The exposed core of a massive star has been observed for the first time, a find that was described as purely “chance” by the team that found it by chance.
Although the cores of stars are where the vast majority of stellar energy is generated by the nuclear fusion of hydrogen into helium, they are usually obscured by the bright outer material that envelops them. Stellar cores are exposed only in rare and extremely short-lived circumstances.
The isolated observation of such a core could help astrophysicists to better understand the nuclear processes that occur in the hearts of stars and the evolution of stellar objects.
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The exposed stellar core in question, a previously observed bright star called Gamma Columbae (γ Columbae). has a mass between 4 and 5 times that of the sun. The team that discovered its exposed nature believe it was once part of a massive star with up to 12 times the mass of the sun.
The nature of γ Columbae was discovered by astronomers including lead research author Andreas Irrgang of Dr. Karl Remeis-Observatory and the ECAP working group at Friedrich-Alexander-University Erlangen-Nuremberg, Bamberg, Germany, so that they observed a group of stars and found that one of them was unusual.
By further studying the light spectrum emitted by this unusual star, astronomers discovered increased abundances of helium and nitrogen. As these nuclear ashes are usually obscured by the outer stellar plasma, this indicates that the outer shell of γ Columbae is missing.
“That’s probably the most interesting factor of all, in terms of scientific output, because all the nuclei are hidden in the other stars and here we have one that’s bare, bare, and will leave a very particular signal in its pulsations. .,” said Norbert Przybilla, director of the Institute for Astrophysics and Particle Physics at the University of Innsbruck and co-author of the study, in a statement. (opens in a new tab) to the motherboard. “We have to follow that.”
This led them to wonder what processes might have stripped γ Columbae of its outer layers by greatly reducing its radius and leaving it as a glowing core.
The team believe the previously massive star may have recently finished fusing hydrogen with helium in its core, with previous research also indicating this to be the case although it has not alludes to the nature of the exposed nucleus of γ Columbae.
The end of hydrogen fusion causes the outer layers of a star to ‘puff up’. If a binary star companion is pulled into this expanding envelope of stellar material, it could cause that material to be ejected.
The team suggests two alternative potential mechanisms that could leave a core exposed. The stripping of outer matter by a companion binary star feeder, or the evacuation of outer matter by stellar winds to expose cores, the latter usually seen in the later stages of incredibly massive stars with mass ranging from between 20 and 25 times that of the sun.
Further study of γ Columbae will be needed to assess the true mechanism behind the exposed nature of the core, as the star does not exactly match the parameters that match these suggested mechanisms. “Having a bare stellar core of such mass is unique so far,” Przybilla told Motherboard, adding that the star so far appears to be a “quirk.”
One thing that astronomers are pretty sure of is that this stripped core existence is a stage in the life of γ Columbae that will last around 10,000 years. Although this is a long period of time in human terms, it is nothing more than the proverbial blink of an eye in cosmic terms.
This further indicates that the discovery of this exposed stellar core is indeed highly fortuitous.
As for the future of this exposed nucleus, the team said that γ Columbae currently uses helium to power nuclear fusion by creating heavier elements, which it will also eventually fuse together. When γ Columbae eventually runs out of fuel for nuclear fusion, the energy preventing the core from collapsing under the internal pressure of its own gravity will also cease.
This will lead to a gravitational collapse triggering a stripped-core supernova and turning γ Columbae into a neutron star – a stellar remnant with the mass of the sun condensed into a diameter around that of the average city on Earth.
Astronomers suggest a better understanding of γ Columbae may come from studying it using asteroseismology, a field of science that studies the oscillations of stars and how sound waves pass through the plasma that contains them to study the Stellar interiors.
The team’s research is published in the journal natural astronomy (opens in a new tab).
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