Alphard

The star Alphard has a barium problem. High levels of the element show up in the star. But the normal explanation for why a star has so much of it doesn’t seem to apply.

Alphard is the brightest star of the constellation Hydra, the water snake. It’s low in the east-southeast as the sky gets good and dark. It’s far to the lower left of Sirius, the brightest star in the night sky.

Alphard is several times as massive as the Sun, dozens of times wider, and hundreds of times brighter. And even though it’s young, it’s already nearing the end of its life.

Astronomers have measured the chemical composition of Alphard’s surface layers. Among other things, they’ve found fairly high levels of barium.

The element is produced slowly — as a by-product of the nuclear reactions that take place in a star’s core. Most stars with high levels of it have “dead” companions — the exposed cores of once-normal stars. As those stars died, they expelled their outer layers of gas. Some of the gas fell onto their companions, “polluting” their surfaces.

Alphard, though, doesn’t appear to have such a companion. Astronomers have looked for any “wiggle” in Alphard’s light as the result of a companion’s gravitational pull. But they’ve come up empty. That suggests that the barium found in Alphard must have been made in the star’s core, then found its way to the surface — creating a minor mystery for astronomers to solve.

More about Hydra tomorrow.

Script by Damond Benningfield