Unexplained Enigmas in the Orion Nebula May Be Victims of Stellar Bullying

Jonthan O’Callaghan

Some 1,350 light-years from Earth, astronomers detected strange pairs of unexplained objects orbiting in the Orion Nebula. Since then, about 12 months ago, other scientists have proposed a new potential explanation for these apparitions, while other researchers wonder whether they exist at all.

“There’s a bit less confidence they exist,” said Rosalba Perna, a theoretical astrophysicist at Stony Brook University. But “even just having one would revolutionize what we thought was possible” for star and planet formation. Using the James Webb Space Telescope, astronomers have started to reveal the Orion Nebula in glorious detail, showcasing the brilliant swirling clouds of dust and gas that will give rise to hundreds of stars in the next few million years.

Two scientists, Mark McCaughrean at the Max Planck Institute for Astronomy in Germany and Samuel Pearson from the European Space Agency in the Netherlands, detected more than 40 pairs of objects similar in mass to Jupiter floating within the nebula. They named the objects Jupiter Mass Binary Objects, or JuMBOs.

The JuMBOs suggested something was wrong in our understanding of star and planet formation. Stars form from the gravitational collapse of dust and gas, but JuMBOs appeared to be too small to have undergone this process, suggesting they formed as planets around stars that were then ejected. However, their presence in pairs complicates this scenario. It is unlikely that dozens of pairs of planets thrown from a star would end up orbiting one another because of their low gravitational attraction.

A new solution to the JuMBO mystery was proposed in a paper accepted for publication in the Astrophysical Journal. Jessica Diamond and Richard Parker from the University of Sheffield in England say the objects could have formed like stars. But their growth was then stunted by a handful of much larger stars in the nebula, called OB stars, that are up to 40 times the mass of our sun.

“The OB stars are the biggest stars in Orion,” Diamond said.

They blast winds of radiation that would remove the hydrogen gas from the younger JuMBOs’ outer layers in a process called photoerosion, she said. Think of the OB’s as stellar bullies that prevented their JuMBO siblings from evolving into proper stars.

Almost all stars, including our sun, are thought to form as multiples, fragmenting from the same star-forming clump of dust and gas. This would explain why so many of the JuMBOs are in pairs: They are twin stellar cores, born together but never quite growing in stature.

McCaughrean said the idea holds promise. “It makes sense,” he said. “You need to be in a place like Orion, where you’ve got these huge monster stars.”

Since the JuMBOs were discovered, a series of other explanations have been presented for what they might be.

Perna said that the masses of the objects “may have been misinterpreted” and that they could be slightly larger than predicted. This could make them brown dwarfs, failed stars 15 to 75 times the mass of Jupiter that never ignited nuclear fusion at their cores. They, too, are known to exist in pairs.

Other ideas include that cosmic rays stunted the growth of the objects, or that they might indeed be ejected planets that somehow managed to cling together when they were ejected from a star.

Yet there also remains the possibility that the objects are simply bright background stars poking through the nebula, and nothing mysterious at all.

Kevin Luhman, an astronomer at Pennsylvania State University, reanalyzed the original JuMBO data and said he could not find many of them. “I was able to identify a few hundred brown dwarf candidates,” he said, but “there was only a small amount of overlap with the JuMBOs.”

“They might be just two random background stars that happen to be close to each other in the sky and are unrelated,” Luhman said.

Searches for JuMBOs elsewhere have also come up empty. Ray Jayawardhana, an astronomer at Johns Hopkins University, and colleagues used the Webb telescope to study another nebula, and found no such pairs of objects. In the past year, McCaughrean said they had revised down their estimates for the number of JuMBOs in Orion, to about 20 from 42. But he remains confident some are hiding in that cloud.

“We still believe these are real objects that need to be explained,” he said.

To truly confirm their existence, they used the Webb telescope for spectroscopy, looking for chemical signatures in the objects’ light that would form only on planet-size objects, such as methane and water, and are now analyzing that fresh data.

It’s unclear how many, if any, of the JuMBOs will turn out to be real planetlike objects. “As an observer, you want to be right,” McCaughrean said.