Science

Ancient ‘guest star’ could mean rare clash of stellar corpses

Centuries after Chinese and Japanese astronomers spotted a bright light in their skies, astronomers have linked it to a stellar collision that sparked a rare supernova 850 years ago.

The researcher photographed the structure of Pa 30, a faint but rapidly expanding nebula that surrounds one of the Milky Way’s hottest stars. New observations show that both the nebula and the star are remnants of a rare type of stellar collision. In addition, astronomers more accurately calculated the age of the nebula, confirmed its wind speed, and came to the conclusion that Ra 30 is indeed, as expected, the remnants of a “guest star” seen by stargazers and astronomers in 1181 AD.

Robert Fesen, an astronomer at Dartmouth College in New Hampshire, took three long-exposure images of Pa 30 using the 2.4-meter Hiltner telescope at the Kitt Peak National Observatory in Arizona. These images show a well-structured, firework-shaped Pa 30 with dozens of very thin filaments ejected outward. While the filaments are stunning, astronomers don’t yet know what they’re made of.

“I have been working with supernova remnants for 30 years,” Fesen told reporters at the 241st meeting of the American Astronomical Society. “I’ve never seen anything like it.”

Related: The Butterfly Nebula glows red in a breathtaking image from NASA’s Spitzer Space Telescope.

“There is no remnant in our galaxy that looks like this”

Named after its discoverer and co-author of this study, Dana Patchik, in honor of its 30th discovery, astronomers already knew that Ra 30 was the result of an explosive collision between two dense dead stars or white dwarfs. The merger, which spanned millions of years, unfolded a rare supernova called a 1ax type event.

During the outbreak of supernova 1a, the white dwarf, which has accumulated material from the companion star, crushing it into pieces, eventually explodes. A Type 1ax supernova is a rare subclass of 1a events in which a white dwarf does not completely explode, but loses about half its mass and leaves behind a hot, heavy-metal-rich core like a zombie star.

Since there are very few 1ax events, we do not fully understand how these explosions leave the surviving stars at their centers. Fesen’s recent work on Ra 30 may provide a better explanation for these processes.

“This remnant will allow astronomers to study a particularly interesting type of supernova that, until now, they have only been able to explore based on theoretical models and examples in distant galaxies,” Fesen said in a statement.

Beauty, science and history

Astronomers have been studying Pa 30 since 1181 AD, when Chinese and Japanese astronomers saw a luminous dot in what is now Cassiopeia that matched or eclipsed the bright star Vega.

In 2014 and 2016, astronomers failed to find the expected signs of a planetary nebula — bursts of hydrogen, oxygen and nitrogen — and struggled to pinpoint exactly what lay in its middle. “You could barely see that there was something there,” Fesen said during a press conference about the blurry images taken earlier.

But then, in 2018, French amateur astronomers using an 8-inch telescope noticed a very blue, very hot star at the center of Pa 30 of any planetary nebula.”

That same year, Russian researchers also discovered a blue star at the center of the nebula and published a paper in 2019 concluding that the star, apparently 36,000 times brighter than the Sun, is actually a merger of two white stars. dwarfs.

Meanwhile, astronomers in Hong Kong have returned to previously collected observations of Pa 30. Their 2021 paper, among other things, reported evidence for sulfur, and this discovery formed the basis of the latest work by Fesen and his team.

In late October 2022, Fesen and his team used a sulfur filter to take three long exposure shots of the nebula. With these images, Fesen and his team confirmed that the nebula is expanding at a rate of 680 miles (1,100 kilometers) per second.

With the Fesen images, the team obtained precise radial measurements of the filaments, which they used to calculate the age of the nebula. While previous studies have estimated its age at around 990 years old, Fesen’s team has estimated it at around 850 years old.

Finally, bringing the circle to a close, this age is “perfect for being the remains of the guest star of 1181,” Fesen said in a statement. (will open in a new tab).

“Striking” winds

The structure of this nebula – filamentous with occasional small knots – is unlike the remnants of any other supernova. Fesen and his team concluded that one possible cause could be extremely strong winds shortly after the collision. In planetary nebulae, wind speeds are typically a couple of thousand kilometers per second, but wind speeds in Pa 30 are as high as 10,000 miles (16,000 km) per second.

“That’s just unheard of,” Fesen said.

According to Fesen, the best modern explanation for such strong winds could be a magnetic field that spins up very quickly due to the rapid rotation of the central star. And current models of type 1ax supernovae suggest that such strong winds most likely occurred in the first two decades after the merger. So while the structure of the nebula looks like the aftermath of an explosion, it’s actually “an explosion altered by the wind,” Fesen said.

The optical images taken by Fesen “only hint at what it really looks like,” he said. In particular, he hopes to determine the nature of the filaments by digging into data from both the Hubble Space Telescope, which shows sulfur emissions more clearly, and the powerful James Webb Space Telescope.

Pa 30 will be bright in infrared, and Webb’s detailed observations “should be amazing,” Fesen said.

The study is also described in an article published in January. 13 to the arXiv preprint server.

Follow Sharmila Kuthunur on Twitter @Sharmilakg. Follow us on Twitter @Spacedotcom and on Facebook.

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