A new study suggests that the mysterious Jupiter-sized pair may have originated from embryonic stars. This theory could explain some features of these Jupiter-mass binary objects (JuMBOs), such as why the members of each pair are so far apart, but more data is needed to confirm the idea.
The James Webb Space Telescope observed these JuMBOs in the Trapezoid region of the Orion Nebula. Each JuMBO pair consists of two gas giants, each between 0.7 and 30 times the mass of Jupiter. These \”rogue\” planetary companions have been found to orbit each other — but not the parent star — at distances of about 25 to 400 astronomical units, or 25 to 400 times the average distance between Earth and the sun.
Astronomers have proposed several ideas about how these mysterious pairs formed. One theory is that they were thrown together from their home systems by a passing star, although some scientists think this is very unlikely. Another idea is that JuMBOs emerged around a star but their gravity pulled them toward each other and knocked them out of orbit during close encounters.
All of these theories, however, assume that JuMBOs arise from planets that have already formed. In contrast, the new study posits a completely different idea: that the JuMBOs of the Orion Nebula are not pre-existing pairs of planets, but the hearts of embryonic stars.
A star forms from a vast and dense cloud of gas and dust called a pre-stellar core. As a core grows, it collapses under its own weight, forming a baby star called a protostar; if the core fragments, it can form twin or even triplet stars.
But such nurseries are not quiet places. They can be surrounded by massive stars — like the Orion Nebula is — that produce incredibly high-energy radiation. Twenty years ago, astronomers Anthony Whitworth and Hans Zinecker showed theoretically that these powerful photons could destroy pre-stellar cores, causing their outer layers to shed.
At about the same time, a compression wave would push against the center of the core, causing it to compress into a smaller mass object. The result was that the star itself turned into a planet or brown dwarf, sometimes called a \”failed star\” because it\’s not massive enough to fuse hydrogen into helium.
The authors of the new study were aware of Whitworth and Zinecker\’s study and wondered if the same mechanism could create JuMBOs as well. They \”observed that JuMBOs[\’] separations were similar to those of stellar binary systems, which contain two stars with masses similar to or greater than the Sun,\” wrote the U.K. Richard Parker, a senior lecturer in astrophysics at the University of Sheffield in 2008 and senior author of the new study, told Live Science in an email.
This makes them different from most brown dwarf twins found elsewhere in the Milky Way, which are separated by only a few Earth-sun distances, so a different mechanism must be involved, Parker said. \”We assumed the core was already fragmenting to form a stellar binary, but then radiation from the massive star removed a lot of the mass,\” he said.
To test this idea, Parker and Jessica Diamond, a graduate student at the University of Sheffield and lead author of the study, turned to theory. First, they created a group of virtual pre-stellar cores, each with a mass within the range observed in nature. They also assumed that the core would split into two parts, and chose a value for the distance between the siblings — again, from observed values between star pairs.
Then, they applied Whitworth and Zinecker\’s calculations to the virtual cores. This essentially hit them with high-energy radiation from a nearby massive star, wiping out the core\’s envelope and compressing its center. Diamond and Parker found that the resulting paired objects had masses and separation distances similar to those of JuMBOs.
The findings suggest that, with strong radiation pressure from neighboring stars, evolving binary stars can form pairs of rogue planets, providing an explanation for the formation of JuMBO pairs. The results of their study were published Nov. 5 in The Astrophysical Journal.
Parker said more data, such as evidence of JuMBOs in star-forming complexes with other massive stars, would help confirm the hypothesis. In his opinion, an example of such a location is the Scorpius-Centaurus Association, a group of thousands of stars that form parts of the constellations Scorpius and Centaurus.
In any case, Parker does not rule out JuMBO formation through other routes. \”I\’ve always had a hard time thinking there\’s only one way objects like these can form,\” Parker said. \”We know so little about them that it\’s possible they could form in a variety of ways.\”