Astronomers get rare glimpse into the exposed core of a star

At first glance, The star Gamma Columbae – a bright blue point of light about 870 light-years away in the southern hemisphere constellation Columba – looks like your average orb. But according to a team of astrophysicists, this is “anything else abnormal”.

A recent study of the surface of the star published in the journal natural astronomyhe says we see Gamma-Columbian in a very short and peculiar phase of an eventful stellar life, one that allows astronomers to look directly into the star’s exposed core.

what’s new – The mixture of chemical elements on the surface of Gamma Columbae looks like byproducts of nuclear reactions that should be buried deep within a massive star, not bubbles on its surface.

University of Geneva astrophysicist Georges Minette and his colleagues observed the light from the star, which is split into the individual wavelengths that compose it — just as light shines through a prism, and we see a rainbow. Each molecule absorbs and emits light at different wavelengths, so looking at the spectrum of light from an object can reveal what it’s made of. Astronomers had never studied the surface composition of the Columbian gamma in detail before, and what Meynet and his colleagues saw surprised them.

In particular, the surface of Gamma Columbae contains more helium and nitrogen — compared to hydrogen, carbon, and oxygen — than should be present on the surface of the star. These ratios look like a mixture of elements left over from nuclear reactions in the core of a massive star, with certain isotopes of carbon, nitrogen and oxygen playing a role in the reactions that fuse hydrogen atoms into helium.

Meynet and colleagues describe this material as “nuclear ash,” and usually only a little of it gets mixed up in the star’s outer layers, thanks to the rippling convective currents. But the spectrum of light from the surface of Gamma Columbae reveals a fingerprint too strong to be from just a handful of nuclear ash stirred up (what should be) the star’s hydrogen-rich outer layers.

“In order to observe this on the surface of a star, you need to remove a lot of mass above these deep layers, to reveal the core of the star,” says Meynet. inverse.

In other words, although Gamma Columbay looks like a typical bright main-sequence star (almost as normal), it is in fact “the bare pulsating core of a star that was once much larger,” Mina and colleagues write.

go into detail – At the moment, the gamma-columbian mass is four or five times the mass of our sun, so it’s still not exactly small. But in its younger years, Mynette and colleagues estimated that it may have weighed roughly twelve times the mass of our sun. It depends on the proportions of the chemical elements nitrogen, carbon and oxygen visible in the light from its surface, which “matches well” with the expected composition of the nuclei of twelve solar-mass stars, specifically the star that burns all the hydrogen in its core and is ready to transition to burning helium.

so what happened?

This illustration shows a star stealing a block from its companion, in a process similar to the one that left Gamma Columbae’s core exposed.Mark Garlick/Science Picture Library/Science Picture Library/Getty Images

The most appropriate explanation for the observations, according to Minette and colleagues, is that Gamma Columbia is, or was, part of a binary star system: two stars orbiting around a common center of gravity, such as Alpha Centauri A and B, or a twin. Tatooine’s Suns If you are a fan of science fiction. When Gamma Columbae finished its hydrogen burning phase, its outer layers had expanded outward (just as our Sun once does). This bloated envelope of gas and plasma fell prey to the gravitational pull of a smaller companion star, perhaps about three times the mass of our sun.

This process may have taken about 10,000 years, Meynet says, as the companion star pulled about 0.01% of our sun’s mass from Gamma Columbae each year, until all that was left was the star’s core, stripped out of the open.

why does it matter – It all adds up to make Gamma Columbia very unusual. What happened to Gamma-Columbian doesn’t happen very often, and the few examples that astronomers know of are all much smaller stars, the size of our Sun. But the Columbian gamma is unusually large and bright. It’s bright enough to be seen with the naked eye, in fact.

Astronomers also know of another strange group of stars called Wolf-Rayet stars. These stars were once much larger than Gamma-Columbian, about 60 times the mass of our Sun. They blasted their outer layers with strong star winds. But there is no indication that this type of stellar wind came from Gamma Columbian. Apparently, it’s in a category by itself.

And it’s a blink phenomenon you miss, at least from an astrological standpoint. For now, we see Gamma Columbae as the exposed core of a hydrogen-burning star, but it will continue to be like this for a few thousand years.

“The phase in which gamma columbae is observed is a short phase of its life,” says Meynet. “And that is why it is so unique because it is such a short timeline. It is developing rapidly now.”

First, the core will contract, dropping inward under its own weight, until the pressure in its center is enough to begin the process of fusing the helium atoms together. At that point, Gamma Columbae will become a brighter and hotter blue star, with another two million years to survive before dying in a stunning supernova.

For now, though, it gives astronomers a rare opportunity to look directly into the star’s core.

What’s Next – To learn more about what’s going on inside Gamma Columbae, Meynet and his colleagues point to a technique called asteroseismology: measuring small changes in light at a star’s surface and using that to infer things about its internal structure.

“Stellar venus is an unusual technique for exploring the physics of the interior of stars,” says Meynet.

The researchers also hope to learn more about the fate of Gamma’s hungry little companion Columbay. The light of the younger star may have just been lost in the bright glow of the Columbian gamma, but it’s also possible that the two stars merged at some point in their history.

Depending on how much the gamma-Columbian stretches, and how close the two stars are about their common center point, they would have gone through what astrophysicists call a “co-sphere phase.” This means that the two stars orbit each other closely, and the Columbian gamma swells outward so far, that the small companion star was actually inside the outer layers of the Columbian gamma – feeding on the larger star from the inside.

If that’s what happened, the mechanics of the entire system meant that the two stars were gradually getting closer to each other — so close that it’s possible that Gamma Columbae would have absorbed its junior partner in envelope-stealing. In the process, whatever material the smaller star didn’t “eat” would be expelled from the star system by gravity or a brief gust of stellar wind.

We told you this star was weird.

To find out if Gamma Columbae still has a companion star, astronomers can turn to a method often used to find exoplanets. By carefully measuring how the star’s light has changed over time, they were able to see the star swaying slightly back and forth on its axis. This means that it is being pulled very slightly by the gravity of something in its orbit, such as an exoplanet or a small companion star.

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