Researchers at the Federal University of Rio Grande do Sul in Brazil have announced the discovery of a white dwarf with an atmosphere comprised of 99.9 percent oxygen. The newly found star, which is named SDSSJ124043.01+671034.68 and nicknamed "Dox," is unique; no other known star has an atmosphere composed of nearly pure oxygen. The star's singular properties are raising questions for scientists, namely how did Dox come to be?
Dox is located 1,200 light-years away from Earth, in the constellation Draco. It's a white dwarf, a star at the end of its life. It is only slightly larger than Earth, but it boasts an incredible mass that is 60 percent of our sun's mass. Dox’s 99.9 percent oxygen atmosphere is even impressive by terrestrial standards; Earth's atmosphere is just 21 percent oxygen.
How was Dox discovered?
The star was first noticed by Gustavo Ourique, an undergraduate student of astronomer S.O. Kepler. Ourique found Dox while working his way through 300,000 observations from the Sloan Digital Sky Survey. Ourique had already spent a year and a half sifting through the data in the form of spectral graphs before he noticed something different about Dox's graph. He presented Kepler with the findings. Kepler and his team investigated Dox and made groundbreaking discoveries about the strange celestial body. The findings were published in the journal Science.
The discovery of this one-of-a-kind star is both exciting and puzzling for scientists as they attempt to discern how all other elements were stripped from Dox's atmosphere, save for oxygen. Until its discovery, a star like Dox was thought to be unable to exist as it defies the reining theories on star composition. According to Popular Mechanics, "By all calculations, Dox would have had to be roughly double its weight to have even forged oxygen atoms in its earlier life."
How could Dox have formed?
Kepler posits theories on how Dox came to be exclusively oxygen rich. He suggests that Dox was once a part of a binary star system. Because binary star systems have not been studied as much as single stars, scientists have not had access to information about stars like Dox. He explains, "I think the main problem is that we [astronomers] have dedicated the last 50 years to calculate the evolution of stars that are not interacting with each other, when at least 30 percent of stars interact with a binary companion."
Kepler theorizes that Dox's partner star became a red giant. As the red giant grew, it might have enveloped Dox. Dox then absorbed the red giant's gasses until it exploded. Kepler explains, "That explosion threw all types of matter out. That's when [Dox] might have lost all its hydrogen and helium. This type of situation is known to have happened with other stars, although it's never been seen to leave just oxygen."
There is a chance that, as scientists investigate the relationships involved in binary star systems, other stars similar to Dox might be discovered. As scientists continue to delve into Dox's unique properties, they hope to learn more about the nature and evolution of stars. However, out of the known 32,000 white dwarfs, Dox certainly stands out as a mystery — for now.