About 8,150 light-years from Earth, a white dwarf star named Gaia22ayj has intrigued astronomers. Its unusual behavior, characterized by extreme pulsations, has led to a major discovery about the life cycle of stars.
This white dwarf, observed using the Zwicky Transient Facility (ZTF) at the Palomar Observatory in California, shows a 700% increase in brightness in just two minutes. Researchers initially thought it was a binary system of two white dwarfs, but further observations revealed a very different reality.
Illustration of a white dwarf. Top right: Gaia22ayj observed in X-rays and visible light. Bottom: images of Gaia22ayj captured by the Zwicky Transient Facility.
Credit: ZTF/Caltech Optical Observatories/A. Rodriguez/ wift/XRT/NASA PanSTARRS/Univ. of Hawaii.
Gaia22ayj is actually a white dwarf siphoning plasma from its companion star, a rare and fleeting phenomenon in stellar evolution. This process, often compared to a stellar vampire, allows the white dwarf to gain mass and energy while slowing its rotation.
Data collected by the W. M. Keck Observatory confirmed the presence of an intense magnetic field around Gaia22ayj, a characteristic feature of white dwarf pulsars. However, Gaia22ayj's behavior differs from that of traditional pulsars, marking an intermediate stage in their formation.
This 'adolescent' phase of the white dwarf, where it begins to accrete matter while slowing its rotation, is extremely brief on a cosmic scale. Lasting about 40 million years, it represents less than 0.4% of the total lifetime of a star like the Sun.
The team's research, published in the
Publications of the Astronomical Society of the Pacific, opens a new window into understanding magnetic white dwarfs and their evolution. This discovery highlights the importance of continuous observations to capture these transient phenomena in the Universe.
What is a white dwarf?
A white dwarf is the dense remnant of a star with a mass similar to or slightly greater than that of the Sun, after it has exhausted its nuclear fuel. Unlike more massive stars that end in supernovae, white dwarfs slowly cool over billions of years.
The white dwarf formation process involves the expulsion of the star's outer layers, leaving behind a hot, dense core. This core, primarily composed of carbon and oxygen, is supported by electron degeneracy pressure, a quantum phenomenon preventing further collapse.
White dwarfs play a key role in the evolution of binary star systems, where they can accrete matter from a companion star. This process can lead to thermonuclear explosions, such as novae, or collapse into a neutron star under extreme conditions.
How do binary stars influence stellar evolution?
Binary star systems, where two stars orbit a common center of mass, provide natural laboratories for studying stellar evolution. In these systems, interactions between stars can significantly alter their fate.
When a star becomes a white dwarf, its proximity to a companion star can lead to mass transfer. This phenomenon, observed in Gaia22ayj, can reignite the white dwarf's activity, allowing it to gain mass and energy.
In some cases, matter accretion can exceed the Chandrasekhar limit, triggering a Type Ia supernova. These explosions help us understand the expansion of the Universe, as they serve as 'standard candles' for measuring cosmic distances.