Stars are the great elemental factories, constantly changing and altering the chemistry of the cosmos. A new study, accepted for publication in the journal Astronomy & Astrophysics, reveals the location and evolution of a carbon star – a stellar furnace producing the element all life on Earth is based on.
This year, astronomers noticed that a giant red star called LX Cygni has a dominantly carbon atmosphere. Although it’s well known that stars begin to burn heavier elements like carbon and oxygen when their original supply of hydrogen and helium has been used up, scientists think this particular star has been observed at the moment of its transition between the two major energy production phases.
Astronomers divide the fuel burning sequence in stars into lower and upper parts. The lower part involves the thermonuclear fusion of hydrogen to form helium. Stars that have sufficiently high core temperatures can transition over time into the upper sequence, which involves the use of carbon, nitrogen and oxygen as catalysts to produce more helium – this is known as the CNO cycle.
In most stars – including our own Sun – oxygen is far more commonplace than carbon. LX Cygni, however, seems to be producing more carbon. The researchers believe that this represents the small window of time wherein an oxygen-rich star has just transitioned into a carbon-rich star, providing them with a rare insight into the evolution of heavier stars.
The researchers looked at the star’s pulsation – expansions and contractions of its outer layers as it seeks to maintain a balance between its gravitational pressure and its internal generation of heat – and noticed that in just 30 years, a dramatic spike in the pulsation rate occurred. They hypothesized that this was due to the sudden production of a new major chemical, and their spectroscopy confirmed that this was indeed carbon.
Image credit: LX Cygni (center), taken by the 80cm telescope at the University of Vienna Observatory. Stefan Uttenthaler et al./University of Vienna.
The findings of this paper have more significant implications other than just cosmochemical ones – carbon forms the chemical basis for all life on Earth. It is vital for the existence of any organism, and almost all of it once originated in the hearts of stars like LX Cygni, released violently into the universe after one of two types of catastrophic explosions.
“Most of the carbon in our bodies comes from an earlier generation of stars such as LX Cygni. We are literally stardust,” lead author Stefan Uttenthaler, a postdoctoral researcher at the University of Vienna, said in a statement, echoing Carl Sagan’s famous declaration.
