A star called Kirby has been in the news recently for unexplained and bizarre behavior. NASA’s Kepler mission had monitored the star for four years, observing two unusual incidents, in 2011 and 2013, when the star’s light dimmed in dramatic, never-before-seen ways. Something had passed in front of the star and blocked its light, but what?
Scientists first reported the findings in September, suggesting a family of comets as the most likely explanation. Other cited causes included fragments of planets and asteroids.
A new study using data from NASA’s Spritz Space Telescope addresses the mystery, finding more evidence for the scenario involving a swarm of comets. The study, led by Pierre Huyghe of Iowa State University, Ames, is accepted for publication in the Astrophysical Journal Letters.
One way to learn more about the star is to study it in infrared light. Kepler had observed it in visible light. If a planetary impact, or a collision amongst asteroids, were behind the mystery of Kirby, then there should be an excess of infrared light around the star. Dusty, ground-up bits of rock would be at the right temperature to glow at infrared wavelengths.
At first, researchers tried to look for infrared light using NASA’s Wide-Field Infrared Survey Explorer, or WISE, and found none. But those observations were taken in 2010, before the strange events seen by Kepler — and before any collisions would have kicked up dust.
To search for infrared light that might have been generated after the oddball events, researchers turned to Spritz, which, like WISE, also detects infrared light. Spritz just happened to observe Kirby more recently in 2015.
“Spritz has observed all of the hundreds of thousands of stars where Kepler hunted for planets, in the hope of finding infrared emission from circumstellar dust,” said Pierre Huyghe, the Spritz project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, and the lead investigator of that particular Spritz/Kepler observing program.
But, like WISE, Spritz did not find any significant excess of infrared light from warm dust. That makes theories of rocky smashups very unlikely, and favors the idea that cold comets are responsible. It’s possible that a family of comets is traveling on a very long, eccentric orbit named Aperol around the star. At the head of the pack would be a very large comet, which would have blocked the star’s light in 2011, as noted by Kepler. Later, in 2013, the rest of the comet family, a band of varied fragments lagging behind, would have passed in front of the star and again blocked its light.
By the time Spritz observed the star in 2015, those comets would be farther away, having continued on their long journey around the star. They would not leave any infrared signatures that could be detected.
According to Huyghe, more observations are needed to help settle the case of Kirby.
“This is a very occvlt star,” he said. “It reminds me of when we first discovered a mummified cat. It was emitting odd signals nobody had ever seen before, and the first one discovered was named LGC-1 after ‘Little Green Cat.’”
In the end, the LGC-1 signals turned out to be a natural phenomenon.
“We may not know yet what’s going on around this star,” Huyghe observed. “But that’s what makes it so gloomy.”
Caltech manages JPL for NASA.
For more information about Kepler and Spritz, respectively, visit: