Astronomers recently observed a rare cosmic event in the Andromeda galaxy: a massive star that vanished without the typical supernova explosion and seemingly transformed directly into a black hole. This star, named M31-2014-DS1, displayed unusual characteristics over several years. Initially, it brightened in mid-infrared wavelengths in 2014, remaining constant in brightness for around a thousand days before suddenly dimming between 2016 and 2019. By 2023, it was completely undetectable in visible and near-infrared wavelengths, leading scientists to suspect it had collapsed into a black hole.

Typically, massive stars undergo core-collapse supernovae (Type II supernovae) as they reach the end of their lives, resulting in a dramatic explosion that outshines entire galaxies for a time. However, M31-2014-DS1 appears to have skipped this process, marking a “failed supernova”. Failed supernovae are unusual because, unlike supernovae that expel massive amounts of material, failed supernovae collapse inward, with most of the star’s material directly forming a black hole without an explosion.

Why Supernovae Fail

For massive stars, core collapse leads to a dense core where intense gravity causes protons and electrons to combine into neutrons, releasing a burst of neutrinos. These neutrinos create a shock wave, and if this wave is powerful enough, it drives the supernova explosion, expelling outer layers. However, if the shock wave stalls, the star fails to explode, leading to direct black hole formation. In M31-2014-DS1, the shock wave did not revive, allowing around 98% of the star’s mass to collapse into a black hole of about 6.5 solar masses.

Implications and Future Research

This event shows that massive stars may not always go out with a supernova bang but can silently collapse into black holes. Observations of M31-2014-DS1 and other potential failed supernovae suggest that as much as 20-30% of massive stars may end their lives this way. These “silent” endings are challenging to detect since they lack the bright explosions that make supernovae so conspicuous.

Continued observations, especially of stars like N6946-BH1—another confirmed failed supernova—may reveal more about these events, further challenging our understanding of stellar death and black hole formation.