The question of whether a “black sun” is possible moves beyond science fiction and into the long-term predictions of stellar evolution. Since a sun is defined as a star that actively radiates light and heat, a “black sun” represents a star that has fundamentally ceased this process. Understanding this possibility requires examining the physics that keeps our Sun shining today, and the inevitable processes that will one day extinguish its light. The ultimate fate of our star, a cold, dark remnant, is the scientifically probable answer to this query.
The Mechanics of Stellar Radiance
The Sun’s brilliance is the result of a continuous, powerful process occurring deep within its core. Here, extreme temperature, exceeding 15 million degrees Celsius, and immense pressure allow for nuclear fusion. The primary reaction is the proton-proton chain, where four hydrogen nuclei combine to form a single helium nucleus.
This transformation is governed by mass-energy equivalence, where a small amount of mass is converted into energy, primarily in the form of photons and neutrinos. The energy released generates a powerful outward pressure that precisely counteracts the crushing inward force of the Sun’s gravity. This dynamic balance, known as hydrostatic equilibrium, is the fundamental mechanism that keeps the Sun stable, ensuring its consistent luminosity and size for billions of years.
The Sun’s Inevitable Transformation into a Black Dwarf
The scientifically accepted path for the Sun to become a non-radiating star involves a multi-stage process culminating in the formation of a black dwarf. The Sun is currently fusing hydrogen in its core, a phase that will last for about 5 billion more years. Once the core hydrogen is exhausted, the Sun will expand dramatically into a red giant, burning helium in a shell around its core.
After this red giant phase, the Sun will shed its outer layers, creating a planetary nebula and leaving behind a dense, hot core called a white dwarf. This white dwarf, composed mainly of carbon and oxygen, will be roughly the size of Earth but possess a density about 200,000 times greater than our planet. It is no longer generating energy through fusion, but it remains incredibly hot, shining brightly from residual thermal energy.
The “black sun” described in the query is the ultimate fate of this white dwarf, a theoretical object known as a black dwarf. A white dwarf becomes a black dwarf once it has cooled sufficiently to no longer emit any significant light or heat. The timescale for this cooling is extraordinarily long, estimated to take at least 10 trillion years. Because the universe itself is only about 13.8 billion years old, not enough time has passed for any star to have completed this entire evolutionary cycle, meaning no true black dwarfs exist yet.
Why Solar Mass Precludes Black Hole Formation
While the term “black” might suggest the formation of a black hole, the Sun lacks the necessary mass to meet this fate. The final destiny of a star’s core is determined by a critical mass threshold known as the Chandrasekhar Limit, which is approximately 1.44 times the mass of our Sun. This limit defines the maximum mass a white dwarf can have and still be supported against gravitational collapse by electron degeneracy pressure.
Electron degeneracy pressure is a quantum mechanical effect where electrons resist being forced into the same space, acting as an outward force to support the stellar remnant against gravity. The Sun, with an initial mass of one solar mass, will lose a significant portion of its material during the red giant and planetary nebula phases, leaving a white dwarf core well below the 1.44 solar mass limit.
Only stars with an initial mass of around eight to ten solar masses or more can create a core massive enough to exceed the Chandrasekhar Limit. When such a core collapses, the pressure fails, leading to a supernova and the formation of a neutron star or, if the core mass is greater, a black hole. The Sun is simply too lightweight to collapse into a singularity.
Planetary Effects of a Lightless Star
If the Sun were to suddenly cease radiating light and heat, the environmental consequences for Earth would be swift and catastrophic. The planet’s surface temperature would begin to drop immediately without the continuous infusion of solar energy. Within just one week, the average global temperature would fall to approximately 0 degrees Celsius, and within a year, it would plummet to nearly -100 degrees Celsius.
The cessation of sunlight would instantly halt photosynthesis, killing nearly all plant life and collapsing the food chain. The surface of the oceans would freeze over, and eventually, the atmosphere would freeze and collapse onto the planet’s surface. Although the Earth’s core would remain warm, providing some geothermal heat, this internal energy would be insufficient to warm the frozen surface environment. The Earth would then face the possibility of drifting out of the solar system entirely, becoming a rogue planet in the dark expanse of interstellar space.