In the quest to understand the universe’s many mysteries, astronomers are looking for potentially trillions of elusive space objects called rogue worlds. These stellar objects blur the lines between planet and star–to better understand the cosmic processes that form both.
A team of astronomers using the James Webb Space Telescope (JWST) recently spotted six new rogue worlds in a young nebula. The findings are detailed in a study published August 27 in The Astronomical Journal and indicate that rogue worlds may help create celestial objects that are even bigger than the planet Jupiter. These newly discovered worlds may even be gas giants 5 to 10 times bigger than our solar system’s biggest planet.
[Related: Space probably has way more ‘rogue planets’ than we thought.]
“We are probing the very limits of the star forming process,” study co-author and Johns Hopkins University astrophysicist Adam Langeveld said in a statement. “If you have an object that looks like a young Jupiter, is it possible that it could have become a star under the right conditions? This is important context for understanding both star and planet formation.”
What are rogue worlds?
Also called rogue planets, these free-floating celestial objects have masses similar to planets. However, unlike planets, they are not tethered to a central star’s gravity, like the way Earth is tethered to the sun’s gravity. Instead, they are cast adrift in space.
However, their formation and size make them similar to stars. Most rogue worlds are formed by material ejected during the early stages of planet formation, when matter is colliding more often. They may also have discs of space dust around them, which is critical for both star and planet formation. Others may originate from collapsing molecular clouds that do not have enough mass to generate the nuclear fusion that powers stars. Even with these similarities, they still straddle the boundary between what is considered a star versus a planet.
While there are about 70 to 170 known or suspected rogue planets, some scientists estimate that there could be trillions in the galaxy.
Importantly, rogue worlds blur classifications because their masses overlap with gas giants like Saturn and Jupiter and brown dwarf stars. While rogue worlds are rare in our home Milky Way galaxy, the new JWST data indicates that they show they account for about 10 percent of celestial bodies in a recently observed targeted star cluster–NGC1333.
Rogue worlds in a young nebula
In the study, the team used data from the JWST’s deepest survey of the young nebula NGC1333. This star-forming cluster is about 1,000 light-years away from Earth in the constellation Perseus. A newly released image of NGC1333 that accompanies the study shows the nebula glowing with dramatic displays of interstellar dust and clouds.
[Related: The Ring Nebula is a glowing gas-filled donut in the latest JWST snap.]
“We used Webb’s unprecedented sensitivity at infrared wavelengths to search for the faintest members of a young star cluster, seeking to address a fundamental question in astronomy: How light an object can form like a star?” study co-author and Johns Hopkins astrophysicist and Provost Ray Jayawardhana said in a statement. “It turns out the smallest free-floating objects that form like stars overlap in mass with giant exoplanets circling nearby stars.”
In the observations, the team did not detect any objects less than five Jupiter masses, even though JWST has the sensitivity needed to detect such bodies. This indicates that any stellar objects lighter than this threshold are more likely to form the way planets do, as opposed to stars.
“Our observations confirm that nature produces planetary mass objects in at least two different ways—from the contraction of a cloud of gas and dust, the way stars form, and in disks of gas and dust around young stars, as Jupiter in our own solar system did,” Jayawardhana said.
Dusty discs
The most intriguing of these starless objects also happened to be the lightest. It has a mass estimated to be about five Jupiters, or about 1,600 Earths and a dusty disc of material nearby.
According to the study, the presence of a disk indicates that the object potentially formed the way a star does. Space dust like this generally spins around a central object in the early stages of star formation.
Disks like these are also a prerequisite for the formation of planets, and this one may also have important implications for forming potential “mini” planets.
“Those tiny objects with masses comparable to giant planets may themselves be able to form their own planets,” Aleks Scholz, a study co-author and astrophysicist at the University of St Andrews in Scotland, said in a statement. “This might be a nursery of a miniature planetary system, on a scale much smaller than our solar system.”
[Related: Astronomers spot an extragalactic star with a disc around it for the first time.]
With the NIRISS instrument aboard the JWST, the astronomers measured the infrared light profile–or spectrum–of every object in the observed portion of the star cluster and reanalyzed 19 known brown dwarf stars. They also found a new brown dwarf with a planetary-mass companion alongside it. According to the team, this is a rare finding that challenges some of the theories of how binary systems form.
“It’s likely that such a pair formed the way binary star systems do, from a cloud fragmenting as it contracted,” Jayawardhana said. “The diversity of systems that nature has produced is remarkable and pushes us to refine our models of star and planet formation.”
In future studies, the team plans to continue examining more of the faint objects’ atmospheres and compare them to atmospheres of heavier brown dwarfs and gas giant planets. They are also going to use the JWST to study similar objects that have dusty disks, to explore the possibility that these disks are forming mini planetary systems that resemble Jupiter’s and Saturn’s numerous moons.
