For the first time, Brazilian researchers have discovered a star with an almost purely oxygen atmosphere.
The newly discovered star, named SDSSJ124043.01+671034.68 and nicknamed “Dox,” is the first-ever seen star with 99% of its atmosphere composed of pure oxygen. The star with an oxygen atmosphere is categorized as what is called a “white dwarf”.
This unique discovery was made amidst surprise of the scientists that had long worked on the project and was first published in the journal Science. The team was composed of Souza Oliveira Kepler and Gustavo Ourique from the Federal University of Rio Grande do Sul and Detlev Koester from Universität Kiel.
The Brazilian undergraduate student of astronomy Gustavo Ourique was the first to notice this weird phenomenon. After more than 1.5 years of work on the spectral data of different stars gathered from about 300,000 observations made by the New Mexico observatory, he discovered anomalies in the light spectrum of Dox.
He subsequently shared his discovery with the astronomer S.O. Kepler with whom he worked, and after a detailed review and many other tests, it became clear that the light spectrum of the star belonged to a white dwarf with an oxygen atmosphere.
White dwarfs have been known since half a century ago. During the course of the evolution of a typical star with a mass less than 8-10 times of the sun, when the internal nuclear fuel of the star is exhausted, the core of the star is depleted from hydrogen. At this stage, nuclear reactions in the core of the star cease while the shell of the star composed of helium continues to burn.
After a lengthy process of rapid expansion of the shell and a subsequent phase of contraction due to the star’s gravity, a compressed star with low size and low internal temperature is formed. At this state, the temperature is not hot enough to ignite the remaining fuel which is mostly carbon, helium, oxygen, etc. and the white dwarf is formed.
It is a highly compressed star with an extremely high density of the order of a few tons per cubic centimeter, meaning that a teaspoon of its material weighs several tons! It is estimated that all stars except the 3% higher mass stars (stars with their mass bigger than 10 times of the sun) end up becoming a white dwarf.
For SDSSJ124043.01+671034.68, S.O. Kepler found out that the outer layer of light elements was virtually stripped away, and there was only a layer of almost pure oxygen in its atmosphere.
This feature of Dox is unique in that until now, all of the observed white dwarfs had been measured to have an atmosphere composed of light elements like hydrogen and helium besides oxygen. As Kepler has explained, the atmosphere of a typical white dwarf is never purely one element.
As a result, this discovery has led to many debates and speculations as to the cause of this phenomenon for a typical white dwarf and there are already some suggestions. One theory suggests that Dox might have once been a member of a binary star configuration and the partner star might have stripped off the lighter elements of its atmosphere leaving only pure oxygen.
Kepler has also suggested another theory assuming that this might have been due to the elimination of lighter elements on the surface of the star by an outwards flaring of a massive pulse of burning carbons at the core of Dox. According to him, such a flare might have virtually eliminated lighter elements in the atmosphere of Dox, leaving only oxygen behind.
The discovery of a star with an oxygen atmosphere is a hint to the researchers that this may not be the only instance and there might be much more that have not yet been discovered.
Until now, binary systems had not been the focus of research on this subject because a star like Dox was never thought to exist; current theories about the composition of white dwarfs rules out the existence of any such stars.
The discovery of Dox will boost research on the subject and will provide scientists with more insight into the formation of white dwarfs and their composition.
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