NASA’s Hubble Space Telescope has discovered the largest known population of brown dwarfs sprinkled among newborn stars in the Orion Nebula, located 1,350 light-years away from the Earth. Brown dwarfs are a strange class of celestial object that have masses so low that their cores never become hot enough to sustain nuclear fusion, which powers stars. Because brown dwarfs are colder than stars, the astronomers used Hubble’s exceptional resolution and infrared sensitivity, to identify them by the presence of water in their atmospheres.

“These are so cold that water vapour forms,” lead researcher Massimo Robberto of the Space Telescope Institute in Baltimore, Maryland, said in a statement. “Water is a signature of substellar objects. It’s an amazing and very clear mark. As the masses get smaller, the stars become redder and fainter, and you need to view them in the infrared. And in infrared light, the most prominent feature is water,” Robberto added. The astronomers identified 1,200 candidate reddish stars. They found that the stars split into two distinct populations: those with water, and those without.

They also found 17 candidate brown dwarf companions to red dwarf stars, one brown dwarf pair, and one brown dwarf with a planetary companion. The presence of water in their atmospheres indicates that most of them cannot be misaligned stars in the galactic background, and thus must be brown dwarfs or exoplanet companions. The study also identified three potential planetary mass companions: one associated to a red dwarf, one to a brown dwarf, and one to another planet.

Finding the signatures of low-mass stars and their companions will become much more efficient with the launch of NASA’s infrared-sensitive James Webb Space Telescope in 2019, the astronomers said.

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