MARK GARLICK / WARWICK UNIVERSITY
Artistic impression of the toi-6894 B Exoplanet, a low-density giant gastry in the toi-6894 star, the smallest mass star to have a giant planet in transit.
Astronomers at the University of Warwick and University College London discovered the smallest star known to host a giant planet in transit that, according to the main planetary formation theories, should not exist.
The star TOI-6894 It’s like many others in our galaxy, a small red dwarf with only 20% of our sun’s dough. As many small stars, it is not expected to provide adequate conditions to form and host a large planet.
However, as in the journal Nature Astronomy, a global collaboration of astronomers, including partners in Chile, USA and Europe, found the unmistakable signature of a giant planet called To 6894 Bin orbit of this little star.
This system was discovered as part of a large -scale research on TESS (Transiting Explanet Survey Satellite), which sought giant planets around low mass stars, led by Edward Bryantwhich completed this work at the University of Warwick and UCL.
“I was very enthusiastic about this discovery. Initially, I looked for giant planets in the Tess observations of over 91,000 low -mass red dwarf stars, ”explains Bryant, first author of the scientific article.
“Then, using observations made with one of the largest telescopes in the world, ESO’s VLT, I discovered toi-6894 B, a giant planet that transits the star of the smallest known mass to date, to welcome such a planet,” says the researcher.
“We did not expect planets like toi-6894 B if they could form around stars of such small dough. This discovery will be a cornerstone To understand the extremes of the formation of giant planets, ”concludes Bryant.
Planet Toi-6894 B is a low -density gaseous giant With a slightly larger radius than Saturn, but with only 50% of its mass. It is, to date, the Mass star to have a giant planet In transit and has only 60% the size of the following smallest star to host such a planet.
“Most of the stars in our galaxy are small stars just like this, with low pasta and previously thought they could not host giant giant planets,” he says Daniel BaylissAssociate Professor at Warwick University.
“Thus, the fact that this star hosts a giant planet has great implications for the total number of giant planets that we estimate exist in our galaxy,” the researcher adds.
A challenge to the dominant theory
Second Vincent van Eylenalso an investigator of the UCL MSSL, this is a intriguing discovery. “We don’t know how a star with such little mass can form such a big planet!”
“This is one of the objectives of looking for more exoplanets. When finding different planetary systems of our solar system, we can Test our models And better understand how our own solar system has formed, ”says the researcher.
The most acceptable theory of planet formation is the Nucleus Acception Theory.
A planetary core First formed by accreation (gradual material accumulation) and, as the nucleus becomes more massive, attracts gases that form an atmosphere. After, it becomes massive enough to enter a uncontrolled gas accreation process and a gaseous giant.
In this theory, the formation of gaseous giants It’s harder Around low mass stars because the amount of gas and dust on a protoplanetary disc around the star (the raw material for planet formation) is too limited to allow the formation of a sufficiently massive nucleus and the occurrence of the uncontrolled accretion process.
However, the existence of TOI-6894 B, a giant planet in orbit of an extremely low mass star, suggests that this model may not be completely accurate and that they are required alternative theories.
“Given the mass of the planet, TOI-6894 B may have been formed through an intermediate process of accretion of the nucleus, in which a protoplanet forms and believes gas constantly without the nucleus becoming massive enough For an uncontrolled gas accord, ”says Edward Bryant.
“Alternatively, it may have been formed due to a gravitatively unstable disc. In some cases, the album surrounding the star becomes unstable due to the gravitational force it exerts on itself. These discs can then fragment with gas and dust collapse to form a planet, ”he adds.
But the team found that None of the theories could explain completely the formation of TOI-6894 BA from the available data, which leaves the origin of this giant planet, for now, as an open question.
