In 2019, scientists discovered something peculiar: a gas giant in a very tight orbit around a low-mass star designated as GJ 3512. This dwarf star has been given the designation M. The finding was unexpected due to the fact that there shouldn’t have been enough material in the area around the star to begin with in order to construct such a large planet.
Now, in a recent study that was published in the Monthly Notices of the Royal Astronomical Society and conducted by Edward Bryant (University College London), scientists have found fifteen probable gas giants that orbit low-mass stars. This research was published by the Royal Astronomical Society. It would appear that the discovery made in 2019 is not unique, which puts into doubt the conventional beliefs on the genesis of planets.
Two stages may be distinguished in the core-accretion model of planet formation: In the beginning, planetesimals bump against one another and cling together, eventually growing into stony cores that are the size of a few Earth masses. After that, they begin to amass significant quantities of gas all around themselves. This hypothesis performs well in simulations of a wide variety of star systems, including the one including our solar system. However, stars with a low mass have planet-forming discs that also have a low mass. Then how are they able to create such massive planets?
A number of hypotheses were been forward by astronomers in an effort to explain the presence of GJ 3512b. It’s possible that the planet got here from somewhere else, or that it was formed by some other method, like disc instability. Both of these are possibilities. In the latter possibility, the formation of gas giants occurs all at once; however, this process should take place further away from the host star. In spite of this, there were some compelling counterarguments presented to defend the theory for this particular circumstance.
However, Bryant’s team was able to demonstrate that our planet is not exceptional. They analysed data from the Transiting Exoplanet Survey Satellite, which included more than 91,000 stars with less than half of the Sun’s mass, and found 15 with massive planets or planet candidates in tight orbits around their host stars. Therefore, despite the fact that the occurrence rate is extremely low (approximately 0.2%), it is higher than the null rate that astronomers had previously thought it to be.
Bryant and his team also attempted to mimic the two primary formation paths using the planets in question, however they discovered that neither of the models was successful in adequately explaining how these planetary systems came into being. Bryant puts out the hypothesis that “perhaps there is a third formation method going on that we don’t know about yet.” “Or it is one of the main two, but it is operating in extreme circumstances,” the alternative may be. It’s possible that planets can develop via a few different processes.
In order to enhance our models of planetary formation, we require additional information on a wider variety of planetary systems at various points in their developmental timelines. The methods that we employ to identify planets, such as the radial velocity approach, which is useful for locating planets around low-mass stars, and the transit method, which is most effective for detecting planets that are orbiting in close proximity to their stars, constrain the observations that we are able to make. However, there are a wide variety of planetary systems in the universe, and in order to locate all of them, we will want additional and unique methods.
Martin Schlecker from the University of Arizona, who was not involved in this work, suggests that microlensing might be one answer to the problem. “Gravitational microlensing is a method that can be used to hunt for exoplanets, and instruments like the upcoming Nancy Grace Roman Space Telescope will make it more feasible,” he explains.
The process of microlensing is dependent on the gravitational pull of a nearby foreground star, which is able to bend and concentrate the light coming from a more distant background star. If there is a planet orbiting the foreground star, its imprint will be clearly seen in the intensification of the gathered light if it is present. This approach can identify planets circling far away from sun-like stars, and it can even find rogue planets that aren’t gravitationally connected to any star at all. It is therefore able to fill in certain blanks in the census of the planet.
Nobody dislikes a good riddle, but astronomers are particularly ecstatic about the fact that neither the core-accretion nor the disc-instability models appear to be applicable to the unusual gas giants that orbit extremely small stars.