If the thought of cosmic crystal balls seems to have emerged from an overly active imagination, this is not just an idea drawn from the depths of science fiction.
ESA's Gaia satellite has observed dead stars that are the first direct evidence of an extraordinary phenomenon predicted 50 years ago. Astronomers at the University of Warwick used Gaia's observations of hundreds of thousands of stars to prove that white dwarfs, or the corpses of stars remaining after the giant red phase, crystallize. This discovery also proves that some ancient stars are billions of years older than previously thought.
The white dwarf stars are already some of the things of the oldest stars in the universe. Their life cycles are predictable enough for astronomers to use them as an ominously accurate base to estimate the ages of the surrounding stars. The observations Gaia returned revealed an extraordinarily high number of stars whose colors and luminosities were not indicative of a single mass or age, also known as plunder.
The development phase of these stars mirrors the stage of stellar evolution when its cooling process slows down because an immense amount of latent heat escapes. So what does this have to do with crystal balls in space?
"All white dwarfs will crystallize at some point in their evolution, although more massive white dwarfs go through the process earlier," said team leader Dr. Pier-Emmanuel Tremblay, whose study was recently published in Nature. "That means that billions of white dwarfs in our galaxy have completed the process and are essentially crystal balls in the sky. The Sun itself will become a white crystal dwarf in about 10 billion years. "
It was the luminosities and colors of specific stars that Dr. Tremblay's team called in their crystallization, which is really just a word that sounds fantastic for the transition from liquid to solid (think water on ice). Extreme pressure in the white dwarf nuclei pushes the densely packed atoms close enough to unlink their electrons. These unbound electrons leave behind a conductive electron gas governed by quantum physics and a liquid form of positively charged nuclei.
Like any other fluid that solidifies at sufficiently low temperatures, the liquefied nuclei will also do so when the temps in the core cool sufficiently and release enough to crystallize. It's just that the temperature required in this case is about 10 million degrees. If you're wondering, yes, it will happen to our sun at some point. You would have to wait for another 10 billion years to actually see it.
"Not only do we have evidence of heat release after solidification, but considerably more energy release is needed to explain the observations," added Tremblay. "We believe this is due to the fact that oxygen first crystallizes and then sinks into the core, a process similar to sedimentation in the bed of a river on Earth. This will push the carbon upwards and this separation will release gravitational energy. "
There are billions of white dwarfs out there who have gone through this process, astral remnants haunting our galaxy as bizarre crystal ghosts. Think about the next time you look at the night sky.
(via University of Warwick)