100 billion failed stars hiding in our galaxy
At least 100 billion failed stars, or "brown dwarfs", could be hidden within our galaxy, the Milky Way, astronomers believe.
The objects, bigger than planets but smaller than stars, are unable to sustain the kind of nuclear fusion reaction that powers the sun.
Because they are so faint and difficult to spot, all the brown dwarfs identified so far have been relatively close to Earth, within a distance of about 1,500 light years.
A new study of near and more distant star clusters has now found that the objects are likely to be widespread throughout the galaxy.
Dr Aleks Scholz, from the University of St Andrews in Scotland, said: "We've found a lot of brown dwarfs in these clusters. And whatever the cluster type, the brown dwarfs are really common. Brown dwarfs form alongside stars in clusters, so our work suggests there are a huge number of brown dwarfs out there."
The scientists used a special adaptive optics camera on the European Southern Observatory's Very Large Telescope (VLT) in the Atacama desert of northern Chile.
They found on average there were five brown dwarfs for every 10 stars in the star clusters. Whether stars were more or less massive, tightly packed, or less crowded had only a small effect on the formation of brown dwarfs.
The astronomers estimate the Milky Way has a minimum of between 25 and 100 billion brown dwarfs, and the true number could be much higher.
The research is published in the journal 'Monthly Notices of the Royal Astronomical Society'.