After you are born star the remaining material forms a Gas and dust disk around him from which the Planets. The less massive the star is, the less massive the remaining material and therefore the disk. This probably happens with cold, small stars around which planets as massive as Neptune cannot form, which would require a fairly massive disk.
But that’s exactly what an international team of astronomers discovered: a planet with a Dimensions at least 13 times larger than Earth (similar to that of Neptune) with a close orbit around LHS 3154, a dwarf star very low mass, about nine times less massive than the Sun.
The discovery, published in the journal Science and under the direction of the teacher Guðmundur Stefansson from Princeton University (USA) shows that small stars can host larger planets than previously thought.
Image of the Earth and the Sun (left) and the planet LHS 3154b and its star (right), with relative sizes at scale but without orbital distance. / Penn State University
“It is well known that the disks around cold and small stars like LHS 3154 are quite small, and collecting from them all the material required to form such a massive planet is quite a challenge,” explains one Authors to SINC. Yamila Miguelfrom Leiden University and the Netherlands Space Research Organization.
“And certainly not impossible,” he emphasizes, “with the classic way of shaping planets from a modeling perspective.” That’s why This planet is very interesting! “It challenges classical theories about planet formation mechanisms.”
It is quite a challenge to collect all the material needed to form such a massive planet from the disk around such a small star.
These theories predict that stars Red dwarfs (especially the M (like this, the lowest-mass star type) should not host close-orbiting exoplanets with masses greater than Neptune’s (17 Earth masses). Although high-mass planet candidates such as GJ 3512b have been discovered near low-mass dwarf planets, all of them have very long orbital periods and can be formed by processes such as gravitational instability.
Evidence from a spectrograph in Texas
However, the new exoplanet is called LHS 3154-b, has a short orbital period of less than 4 days. It was discovered with the so-called Radial velocity method, which measures the motion of the star due to the gravitational interaction caused by these worlds. The instrument used is HPF spectrograph (Planet finder for habitable zones), installed on the Hobby-Eberly Telescope at McDonald Observatory (Texas, USA).
The HPF (Habitable-zone Planet Finder) instrument during installation in the clean room of the Hobby-Eberly Telescope at the McDonald Observatory. / Guðmundur Stefánssonn/Penn State
The Infrared spectroscopic observations The star LHS 3154 confirmed that an exoplanet with a mass near Neptune was moving around it, with a Orbital period of 3.7 days. According to the authors, current theories of planet formation, including the mechanisms of core formation and gravitational instability, have difficulty explaining the formation of this massive planet.
They did too Simulations to show that the amount of dust in the protoplanetary disk that would be required to form LHS 3154-b would have to be at least ten times greater than the amount normally observed in stars like its own. How did this exoplanet form?
Possible explanations of the mystery
Yamila Miguel points out some ideas: “One could be that the protoplanetary disk That was the origin of the planet more massive than what the classical theory predicts or what has more dust, which also favors the formation of more massive planets. It could also be that the Material distribution in the disk is such that most of the dust accumulates in the inner regions of the disk where the planet is born, which favors its formation.”
“In any case,” he concludes, “these are all scenarios that deviate from the classic picture of emergence.” Giant planetsalthough they are consistent with N“New theories are being formulated by observing these protoplanetary disks, so this is a very interesting case to confirm them.”
Astronomers will continue with the help of LHS 3154b and other giant planets like TOI-4860 b recently discovered around small stars Updating planet formation models which explain how these worlds came into being in our universe.
Reference:
Guðmundur Stefánsson, Yamila Miguel et al. “A Neptune-mass exoplanet in a close orbit around a very low-mass star challenges formation models.” Science2023