Luhman 16

Apr 4, 2015

by Nonhle Skosana

Ultra Cool Dwarf Stars & Luhman 16


This is an artist’s impression of the brown dwarf Luhman 16B based on the first ever map of the weather on its surface. Image credit: ESO / I. Crossfield / N. Risinger.

In 2013, an astronomer at the Pennsylvania State University, Kevin Luhman, discovered a binary of brown dwarf stars 6.2 Light years away from our solar system. Being the third closest star after Alpha Centauri and Barnard Star to Earth, the Southern African Large Telescope (SALT) astronomers were given the opportunity to investigate its characteristic traits.

A brown dwarf star is a failed star and is different from the stars we see at night. Because of their low mass density and cool temperature, it is hard to see them normally. Instead, to see them, one would have to move away from the optical and into the infrared where they are much more visible.

According to Petri Vaisanen, an astronomer investigating the characteristics of Luhman 16 at the SALT base in Sutherland, “In science, the blue stars mean that they are hot stars and the red stars –which characterise the dwarf stars- are the cold faint stars”. As a result, what the human eye sees every night are the high mass and temperature stars that allow light to transfer visibly into Earth’s hemisphere.

Despite the fact that it’s a newly found star and the faintest in comparison to Alpha Centauri and Barnard’s star, the Luhman 16 is identified as being a binary star system. This means that instead of being a single standing star on its own, it consists of two stars which orbit around a common point. One constitutes of a bigger mass than the other, assuming the primary role making the other a simple companion.


Image: Janella Williams, Pennsylvania State University.

Using the SALT telescope, South African astronomers have been the first to not only distinguish, but prove the Luhman 16s unique characteristics. According to a report by astronomer David Buckley, on 12 March 2013 (a day after the Luhman 16 brown dwarf star was discovered), “SALT took a spectroscopy under Director’s Discretionary Time to measure the radial velocities and spectral typing of both components”. By doing so, the SALT astronomers were able to confirm the speed at which the stars are orbiting, approximating it to about 20 years at a speed of 19.5km/s.

YouTube video by European Southern Observatory (ESO)

In addition, SALT was also used to determine the features of the second companion star in the binary system. The primary star which is distinctively identified as a brown dwarf is a L8±1 type whereas the second, slightly fainter lower mass star, is a T1.5±2 type dwarf. Knowing this difference has allowed astronomers to study its properties and perhaps determine other qualities that may reveal greater factors using other telescopes.

Access the PDF report of SALT’s investigation of the characteristics of WISE J1049 (aka Luhman 16) on the provided link.