When stars are born, most of the time they arrive in the universe as twins. In the first stage of stellar creation, a large cloud of gas and dust collapses due to gravity, often breaking into pieces. If each piece collapses again, multiple stars will be born from the same gas cloud. These nascent suns are then surrounded by a halo of matter, the precursor to the planets, known as the planetary disc. And, if these stars are close enough, the planet-forming disks around them can even swirl together, creating fantastic spiral tails.
New astronomical images published in the Royal Astronomical Society Monthly Notices November 28 will reveal three of these interacting twin planetary discs in stunning detail. The team took these photos using the European Southern Observatory’s Very Large Telescope in Chile. While this isn’t the first time these disks have been imaged, advances in astronomical technology provide a new, more comprehensive perspective on the dramatic cosmic scene.
The stars are all in the Milky Way, quite close by galactic standards. The astronomers photographed these three sets of known twins in polarized light, which can help untangle the dust from each disk. Some telescope technologies, like those used in this study, can record the specific direction, or polarization, of incoming light waves. Polarized light is a great trick for finding faint structures such as the dusty disks around bright stars. Stars are not expected to emit this type of light, but starlight scattered by dust will become polarized, making the disks and their spirals easier to see.
Polarization is also a powerful tool for astronomers: it encodes a lot of information about how light traveled to our telescopes. As starlight travels through space, if it hits small bits of dust, it will bounce off those particles in specific ways. The polarization of this light is a result of the precise angle at which it bounces and the type of material it hits. “Many complex processes are involved,” says Sebastián Perez, an astronomer from the University of Santiago in Chile, co-author of the new study. The research team used information provided by polarization to plot which star was illuminating each part of the disks, helping them to understand the geometry of the systems.
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Their goal is to understand how nearby stars influence planet-forming disks. “A lot of stars probably go through such a phase,” Perez says, referring to their sibling-filled childhoods, “but we know little about that.” Neighboring stars may orbit each other, or one star may pass by to visit another, known as a flyby. These new images are a first step in determining which scenario occurred for each of the three systems.
“We expect most stars to form in dense regions of the galaxy and be surrounded by other stars forming at almost the same time,” says Philipp Weber, astronomer at the University of Santiago de Chile and author principal of the study. Despite this fact, astronomers “mainly treat protoplanetary disks as isolated systems.”
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Their new observations suggest that, for many star systems, this is the wrong assumption to make. Flybys “could have lasting effects” on the structure of these planet-forming disks, says Weber, who still has a number of unanswered questions. What is the frequency of overflights? How do sister stars alter the evolution of disks and their planets? This new data will no doubt keep astronomers busy refining their theories as they seek to understand how planets form.
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