Betelgeuse, the bright red star marking the shoulder of the constellation Orion, is a massive red supergiant. This colossal star has reached an advanced stage, having exhausted the hydrogen fuel in its core. Stars of this size are destined for a spectacular death known as a core-collapse supernova, a violent explosion that briefly outshines an entire galaxy. The duration of this visible event is tied to the physics of the explosion and the star’s distance from Earth, estimated at 600 to 700 light-years away. The visible phenomenon will be an astonishing celestial event lasting months, not minutes.
The Stellar Lifecycle and Precursors to Explosion
Betelgeuse will die young due to its enormous mass, estimated to be 10 to 20 times that of the Sun. Its size causes it to burn through nuclear fuel at an incredible rate, accelerating its stellar evolution. After consuming core hydrogen, the star began fusing helium into carbon. This caused its outer layers to swell and cool, giving it the characteristic red color and supergiant status.
This fusion process continues in concentric shells, moving through progressively heavier elements like carbon, neon, oxygen, and silicon. Each stage occurs faster than the last. The star is exhibiting clear signs of instability, such as the dramatic Great Dimming event observed in 2019 and 2020, which involved ejecting a massive cloud of dust. This variability indicates the star is in the final, highly unstable phase before its ultimate collapse, which will yield a core composed of iron and nickel.
Iron is the final element that can be created through fusion because fusing it consumes energy rather than releasing it. When the inert iron core reaches a critical mass, gravity overwhelms the outward pressure, and the core collapses inward in a fraction of a second. This catastrophic core collapse triggers a massive shockwave that rebounds and blasts the star’s outer layers into space, marking the moment of a Type II core-collapse supernova.
Duration of the Visible Supernova Event
The physical collapse of the core is virtually instantaneous, but the resulting light show observed from Earth will last for many months. The duration of the visible event is determined by the supernova’s light curve, which plots the object’s brightness over time. After the initial shockwave breaks through the star’s surface, the light will rapidly brighten over a period of days, reaching its maximum luminosity.
As a Type II supernova, Betelgeuse is expected to follow the Type II-Plateau (II-P) subtype light curve. This type is characterized by a long period where the light remains nearly constant in brightness, known as the plateau phase. This phase can last for weeks to a few months, during which the supernova will be visible to the naked eye, even during daylight hours.
Following the plateau, the visible light slowly begins to fade as the expanding gas cools. This slower decay phase is powered by the radioactive decay of new elements created during the explosion. The light is sustained by the decay of radioactive nickel-56 (\(^{56}\text{Ni}\)) into cobalt-56 (\(^{56}\text{Co}\)) and eventually to stable iron-56 (\(^{56}\text{Fe}\)). The energy released by this decay chain is absorbed by the expanding stellar material and re-emitted as visible light. The light will remain significantly brighter than Betelgeuse’s current state for six to eighteen months before fading back to near-invisibility.
Expected Visual Impact from Earth
When the supernova light reaches Earth, it will be an unprecedented sight, transforming the familiar night sky. At peak brightness, the Betelgeuse supernova is expected to be brighter than any object except the Moon. Estimates suggest it could reach an apparent magnitude between -12 and -13, comparable to a quarter or half-Moon.
This immense luminosity will be concentrated into a single, brilliant point of light. The supernova will be easily visible during the day for several weeks to a few months. At night, this temporary celestial body will dominate the constellation Orion.
The star’s distance, approximately 640 light-years, places it safely outside the range where high-energy radiation poses any threat to life on Earth. Dangerous events, such as gamma-ray bursts, are only a concern if they originate within a few dozen light-years. The visual impact will be a spectacular, harmless light show.
The Stellar Remnant
After the visible glow fades, the stellar remnant remains as a lasting consequence of the star’s death. The fate of Betelgeuse’s core depends on the mass left after the explosion blows away the outer layers. If the remaining core mass is below a certain threshold, it will stabilize as an extremely dense, compact object known as a neutron star.
The outer layers, violently ejected into space, will continue to expand outward for millennia. This expanding shell of gas and dust is known as a supernova remnant. These remnants are cosmically significant because they enrich the interstellar medium with heavy elements like iron, created during the explosion. If the remaining core mass is extremely high, the gravitational collapse will be so complete that it forms a stellar-mass black hole.