Astronomers studying RZ Piscium, a variable Sun-like star located approximately 555 light-years away in the constellation Pisces, have found evidence suggesting its strange, unpredictable dimming episodes may be caused by orbiting clouds of gas and dust, the remains of one or more destroyed exoplanets. The research appears in the Astronomical Journal.
This illustration shows a ‘disrupted planet’ broken up into a cloud of gas and dust as it orbits RZ Piscium. Image credit: NASA.
“Our observations show there are massive blobs of dust and gas that occasionally block the star’s light and are probably spiraling into it,” said lead author Kristina Punzi, a doctoral student at the Rochester Institute of Technology.
“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.”
“We know it’s not uncommon for planets to migrate inward in young solar systems since we’ve found so many solar systems with hot Jupiters,” added Dr. Catherine Pilachowski, an astronomer with Indiana University.
“This is a very interesting phase in the evolution of planetary systems, and we’re lucky to catch a solar system in the middle of the process since it happens so quickly compared to the lifetimes of stars.”
Doomed worlds that fly too close to their parent star — only to be ripped apart by its tidal forces — are officially known as ‘disrupted planets.’ In the case of RZ Piscium, the material near the star is being slowly pulled apart to create a small circle of debris about the same distance from the star as the planet Mercury’s orbit is from our Sun.
“Based on our observations, it seems either that we’re seeing a fairly massive, gaseous planet being pulled apart by the star, or perhaps two gas-rich planets that have collided and been torn apart,” Dr. Pilachowski said.
“Even planetary systems whose planets are not lost to their host star are unstable in their early history, since newly born planets interact strongly with one another — as well as their star — through gravity.”
“In our Solar System, for example, some astronomers speculate that Uranus and Neptune swapped orbits about 4 billion years ago. But erratic orbits tend to stabilize over time, falling into regular patterns.”
The astronomers observed RZ Piscium using ESA’s XMM-Newton satellite, the Shane 3-m telescope at Lick Observatory in California and the 10-m Keck I telescope at W. M. Keck Observatory in Hawaii.
The observations revealed the star’s surface temperature to be about 9,600 degrees Fahrenheit (5,330 degrees Celsius), only slightly cooler than the Sun’s.
They also show the star is enriched in the tell-tale element lithium, which is slowly destroyed by nuclear reactions inside stars.
“The amount of lithium in a star’s surface declines as it ages, so it serves as a clock that allows us to estimate the elapsed time since a star’s birth,” explained co-author Dr. Joel Kastner, director of the Rochester Institute of Technology’s Laboratory for Multiwavelength Astrophysics.
“Our lithium measurement for RZ Piscium is typical for a star of its surface temperature that is about 30 to 50 million years old.”
Another sign of RZ Piscium’s relative youth – the star produces X-rays at a rate roughly 1,000 times greater than our Sun.
“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,” Dr. Pilachowski said.
“It helps us understand why some young solar systems survive — and some don’t.”
_____
K.M. Punzi et al. 2018. Is the Young Star RZ Piscium Consuming Its Own (Planetary) Offspring? AJ 155, 33; doi: 10.3847/1538-3881/aa9524
