Our galaxy is teeming with brown dwarfs – failed stars that fill a gap between planets and stars. Now, by studying a nearby one, astronomers might have made an epochal discovery.
A team based at UC Santa Cruz has obtained the first infrared spectrum of the brown dwarf WISE 0855, the coldest single object outside of the Solar System at only 7.2 light-years from Earth. Among many interesting features, they discovered that the object is dominated by atmospheric bands, like Jupiter, and it has a cover of water clouds.
"It's five times fainter than any other object detected with ground-based spectroscopy at this wavelength," lead author Andrew Skemer said in a statement. "Now that we have a spectrum, we can really start thinking about what's going on in this object. Our spectrum shows that WISE 0855 is dominated by water vapor and clouds, with an overall appearance that is strikingly similar to Jupiter."
Brown dwarfs are a class of almost-stars that were not big enough to ignite a nuclear fusion reaction at their core. They are made of the same elements that stars are made of, and although they are very warm when they first form, over time they become cooler and cooler.
According to the latest analysis, to be published in Astrophysical Journal Letters and currently available on arXiv, WISE 0855 has a temperature of -23°C (-10°F). It is very difficult to do spectroscopic analysis on such a cold and far away object, so the light spectrum took almost 14 hours of observations over 13 nights to observe the incredible new details of this extrasolar world.
"WISE 0855 is our first opportunity to study an extrasolar planetary-mass object that is nearly as cold as our own gas giants," Skemer said.
An interesting difference between WISE 0855 and Jupiter is the lack of phosphine in the brown dwarf. Phosphine is a toxic gas produced in the hot interior of gas giants. In order for it to move to the outer atmosphere, turbulent motion is needed, which implies that WISE 0855 has a much calmer atmosphere than Jupiter.
This research highlights how the distinction between gas giant planets and brown dwarfs is actually quite arbitrary. In the future, investigations will likely delve futher into the similarities between failed stars and large planets.