Twin stars could devour entire planets – 03/21/2024 – Science

The Solar System has been remarkably stable during its 4.5 billion years. But not all planetary systems are so lucky, according to a study involving twin stars published this Wednesday (20) in Nature.

Analysis of 91 pairs of stars with matching sizes and chemical compositions indicated that a surprising number of these celestial bodies exhibited signs of having ingested a planet. And this likely occurred after the planet was knocked out of a stable orbit for whatever reason.

The study looked at pairs of stars that formed within the same interstellar cloud of gas and dust, giving them the same chemical composition. Furthermore, they were of approximately equal mass and age.

The chemical composition of a star changes when it swallows a planet because it incorporates the elements that made up the doomed world.

Researchers looked for twin stars with differences in the same pair. In this case, they had greater amounts of elements such as iron, nickel or titanium, which indicated remnants of a rocky planet, compared to other elements.

In seven pairs, one of the two stars showed evidence of planetary ingestion.

Possible reasons for a planet diving into its host star include an orbital disturbance caused by a larger planet, or another star passing uncomfortably close, destabilizing the planetary system, researchers said.

“This really puts our fortuitous position in the Universe into perspective,” said astrophysicist and study co-author Yuan-Sen Ting of the Australian National University and Ohio State University. “The stability of a planetary system like the Solar System is not guaranteed.”

To identify the twin stars, the team of scientists turned to the European Space Agency’s (ESA) Gaia space observatory. And, to determine their composition, telescopes were used in Chile and Hawaii. The stars were between 70 light-years and 960 light-years from the Solar System — a light-year is the distance that light travels in one year, 9.5 trillion km.

According to the researchers, although it is more likely that their observations signaled entire planets being ingested, it is also possible that they were planetary building blocks consumed during the period of planet formation in the system.

The stars of this study were all in the prime of their lives.

Instability in planetary systems may be more common than previously known, considering that about 8% of stellar pairs studied had a star that apparently devoured a planet.

Most planetary systems should be stable because, like in our Solar System, planets are under the influence primarily of their host star, not their sister planets, according to Ting.

“But for other planetary systems with different initial conditions and configurations this can fall apart, leading to very chaotic dynamics,” said the astrophysicist.

According to him, the study indicates that “a non-negligible fraction of planetary systems are in fact unstable, which means that there are always planets being ejected in or out.”

Given that only a small fraction of these rogue planets may actually be swallowed by their host star rather than simply wandering around the cosmos, there may be more of these planetary exiles than previously suspected.

“Understanding which planetary systems are stable or not is a long-standing goal of planetary dynamics theorists,” Ting said.