White dwarfs, including our sun, are remnants of stars that have exhausted their nuclear fuel. Over time, these stellar remnants cool, albeit extremely slowly, and it may take trillions of years before they reach a state known as a black dwarf.

Given the relatively young age of the universe, it is believed that black dwarfs have not yet appeared. However, a group of Australian astronomers recently discovered a white dwarf that is in a transitional stage caused by crystallization of the coolant.

The theoretical concept of black dwarfs includes an incredibly long span of time, perhaps hundreds of billions to trillions of years. However, Alexander Wenner of the University of South Queensland and colleagues recently found signs of such a transition occurring in a white dwarf relatively close to our planet.

How is a black dwarf formed?

When a star depletes its thermonuclear resources, its fate is determined by its mass. Medium-sized stars like the Sun eventually become white dwarfs. As they can no longer withstand the internal pressure required for fusion reactions, they shed their outer layers, causing the core to collapse. The resulting object is compact and incredibly dense, rich in relatively heavy elements such as carbon formed during the star’s previous life.

Although white dwarfs are faint compared to other stellar bodies, they gradually lose heat and continue to emit. This process continues until it becomes a black dwarf.

Crystallization takes place

When the white dwarf cools, its substance crystallizes. The previously freely moving carbon and oxygen atoms are arranged in a regular lattice, representing a lower energy state. During the crystallization process, heat is released, which further slows the star’s cooling rate. As a result, a white dwarf’s temperature does not match its true age. A few years ago, an extensive study of white dwarfs confirmed that many have much higher temperatures than expected.

The discovery of this temporary white dwarf provides valuable insight into the final stages of stellar evolution and processes in the formation of black dwarfs. Astronomers will continue to observe and study this intriguing object, hoping to learn more about the nature of these mysterious celestial formations.