?