Rogue planet? Failed star? This far-out enigma could be either one.
Isolated object CFBDSIR 2149-0403 was recently investigated by an international team of astronomers trying to confirm whether it is closer to a star or planet. From Earth, planets appear to glimmer in the night sky because they reflect light off stars. Stars do not need to borrow anything for their radiance since they make their own light from the intense energy released by the hydrogen at their cores fusing into helium. As clear as the divide may seem, the object’s identity is nebulous.
"CFBDSIR 2149-0403 is an atypical substellar object that is either a 'free-floating planet' or a rare high-metallicity brown dwarf. Or a combination of both," said team lead Phillipe Delorme of the Grenoble Alpes University in France, whose observations were recently published.
While planetary mass doesn’t instantly classify an object as a planet, if CFBDSIR 2149-0403 is a planet, it came into being from dust particles scattered in the wake of star formation. Multiple collisions cause these particles to stick together and keep accreting over millions of years into something resembling a giant orb. When a planet is in its embryonic phase, temperatures are never high enough to cause particles to fuse, changing their chemical composition. Not being hot or heavy enough to generate their own radiation, planets seem to shine in the darkness only because they reflect the light of stars. You could call it stealing the spotlight.
The researchers remained skeptical about the planet hypothesis, which is why the possibility of it being a high-metallicity, low-mass brown dwarf also exists. Brown dwarves aren’t necessarily brown. While most of their radiation is infrared (read: invisible to the human eye) they can actually appear magenta or orange-red when imaged by a telescope. Unfortunately, they are forever doomed to be looked at as “failed stars” since they are too small to fuse hydrogen into helium for that unearthly glow. Scientists even speculate that much of the unseen mass in the universe is floating out there in the form of brown dwarves that have yet to be detected because of their low luminosity.
CFBDSIR 2149-0403 was observed through the Very Large Telescope’s X-Shooter spectrograph and HAWK-1 near-infrared imager, along with NASA’s Spitzer Space Telescope (which measured the intensity of its light in infrared) and the Canada-France-Hawaii Telescope’s WIRCam imager. Spectral analysis has so far revealed to the team that the object displays either low gravity, high metallicity, or both. They have also been able rule it out as a member of any star system, including AB Doradus, which it was previously assumed to belong to. With no group of stars that formed around the same epoch as a basis for comparison, it keeps its age a secret, at least for now.
"We now reject our initial hypothesis that CFBDSIR 2149-0403 would be a member of the AB Doradus moving group,” explained Delorme. “This removes the most robust age constraint we had. Though determining that certainly improved our knowledge of the object it also made it more difficult to study, by adding age as a free parameter.”
Other unsolved mysteries will come to light as scientists develop a more detailed understanding of low-gravity and high-metallicity atmospheres. Until then, CFBDSIR 2149-0403 will remain a mystery.