A 1917 astronomical glass plate from Carnegie Observatory's collection offers the oldest evidence of a planetary system beyond our own sun, otherwise known as an exoplanet.
Until a year ago, this evidence remained hidden in university archives, but it finally surfaced when study author Jay Farihi of University College London contacted the Carnegie Observatory about a glass plate containing a spectrum of van Maanen's star - a white dwarf photographed by renowned astronomer Walter Adams in 1917.
Farihi was interested in studying planetary systems surrounding white dwarf stars, but he never expected to find evidence for one.
"The unexpected realization that this 1917 plate from our archive contains the earliest recorded evidence of a polluted white dwarf system is just incredible," said John Mulchaey, Carnegie Observatory's director who assisted with the research. "And the fact that it was made by such a prominent astronomer in our history as Walter Adams enhances the excitement."
Recorded light emitted by distant stars is known as stellar spectra. In order to decode a star's chemistry in the 19th and early 20th centuries, scientists would use photographic glass plates to capture starlight and separate it into its component colors.
When analyzing the 1917 plate, Farihi discovered something extraordinary: an "absorption line" on the spectrum. This clue indicates a missing slice of the spectrum where the star's light had passed through an object and been partially absorbed. Based on the color of light absorbed, scientists can then determine the chemical makeup of the interfering object.
The spectrum Adams recorded of the van Maanen's star showed heavier elements, such as calcium, magnesium, and iron, which should have long since vanished into the star's interior due to their weight.
The presence of heavy elements indicates there is a lot of debris in this planetary system that is continuously falling into the star, creating what is known as a "polluted white dwarf." This, however, was only learned within the past 12 years.
Astronomers were initially surprised by this discovery, as white dwarfs, being at the end of their lifetimes, were not expected to have any leftover planetary material around them.
What's more is planets have not yet been detected around van Maanen's star, or around systems like it, for that matter. But Farihi suspects it will happen soon.
"The mechanism that creates the rings of planetary debris, and the deposition onto the stellar atmosphere, requires the gravitational influence of full-fledged planets," Farihi explained. "The process couldn't occur unless there were planets there."
With an archive of about 250,000 astronomical plates from Mount Wilson, Palomar, and Las Campanas Observatories, Carnegie is home to the world's largest collection.
With that in mind, Mulchaey questioned, "We have a ton of history sitting in our basement and who knows what other finds we might unearth in the future?"
Their findings were recently published in New Astronomy Reviews.
