‘Winking’ Star RZ Piscium May Be Destroying And Consuming Its Planets

An unusual star about 550 light-years away in the constellation Pisces is known for its erratic dimming episodes, but it turns out RZ Piscium may also be doing something else not commonly seen. The star may be actively destroying the planets and planetesimals in orbit around it and then consuming the remains.

Compared to most other stars, RZ Piscium has been known to exhibit two irregularities. One is the variation in its brightness, with episodes that last up to two days, when the light from the star, as seen from Earth, drops by as much as 90 percent. The other is the fact that a lot of its emissions are in the infrared. With about 8 percent of its total luminosity in infrared, it is in a group of rare nearby stars among the thousands that have been studied over the last four decades.

A group of astronomers from the United States used data from three different instruments — European Space Agency’s XMM-Newton satellite, the Shane 3-meter telescope at Lick Observatory in California and the 10-meter Keck I telescope at W. M. Keck Observatory in Hawaii — to study the star’s “winking” behavior.

“Our observations show there are massive blobs of dust and gas that occasionally block the star’s light and are probably spiraling into it. Although there could be other explanations, we suggest this material may have been produced by the break-up of massive orbiting bodies near the star,” Kristina Punzi, a doctoral student at the Rochester Institute of Technology in New York and lead author of a paper describing the findings, said in a statement Thursday on NASA’s website.

First, using X-ray data from the star, recorded by XMM-Newton, the researchers concluded RZ Piscium is a young star. Its X-ray output is about 1,000 times greater than the sun’s, and such large amounts of X-ray emission is typical of younger stars. Based on the amount of lithium in the star’s surface, and given the surface temperature of about 5,330 degrees Celsius (9,600 degrees Fahrenheit, which is a bit cooler than the sun’s surface), its age was estimated to be between 30 million and 50 million years.

That is still too old to have the sort of dense planet-forming disk of gas and dust around it that RZ Piscium exhibits.

“I’ve been studying young stars near Earth for 20 years and I’ve never seen anything like this one. Most sun-like stars have lost their planet-forming disks within a few million years of their birth. 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,” Benjamin Zuckerman from the University of California, Los Angeles, who was a coauthor on the paper, said in a statement on the university’s website.

Observations of the star’s environment from ground-based telescopes showed the dust around the star has a temperature of about 230 degrees Celsius, leading the astronomers to estimate the distance between the star and the debris to be about 50 million kilometers (30 million miles). That is about a third of the Earth-sun distance.

“While we think the bulk of this debris is about as close to the star as the planet Mercury ever gets to our sun, the measurements also show variable and rapidly moving emission and absorption from hydrogen-rich gas. Our measurements provide evidence that material is both falling inward toward the star and also flowing outward,” coauthor Carl Melis from University of California, San Diego, explained.

To account for all the available data, the researchers suggest that the debris surrounding the star are remnants from a planetary-scale disaster. The star is either pulling material from a nearby giant planet or substellar companion that maybe still exists or is already completely destroyed, or that a massive gas-rich planet in the stellar system was involved in a deathly collision in the relatively recent past.

“This discovery really gives us a rare and beautiful glimpse into what happens to many newly formed planets that don’t survive the early dynamical chaos of young solar systems. It helps us understand why some young solar systems survive — and some don’t,” Catherine Pilachowski from Indiana University, also a coauthor on the study, said in a statement.

The paper, titled “Is the Young Star RZ Piscium Consuming Its Own (Planetary) Offspring?” appeared online Thursday in the Astronomical Journal.