The Sun's future version holds the key to unknown physics and understanding dark matter: here's what we know.

Scientists have examined 26,000 white dwarfs, often referred to as dead stars, and have validated a long-standing theory that the hotter they are, the more their outer layers are inflated. While this discovery may seem trivial, understanding the structure of white dwarfs could be crucial for grasping dark matter and potentially uncovering new physics. The study is published in The Astrophysical Journal, reports Space.

White Dwarf – The Future Version of the Sun

White dwarfs are the remnants of dead stars, like the Sun, which have exhausted their hydrogen fuel necessary for sustaining life. In about 5 billion years, the Sun will also become a white dwarf. These dead stars are roughly the size of Earth but have a mass comparable to that of the Sun. This means they are extremely dense objects.

White dwarfs form with very high temperatures, reaching up to 100,000 degrees Celsius. It’s no surprise that these dead stars are so hot, as they represent the core of a deceased star and have undergone gravitational collapse after they stopped producing energy. Over time, white dwarfs gradually cool down.

Proof of the Theory

The minimum size of a white dwarf is governed by what is known as electron degeneracy pressure. Inside a white dwarf, electrons can be compressed together only until quantum mechanical effects prevent them from condensing further.

The maximum size of a white dwarf depends on its mass; that is, the more massive the dead star, the larger it is, as well as its temperature. The theory predicts that the hotter the white dwarf, the more inflated its outer layers should be. Now, astronomers have for the first time proven that this theory holds true.

Astronomers studied the gravitational redshift of light emitted from 26,000 white dwarfs in our Milky Way galaxy. Gravitational redshift is an effect that occurs because the mass of a white dwarf distorts the space around it, according to Einstein's general theory of relativity. This results in the wavelength of the white dwarf's light being stretched.

Smaller white dwarfs exhibit strong gravitational redshift because their gravity is stronger than that of larger dead stars. Astronomers found that the observed gravitational redshifts indeed correspond to the theory. This means that hotter white dwarfs will be more inflated, even if they have the same mass as cooler white dwarfs.

New Physics and Dark Matter

The findings have much greater implications for understanding the entire universe. According to the study's authors, white dwarfs are among the most well-studied stars with extreme physics, making them suitable for testing classical physics theories or discovering new fundamental physics. They may also help in understanding the nature of dark matter.

For decades, scientists have believed that dark matter consists of a particle called WIMP, or weakly interacting massive particle. However, WIMPs have yet to be detected, leading researchers to consider that dark matter might be another hypothetical particle called axion.

It is thought that in a galaxy filled with a halo of dark matter, quantum characteristics will lead to such a distribution of axions in this halo that it will have peaks and troughs, each extending thousands of light-years.

If two or more white dwarfs are located in one of the axion peaks, dark matter could alter the internal structure of these dead stars. This could lead to unexpected changes in temperature, mass, or gravitational redshift of the white dwarf. Such changes could be detectable, indicating the influence of dark matter and its composition, scientists believe.