Who needs a star? Astronomers discover rogue ‘planets’ in Orion

10 Oct 2023

The Orion Nebula as captured by the James Webb Telescope. Image: ESA/NASA/CSA/M McCaughrean/S Pearson

Cushioned in the Orion Nebula are free-floating binary objects the size of Jupiter, discovered using the James Webb Telescope, that have scientists bewildered.

Big things come in small packages, and so do big discoveries.

In an attempt to find the smallest objects in the resplendent Orion Nebula, the closest cluster of massive stars to Earth, scientists have stumbled upon mysterious Jupiter-sized objects floating around in space that are not under the influence of any star – a highly unusual phenomenon.

The objects, which have been named Jupiter-mass binary objects (Jumbos) were discovered using the powerful James Web Space Telescope (JWST) and findings of the discovery were submitted to the journals Astronomy & Astrophysics and Nature earlier this month.

Co-authored by Prof Mark McCaughrean, a senior scientific advisor to the European Space Agency (ESA), the papers (which are still awaiting peer-review) detail findings from a near-infrared survey of the trapezium cluster and inner Orion Nebula using the James Webb.

“One of the key things about this region is that it has massive stars in the middle of it,” McCaughrean told SiliconRepublic.com in an interview last week. These are stars up to 50 times more massive than the sun that burn their nuclear fuel very quickly and don’t live very long.

“We don’t have any around us today, but we think we were born in a region like Orion. There are all sorts of traces in our solar system that suggest we were born in a cluster, like the Orion Nebula, but then as that dissolved over billions of years, we’re now just floating freely around.”

‘I had not dreamed of that in 20 years’

According to McCaughrean, the region is an interesting place to study because it sheds light on our own history. And now, in a quest to find the smallest objects in this region, we have discovered Jumbos – flinging into question some of the most basic assumptions in astrophysics.

But the story of these rogue planet-like objects traipsing around the universe goes all the way back to the year 2000, when McCaughrean first proposed looking for the smallest mass objects in the Orion Nebula using the Hubble Space Telescope.

“Now this was going to be interesting because theoreticians only know how to form things down to about three Jupiter masses. There’s all sorts of physics that kicks in there that says a four Jupiter mass clump of gas and dust should never be able to split into two objects that are two Jupiter masses,” he explained.

“And that’s how we get this whole arrangement of different masses. Giant clouds form into different chunks and split apart and form smaller and smaller objects. So they couldn’t make anything below three Jupiter masses, but when we found in our data with the JWST, we find things to one, even 0.6 times the mass of Jupiter.”

While the discovery of free-floating objects that small was surprising, the plot thickened when McCaughrean’s postdoc Dr Samuel Pearson, first author on one of the papers, discovered that many of these objects were binary – two objects that share an orbital axis external to each other.

“That was totally unexpected. I had not dreamed of that in 20 years. It really doubles the problem for theoreticians, who now must explain not only how such small objects are formed but also how they form in binaries,” McCaughrean went on.

One of the theoretical solutions to forming individual objects with those masses, he explained, is that they might not have just formed out of a cloud but been born going around a star as “real planets” that were ejected out of the stellar system after an “interaction”.

“We know that happened in the solar system. We had more planets early on in the solar system, and some were probably kicked out and some were swallowed by the sun.

“So, maybe you could inject some individuals, but how do you inject two at once in a pair and keep them stuck together? This is the essence of what we discovered, and it’s got all the theoreticians going.”

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Vish Gain is a journalist with Silicon Republic