Unlike the usual spectacular supernova where a massive star explodes completely, a type Iax supernova is a fizzle, leaving a leftover core called the Zombie Star.
What are Zombie Stars?
A zombie star is the leftover core of a massive star, a white dwarf, that should have exploded in a brilliant supernova explosion but somehow cheated death. The typical supernova destroys the white dwarf, leaving behind a neutron star or black hole.
However, in a theorized event called a type Iax supernova, the explosion is weaker. This weaker blast might leave some of the white dwarf intact, creating the “zombie star”. If this zombie star resides in a binary system, it can feed on its companion, potentially triggering the very supernova it narrowly avoided the first time.
What are Type Iax Supernovae?
A type Iax supernova is an uncommon form of type Ia supernova that does not totally disperse the whiter dwarf star, instead, it leaves behind a remnant star called a zombie star.
Supernovae of type Iax resemble those of type Ia, however they are less bright and have a slower ejection velocity. Supernovae of type Iax have the potential to occur at a rate ranging from 5 to 30 percent of that of type Ia. In this category, thirty supernovae have been discovered.
When a white dwarf and companion star form a binary system, the white dwarf takes material from the partner. In a typical white dwarf supernova, just a portion of the dwarf’s mass is lost, otherwise, fusion processes would cause the white dwarf to burst and totally disintegrate when it reached a critical mass.
The Mystery of Type Iax Supernovae:
While the theory behind type Iax supernovae is intriguing, their existence is yet to be definitively proven. Here’s why they are a subject of ongoing research:
Candidate Events:
Astronomers have identified a few stellar explosions with characteristics consistent with type Iax supernovae.
Supernova SN 2012Z:
Supernova SN 2012Z’s discovery in 2012 in the spiral galaxy NGC 1309 was the first time astronomers using the Hubble Space Telescope observed a potential zombie star. The international team behind the Hubble observations, led by astronomers Nathan Smith and Dovi Poznanski from the University of California, Berkeley, were astounded.
Before and after images revealed the star appeared to be brighter after the explosion, defying expectations for a destroyed core. This anomaly is a key signature of a type Iax supernova, where the white dwarf survives the blast.
Supernova SN 1181:
Supernova SN 1181 was a historical event, witnessed in 1181 AD, has a fascinating backstory. Unlike SN 2012Z, it wasn’t spotted with advanced telescopes but with the naked eye. Astronomers across Asia, including observers in China and Japan, documented this “guest star” in meticulous detail over several months.
Fast forward to the 20th century, astronomer F.R. Stephenson recognized the descriptions matched a supernova event. While centuries separate them, SN 1181’s light curve, its brightness variation over time, and location within the Milky Way galaxy align with the properties expected for a type Iax supernova.
The Search Continues:
With advancements in telescopes and our understanding of stellar evolution, the hunt is on for more conclusive proof. Studying these rare events could provide valuable insights into the diverse pathways massive stars take at the end of their lives.
The Significance of Type Iax Supernovae:
If confirmed, type Iax supernovae would have a significant impact on our understanding of stellar evolution and supernovae:
Expanding the Spectrum:
They would show that supernovae aren’t a one-size-fits-all phenomenon. Some, like the type Iax, can leave behind a remnant, challenging the traditional view of complete stellar destruction.
Binary Star Dynamics:
Studying these supernovae could shed light on the complex interactions between stars in binary systems and how these interactions influence the evolution of both stars. A binary star system is simply two stars gravitationally bound to each other, orbiting a common center of mass. It’s like a cosmic dance where two stars waltz around each other instead of just one.
Enrichment of the Universe:
Even a failed supernova like the type Iax might play a role in enriching the interstellar medium with heavier elements forged in the explosion. These elements are crucial for the formation of planets and potentially, life itself.
Conclusion:
The search for definitive evidence of type Iax supernovae and the resulting zombie stars is ongoing. These unusual events hold the potential to rewrite our understanding of stellar death and the intricate processes that govern the life cycle of stars in our vast universe.