Research on White Dwarfs: New Discoveries in Astronomy

The recent investigation into two white dwarfs, known informally as Gandalf and Moon-Sized, has uncovered their surprising ability to emit X-ray light without the presence of companion stars. This revelation contradicts earlier beliefs that X-ray emission could only occur when a white dwarf is paired with another star in a binary system. The findings were reported by Interesting Engineering.

Typically, stars similar to our Sun contract into extremely dense objects known as white dwarfs at the end of their life cycles. It was previously thought that these stars could only emit X-ray light when they 'accreted' gas from a neighboring star in a binary system. However, new observations of Gandalf and Moon-Sized suggest that this is not always the case.

The object Gandalf became the subject of detailed study in 2025. Initially, scientists believed it had a companion star, but this assumption was later disproven. This white dwarf rotates at an astonishing speed, completing one rotation every six minutes, a characteristic that does not align with any known binary system. The light emitted by Gandalf displays an unusual structure; instead of a complete disc of material surrounding it, only a semicircle is observed, indicating the presence of a very strong and uneven magnetic field.

Researchers speculate that Gandalf may have formed as a result of the merger of two stars and belongs to a rare type of object. However, even among such objects, it stands out due to its unique properties. The study of the second object, Moon-Sized, has provided further insights into this phenomenon. This object has a mass approximately equal to that of the Sun, but its size is equivalent to that of the Moon, making it extraordinarily dense. Like Gandalf, Moon-Sized also lacks a companion star, rotates rapidly, and emits X-ray light.

These two objects differ significantly in age. Gandalf is considered relatively 'young' at around 60 to 70 million years old and is still surrounded by material. In contrast, Moon-Sized is much older, approximately 500 million years old, and has almost no surrounding material, with its X-ray emission being about 100 times weaker than that of Gandalf. This may indicate that such objects evolve over time and gradually lose their energy source.

Scientists have proposed several hypotheses regarding the origin of the X-ray emission in these white dwarfs. One theory suggests that a highly magnetized, rapidly rotating white dwarf could 'strip' material from its own surface. Another theory pertains to remnants formed from the collision of stars, which slowly fall back onto the object over millions of years. However, none of these explanations are currently fully satisfactory.

As only two such objects are known, researchers plan to search for more examples to better understand this phenomenon. Studying white dwarfs capable of emitting X-ray light without companions could open new horizons in astronomy and help scientists comprehend the complex processes occurring in the final stages of stellar life cycles.