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This planet-eating star consumes its ‘offspring’

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A star 550 light years from Earth is slowly consuming its “offspring”—crushing one or more planets in its orbit into vast clouds of gas and dust—according to a new study.

The discovery that RZ Piscium—located in the constellation Pisces—is an insatiable “eater of worlds” may shed light on a brief but volatile period in the history of many solar systems, including our own.

“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’—gaseous planets similar in size to Jupiter but orbiting very close to their stars,” says Catherine Pilachowski, chair of the astronomy department at Indiana University Bloomington and coauthor of the study, which appears in The Astronomical Journal.

"disrupted planet" orbiting RZ Piscium
This illustration shows a “disrupted planet” slowly broken up into a cloud of gas and dust as it orbits the star RZ Piscium about 550 light years from Earth. (Credit: NASA)

“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,” Pilachowski says.

Doomed worlds that fly too close to their sun—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 sun-like 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,” Pilachowski says.

Even solar systems whose planets are not lost to their sun are unstable in their early history, since newly born planets interact strongly with one another—as well as their sun—through gravity, she adds.

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.

This discovery “helps us understand why some young solar systems survive—and some don’t.”

In the new study, Pilachowski, an expert on the analysis of light spectrum from distant stars to determine their temperature, gravity, and elemental composition, was responsible for determining the gravitational strength near RZ Piscium’s surface.

Her findings helped shed light on the star’s radius and brightness, both of which suggest a young star in the midst of a freewheeling solar system with unstable planets.

This is significant because researchers weren’t sure of RZ Piscium’s age. The debris field around a star can result from either the erratic orbits in young solar systems or the destruction of planets that occurs as an old star grows before collapsing and dying.

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Pilachowski’s analysis of the star’s light also helped determine the amount of lithium in the star, marking the star as a relatively young 30 million to 50 million years. Astronomers can use lithium levels to estimate a star’s age because the element declines over time.

Further, researchers discovered that the star’s temperature is about 9,600 degrees Fahrenheit (5,330 degrees Celsius)—only slightly cooler than our sun’s. Another sign of the star’s relative youth: It 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,” Pilachowski says. “It helps us understand why some young solar systems survive—and some don’t.”

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Researchers at the Rochester Institute of Technology led the study. Other researchers from Indiana University; the University of California, Irvine; the University of California, Los Angeles; Haverford College; and Ithaca College are coauthors.

The team investigated the star using the 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.

Source: Indiana University

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