Astronomers have found an object that disrupted the scientific picture of the universe

An international team of astronomers has discovered a planetary system so strange that to describe one of its objects they had to come up with a new term on the fly — “exosatellite”. The discovery, published in Nature, shows that the vocabulary scientists have used to describe the cosmos for the past thirty years has begun to break down.

Matryoshka instead of the system

Imagine a nesting doll in reverse: a small star — a red dwarf with a mass of about 40% of the Sun — holds in orbit an object much stranger than a planet, writes xrust. This is a brown dwarf: a body that wanted to become a star, but did not gain enough mass to trigger nuclear fusion of hydrogen in the core. And around this failed star, in turn, another object is spinning — approximately the size of Jupiter.

The system was found using the Very Large Telescope of the European Southern Observatory in Chile — the same instrument that once helped detect the first exoplanet around a solar-type star. This time, the CRIRES+ instrument did not catch light, but microscopic fluctuations in the spectrum of the brown dwarf — a sure sign that there is a gravitationally bound companion next to it. The observations lasted for two years and 23 nights, which made it possible to obtain measurement accuracy an order of magnitude higher than in previous attempts to find similar objects.

The system, designated CD-35 2722, is located 71 light years from Earth — by cosmic standards, almost at our side.

What the hell should I call it

The team has no questions left with physics: the mass of the new object is no less than the mass of Jupiter, it makes an orbit around the brown dwarf every 170 days, being at a distance of about five times less than from the Earth to the Sun. But the circus began with terminology.

Formally, if you follow the logic of the Solar System, a body orbiting a body orbiting a star is a moon, and outside the home system is an exomoon. But as study lead author Kevin Hoy, a graduate student at the University of Diego Portales, explained, all the moons we know of in our system are relatively small balls of rock or ice. The new object is not similar to them either in size or composition.

According to Hoy, the words coined to describe the solar system are already bursting at the seams when it comes to other worlds. Therefore, the team deliberately abandoned the term “moon” and proposed a temporary designation — “exosatellite”. Co-author of the study, astrophysicist and YEMS project director Alisa Zurlo, added: the object does not revolve around a planet, it revolves around a body hovering somewhere between a planet and a star, so there are simply no direct analogies in our system.

It’s funny that formally the problem is deeper than it seems: the International Astronomical Union does not have an official definition of what a “moon” is — there is only a definition of a planet, and even then with the caveat that it applies only to bodies revolving around the Sun.

Pandora's box is already open

Zurlo does not mince words: according to her, the discovery opened a whole Pandora's box for the scientific community. The object is so atypical that now theorists have to figure out how such bodies are formed in general and how common they are in the Universe.

There are currently two versions of the origin of the exo-satellite. First: it was born right on the spot, from a disk of gas and dust around a brown dwarf — in much the same way that ordinary planets form around stars. Second: the object formed somewhere else and was later gravitationally captured by a brown dwarf. The system is still very young, and the brown dwarf itself still glows with the residual heat of its own formation — this, by the way, made it possible to see it against the background of a brighter star.

For comparison: the brown dwarf in this system is about 33 times more massive than Jupiter, while being almost one and a half times larger and noticeably hotter. This alone distinguishes CD-35 2722 from the usual picture of planetary systems, where objects of intermediate mass are rare.

Why the hunt for exomoons is going so hard

class=»notranslate»>__GTAG7__Since the 1990s, when the first exoplanets were discovered, astronomers have amassed an impressive collection of over 6,300 confirmed worlds beyond the solar system. But with exomoons, everything is much worse: there are only a few suitable candidates, and the evidence base for each of them is still considered controversial.

The reason is simple: satellites are several times smaller and dimmer than their “masters,” which means that catching their signal against the background of a bright star or planet is a task at the limit of the capabilities of modern instruments. A similar story recently happened with the HD 206893 system: a team led by Quentin Krahl using the VLTI interferometer found hints of the presence of a satellite, but could not confirm the discovery. Against this background, the discovery of CD-35 2722 looks much more confident — the authors directly call it the first plausible evidence of the existence of an exosatellite.

What's next

The team expects that the find is not a one-time accident, but the first sign. More sensitive instruments, including ESO's currently under construction Extremely Large Telescope (ELT), should be able to find much smaller satellites in the coming years and perhaps reveal how typical the star-brown-dwarf-companion architecture is for our Galaxy.

In the meantime, in the astronomical community there is a debate that is not so much scientific as linguistic: how to name an object for which a word has simply not been invented. And this is, perhaps, the main charm of the discovery — it reminds that the catalog of the Universe is still written from scratch, and not checked from an earthly textbook.

Other news

Previously, astronomers had already recorded similar boundary cases: for example, in the star TOI-201, a brown dwarf in an elongated orbit did not prevent the formation of two full-fledged planets at once — a rare example of how gravitational chaos does not destroy, but forms a system. And in the pair Gliese 229ba and Gliese 229bb, they previously found two brown dwarfs orbiting each other — another reminder that the boundary between “almost a star” and “just a large planet” in space is much more arbitrary than in textbooks.

Sources:

• Reuters — https://www.reuters.com , https://www.eso.org , https://skyandtelescope.org

Xrust Astronomers found an object that violated the scientific picture of the universe