Astronomers Discover Rare Heavy Metal Stars Clouded by Lead Atmospheres

There are some strange and unusual stars in our universe. There are supergiant stars, such as Betelgeuse; there are dim stars, such as white dwarfs; and then there are binary stars, which orbit one another. Now, scientists have discovered two unusual stars with extremely high concentrations of lead in their atmospheres.

The two stars are known as HE 2359-2844 and HE 1256-2738. They're located about 800 and 1,000 light years away from Earth, respectively. Although located far apart, these stars both possess similar atmospheres that have intrigued astronomers. These stars contain 10,000 times more lead than is present on the surface of the sun.

In order to properly examine the stars, the researchers used observations from the archives of the European Southern Observatory's Very Large Telescope in Chile. After studying the light signatures, or spectra, of both stars, the astronomers noted a few features which did not match any atoms expected to be present. These features were mainly due to the presence of the lead.

Lead is one of the heaviest naturally occurring elements. In our own sun, there's less than one lead atom for every ten billion hydrogen atoms. On the surfaces of these two unusual stars, though, the lead causes ions to form that produce distinctive lines on their two spectrums. This allowed the scientists to measure the amount of lead that each star contained, which lead them to name them "heavy metal subdwarfs."

These new stars may be a crucial link between bright red giants and faint blue subdwarfs. While red giants can be thirty or forty times the size of the sun, blue subdwarfs are one fifth the size, but seven times hotter and seventy times bright than the sun. When red giants lose their thick hydrogen skin, they shrink to become hot subdwarfs. As they shrink, light from the helium stars can act on individual atoms to sort the elements into separate layers. A layer of heavy metal at just the right height and concentration could, in theory, form clouds that become visible from Earth. This particular phenomenon could explain the heavy metal subdwarfs that the scientists saw.

Currently, the researchers are continuing to search for evidence of other heavy metals forming cloud layers in these rare stars. They hope that they will be able to determine exactly how these stars form and what they will eventually become.

The findings are published in the journal Monthly Notices of the Royal Astronomical Society.