What is the minimum mass that an object can have in the cradle of stars, in molecular gas nebulae? In their search for objects that are less massive and hotter than stars, astronomers have already discovered objects that are less than ten times the mass of Jupiter. This mass is similar to the mass of giant planets outside the solar system, except that they do not orbit any stars.
International team, you are part of it Coralica Muzicfrom the Institute of Astrophysics and Space Sciences (Amnesty International) and the Faculty of Science of the University of Lisbon (Science ULisboa), use the telescope.James Webb (JWST) has discovered six new potential planetary-mass objects in the molecular cloud star cluster NGC 1333, in the constellation Perseus, more than 960 light-years away. None of them are less than five times the mass of Jupiter, suggesting that lighter objects will be rare or even nonexistent in this cluster.
European Space Agency Post the image The clearest image of NGC 1333 was produced from these JWST observations made in August 2023. The scientific results are presented in an article2Now available on ArXiv platform Which will be published in the next few days in the magazine. Astronomical JournalThe first author is Adam Langfield, of Johns Hopkins University and the Carl Sagan Institute – Cornell University, USA.
How many of these planetary-mass objects are there freely in interstellar space? And how are they formed? “The two questions are related, because the numbers of these objects will tell us something about their formation processes,” says Koralica Muzic, the paper’s second author. “We found that planetary-mass objects make up ten percent of the total number of objects in the star cluster NGC 1333.”
Planetary mass objects (less than 13 times the mass of Jupiter) are also thought to be3) It may have two origins. One is that they form like stars—by the gravitational collapse of matter into dense, cold clouds—but are unable to accumulate enough material to reach the temperatures needed to ignite nuclear fusion inside. The other origin would be shared with planets: in orbit around a star, but from where they would later be ejected by interaction with a larger planet, or another nearby star. Either process could generate two families of objects with different properties.
The researchers say the ratio of one planetary mass to every ten planets larger than 13 Jupiters is consistent with studies of other groups. However, the objects the team discovered were mostly created through the process of star formation, and would be the least massive to form this way.
“The most important result is that we did not find objects with masses less than five Jupiter masses, even though it was technically possible to find them,” adds Muzic. “If the smallest planets are the most common, according to exoplanet studies, and also the easiest to get out of orbit, then we would expect to see more of these low-mass stray objects.” But the researcher stresses that there are no simulations or theoretical work yet that provide comparable quantities.
The team of researchers hypothesizes that the gravitational processes that eject planets from their orbits may not be effective in this cluster NGC 1333: “The ejection of planets is expected to depend on the environment, for example, if there is a higher density of stars, this leads to the ejection of stars,” explains Koralica Muzic. “So we want to look at other denser clusters, which have a higher density of stars, to see if there is any difference.”
This team has been studying the star cluster NGC 1333 since 2009 using other infrared instruments, such as Subaru telescopeIn Hawaii, from the National Astronomical Observatory of Japan (NAOJ). But only now, with the infrared sensitivity of the James Webb Telescope, has it become possible to find objects less than five times the mass of Jupiter, if they even exist.
To calculate the mass of these objects, you first need to know their age and temperature, because the three properties are related. Scientists look for them in star clusters because they should be about the same age as the stars in the cluster. In NGC 1333, these objects are very young, about three million years old at most. The temperature is determined by the frequencies of light at which its surface emits the most intensely.
These wandering worlds have little in common with Jupiter. In addition to not orbiting a star, their surface temperatures can reach 1,700 degrees Celsius. But there is still little information about their chemical composition, which could perhaps reveal the process of their formation, by comparing it to that of brown dwarfs and exoplanets. “Modeling the spectra of the light emitted by these objects is very difficult, because at these very low temperatures molecules are formed in their atmospheres,” says Koralica Muzic.
Molecules like water, methane or carbon monoxide are what make it possible to distinguish a brown dwarf from a normal star. But for lower mass, lower temperature objects, heavier molecules and atoms generate too many signals in the spectra, and it is difficult to combine all the physics to simulate them.
Of the six objects discovered, the lightest has a disk of material around it. Muzic explains the significance of this finding: “If it has a disk, it must have formed like a star, because an ejected planet would in principle not have a disk. All young stars go through a phase where they have a protoplanetary disk.
It will be important to understand whether these discs can give rise to miniature planetary systems, such as Jupiter’s moons, comments Adam Langfield, the study’s first author. “We also discovered a planetary-mass object with a brown dwarf companion. The pair would have formed in the same way as binary stars. This is a rare discovery and provides context for theories about star and planet formation,” Langfield adds.
“We plan to characterize in more detail the chemistry, the disks, the pairs of objects and their motions in the cluster,” says Alex Schultz, of the University of St Andrews in the UK, co-author of the paper and coordinator of the study. Monitoring projectsWith JWST. “The main goal is to find signs that tell us something about their origin.”
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