spaceSpace and Physics

Scientists Are Trying to Figure Out What This Weird Rogue Object In Our Galaxy Is


Jonathan O'Callaghan

Senior Staff Writer

The object may be similar to the exoplanet 51 Eridani b, artist's impresion shown. Danielle Futselaar/Franck Marchis/SETI Institute

Scientists have been studying a “rogue” object in our galaxy, but they’re not sure if it’s a planet or a brown dwarf.

The planetary mass object has the catchy moniker of CFBDSIR J214947.2-040308.9 (CFBDSIR 2149-0403 for short). It was first discovered in 2012, when scientists thought it was in a group of 30 stars known as AB Doradus, 65 light-years from Earth.


A new study to be published in the journal of Astronomy and Astrophysics (available on arXiv) may force a rethink, however. An international team of astronomers led by Philippe Delorme of the Grenoble Alpes University in France (who led the initial research) has found the object is not in this group at all, and its true classification is a bit of a mystery.

“[Our] results show that it is very unlikely that CFBDSIR 2149 is a member of the AB Doradus moving group,” the team notes in their paper.

Instead, they say this isolated object is located about 178 light-years from Earth on its own. Using a variety of instruments including the Very Large Telescope (VLT) in Chile, they also further constrained what this object might be by measuring its absorption spectrum, the light that made its way to us.

One possibility is that CFBDSIR 2149-0403 is a free-floating planet between 2 and 13 times the mass of Jupiter (similar to one called 51 Eridani b), and less than 500 million years old. The other is that it's an older metallicity-enhanced brown dwarf, about 2 to 3 billion years old, with a mass of between 2 to 40 times that of Jupiter. This type of object has more heavy elements than your average brown dwarf.


Isolated objects like this are not unheard of. Just last year, for example, astronomers found a rogue planet 95 light-years from Earth, seen by its powerful infrared emissions. Free-floating planets are typically kicked out of planetary systems by one of a number of methods, such as a star passing nearby.

A brown dwarf, on the other hand, is essentially a failed star. It is a large object that has not been able to start nuclear fusion in its core, but larger than a typical gas giant planet, although the distinction between the two is a bit murky.

The team behind this latest study thinks their findings may help work out the difference between them. If they can identify which type this object is, then its spectrum could be used to identify similar objects in future.



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