Supernova leaves behind "zombie star" defying death

Almost a thousand years ago, stargazers in ancient China and Japan noticed a new star near the constellation of Cassiopeia. The star glowed brightly for six months before vanishing.

This celestial event, known as a ‘guest star,’ mystified astronomers for centuries. Part of it was later discovered to be a ‘zombie star,’ reigniting debates and curiosity in the scientific community.

It was one of the few supernovas recorded before the invention of telescopes. The question remained, where did it go?

Traceable at last

The mystery deepened for centuries as the star remained an “orphan,” meaning none of the celestial objects visible today are linked to it.

Fast forward to the 21st century, and the orphan found a home. Scientists traced the remnant of supernova SN 1181 to the nebula Pa 30.

Amateur astronomer Dana Patchick discovered this in 2013 while rummaging through archives of the WISE telescope’s images as part of a citizen scientist project.

“Zombie star” that never died

The SN 1181 remnant is not the usual supernova remnant. It has a “zombie star” at its heart. This is a dense, dead star called a white dwarf that triggers a thermonuclear explosion resulting in a supernova.

In most cases, the explosion obliterates the white dwarf. With SN 1181, some of the star survived and turned into a zombie star. This unusual partial explosion is a type Iax supernova.

Strange filaments of zombie star

The zombie star radiates dandelion petal-like filaments. With the aid of Caltech’s Keck Cosmic Web Imager (KCWI), the research team went deep into the supernova remnant.

Assistant Professor Ilaria Caiazzo from ISTA and lead author Tim Cunningham, a NASA Hubble Fellow at the Center for Astrophysics, Harvard & Smithsonian studied these features in unprecedented detail.

Positioned above 4,000 meters at the W. M. Keck Observatory in Hawaii, near the summit of Mauna Kea volcano, KCWI is a powerful asset for exploring deep space.

The highly sensitive KCWI captures spectral information for every pixel in an image and analyzes the matter’s motion in a stellar explosion, similar to watching a 3D movie of a supernova.

Using Doppler shift, the principle that changes the frequency of objects as they move toward and away from a source, the researchers created a detailed 3D map of the nebula and its filaments.

Unusual asymmetry of zombie star

Researchers discovered the remnants of SN 1181 aren’t flying through space in every direction like fireworks. Instead, there’s an asymmetry to the shapes that show a gap around the zombie star.

This suggests the asymmetry stems from the initial explosion and offers a unique peek into the celestial spectacle that amazed humanity centuries ago.

Understanding supernova basics

A supernova is an amazing explosion that happens when a massive star dies or when two white dwarfs crash together. Picture a star way bigger than our Sun running out of fuel; without enough energy to fight gravity, it collapses under its own weight.

This collapse releases a massive amount of energy, blowing the star apart in a spectacular burst of light and energy that can outshine entire galaxies for a little while. There are different types of supernovae, but they all wrap up with this incredible explosion.

When a star explodes, it spreads heavy elements like carbon, oxygen, and iron into space, which eventually become the building blocks for planets and even life.

These explosions also kickstart the formation of new stars by compressing nearby gas clouds. Plus, supernovae can impact how galaxies evolve, contributing to their development over billions of years.

Life cycle of a type Iax supernova

Understanding the life cycle of a type Iax supernova like SN 1181 provides astronomers with insights into the universe’s lifecycle and stellar evolution.

Unlike the more commonly studied type Iax supernovas, which result from the disintegration of a white dwarf in a close binary system, type Iax supernovas only partially destroy their progenitor stars.

This leads to enigmatic phenomena such as the “zombie star,” which exists after the explosion. The study of SN 1181 challenges conventional models and suggests there may be more diversity in supernova types than previously understood.

The findings urge the scientific community to reconsider certain fundamental theories about stellar deaths and to explore the potential for other oddities lurking across the cosmos.

Future exploration

The discoveries surrounding SN 1181 and its surviving zombie star hold substantial implications for future astronomical research and the comprehension of stellar phenomena.

By analyzing remnants like SN 1181, scientists can better predict potential supernova appearances and refine the criteria for persistent stellar survivability post-explosion.

This expanded understanding invites new investigative strategies about asymmetric structures formations in supernova remnants.

Tale of a vanishing star

While the study brought researchers closer to understanding the story of the SN 1181 supernova, it also posed new questions to astronomers worldwide.

“Our first detailed 3D characterization of the velocity and spatial structure of a supernova remnant tells us a lot about a unique cosmic event that our ancestors observed centuries ago. But it also raises new questions and sets new challenges for astronomers to tackle next,” said Caiazzo.

As technology advances, instruments like the Keck Cosmic Web Imager provide more detailed views of distant phenomena and pave the way for uncovering further anomalies.

As scientists examine each puzzle piece, the astronomical community edges closer to demystifying the secrets of these cosmic events.

The study is published in The Astrophysical Journal Letters.

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