August 1, 2013
Astronomers Find Unusual Heavy Metal Stars
Lee Rannals for redOrbit.com - Your Universe Online
Astronomers from the Armagh Observatory in Northern Ireland say they have discovered two unusual, heavy metal stars.The team wrote in the journal Monthly Notices of the Royal Astronomical Society that they found the stars HE 2359-2844 and HE 1256-2738 to contain extremely high concentrations of lead in their atmospheres. Naslim Neelamkodan, Simon Jeffery, Natalie Behara and Alan Hibbert said these two stars have surfaces containing ten thousand times more lead than what is found on the surface of the sun. Lead is one of the heaviest naturally occurring elements, and on the sun there is less than one lead atom for every ten billion hydrogen atoms.
The surface temperatures on these stars are so hot that three electrons are removed from every lead atom. The resulting ions produce distinctive lines in the star's spectrum, a phenomenon which allows scientists to measure the concentration of lead. According to the study, HE 2359-2844 was also found to have ten thousand times more yttrium and zirconium than the sun, placing it in the star category of so-called "heavy metal subdwarfs."
Heavy-metal subdwarfs are considered a crucial link between bright red giants and faint blue subdwarfs. Red giant stars are thirty to forty times the size of our Sun, while blue subdwarfs are just one-fifth the size yet seven times hotter and 70 times brighter. As red giants shrink and lose their thick hydrogen coat they become hot subdwarfs, or nearly-naked helium stars. These conditions allow elements to be sorted into separate cloud layers which can be detected from Earth.
The astronomers estimate that the lead cloud layer on these stars could be about 62 miles thick and weigh 100 billion tons. The team will be continuing to search for evidence of other heavy metals forming cloud layers in these stars. They will also look for more information about how light pressure sorts the chemistry of helium-rich subdwarfs over time.
Understanding more about stars allows scientists to determine whether they host planets and what kind of planets could be orbiting them. A few weeks ago, astronomers writing in the journal Astrobiology said cooler stars may be more likely to host ice-free planets than hotter stars. A new climate model found that planets orbiting cooler stars may be warmer and less icy than their counterparts because the ice on these planets absorbs more of the near-infrared light being emitted by these stars.