Planetary destruction in the system of the young star RZ Piscium

Artist's concept of the star RZ Piscium surrounded by blobs of gas and dust (Image NASA's Goddard Space Flight Center/CI Lab)
Artist’s concept of the star RZ Piscium surrounded by blobs of gas and dust (Image NASA’s Goddard Space Flight Center/CI Lab)

An article published in “The Astronomical Journal” describes a research on the young star RZ Piscium that offers an explanation for the strange variations of its brightness. A team of astronomers used detections made with ESA’s XMM-Newton space observatory, the Shane telescope at Lick Observatory in California and the Keck I telescope at W. M. Keck Observatory in Hawaii concluding that probably RZ Piscium is destroying at least some planets in its star system or two gas-rich planets collided.

About 550 light years away from Earth, the star RZ Piscium has been at the center of discussions for years because its brightness increases and decreases considerably in very short periods, becoming up to 10 times dimmer. Its characteristics have been studied to try to understand that really anomalous variability leading to the collection of information that could have led to the explanation.

The observations showed that the temperature on the surface of the star RZ Piscium is about 5,330° Celsius (9,600° Fahrenheit), slightly lower than the Sun’s. It also turned out to be rich in lithium, in an amount that led to estimate its age among the 30 and 50 million years, making it a very young star in astronomical terms. Its age is confirmed by an emission of X-rays at levels 1,000 times higher than the Sun’s, a characteristic typical of young stars.

The problem is that the star RZ Piscium emits many more infrareds than stars like the Sun and this indicates that it’s surrounded by masses of hot gas and dust. When there’s a disk around a newborn star, it gets dispersed in a few million years forming planets and other small celestial bodies but the mass around RZ Piscium is much less homogeneous. Its presence suggests that at least some of the planets were destroyed and reduced to dust concentrated in blobs of debris that obscure in a very variable way RZ Piscium. The problem is to understand the cause of this destruction.

If RZ Piscium were an old star, the explanation would be simple because at the end of their life the stars with masses similar to the Sun’s start inflating and destroy their inner planets. Because this is a young star, the possible explanations are different. In a newly formed solar system there can be a chaotic situation in which the planets migrate and their orbits can be unstable with the consequence that some may be destroyed by their star or may collide.

Planetary migrations are a growing subject of studies thanks to the increasing knowledge on exoplanets. With regard to the solar system, there are various theories about the movement of Mars, Jupiter and perhaps other planets. In essence, it’s possible that in the RZ Piscium system a gas giant planet approached the star so much that it got destroyed.

Another possibility is a planetary collision. According to the most likely theory, the Moon was born following the collision between the early Earth and a Mars-sized planet. A collision between two more massive and gas-rich planets would generate much more debris that could form blobs of gas and dust like the ones around the star RZ Piscium.

Astronomer Catherine Pilachowski of Indiana University, one of the authors of the article, stated that the RZ Piscium system is very interesting because it shows a phase of a solar system’s evolution in which some planets are moving towards their star. Studying it will help to understand why some young solar systems survive and have several planets while others end up badly.

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