Space + Flight

31
Jan

On the Failed Star of Luhman 16B, It Rains Molten Iron

Is the weather forecast here on Earth leaving you feeling a bit down?

At least you can be glad you’re not on the brown dwarf Luhman 16B, where the temperature is 2000 ˚F and storm clouds rain drops of molten iron. This “failed star” is the first of its kind to have its weather mapped, in research published this week in the journal Nature.

Brown dwarfs are a class of diminutive celestial bodies too small and cool at their cores to burn with the fury of a larger, brighter star. The images of Luhman 16B’s surface reveal what appear to be patches of clouds, making them strikingly similar to gas giant planets like Jupiter or Saturn.

Surface map of Luhman 16B recreated from VLT observations
Looks like the weather on Luhman 16B is partly cloudy with showers of molten iron.

To make the map, the team, led by Ian Crossfield of the Max Planck Institute for Astronomy in Germany, used a technique called Doppler imaging. It works like this: As a star spins in space, half of it appears to be rotating toward us, and half of it is rotating from away us. Depending upon where on the star’s surface the light is coming from, it appears to be shifted slightly bluer or redder—the famed redshift. It’s similar in principle to how the sound of a train whistle changes as it rushes past us.

If a star is totally blank and featureless, it always appears to be a perfect blend of slightly-more-reddish light and slightly-more-bluish light that more or less cancel each other out. But if there are surface features—like patches of clouds that dim the light on one side or another—then that balance is thrown off, and the color of the star appears to shift slightly. By tracking these shifts in color, astronomers can reverse-engineer the patterns of clouds that produced them.

Scientists have used this technique before to map large stars, but this is the first time it has been applied to an elfin brown dwarf. The only reason it was possible is that Luhman 16B is one of our closest stellar neighbors.

Despite its proximity, the system was only discovered last year, by Kevin Luhman of Penn State University. Markus Pössel, the public information officer of the Max Planck Institute, writing for Universe Today, called it a “momentous discovery”:

Remarkably, this system was at a distance of a mere 6.5 light-years from Earth. Only the Alpha Centauri star system and Barnard’s star are closer to Earth than that. In fact, Barnard’s star was the last time an object was discovered to be that close to our Solar system—and that discovery was made in 1916[…]

For Crossfield and his colleagues at MPIA, this was a game-changer. Suddenly, here was a brown dwarf for which Doppler imaging could conceivably work, and yield the first ever surface map of a brown dwarf.

Astronomers hope that with the next generation of extremely large telescopes, they will be able to apply these techniques to brown dwarfs that are more distant—and eventually, even smaller objects like Jupiter-sized planets in other solar systems.

If you want to craft yourself a physical reminder of how much worse your weather forecast could be, you can download an origami template to print out and fold your own globe of Luhman 16B at the Max Planck Institute’s website.