Like how the 1960s are remembered for miniskirts, the 2010s will be remembered for exoplanets. (Hey! An astronomer can dream!) In this decade, we went from only a handful of known exoplanets to thousands that have been discovered.
So many have been found that it seems there should have been clues about their existence before. Well, astronomers have now actually uncovered historical observations of a white dwarf that provide the first indirect evidence for exoplanets. These early observations were conducted in 1917.
The (re)discovery happened thanks to Dr Jay Farihi, after discussions with Professor Ben Zuckerman from UCLA. Farihi wrote a paper in New Astronomy Review about white dwarfs last year, mentioning this important piece of historical astronomy.
White dwarfs are the dim, dense remnants of very old stars that have blown away their outer layer. They have been extensively studied, and researchers have noticed that they can become polluted with heavy elements. Since these stars are really hot and dense, heavy elements are only detectable for a short period of time before they sink deeper into the star.
If heavy elements are witnessed for a long time, however, they must be replenished regularly. The most compelling argument so far for how this happens suggests that asteroids are responsible for the contamination. But they don’t tend to fly into stars unaided, so the researchers suspect that the influence of exoplanets might be what pushes space rocks into the aged stars.
The presence of heavy elements can be detected by looking at a white dwarf spectrum. The first polluted white dwarf was observed for the first time in 1917, with a spectrum taken on October 24 of that year.
"This star is an icon," Farihi said in a statement. "It is the first of its type. It's really the proto-prototype."
It’s called van Maanen’s Star, after its discoverer Adriaan van Maanen, and is located 14 light-years from Earth.
Farihi consulted the archives of the Carnegie Observatories, where the original observation plates are kept, and discovered that there were indeed clear indications that this star was polluted.
"I can't say I was shocked, frankly, but I was pleasantly blown out of my seat to see that the signature was there, and could be seen even with the human eye," Farihi said.
The observations of van Maanen’s Star show calcium pollution, which Farihi suggests in his review could indicate an exoplanet. No exoplanets have been confirmed orbiting white dwarfs (although there’s a candidate), so it definitely would be interesting if astronomers were to find one around van Maanen’s Star.