An international team of astronomers has discovered very hot stars with surface temperatures in excess of 100,000 degrees Celsius. The work was published in Monthly Notices of the Royal Astronomical Society.
The article is based on data collected with the South African Large Telescope (SALT), the largest optical telescope in the southern hemisphere, with a 10 by 11 meter mirror. The study describes how the study of helium-rich subdwarfs led to the discovery of several very hot white dwarfs, the hottest of which has a surface temperature of 180,000 degrees Celsius. For comparison, the temperature on the surface of the Sun does not exceed 5800 degrees Celsius.
One of the identified stars is the central star of a recently discovered planetary nebula that is one light-year across. The other two are pulsating or variable stars.
All these stars are at the final stage of their life cycle and are approaching the end of their existence. Due to the extremely high temperatures, each of these newly discovered stars is over a hundred times brighter than the Sun, which is considered unusual for white dwarfs.
White dwarfs are about the same size as the planet Earth, but a million times more massive, and their masses are closer to that of the Sun. These are the densest stars found in the Universe, consisting of ordinary matter.
Simon Jeffrey, an astronomer at the Armagh Observatory and Planetarium who led the study, says: “Stars with an effective temperature of 100,000 degrees Celsius and above are incredibly rare. It was a real surprise to find so many of these stars in our survey. These discoveries will help improve our understanding of the late stages of stellar evolution and demonstrate that SALT is a fantastic telescope for our project.” He adds: “It was exciting to work with an experienced team that together made it possible to discover stars, analyze their atmospheres, and detect pulsations and nebulae in a very short amount of time.”
Klaus Werner, professor at the University of Tübingen, co-author of the paper, comments: “I am proud to have helped carry out this groundbreaking study. The discovery of eight very hot white dwarfs and other stars, as well as a new planetary nebula, is of great importance, and we hope that these discoveries will help shed new light on the formation of our galaxy.”
Dr. Itumeleng Monageng from the Department of Astronomy at the University of Cape Town and the South African Astronomical Observatory said: “I am honored to play a part in this incredible discovery, as well as to study very hot stars and their evolution.