Hubble telescope finds brown dwarfs inside the Orion Nebula

Stellar nursery found to host numerous low-mass objects, including a rogue binary planet system.
By Laurel Kornfeld | Jan 15, 2018
NASA's Hubble Space Telescope discovered the largest known grouping of brown dwarfs, a class of objects more massive than the largest planets but not massive enough to sustain hydrogen fusion in their cores, in a region of young stars within the Orion Nebula, located 1,350 light years away.

Classified at the lowest end of the stellar category, some brown dwarfs fuse deuterium, an isotope of hydrogen, in their cores for a limited time. As they age, they tend to cool and fade.

Fainter, cooler, and more difficult to find than even low-mass stars, brown dwarfs are identified by water vapor in their atmospheres.

"These are so cold that water vapor forms," explained research team leader Massimo Robberto of the Space Telescope Science Institute in Baltimore, Maryland.

"Water is a signature of sub-stellar 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."

Hubble's high resolution, infrared capability, and location above Earth's atmosphere enable it to detect the water vapor in brown dwarfs' atmospheres.

In addition to the brown dwarfs, the researchers discovered 1,200 red star candidates, binary brown dwarf companions of these stars, a pair of binary brown dwarfs, a binary system of a red dwarf and a planet, a binary system of a brown dwarf and a planet, and a binary system of two rogue planets that orbit one another without orbiting any star.

Among the candidate red stars, some contained water while others did not.

"We experimented with a method, high-contrast imaging post processing, that astronomers have been relying on for years," explained Laurent Pueyo, also of the Space Telescope Science Institute, who developed the technique.

"We originally used it to look for very faint planets in the vicinity of nearby stars, by painstakingly observing them one by one. This time around, we decided to combine our algorithms with the ultra-stability of Hubble to inspect the vicinity of hundreds of very young stars in every single exposure obtained by the Orion survey. It turns out that even if we do not reach the deepest sensitivity for a single star, the sheer volume of our sample allowed us to obtain an unprecedented statistical snapshot of young exoplanets and brown dwarf companions in Orion."

Key to the discoveries was the combining of the two techniques--searching for atmospheric water vapor and high-contrast image processing. Robberto estimated this processing could locate many more previously undiscovered objects in Hubble archives.

NASA's infrared James Webb Space Telescope (JWST), scheduled for launch in 2019, will significantly increase scientists' ability to find low-mass objects.

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