White dwarfs are giving up more secrets, and it’s been discovered that the hotter they are, the more their outer layers expand. While the discovery may sound insignificant, understanding the structure of white dwarfs could ultimately hold the key to discovering what mysterious dark matter is made of.
white dwarf It is the core relic sun– Like a star that has used up all its available nuclear fuel. In five billion years, our sun will become a white dwarf star red giant star stage. The sun’s outer layers will be flung into deep space, exposing its pearly core. White dwarfs can compress a star’s mass into Earthmeaning they are extremely dense—a tablespoon of white dwarf material can weigh several tons. Their internal structure pushes physics to its extreme, but theory can predict white dwarfs based on their mass and temperature.
White dwarfs are born at very high temperatures, usually around 180,000 degrees Fahrenheit (100,000 degrees Celsius), although some white dwarfs have been found to be even hotter. It’s not surprising that they are so hot – after all, they are the quenching cores of stars, which undergo gravitational contraction when they stop producing energy. Then, over time, they begin a slow cooling process.
The minimum size of a white dwarf is controlled by electron degeneracy pressure. Inside the white dwarf, electronic They can only be crushed together before quantum mechanical effects prevent them from compressing further. (neutron starwith greater mass, can overcome electron degeneracy pressure and force electrons and protons to merge to form neutrons, so neutron stars are controlled by neutron degeneracy pressure.
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This therefore determines the minimum size of white dwarfs, while their maximum size depends on their mass (the more massive they are, the larger they are) and their temperature. Theory predicts that the hotter a white dwarf, the more its outer layers should expand.
Now, for the first time, astronomers have proven that this theory is correct. Researchers led by Nadia Zakamska of Johns Hopkins University measured the gravitational redshift of light from more than 26,000 white dwarfs scattered around us. Milky Waybased on observations from the Sloan Digital Sky Survey and the European Space Agency Gaia spaceship.gravity red shift It is the effect caused by the mass of the white dwarf distorting the space around it. According to albert einsteinof general relativitywhich causes the wavelength of the white dwarf’s light to be stretched.
Dense white dwarfs have strong gravitational redshifts because their gravity is stronger than that of larger white dwarfs. Zakamska’s team found that the observed gravitational redshift was indeed consistent with the prediction that hotter white dwarfs would expand more, even if they have the same mass as cooler white dwarfs.
So, it’s no surprise – but these findings may be more important for what they ultimately reveal to us. This is because astronomers can use our understanding of white dwarfs as a baseline to look for weirder phenomena, such as dark matter.
“White dwarfs are among the most characteristic stars that we can use to test these fundamental theories of ordinary physics, and hopefully we’ll find some weird stuff that points to new fundamental physics.” Johns Hopkins University in statement. “If you want to look for dark matter, Quantum gravity or other exotic stuff, you’ll understand normal physics better. Otherwise, what appears to be novel might just be a new manifestation of an effect we already know.
For decades, many astronomers have been betting that dark matter is a hypothetical particle called a WIMP: a weakly interacting, massive particle. However, failure to detect WIMPS has led to the rise of another candidate: axion. Quantum Chromodynamics predicts the existence of axions, another hypothetical particle that is our best quantum theory powerful force binding Quark formed together protonneutrons and ultimately the nucleus.
in a galaxy WIMPs permeate the halo of WIMP dark matter, which accumulates near the center of a galaxy and thins smoothly toward the edges of the galaxy. Not so with axions. Quantum interference patterns will cause peaks and troughs in the distribution of axions in the galaxy’s dark matter halo, with each axion extending thousands of light-years.
Related: What is dark matter?
So what does this have to do with white dwarfs? If two (or more) white dwarfs are located in one of the axion peaks, the additional dark matter could alter their internal structure in subtle ways that would become apparent as unexpected changes in temperature, mass, or gravitational redshift. We can only discern these changes because of how well we understand white dwarfs.
“That’s why understanding simple astrophysical objects like white dwarfs is so important, because they give hope of discovering what dark matter might be,” Crumpler said.
We’re not there yet, though—there’s still more to learn about white dwarfs.
“The next frontier could be detecting extremely subtle differences in the chemical composition of the cores of white dwarfs of different qualities,” Zakamska said.
Therefore, understanding white dwarfs not only provides a window into the future of the sun when it becomes a white dwarf in about 5 billion years. They may also serve as gateways into the fields of general relativity, quantum physics and dark matter.
this new discovery Published December 18 in the Astrophysical Journal.