Astronomers accidentally discover the exposed core of a ‘strange’ star
The exposed core of a massive star has been observed for the first time, a discovery described as purely “accidental” by the team that happened upon it.
Although the cores of stars While the vast majority of stellar energy is generated by the nuclear fusion of hydrogen into helium, they are mostly obscured by the bright outer material that surrounds them. Stellar nuclei are exposed only in rare and extremely short-lived conditions.
By observing such a core in isolation, astrophysicists can better understand the nuclear processes that take place in the hearts of stars and how stellar objects evolve.
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The exposed stellar core in question is a bright previously observed star named Gamma Columbae (γ Columbae). has a mass between 4 and 5 times that of the sun. The team that discovered its exposed nature thinks it was once part of a massive star with a whopping 12 times the mass of the sun.
The nature of γ Columbae was discovered by astronomers, including lead study author Andreas Irrgang of Dr. Karl Remeis-Observatory and the ECAP working group at Friedrich-Alexander University Erlangen-Nuremberg, Bamberg, Germany, while looking at a group of stars and found that one of them was unusual.
Upon further investigation of the light spectrum emitted by this unusual star, the astronomers discovered increased amounts of helium and nitrogen. Since these core axes are usually obscured by outer stellar plasma, this indicates that the outer envelope of Columbae is missing.
“This is probably the most interesting factor of all, in terms of scientific outcome, because all the nuclei are hidden in the other stars and here we have a naked one, a stripped one, and that will leave a very special signal in its pulsations,” he says. Norbert Przybilla, head of the Institute of Astro- and Particle Physics at the University of Innsbruck and co-author of the study, in a statement (opens in new tab) to motherboard. “We have to follow up on that.”
This led them to wonder what processes could have stripped γ Columbae of its outer layers, significantly reducing the radius and leaving it as a glowing core.
The team thinks the previously massive star was recently completed fuse hydrogen to helium in its core, with previous research also indicating this to be the case, despite not being suggested on the exposed core nature of γ Columbae.
The end of hydrogen fusion causes a star’s outer layers to “bulge out.” If a binary companion is drawn 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 an exposed core. The stripping of outer material by a feeding companion binary, or the evacuation of outer material by stellar winds to expose cores, the latter usually seen in the late stages of incredibly massive stars with masses between 20 and 25 times that of the sun.
Further study of 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 corresponding to these proposed mechanisms. “Having a naked stellar core of such mass is so far unique,” Przybilla told Motherboard, adding that the star appears to be a “strange” one so far.
One thing the astronomers are pretty sure about is that this stripped core existence is a phase in γ Columbae’s life that will last only about 10,000 years. While it is a long period in human terms, in cosmic terms it is no more than a proverbial blink of the eye.
This further indicates that the discovery of this exposed stellar core is indeed highly accidental.
As for the future of this exposed core, the team said γ Columbae is currently using helium to fuel nuclear fusion, creating heavier elements, which it will eventually fuse as well. When γ Columbae eventually runs out of fuel for nuclear fusion, the energy that prevents the nucleus from collapsing under the internal pressure of its own gravity will also cease.
This will lead to a gravitational collapse, creating a stripped-core supernova, turning γ Columbae into a neutron star — a stellar remnant with the sun’s mass condensed to a diameter around that of the average city on Earth.
The astronomers suggest that a better understanding of Columbae could come from studying it using asteroseismologya field of science that studies the oscillations of stars and how sound waves pass through the plasma that encompasses them to study the interiors of stars.
The team’s research is published in the journal Natural Astronomy (opens in new tab).
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