Strange supernova remnant is driving scientists mad

Normally, when dying stars explode as supernovae, they eject a chaotic web of dust and gas. But a new image of a supernova’s remnant looks very different — as if its host star ignited cosmic fireworks. It’s the most unusual remnant researchers have ever found and could point to a rare type of supernova that astronomers have long struggled to explain.

“I’ve been working on supernova remnants for 30 years and I’ve never seen anything like this,” says Robert Fesen, an astronomer at Dartmouth College in Hanover, New Hampshire, who photographed the remnant late last year. He reported his findings at a meeting of the American Astronomical Society on Jan. 12 and published them in a peer-reviewed paper the same day.

An 850 year old fireworks display

In 2013, amateur astronomer Dana Patchick spotted the object in archival images from NASA’s Wide-field Infrared Survey Explorer. Over the next decade, several teams studied the remnant, known as the Pa 30, but the results became increasingly confusing.

Vasilii Gvaramadze, an astronomer at Lomonosov Moscow State University in Russia, and his colleagues found an extremely unusual star at the dead center of Pa 30 in 2019. This star had a surface temperature of about 200,000 Kelvin, with a stellar wind blowing outward at 16,000 Kelvin Kilometers per second – about 5% of the speed of light. “Stars just don’t have wind speeds of 10,000 miles per second,” says Fesen. Speeds of 4,000 kilometers per second are not uncommon, he says – but 16,000 are wild.

Pa 30 was the subject of intrigue again in 2021, when Andreas Ritter, an astronomer at the University of Hong Kong, and his colleagues suggested that the remnant was the aftermath of a supernova that lit up the sky in 1181, nearly 850 years ago. Chinese and Japanese astronomers observed the object for about six months before it faded.

During their study of Pa 30, Ritter and his colleagues found that the remnant’s emission spectrum contained a distinct line associated with the element sulfur. Intrigued, Fesen’s group later photographed the remnant with an optical filter sensitive to this line with the 2.4-meter Hiltner Telescope at the Michigan-Dartmouth MIT Observatory in Kitt Peak, Arizona.

The Crab Nebula
The Crab Nebula is a more typical example of a supernova remnant, where a dying star ejects a chaotic web of gas and dust. Photo credits: NASA, ESA, J. Hester and A. Loll (Arizona State University)

The data they collected not only helped confirm that Pa 30 is indeed what remains of the supernova observed in 1181, but also provided a picture of the remnant like no other. It contains hundreds of fine filaments that radiate outward. Typically, researchers expect supernova remnants to look like the Crab Nebula — which looks less like a crab and more like a sea anemone, with a smooth region at the center of an oval mass of tentacle-like filaments. They also often look like the Tycho Supernova, which looks like a ball of jumbled knots.

But Pa 30, by comparison, “makes just an amazing picture,” says Saurabh Jha, an astronomer at Rutgers University in Piscataway, New Jersey. “I’ve never seen anything like it. It’s really overwhelming.”

cheat death

What could have caused such a remnant? In 2021, Ritter and his colleagues speculated that it was a rare supernova explosion classified as Type Iax.

A normal Type Ia supernova occurs when a white dwarf siphons material from a companion star and eventually grows so massive that it cannot support the extra weight and blasts itself into pieces – spilling its innards across the galaxy. But in a Type Iax supernova, the star somehow survives. “We often call these zombie stars,” says Jha.

Although theorists have developed many possible mechanisms to explain Type Iax supernovae, Ritter and his colleagues believe two white dwarfs collided to produce the Pa 30 fireworks. That’s evident from the amount of sulfur in the remnant, which is a byproduct of a white dwarf’s explosion, and the lack of lighter elements you’d see from more massive stars.

Anthony Piro, an astronomer at Carnegie Observatories in Pasadena, California, believes these results crystallize at least one way by which a Type Iax can form. But it differs from the previously favored scenario of a white dwarf siphoning material from a companion. This idea was developed in 2014 when astronomers successfully identified the stars involved in an Iax explosion by searching through archived images from before the event.

Finding Pa 30 “definitely expands, in my opinion, what could have resulted in a Type Iax supernova,” says Jha.

These rare explosions tend to occur in distant galaxies, making them difficult to study. But Pa 30 (if it really is Iax type) is only 2.3 kiloparsecs away – meaning future observations will shed more light on this unusual type of supernova.

Fesen has already applied for observing time at both the Hubble Space Telescope and the newer James Webb Space Telescope (JWST). “The optical image that was captured only gives, I think, an indication of what it really looks like,” says Fesen. “But the JWST image will be just stunning.”

This article is reproduced with permission and was first published on January 26, 2022.

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