Astronomy Picture of the Day - Apep: Unusual Dust Shells from Webb

Explanation: What created this unusual space sculpture? Stars. This unusual system of swirls and shells, known as Apep, was observed in unprecedented detail by NASA’s James Webb Space Telescope in infrared light in 2024. Observations indicate that the unusual shape originates from two massive Wolf-Rayet stars orbiting each other every 190 years with each close passes causing a new shell of dust and gas to be expelled. Holes in these shells are thought to be caused by a third orbiting star. This stellar dust dance will likely continue for hundreds of thousands of years, possibly ending only when one of the massive stars runs out of internal nuclear fuel and explodes in a supernova punctuated by a burst of gamma-rays.

I wouldn’t even want to be under 100 million lights from that when it goes off. A Wolf-Rayet star is a very massive, evolved star that has shed its outer hydrogen layers, revealing helium, carbon, and oxygen. These stars are characterized by extremely high temperatures, luminosities, and powerful stellar winds that strip away mass and create nebulae. Wolf-Rayet stars represent a late, brief stage of a massive star’s life before it ultimately explodes as a supernova.

Key characteristics

Massive: Initially at least 20 times more massive than the Sun.
High Luminosity: Can be up to a million times more luminous than the Sun.
Stellar Winds: Extremely strong stellar winds, driven by radiation pressure, that can reach speeds of up to millions of miles per hour.
Spectral Lines: Unique spectra with broad emission lines of helium, nitrogen, carbon, and oxygen, which is how they are identified.

Evolution and classification

Late Stage: They represent a late stage in the evolution of very massive stars.
Mass Loss: The strong winds cause the star to lose mass rapidly, stripping away its outer hydrogen envelope.
Classification: They are subclassified based on their dominant emission lines:

WN stars: Dominated by helium and nitrogen emission lines.
WC stars: Dominated by carbon and oxygen emission lines.
WO stars: A final stage before a supernova, dominated by oxygen emission lines.

Supernova Progenitors: They eventually end their lives in a spectacular supernova explosion.

A safe distance from a supernova is at least 160 light-years away to avoid the most significant harmful effects, such as ozone layer depletion caused by X-ray radiation. Within 50 light-years, a supernova could potentially cause mass extinction due to cosmic rays and other radiation. However, a supernova could still cause long-lasting harm at distances like 320 light-years, with effects that are still noticeable.
Within 50 light-years: A supernova would likely trigger a mass extinction event due to a high flux of cosmic rays that would damage the atmosphere and DNA.
160 light-years: A supernova at this distance could still cause damage, potentially increasing cosmic ray levels by 10 times and lasting for centuries.
Over 160 light-years: A supernova at this distance is considered safe for Earth, with no damaging effects on the planet’s atmosphere or life.
It is important to note that the effects of a supernova can vary depending on the type of star and its characteristics. Some supernovae may be more dangerous than others.

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