How Massive Stars Steal Planets

Our sun has a rather lonely existence in the Milky Way galaxy. It stands alone, four light years from the nearest star, with only its planetary system for company. But it wasn’t always like that. We almost exclusively observe young stars in groups called stellar nurseries, where they lie shoulder to shoulder with stellar siblings.

Our sun has a rather lonely existence in the Milky Way galaxy. It stands alone, four light years from the nearest star, with only its planetary system for company. But it wasn’t always like that. We almost exclusively observe young stars in groups called stellar nurseries, where they lie shoulder to shoulder with stellar siblings.

These stellar nurseries are densely populated places, where hundreds of thousands of stars often reside in the same volume of space that the sun alone inhabits. Violent interactions, in which stars exchange energy, are common, but not for long. After a few million years, the groups of stars disappear and fill the Milky Way with more stars.Our new paper, published in the Monthly Notices of the Royal Astronomical Society, shows how massive stars in such stellar nurseries can steal planets from each other — and the signs of such theft. Almost immediately after young stars are born, planetary systems begin to form around them. We’ve had circumstantial evidence of this for over 30 years. Observations of the light from young stars show an unexpected excess of infrared radiation. This was (and still is) explained as coming from small dust particles (100th of a centimeter) orbiting the star in a disk of material. Planets are (eventually) formed from these dust particles.Also read: These tourists like to stare at the sky The field of star and planet formation was revolutionized in late 2014 when the first images of planet-forming disks around stars were seen with the Atacama Large Millimeter Array (Alma) telescope in the Chilean desert. The first and subsequent images of Alma were nothing short of spectacular. Many of the disks had features and structures that can be attributed to the presence of fully formed, Jupiter-like planets.Planet formation occurs soon after star formation begins, especially while the star is still interacting with its siblings in the stellar nursery. Because planets form so quickly, they will be affected by the densely populated star-forming environment. Planets can have their orbits changed, which can manifest itself in different ways.Wandering Planets Sometimes the distance from the planet to the parent star becomes smaller or larger, but more often there is a change in the shape of the orbit – usually less circular (more “eccentric”). Occasionally, a planet is freed from its orbit around its parent star and becomes “free-floating” in the star-forming region, meaning it is not bound to a star by gravity.A significant portion of the free-forming planets are trapped and gravitationally bound to a star other than the star around which they are formed. In fact, a similar number of planets are stolen from their orbits – exchanged directly between stars without first floating freely.In studying this great planetary raid, we learned that planets formed in the most populous star-forming regions can easily be captured or stolen by stars much more massive than our own sun. Stars form with a wide range of masses. Our sun is somewhat unusual in that it is about twice as massive as the average star in the universe. However, a relatively small number of stars are even more massive, and these “OB-type” stars dominate the light we see in the Milky Way (and other galaxies). beasts. These massive stars are very bright, but have a much shorter lifespan than the Sun, and in some cases live only a few million years (rather than billions). We would therefore not expect to find planets around them. However, in 2021, the B-star Exoplanet Abundance Study (Beast), led by researchers at Stockholm University, discovered a planet orbiting more than 550 times the Earth-sun distance from a star weighing up to ten times the mass of the Earth. sun, and another planet that orbits a star nine times the mass of the sun at 290 times the Earth-Sun distance.The Beast collaboration found that these planets (“Beasties”) orbit stars in the star-forming region of Sco Cen, which is currently gradually dissolving into the Milky Way. The original explanation for these Beasties is that they formed just like the gas giant planets in our solar system, but they are more massive and distant because they are an upscaled version of our own planetary system. Also Read:Space technology helps the country’s development, says senior ISRO scientist in Mysuru However, massive stars emit large amounts of ultraviolet radiation, which can vaporize the gas from which giant planets such as Jupiter and Saturn are to be formed. So how do Beasties get around them? We know from our previous work that theft and conquest of planets can take place in densely populated star-forming regions, so we looked in our simulations for planets captured or stolen by massive stars.Our new explanation for the Beasties is that they got into orbit through a planetary raid – they were born around other stars and then captured or stolen by the massive stars. These planetary systems are usually in broad (at least 100 Earth-Sun) orbits and are highly eccentric — very different from the circular, closely spaced planets in our solar system, which we believe formed there.There may be a trapped planet in our solar system — the elusive and hypothetical planet 9 — but Jupiter and the other giant planets formed around our sun.Our computer simulations also seem to predict the frequency of these systems (one or two per star-forming region) and the orbital characteristics of the Beasties. Future observations will shed more light on the origins of these planets, but for now they represent yet another exciting discovery in the field of exoplanet science. (The conversation)
SOURCE – www.thehindu.com

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