Hubble Finds Three Giant Exoplanets and Several Brown Dwarfs in Orion Nebula

Using the NASA/ESA Hubble Space Telescope to peer deep into the famous Orion Nebula, Space Telescope Institute researcher Massimo Robberto and colleagues searched for small, faint bodies. They found 17 very-low-mass brown dwarf companions to red dwarf stars, one brown dwarf pair, and one brown dwarf with a planetary companion. The astronomers also found three giant exoplanets, including a binary system where two planets orbit each other in the absence of a host star.

This Hubble image shows the Orion Nebula. Image credit: NASA / ESA / M. Robberto, Space Telescope Science Institute & ESA / Hubble Space Telescope Orion Treasury Project Team.

The Orion Nebula, also known as NGC 1976, Messier 42 (M42), LBN 974, and Sharpless 281, is a diffuse nebula in the constellation Orion.

It spans about 24 light-years and is located approximately 1,350 light-years away from Earth. It can be seen with the naked eye as a fuzzy patch surrounding the star Theta Orionis in the Hunter’s Sword, below Orion’s belt.

The Orion Nebula is an excellent laboratory for studying the star formation process across a wide range, from opulent giant stars to diminutive red dwarf stars and elusive, faint brown dwarfs.

Because brown dwarfs are colder than stars, Dr. Robberto and co-authors used Hubble to identify them by the presence of water in their atmospheres.

“These are so cold that water vapor forms. 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,” Dr. Robberto explained.

“But hot water vapor in the atmosphere of brown dwarfs cannot be easily seen from Earth’s surface, due to the absorbing effects of water vapor in our own atmosphere. Fortunately, Hubble is up above the atmosphere and has near-infrared vision that can easily spot water on distant worlds.”

The astronomers identified 1,200 candidate reddish stars. They found that the stars split into two distinct populations: those with water, and those without. The bright ones with water were confirmed to be faint red dwarfs.

This image is part of a Hubble survey for low-mass stars, brown dwarfs, and planets in the Orion Nebula. Each symbol identifies a pair of objects, which can be seen in the symbol’s center as a single dot of light. Special image processing techniques were used to separate the starlight into a pair of objects. The thicker inner circle represents the primary body, and the thinner outer circle indicates the companion. The circles are color-coded: red for a planet; orange for a brown dwarf; and yellow for a star. Located in the upper left corner is a planet-planet pair in the absence of a parent star. In the middle of the right side is a pair of brown dwarfs. The portion of the Orion Nebula measures roughly 3 x 4 light-years. Image credit: NASA / ESA / G. Strampelli, STScI.

Compass image for substellar objects in the Orion Nebula. Image credit: NASA / ESA / G. Strampelli, STScI.

The team also looked for fainter, binary companions to these 1,200 reddish stars.

Because they are so close to their primary stars, these companions are nearly impossible to discover using standard observing methods.

But by using a unique, high-contrast imaging technique developed by the astronomers, they were able to resolve faint images of a large number of candidate companions.

This first analysis did not allow Hubble astronomers to determine whether these objects orbit the brighter star or if their proximity in the Hubble image is a result of chance alignment.

As a consequence, they are classified as candidates for now. However, 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.

In all, the researchers found 17 candidate brown dwarf companions to red dwarf stars, one brown dwarf pair, and one brown dwarf with a planetary companion.

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.

The scientists presented their results this week at the 231st Meeting of the American Astronomical Society in Washington, D.C.

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Giovanni Maria Strampelli et al. 2018. A HST/WFC3 Search for Substellar Companions in the Orion Nebula Cluster. 231st AAS Meeting, abstract # 414.07

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