University of Warwick | 2019 Jan 09
Observations have revealed that dead remnants of stars like our Sun, called white dwarfs, have a core of solid oxygen and carbon due to a phase transition during their lifecycle similar to water turning into ice but at much higher temperatures. This could make them potentially billions of years older than previously thought. ...
White dwarf stars are some of the oldest stellar objects in the universe. 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. They are the remaining cores of red giants after these huge stars have died and shed their outer layers and are constantly cooling as they release their stored up heat over the course of billions of years.
The astronomers selected 15,000 white dwarf candidates within around 300 light years of Earth from observations made by the Gaia satellite and analysed data on the stars’ luminosities and colours.
They identified a pile-up, an excess in the number of stars at specific colours and luminosities that do not correspond to any single mass or age. When compared to evolutionary models of stars, the pile-up strongly coincides to the phase in their development in which latent heat is predicted to be released in large amounts, resulting in a slowing down of their cooling process. It is estimated that in some cases these stars have slowed down their aging by as much as 2 billion years, or 15 percent of the age of our galaxy. ...
Gaia Reveals How Sun-like Stars Turn Solid after Their Demise
ESA | Space Science | Science & Technology | Gaia | 2019 Jan 09
Core Crystallization and Pile-up in the Cooling Sequence of Evolving White Dwarfs ~ Pier-Emmanuel Tremblay et al
- Nature 565(7738):202 (10 Jan 2019) DOI: 10.1038/s41586-018-0791-x