Chapter 2: Insights from HD 106906

Recent research led by astronomers from UC Berkeley and Stanford University has unveiled intriguing evidence regarding this phenomenon in the distant binary star system known as HD 106906. Located about 300 light-years away in the direction of the constellation Crux, this system features a peculiar planet, HD 106906 b, which orbits the binary star at an unusually wide distance and is believed to have been influenced by a close encounter with other stars roughly 3 million years ago.

The study, published in The Astronomical Journal, indicates that HD 106906 b's orbit may have been altered by the gravitational effects of two stars that passed near the system during the planet's formative years. If validated, this finding supports the hypothesis that close encounters with other stars play a significant role in shaping planetary systems and determining the stability of their orbits.

Paul Kalas, an adjunct professor of astronomy at UC Berkeley, elaborates: “One of the mysteries in exoplanet studies is the misalignment of planets in systems that should ideally be flat. This suggests that something, perhaps a cosmic disturbance, has influenced their arrangement. Our research provides rare observational evidence of such stellar interactions.”

Chapter 3: Past Encounters and Current Discoveries

While astronomers are actively investigating potential stellar fly-bys in our solar system's ancient history, solid evidence has become increasingly elusive due to the vast time span of approximately 4.6 billion years. However, HD 106906, being a relatively young system at around 15 million years old, offers a unique opportunity for study.

The observations suggest that the gravitational interactions of nearby stars may have stabilized the orbit of HD 106906 b, preventing it from drifting into interstellar space like the well-known object ‘Oumuamua. Kalas, who has been investigating young planetary systems since 2015, initially focused on HD 106906 due to its strange planetary dynamics.

The planet, which is about 11 times the mass of Jupiter, resides in an orbit 738 times wider than Earth's and is inclined at about 21 degrees relative to the plane of the surrounding dust and gas. Through the use of advanced imaging technology, including the Gemini Planet Imager and the Hubble Space Telescope, researchers discovered that the system hosts an asymmetrical comet belt, further indicating disruption by external forces.

Kalas and his team, including Robert De Rosa, propose that both interactions with a hidden planet and close stellar encounters have contributed to the planet's current orbit. This dual influence could explain the planet's peculiar trajectory.

Using data from the Gaia space observatory, which tracks the motion of billions of stars, the researchers have begun to piece together the puzzle of HD 106906's past. They calculated the positions of stars within the same cluster and uncovered evidence suggesting a close approach of another binary star system around 3 million years ago.

Kalas asserts, “Our findings indicate that certain stars may have provided the necessary gravitational adjustments to HD 106906 b, allowing it to maintain its orbit over time, similar to how a hypothetical Planet Nine might function within our own solar system.”

As research continues, astronomers hope to clarify the influence of these past fly-bys on HD 106906 and their broader implications for understanding our solar system's evolution. The investigation has begun to identify the two stars that may have played a pivotal role in this cosmic event, with further evidence expected to unveil their exact contributions.

Originally published at sciscomedia.co.uk on March 1, 2019.