An international team of astronomers, led by Simon Jeffery at the Armagh Observatory and Planetarium, has made a groundbreaking discovery of eight of the hottest stars in the universe, all with surface temperatures exceeding 100,000 degrees Celsius. The findings, published in the Monthly Notices of the Royal Astronomical Society, were based on data gathered using the Southern African Large Telescope (SALT), the largest single optical telescope in the southern hemisphere.
The team conducted a survey of helium-rich subdwarf stars, which led to the identification of several white dwarf and pre-white dwarf stars. The hottest of these stars has a surface temperature of 180,000 degrees Celsius, making it more than one hundred times brighter than the sun. For comparison, the sun's surface temperature is a relatively cool 5,800 degrees Celsius.
One of the newly discovered stars is the central star of a planetary nebula, a cloud of gas and dust created when a star sheds its outer layers at the end of its life. This particular nebula is one light year in diameter. Two of the other stars are classified as pulsating, or "variable," stars. All of these stars are at an advanced stage in their life cycle and are approaching the end of their lives as white dwarfs.
White dwarfs are extremely dense, with masses similar to that of the sun, but they are only about the size of Earth. Pre-white dwarfs are slightly larger and will eventually shrink to become white dwarfs in a few thousand years. These hot, bright stars are unusual for white dwarfs, which are typically much dimmer.
The discoveries made by the team will help to increase our understanding of the late stages of stellar evolution, and demonstrate the capabilities of SALT as a telescope. Professor Klaus Werner of the University of Tuebingen, a co-author on the paper, said, "The discovery of eight very hot white dwarf and pre-white dwarf stars and a new planetary nebula is hugely significant, and we hope that these findings will help to shed new light on the formation of our galaxy."
Dr. Itumeleng Monageng, of the Department of Astronomy at the University of Cape Town and the South African Astronomical Observatory, added, "It is fascinating to have discovered eight new extremely hot stars in the process, one of which is surrounded by a planetary nebula."
The research team included astronomers from the Armagh Observatory and Planetarium, the University of Tuebingen, the University of Cape Town, and the South African Astronomical Observatory. Their work highlights the importance of international collaboration in advancing our understanding of the universe.