Last year, astronomers using the James Webb Space Telescope (JWST) made the surprising discovery of several free-floating planetary-mass objects in the Orion Nebula, challenging their ideas about planet and star formation. And now, new research has further deepened the mystery surrounding these so-called Jupiter-mass binary objects, or JuMBOs.
JuMBOs aren’t stars, but they aren’t really planets either. Mark McCaughrean, senior scientific advisor at the European Space Agency (ESA), and colleagues originally located the objects in the Orion Nebula. This nebula is a star birth region, also known as Messier 45, and is located approximately 1,350 light-years away from Earth.
Building on that observation, a team of researchers used data collected by the U.S. National Science Foundation National Radio Astronomy Observatory’s Karl G. Jansky Very Large Array (VLA) to study radio signals coming from some of those JuMBOs. But despite the fact that McCaughrean and colleagues found 40 pairs of JuMBOs, only one pair of these strange objects was found to emit radio waves.
“It’s already difficult to explain JuMBOs with star and planet formation models, and now we have this strong radio emission, and it’s not clear what causes it,” said Luis F. Rodriguez, team member and professor at the National Autonomous Organization. University of Mexico, told Space.com.
The radio signal came from both components of “JuMBO 24.” Both components appear to have about 11 times the mass of Jupiter, making them the largest of their kind as seen by the JWST, while the others have a mass between 3 and 8 times that of the solar system’s heaviest planet.
Related: Surprise! Baby exoplanets may look more like Smarties candies than spheres
The signal was significantly stronger than radio signals associated with objects similar to JuMBOs, also known as brown dwarfs. Brown dwarfs are objects that are born in the same way as stars, but fail to accumulate enough mass to trigger the fusion of hydrogen into helium in their cores, as your standard star does. This inability to initiate the process that defines a star in its main sequence life has led to brown dwarfs, with masses between 13 and 75 times the mass of Jupiter, being given the unfortunate nickname of “failed stars.”
“For ordinary stars and brown dwarfs, there are mechanisms that explain the radio emission. For JuMBOs, we have no mechanism to explain this very strong radio emission,” Rodriguez said.
No stars and no planets
JuMBOs are hot, gaseous and relatively small celestial bodies that exist in pairs, a combination that defies usual observations of binary stars. Normally, scientists believe that only the most massive stars prefer life in binary pairs; the smaller a stellar body is, the less likely it is to be found in a binary partnership.
Binary stars form when overly dense spots in a disk of gas and dust fragments collapse and collect mass, creating twin stars. About 75% of massive stars are binary stars, with this percentage dropping to 50% for stars around the size of the Sun and 25% for the smallest stars. The chance of finding brown dwarfs in double stars is almost zero. This means that JuMBOs, which fall below the mass limit for brown dwarfs, should not really exist in binaries if they indeed formed as stars.
But if JuMBOs formed as stars, the sheer number discovered in Orion would indicate that the binary frequency of stellar bodies for some reason “jumps up” at masses below that of brown dwarfs. This is something that cannot yet be taken into account in star formation models.
So if these planetary-mass objects can’t form according to current star formation models, they are still born as planets? Well, maybe, but JuMBO pairs are just as difficult to explain as they are created as planets, which form from remnants of material in the same disks of gas and dust from which their parent stars emerged.
Some planets are known to be thrown around their parent star due to internal or external gravitational effects, such as encounters with other star systems. From there, those worlds become “rogue planets” and wander the cosmos without a parent star, just as JuMBOs appear to be orphans in Orion. However, the process that creates these orphan planets is so violent that it should split apart any gravitationally bound planet pairs.
The ejection mechanism cannot explain why Jupiter-like planets would have been ejected together. That means the planetary evolutionary pathway can explain how JuMBOs emerged, but not why they still have their binary partners. Even if something like this might happen occasionally, there aren’t just one or two JuMBO links in Orion. There are 42.
These JuMBOs are probably not the result of a single freak ejection event.
JuMBOs in Orion become even more challenging to explain when you consider that some of the binaries they reside in are extremely far apart. In fact, a pair of JuMBOs appear to be as much as 300 times the distance between Earth and the Sun. Others fall as far apart as the width of the entire solar system, meaning they are very weakly bound by gravity.
Radio signals from JuMBO24 mean no life
Rodriguez and colleagues knew Orion well, having previously studied the nebula with the VLA. So when JuMBOS showed up in the JWST infrared data, they decided to go further by scouring archival data from radio wave observations to look for radio wave counterparts to these detections.
“We said, ‘Hey, let’s go see if any of the JuMBOs have been detected before.’ We took VLA archive data and calibrated it, finding JuMBO 24 in all three ‘eras’ of data,” said Rodriguez. “We detected radio wave emissions from the most massive JuMBO binary, but it’s not clear why the others were not detected in radio waves.”
He explained that the team thinks the other JuMBOs could also emit radio waves because their components are smaller than the two 11 Jupiter mass objects in the JuMBO 24 binary.
“We are asking for time with the VLA to take deeper images in the hope of perhaps finding a few more, and this will allow us to much better understand the process that creates radio waves from JuMBOs,” Rodriguez said.
These deeper observations could also reveal the speed of the JuMBOs in the sky relative to the Orion Nebula. Rodriguez explained that if the JuMBOs are moving quickly, it would indicate that they formed as planets around stars and were removed from these systems. On the other hand, he pointed out that if these curious celestial bodies are nearly stationary relative to Orion, this would imply that they formed from huge clouds of collapsing gas and dust, like stars.
Both explanations would prompt a reconsideration of how stars and planets form and evolve in their respective systems.
Radio signals may also be indicative of intelligent life on Earth, but Rodriguez is quick to shut down speculation that this is the case for JuMBO 24.
“Life is not expected in Jupiter-like objects without a solid surface, and JuMBOs would be pretty cool because there is no star associated with them,” he said. “If JuMBOs had moons, one might speculate that life could exist in a subsurface ocean like those suspected in Europa, Ganymede and Enceladus. However, the objects in Orion are only a few million years old. [compared to our 4.6 billion-year-old solar system]meaning there probably hasn’t been enough time for life to appear on these moons, if they exist.”
RELATED STORIES:
— Star blows away the atmosphere of a giant exoplanet, leaving behind a huge tail
—James Webb telescope detects the earliest strand in the ‘cosmic web’ ever seen
— James Webb Space Telescope catches a glimpse of Earendel, the most distant star known in the universe
Rodriguez added that, in the unlikely event that these objects or moons around them could support life, researchers pursuing alien organisms on JuMBO 24 would also have to explain why radio emissions are coming from both components of this strange binary star system, and not just An.
So while JuMBOs may be the astronomical discovery of the 2020s and are fascinating targets for scientists looking to better understand the formation of stars and planets, they may not be great targets for scientists exploring the possibility of life outside the solar system.
The team’s research was published in January in the Astrophysical Journal Letters.