Star flyby leaves permanent imprint on newly formed planetary system

Artist’s impression of one of the two stars in the Orion FU binary system. It is surrounded by a disk of accreting matter. Credit: NASA/JPL-Caltech

What do UX Tauri, RW Aurigae, AS 205, Z CMajoris, and FU Orionis have in common? They are young star systems with disks in which planets can form. These disks were likely disturbed by recent stellar flybys or other close encounters. Astronomers want to know: Did these events disrupt planet formation in the disk? What do they do? Does this happen in other systems as well, and did our own solar system have a strange encounter in its youth?

Some answers lie in research done by Nicolás Cuello, an astronomer at the University of Grenoble Alpes, who leads a team investigating the role of stellar flybys. In a recent paper, they discuss the processes these systems go through. They looked at the specific disc occurrence possibilities. FlyCreated /encounter to categorize encounter types. The team also researched a series of discs to understand what happens during each type of encounter and to find out what flybys mean. planet formation on other systems. Finally, they looked for clues to flybys our solar system may have experienced.

when does it all start birth of a star It happens in clouds of gas and dust. This process creates a hot batch. young star I got it together. Over time, some of these clusters will disappear. When a star leaves its nest, it can pass close to other star systems and cause chaos in planet-forming disks. Cuello and his team came to the conclusion that close encounters stimulate or even confuse the evolution of these discs at some point.

“Stellar flybys and encounters are occurring more frequently than previously realized,” Cuello said in an email discussion. “These can occur when the star is very young (less than a million years old) and has a planet-forming disk around it. These disks are greatly affected by the gravitational perturbations of nearby stars, causing planets to We change the initial conditions at the start of formation, which is why we have to account for it in this our model.”

Star flyby leaves permanent imprint on newly formed planetary system

FU Orionis and its associated nebula. The nebula was likely destroyed by a flyby, and its brightening is one of the effects of this event. Credit: ESO

According to Cuello, flybys aren’t all that uncommon. “We can say that at least half of the star and its disk are formed under the influence of flybys,” he said. “One important aspect to emphasize is that the probability of such perturbations decreases over time, but never goes to zero. Therefore, even more evolved stars ( planetary system around) can experience a flyby in a lifetime. In that case, some planets could become misaligned with respect to the rest of the planetary system, or even become trapped by perturbation stars. “

How much damage can a stellar flyby do?

In typical star-forming regions, distance matters.most of the stars protoplanetary disk Experience a close flyby within 1,000 AU. This corresponds to about half the distance from the Sun in our solar system to the Oort Cloud. Some of these encounters can really mess up your disc.For example, if an intruding star is moving prograde in a parabola trajectory Penetrating the disc can cause enough damage to reshape the disc. Damage by an intruder can cause her second disc of matter to form.

In fact, this is what is happening on the star FU Orionis. FU Orion appears 1000 times brighter than her in about a year, thanks to the flyby of a star that pierced its disk and approached. And such confusion is evident in other young systems as well.

During some encounters, the disc passes through what is called a “tidal truncation”. This can remove up to 80% of the mass of the disc. This has a devastating effect on planet formation, as it reduces the amount of material needed to form a protoplanet. Such flybys can also create dust traps. Theoretically, given enough time, it could be a place where planetesimals could grow.

Star flyby leaves permanent imprint on newly formed planetary system

A gallery of flyby candidates punctuated by stellar flybys is shown in scattered light. Credits: Francois Menard (ISO-Oph 2, DO Tau, RW Aur, and FU Ori courtesy of Iain Hammond), Nicolas Cuello, Daniel J. Price

In some cases, close flybys can even scatter or eject planets within a system. Those left behind may move into orbits reminiscent of Pluto. It is eccentric and out of the plane of the system. (To be clear, Pluto’s odd orbits are not due to flybys; gravitational influences from Neptune or other giant planets likely formed Pluto’s odd orbits.)

Stellar flyby and solar system

Did our own solar system experience a stellar flyby during its formation? a possibility Cuello and his colleagues explore in their paper. In or very close to our birth clouds Such collisions of may have shaped the solar nebula. Ultimately, that would have affected the size of the disk and its mass. , and most planets move in fairly circular, regular orbits.

However, Cuello and his team concluded that the orbital geometry of the Solar System may have influenced the distribution of trans-Neptunian objects (the region just above Neptune where Pluto orbits). It is also possible that one or more stars passed through and disturbed the Oort Cloud. Astronomers have found several candidates they are studying to see if this hypothesis holds.

Indeed, our solar system has experienced other, more recent encounters in its long history. For example, Scholz’s star is thought to have passed through the Oort Cloud about 70,000 years ago.Currently this Binary star About 22 light years away from us. This passage does not appear to have affected either trajectory. planetbut it probably had a very small effect on the number of Oort Cloud objects ejected into long-period orbits around the Sun. remains as an example disk.

A close encounter more than 10,000 years ago stirred the accretion disk spiral

For more information:
Nicolás Cuello, François Ménard, Daniel J. Price, Close Encounters: How Star Flybys Form Planet-Forming Disks. arXiv:2207.09752v1 [astro-ph.EP],

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Star flyby leaves permanent imprint on newly formed planetary system

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