Distant Sun-Like Star May Be Devouring Its Own Planets

RZ Piscium, a star located 550 light-years away in the constellation Pisces, has long intrigued researchers with its strange “winking” behavior. During the erratic episodes, which last as long as two days, the celestial body becomes about ten times dimmer and emits a larger than normal amount of energy at infrared wavelengths, indicating the presence of enormous dust clouds.

Over the years, there have been various theories about the cause of the periodic debris. Some astronomers thought that RZ Piscium is a young sun-like star in the midst of a dense asteroid belt that is prone to frequent collisions, resulting in the dust. Others, however, maintained that RZ Piscium is much older than our 4.6-billion-year-old Sun and is beginning its transition into the red giant stage. They believed that as the aging star was growing, it was destroying planets in the nearby orbits, resulting in the massive amounts of dust.

Now, a new study by a team of scientists led by Kristina Punzi, a doctoral student at the Rochester Institute of Technology (RIT), has come up with a more radical explanation. They believe the dust around RZ Piscium is caused by the star devouring its “offspring” — planets in its orbit, similar to the ancient Greek god Kronos who purportedly swallowed his children.

The team began by investigating the star using the European Space Agency’s (ESA) XMM-Newton satellite, the Shane 3-meter telescope at California’s Lick Observatory and the 10-meter Keck I telescope in Hawaii. Their observations revealed that RZ Piscium showed characteristics of both — a young sun-like star and an old red giant. Its X-ray output, about 1,000 times greater than that of our Sun, was a strong indicator of its relative youth. However, RZ Piscium’s surface temperature, about 9,600 degrees Fahrenheit (5,330 degrees Celsius), only slightly cooler than that of our Sun, as well as the lithium level surrounding it, proved the star was between 30 to 50 million years old. According to the scientists, who published their study in The Astronomical Journal on December 21, 2017, this makes RZ Piscium too old to be covered by so much gas and dust.

Though there is a slight possibility that the dust is the result of the collision of two nearby gaseous planets, the researchers say the evidence suggests a much more gruesome reality. They think the debris is a result of RZ Piscium’s tidal forces, which rips apart and devours orbiting planets that fly too close. “Most Sun-like stars have lost their planet-forming disks within a few million years of their birth," said team member Ben Zuckerman, an astronomy professor at the University of California, Los Angeles. "The fact that RZ Piscium hosts so much gas and dust after tens of millions of years means it's probably destroying, rather than building, planets." If true, it will help astronomers better understand the evolution of solar systems, and also explain why some survive and others don’t.

As it turns out, RZ Piscium may not be the only sun guilty of eating its planets. A 2016 study conducted by researchers at the University of Nevada, Las Vegas, suggests that our Sun may also have gobbled up a nearby planet, dubbed Super-Earth, during the early years of the Solar System.

Resources: NASA.gov,cbc.ca