Two of the Oldest Brown Dwarfs in the Galaxy Reveal Hidden Population of Objects

A team of astronomers have discovered two of the oldest brown dwarfs in the galaxy. Moving at speeds of up to 100 to 200 kilometers per second, these star-like objects are thought to have formed more than 10 billion years ago. Now, astronomers believe that these brown dwarfs may just be two of a vast population of previously unseen objects.

Brown dwarfs are much less massive than actual stars, and they don't generate internal heat through nuclear fusion. Because of this, brown dwarfs cool and fade with time. The latest discoveries actually have temperatures that are just 250 to 600 degrees Celsius, which is practically frigid when compared to our own Sun, which has a surface temperature of about 5,600 degrees Celsius.

The astronomers first spotted the brown dwarfs when they used NASA's Wide-field Infrared Survey Explorer (WISE). After discovering them, the astronomers named them WISE 0013+0634 and WISE 0833+0052. Located in the Pisces and Hydra constellations respectively, these brown dwarfs are located among a messy mixture of nebulous gas and dust.

So what did they find out about these brown dwarfs? The scientists examined the infrared light emitted from these objects, which are unusual compared to typical slower moving brown dwarfs. They found that the spectral signatures of their light reflects their ancient atmospheres, which are almost entirely made up of hydrogen.

"Unlike in other walks of life, the galaxy's oldest members move much faster than its younger population," said David Pinfield, one of the researchers, in a news release.

What's most interesting is what these brown dwarfs can tell us about the rest of the population of objects in the galaxy. There are thought to be as much as 70 billion brown dwarfs in the galaxy's thin disk, and the thick disk and halo occupy much larger galactic volumes. This means that even a small (3 percent) local population means that there's a huge number of ancient brown dwarfs in the galaxy.

"These two brown dwarfs may be the tip of the iceberg and are an intriguing piece of astronomical archaeology," said Pinfield in a news release. "We have only been able to find these objects by searching for the faintest and coolest things possible with WISE. And by finding more of them we will gain insight into the earliest epoch of the history of the galaxy."

The findings are published in the journal Monthly Notices of the Royal Astronomical Society.