Friday , September 17 2021

This four-star system does not look like anything we've seen before

The image of the artist HD 98800 with a protoplanetary disk and an internal binary pair. The external binary pair is not shown.
Image: University of Warwick / Mark Hurric

Astronomers using the ALMA telescope have discovered the amazing formation that forms the planet within the double binary star system, the configuration of which until this time existed only in theory.

Four-star systems with two binary pairs are not unusual, as well as the discovery of the surrounding protoplanetary disk – the rings of gas and dust, which gradually become confined to the formation of planets. The star system, located 146 light years from the Earth, is called HD 98800, has all these things, but, according to a new study published today in Nature Astronomy, this system has an extremely strange protoplanetary disk.

The HD 98800 has an internal binary pair of stars and an external pair. A pair inside, called BaBb, is in close proximity to each other, about 1 AU, which is the average distance from Earth to the Sun. His outer pair, called AaAb, is much further at 54 AU – far greater than the space between Pluto and the Sun (40 AU). But do not forget about the exterior pair – it's an interesting inner pair and its surrounding disk.

As a rule, a protoplanetary disk is in the same plane as the plane of the orbit of its binary stars. But not HD 98800 – its protoplanetary disk is perpendicular to the plane of the binary pair at right angles. It is located in a polar configuration, where instead of east to west, so to speak, the drive moves from north to south. Here's another analogy: the inner binary pair resembles two horses rotating on a carousel, while a protoplanetary disk is similar to a giant review wheel with a carousel in the center.

To this conclusion, systems such as HD 98800 existed only in theory.

"Disks that are rich in gas and dust are observed around almost all young stars, and we know that at least one third of the rotation around single stars form the planet," Grant Kennedy, an astronomer at the University of Warwick and lead author of the new study, says in a statement. "Some of these planets eventually change with the back of the star, so we were wondering if such a thing could be possible for circular rays. The fiction of the dynamics means that the so-called polar discrepancy should be possible, but so far we have not had any evidence displaced disks in which these planets could have been formed.

About the HD 98800 astronomers have known for several years. Earlier, scientists tracked the movements of their internal stars to see how they move toward each other. Now, using the Atacama Large Millimeter / Submillimeter Array (ALMA) matrix, the Kennedy team was able to visualize the system and characterize the orientation of the protoplanetary ring surrounding the internal binary pair.

Exciting, and despite this unusual configuration, the HD 98800 still has features that fit the early planetary formation.

"We understand that this means that the formation of the planet can at least start to work in these polar circular mineral disks," explained Kennedy. "If another process of formation of the planet can occur, there may be an entire population of uneven planets that we still have to open and things like weird seasonal changes."

An image of an artist's appearance from a hypothetical object within a protoplanetary disk, with the binary pair shown at the top.
Image: University of Warwick / Mark Hurric

But while the planetary formation can begin, it is not clear to what extent the planets can be formed and remain stable in such seemingly chaotic system. But if there are planets or planetals, then the look of one object in such a system will be remarkable. Standing on one of these planets, you will see the arc of a protoplanetary disk that extends beyond the horizon, reaching directly above the head, and returning to the horizon behind you. Meanwhile, in a location along the disk, two stars would be visible, turning back and forth around the protoplanetary disk.

"This is a very exciting result," said Constantine Batigin, an astronomer from Caltech who is not involved with a new study, told Gizmodo. "Configurations of this type are what one would expect from the interaction between gravity and internal dissipation in protoplanetary disks. The discovery of the first such system suggests that the simulation attempts were essentially spot-on. No doubt, more such systems will be opened in the future. "

Danish Tamayo, an astronomer from Princeton, also disagreed with a new study, calling it "fantastic paper" with "unambiguous and beautiful discovery."

"This is a funny mathematical whim of orbital dynamics that polar orbits around a binary star system are a very stable configuration, but it was not clear if they could ever create nature," said Tamayo. "There were several previous examples of highly inclined disks, but this is the first case that causes the helmet, and a true testimony to the careful work of the authors and the fantastic technical capabilities of the ALMA Observatory."

The next task for astronomers will be the detection of similar systems and at different stages of their development. The discovery of real planets within such a system would be particularly daunting.

[Nature Astronomy]

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