There’s a lot we can’t see in our galaxy. Neutrinos, dark matter, black holes; we know they are there but we can’t see them. And according to new research, we might have also missed up to 100 billion brown dwarfs.
An international team of researchers has been looking for brown dwarfs – the extremely faint stellar objects that failed to become stars – focusing on star-forming region NGC 1333, which is located 1,000 light-years away. They discovered that there were half as many brown dwarfs as there were stars, which is actually a much higher number than expected.
The research, which is presented this week at the National Astronomy Meeting in the UK, didn’t stop there. The region was just one of the targets the team had decided to explore after the unexpected finding. Another stellar cluster, called RCW 38, in the constellation of Vela, also sported the same ratio of brown dwarfs to stars.
RCW 38 is actually quite different from NGC 1333. It has a lot more massive stars and is a lot further than the other cluster observed, about 5,500 light-years away. The team used the Very Large Telescope to observe this cluster and pick out the dim brown dwarfs among the bright stars.
“We’ve found a lot of brown dwarfs in these clusters. And whatever the cluster type, the brown dwarfs are really common,” team member Aleks Scholz from the University of St Andrews, said in a statement. “Brown dwarfs form alongside stars in clusters, so our work suggests there are a huge number of brown dwarfs out there.”
According to the statistical estimate based on these two objects, there should between 25 and 100 billion brown dwarfs currently in the Milky Way. And since there are many brown dwarfs smaller than the ones detected in this survey, this could be a significant underestimation.
Brown dwarfs are missing link objects, aan intermediate stage between stars and gas giant planets. They are mostly made of hydrogen but they are not heavy enough to achieve nuclear fusion in their core, meaning they fail to become stars. Scientists this year were finally able to put some constraints on these objects – namely, if they are lighter than 70 times the mass of Jupiter and cooler than 1,300°C (2,400°F) then they will remain a brown dwarf.