An image taken in 1917 and kept on an astronomical glass plate with the Carnegie Institution for Science (CIS) has revealed the first-ever evidence of a planetary system beyond our own Sun.
The unexpected find was recognised in the process of researching an article about planetary systems surrounding white dwarf stars in the journal New Astronomy Reviews.
The Review’s author Jay Farihi from University College London and Carnegie Observatories’ director John Mulchaey were looking for a plate in the Carnegie archive that contained a spectrum of van Maanen’s star.
It is a white dwarf discovered by Dutch-American astronomer Adriaan van Maanen in the very year the plate was made.
Stellar spectra images allowed 19th century astronomers to develop a system for classifying stars that is still used today.
Modern astronomers use digital tools to image stars but for decades, they would use glass photographic plates both to take images of the sky, and to record stellar spectra.
When Farihi examined the spectrum, he found something quite extraordinary.
Carnegie’s 1917 spectrum of van Maanen’s star revealed the presence of heavier elements such as calcium, magnesium, and iron, which should have long since disappeared into the star’s interior due to their weight.
Astronomers now know that that van Maanen’s star and other white dwarfs with heavy elements in their spectra represent a type of planetary system featuring vast rings of rocky planetary remnants that deposit debris into the stellar atmosphere.
“The unexpected realisation that this 1917 plate from our archive contains the earliest recorded evidence of a polluted white dwarf system is just incredible,” said Mulchaey.
Planets themselves have not yet been detected orbiting van Maanen’s star, nor around similar systems, but Farihi is confident it is only a matter of time.
Carnegie has one of the world’s largest collections of astronomical plates with an archive that includes about 250,000 plates from three different observatories.
“We have a ton of history sitting in our basement and who knows what other finds we might unearth in the future?” asked Mulchaey.