Thursday, 17 January, 2019

Stars Like The Sun Become Giant Crystal Ball When They Die

Earth's Sun Will Turn into a Pure Crystal Ball Before It Dies Before a white dwarf dies it turns into a crystal ball research suggests. Credit University of Warwick Mark Garlick
Theresa Hayes | 11 January, 2019, 21:16

The astronomers said that their observation provides the first direct evidence that white dwarf stars would solidify into crystal.

"We could visualise crystallised white dwarfs as giant balls of solid oxygen and carbon, with only tiny amounts of other residual elements", Pier Emmanuel Tremblay, assistant professor of astronomy at Warwick who led the study, told The Telegraph.

About 50 years ago, scientists predicted that the gaseous cores of white dwarfs should crystallise and become solid with the cooling of the hot gases inside them. They are incredibly useful to astronomers as their predictable lifecycle allows them to be used as cosmic clocks to estimate the age of groups of neighboring stars to a high degree of accuracy.

The heat released during this crystallisation process, which lasts several billion years, seemingly slows down the evolution of the white dwarfs: the dead stars stop dimming and, as a result, appear up to two billion years younger than they actually are.

Tremblay said their studies suggested that white dwarfs stop their cooling by turning from liquid to almost 99 per cent solid over about 1.5 billion years.

They found a "pile-up", or excess, in the numbers of stars at specific sets of luminosities and colours but not corresponding with any single mass or age.

White dwarfs are the remains of medium-sized stars similar to our Sun. More massive stars cool down more rapidly and will reach the temperature at which crystallization happens in about one billion years.

For the new study, the researchers looked at Gaia measurements of about 15,000 white dwarfs, all of which lie within 330 light-years of the sun.

As temperatures cool, the white dwarf's liquid begins to solidify. As it cools over time, the core transforms into an solid crystal.

"We saw a pile-up of white dwarfs of certain colors and luminosities that were otherwise not linked together in terms of their evolution", said Tremblay. The process really kicks into gear when a white-dwarf interior cools down to about 18 million degrees Fahrenheit (10 million degrees Celsius), the researchers said. Before Gaia we had 100-200 white dwarfs with precise distances and luminosities - and now we have 200,000. They believe that the missing energy could be released in the form of gravitational energy, created as carbon is pushed to the surface of the star by falling oxygen that had crystallized earlier in the process.

Dr. Tremblay added that all white dwarfs will eventually crystallize, meaning that "billions of white dwarfs in our galaxy have already completed the process and are essentially crystal spheres in the sky. This experiment on ultra-dense matter is something that simply can not be performed in any laboratory on Earth".