Last year, using the James Webb Space Telescope (JWST), astronomers made the startling discovery of some free-floating, planetary-mass objects in the Orion nebula that threw their ideas of planet and star formation into doubt. And now, new research has further deepened the mystery around these so-called Jupiter-mass binary objects, or JuMBOs.
JuMBOs aren't stars, but aren't really planets either. Mark McCaughrean, senior science advisor at the European Space Agency (ESA), and colleagues originally located the objects in the Orion nebula. This nebula is a star birthing region, also known as Messier 42, and sits around 1,350 light years from Earth.
Building on that observation, a team of researchers used data collected by the Karl G. Jansky Very Large Array (VLA) at the U.S. National Science Foundation National Radio Astronomy Observatory to study radio signals coming from some of those JuMBOs. Yet, despite the fact that McCaughrean and colleagues found 40 pairs of JuMBOs, only one pair of these strange objects was seen to be emitting radio waves.
"It is already hard to account for JuMBOs with star and planet formation models, and now we have this strong radio emission, and it is not clear what is producing it," Luis F. Rodriguez, team member and a professor at the National Autonomous University of Mexico, told Space.com.
The radio signal was seen coming from both components of "JuMBO 24." Both components seem to have around 11 times the mass of Jupiter, making them the largest of their kind seen by the JWST, with the others having masses between 3 and 8 times that of the solar system's most massive planet.
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The signal was significantly stronger than radio signals associated with objects similar to JuMBOs, aka brown dwarfs. Brown dwarfs are objects born in the same way as stars, but that fail to gather enough mass to trigger the fusion of hydrogen to helium at their cores like your standard star does. This failure to kickstart the process that defines a star in its main sequence lifetime has led to brown dwarfs, with masses between 13 to 75 times the mass of Jupiter, receiving the unfortunate nickname of "failed stars."
"With regular stars and brown dwarfs, there are mechanisms that explain radio emissions. For JuMBOs, we have no mechanism to explain this very strong radio emission," Rodriguez said.
Not stars nor planets
JuMBOs are hot, gassy, and relatively small bodies that exist in pairs, a combination that defies common observations of binary stars. Normally, scientists believe only the most massive stars prefer life in binary pairings; the smaller a stellar body is, the less likely it is to be found in a binary partnership.
Binary stars are born when overly dense patches in a disk of gas and dust fragments collapse and gather mass, forming twin stars. Around 75% of massive stars exist found in binaries, 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 binaries is close to zero. That means JuMBOs, which are under the mass limit for brown dwarfs, shouldn't really exist in binaries if they are indeed formed like stars.
But if JuMBOs are formed like stars, the sheer number of them discovered in Orion would suggest the binary frequency of stellar bodies "jumps up" for some reason at masses below that of brown dwarfs. This is something that can't be accounted for in stellar formation models yet.
So, if these planetary-mass objects can't form according to current star formation models, they are born like planets, surely? Well, maybe, but JuMBO pairings are equally difficult to explain if they are created like planets, which form from leftover material in the same disks of gas and dust that birthed their parent stars.
Some planets are known to be ejected from around their host star as a result of 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 like how JuMBOs in Orion appear to be orphans. However, the process that creates these orphan planets is so violent that it should split apart any gravitationally bound planet pairs.
The ejection mechanism can't account for why Jupiter-like planets would have been ejected together. That means the planetary evolution route can explain how JuMBOs came to be, but not why they still have their binary partners. Even if such a thing could happen on some occasions, there aren't just one or two JuMBO pairings in Orion. There are 42.
These JuMBOs likely aren't the result of a single freak ejection event.
JuMBOs in Orion become even more challenging to explain when considering the fact that some of the binaries they dwell in are extremely widely spaced. A few JuMBOs appear to even be separated by as much as 300 times the distance between the Earth and the sun. Others fall as far apart as the width of the whole solar system, meaning they are very weakly gravitationally bound.
Radio signals from JuMBO24 don't mean life
Rodriguez and colleagues were well-acquainted with Orion, having studied the nebula before with the VLA. So, when JuMBOS showed up in infrared data of the JWST, they decided to follow up by looking through archival data of radio wave observations to hunt for radio wave counterparts to these detections.
"We said, 'Hey, let's go and see if one of the JuMBOs has been detected before.' We took VLA archive data and calibrated it, finding JuMBO 24 in all three 'epochs' of data," Rodriguez said. "We detected radio wave emissions from the most massive JuMBO binary, but it is not clear why the others were not detected in radio waves."
He explained that the team thinks the other JuMBOs could also be emitting 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 create deeper images with the hope of finding maybe a few more, and this will allow us to understand the process that is creating radio waves from JuMBOs much better," Rodriguez said.
These deeper observations could also reveal the velocity of the JuMBOs in the sky with relation to the Orion nebula. Rodriguez explained that, if the JuMBOs are moving rapidly, this would suggest that they formed like planets around stars and were ejected from these systems. On the other hand, he pointed out that if these curious celestial bodies are almost stationary in relation to Orion, this would imply they are created from massive clouds of collapsing gas and dust like stars.
Either explanation would prompt a rethink 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 quite cool since no star is associated with them," he said. "If JuMBOs had moons, one could speculate that life could exist In a subsurface ocean like it is suspected in Europa, Ganymede, and Enceladus. However, the objects in Orion are young at just a few million years old [compared to our 4.6 billion-year-old solar system], meaning there probably has not been enough time for life to appear on these moons if they exist."
Rodriguez added that, in the unlikely event these objects or moons around them could support life, researchers chasing alien organisms on JuMBO 24 would also have to explain why radio emissions are coming from both components of this strange binary, not just one.
Thus, while JuMBOs may be the astronomical discovery of the 2020s and are fascinating targets for scientists who want to understand the formation of stars and planets better, they may not be great targets for scientists investigating the possibility of life outside the solar system.
The team's research was published in January in the Astrophysical Journal Letters.
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