Incredible Space Event! Andromeda Star Goes Dark, Becoming a Black Hole

Astronomers have discovered a massive star in the Andromeda galaxy that skipped the typical explosive supernova and collapsed directly into a black hole. This rare “failed supernova” challenges our understanding of how stars die and black holes form.

The Traditional End of Massive Stars

Massive stars—those with at least eight times the mass of our Sun—typically have spectacular and explosive endings. These stars spend millions of years in a delicate balance between two competing forces: the outward pressure created by nuclear fusion and the inward pull of gravity. As they reach the end of their life cycle, they exhaust their nuclear fuel, particularly hydrogen, which has been powering their fusion reactions. Without this outward pressure, gravity takes over, causing the core to collapse in on itself in a dramatic fashion.

In most cases, this collapse creates a powerful shock wave that propels the outer layers of the star into space, producing an incredibly bright explosion known as a supernova. Supernovae can outshine entire galaxies for weeks or even months, releasing energy that can influence their galactic neighborhoods. The remnants of these massive explosions leave behind dense cores, which can either form neutron stars or black holes depending on the mass of the collapsed core.

The Anomaly of M31-2014-DS1

The star known as M31-2014-DS1, located in the Andromeda galaxy, has turned this conventional wisdom on its head. Rather than ending its life in a supernova, M31-2014-DS1 seemingly skipped the explosion altogether and collapsed directly into a black hole, a phenomenon known as a “failed supernova.” Astronomers first observed this star’s unusual behavior in 2014 when it exhibited a brightening in the mid-infrared range. For about 1,000 days, its luminosity remained stable, and then over the next 1,000 days, it faded dramatically.

By 2023, the star had completely vanished from optical and near-infrared observations, leaving no signs of a supernova explosion. There was no luminous outburst, no shock wave pushing material outward—only the quiet disappearance of a once-massive star. Researchers concluded that M31-2014-DS1 underwent a failed supernova, collapsing directly into a black hole.

Understanding Failed Supernovae

In a typical supernova, a massive star’s core collapse leads to an extraordinary release of energy in the form of neutrinos—nearly massless particles that carry away about 10% of the star’s energy. This “neutrino shock” is critical to the supernova process. It generates heat and a pressure wave, which revives the initial shock wave that had stalled within the collapsing star. When this shock is strong enough to overcome the gravitational forces, it propels the star’s outer layers into space, resulting in a supernova explosion.

However, in a failed supernova, the neutrino-driven mechanism doesn’t manage to revive the shock wave. Instead, the shock wave weakens, the material continues to fall inward, and the star collapses directly into a black hole. This silent end, without the usual fireworks of a supernova, is what astronomers believe happened to M31-2014-DS1.

Implications for Stellar Evolution and Black Hole Formation

The discovery of M31-2014-DS1’s failed supernova has significant implications for our understanding of stellar evolution and the formation of black holes. The silent collapse of this massive star suggests that not all stars in the final stages of their lives explode. Instead, some may bypass the supernova stage entirely, forming black holes through a direct collapse. This finding challenges existing astrophysical models, which have largely assumed that black holes form primarily through supernova explosions.

If failed supernovae are more common than previously thought, it could reshape our understanding of how black holes form and how frequently they are produced in the universe. Additionally, failed supernovae might contribute to the population of stellar-mass black holes that astronomers observe but have difficulty explaining through traditional supernovae-based models. This phenomenon also raises questions about the fate of heavy elements, which are typically dispersed by supernova explosions and play a crucial role in the chemical evolution of galaxies.

The Rarity and Detection of Failed Supernovae

Failed supernovae are particularly challenging to detect due to their lack of observable explosions. Instead of a bright supernova, astronomers look for signs of what doesn’t happen—such as the sudden disappearance of a massive star. This subtlety makes identifying failed supernovae difficult. Before the discovery of M31-2014-DS1, only one other failed supernova had been confirmed: a red supergiant star called N6946-BH1 in the “Fireworks Galaxy,” NGC 6946. This star, with a mass about 25 times that of the Sun, similarly vanished without a supernova, leaving only a faint infrared glow.

The rarity of observed failed supernovae highlights the need for continuous monitoring of massive stars to capture these elusive events. Long-term observational campaigns are critical in this effort, as astronomers need to track individual stars over extended periods to notice the absence of expected supernova explosions. Advances in infrared astronomy, which allow scientists to observe stars that may no longer be visible in optical wavelengths, are also essential in identifying failed supernovae. Detecting more of these events could provide insight into how common they are and refine our understanding of stellar death.

Broader Implications and Future Research

The discovery of M31-2014-DS1’s failed supernova has opened new avenues of research into the life cycles of massive stars and the mechanics of black hole formation. This finding underscores the complexity of stellar evolution, demonstrating that stars may have multiple pathways to becoming black holes. The study of failed supernovae not only challenges current models but also has broader implications for astrophysics, as it affects our understanding of galactic chemical enrichment, the lifecycle of massive stars, and the population of black holes in the universe.

Future research may focus on locating more failed supernovae to determine how common they are among massive stars. The Large Binocular Telescope (LBT) and other advanced observatories are actively engaged in monitoring massive stars in nearby galaxies, searching for those that suddenly disappear. This data could help astronomers develop more accurate models of stellar death, predict the types of stars likely to undergo failed supernovae, and understand how these events fit into the broader narrative of cosmic evolution.

In addition, this discovery highlights the importance of multi-wavelength observations—using infrared, optical, and other wavelengths—to capture the full range of stellar phenomena. As our observational capabilities improve, we may be able to detect other “invisible” events that elude traditional methods. This could reveal a hidden side of the universe, where some of the most massive objects silently transform without the usual cosmic spectacle.

Conclusion

The case of M31-2014-DS1 marks a significant breakthrough in our understanding of the life and death of massive stars. This star’s direct collapse into a black hole without a supernova explosion forces scientists to reconsider the established models of stellar death and black hole formation. While traditional theories have long assumed that massive stars must go supernova to produce black holes, M31-2014-DS1 suggests a different path—one where some stars simply “fade to black,” bypassing the explosion entirely.

Reference:

Kishalay De et al, The disappearance of a massive star marking the birth of a black hole in M31, arXiv (2024).