When a nova stops being a nova? When a white dwarf and a brown dwarf collide
When a nova stops being a nova? When a white dwarf and a brown dwarf collide
When a nova stops being a nova? When a white dwarf and a brown dwarf collide
Thanks to the Atacama Large Millimeter / submillimeter Array (ALMA), an international team of astronomers found indications that there was a short-term collision between a white dwarf (the ancient remains of a star similar to the Sun) and a brown dwarf (a star that it never became a star due to the lack of enough mass to maintain a nuclear fusion). This collision, observed from the Earth in 1670 and baptized as Nova sub Capite Cygni ('new star under the head of the swan'), is today known as CK Vulpeculae.
In July 1670, astronomers observed from Earth the appearance of a "new star," or nova, in the constellation Cygnus. What they witnessed was the appearance of a bright spot that then vanished, reappeared and then disappeared altogether in a dark part of the sky. The astronomers who recently studied the remains of this cosmic event at first thought that it was the fusion of two stars of main sequence, that is, stars that follow an evolution similar to that of the Sun.
However, the new observations made with ALMA point to a more intriguing explanation. After studying the debris from this explosion, which produced two rings of dust and gas reminiscent of an hourglass, with a compact central object, the researchers concluded that this structure is the result of the merger of a brown dwarf (called "failed star"). "Because it lacks the mass necessary to maintain a nuclear fusion) with a white dwarf.
"Now it seems that what we observed a few centuries ago was not what we would today consider a nova properly so. It was, rather, the fusion of two stellar objects: a white dwarf and a brown dwarf. The collision of these two stars threw into space a cocktail of unusual molecules and isotopes that gave us new information about the nature of this phenomenon, "explains Sumner Starrfield, an astronomer at Arizona State University and co-author of an article published in the Monthly Notices magazine. of the Royal Astronomical Society.
They find evidence of a short-term collision between a white dwarf and a brown dwarf. (Photo: ALMA Observatory)
According to the researchers, the white dwarf may have been about ten times more massive than the brown dwarf, despite being much smaller. While the white dwarf spiraled inward, the gravitational forces exerted by the white dwarf could have disintegrated it. "This is the first time that this type of phenomenon is reliably identified," says Starrfield.
Since most of the star systems of the Milky Way are binary, collisions between stars are not so rare, astronomers say. The ALMA observations revealed new details about the 1670 event. By studying light from two more distant stars that traverses the remains of dust left by the fusion, the researchers detected the characteristic footprint of lithium, an element that is easily destroyed within of a main sequence star, but not within a brown dwarf.
"The presence of lithium, together with unusual isotopic ratios of the elements carbon, nitrogen and oxygen, suggest a flow of material from a brown dwarf star to the surface of a white dwarf. Thermonuclear 'burning' and the eruption of this material gave rise to the hourglass we see today, "explains Stewart Eyres, vice dean of the Faculty of Computing, Engineering and Science of the University of South Wales and lead author of the article.
To the surprise of the researchers, the hourglass also has abundant amounts of organic molecules such as formaldehyde (H2CO) and formamide (NH2CHO), a derivative of formic acid. Since these molecules would not survive a nuclear fusion, they are most likely to have formed in the debris of the explosion, which supports the conclusion that a brown dwarf would have disintegrated after encountering a white dwarf. (Source: ALMA OBSERVATORIO / DICYT)
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