An international research team has discovered that anywhere from 25 to 100 billion failed stars reside in the Milky Way Galaxy. The Milky Way Galaxy is the celestial home to Earth.
Ray Jayawardhana
The failed stars, which are known as Brown dwarfs, are astronomical entities that are too large to be planets and too small to be stars.
Astronomer Ray Jayawardhana, who is dean of the Faculty of Science at York University, is a member of the research team that made the discovery.
Classified as substellar objects, Brown Dwarfs are unable to sustain stable hydrogen fusion in their core, a hallmark of stars like the Sun and they are too large to be planets. Many are found in star clusters, which are thought to be the universe’s nursery for new stars.
The seven-member research team cautions that their finding of 25 to 100 billion brown dwarfs could be a significant underestimation as there are many lower mass and fainter brown dwarfs present in star clusters.
“It seems that brown dwarfs form in abundance in a variety of star clusters,” says Jayawardhana. “They are ubiquitous denizens of our Milky Way galaxy.”
The research team surveyed brown dwarfs in a massive star cluster and found that there was one brown dwarf for every two stars in the cluster. The ratio is similar to what researchers found in nearer, less dense star clusters.
Their findings were presented at the National Astronomy Meeting presented by the Royal Astronomical Society, at the University of Hull in the United Kingdom, July 2 to 6.
The project’s lead researcher is University of Lisbon Astronomer Koraljka Muzic. Muzic collaborated with Aleks Scholz, an astronomer and researcher at the University of St Andrews in Scotland, and Jayawardhana, their former postdoctoral supervisor.
“We’ve found a lot of brown dwarfs in these clusters,” said Scholz, “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.”
False-colour near-infrared image of the core of the young massive cluster RCW 38 taken with the adaptive-optics camera NACO at the ESO’s Very Large Telescope. RCW 38 lies at a distance of about 5500 light years from the Sun. The field of view of the central image is approximately 1 arc minute, or 1.5 light years across. (Photo courtesy of the research team)
Since the discovery of the first brown dwarf in 1995, astronomers have identified thousands more. The overwhelming majority of brown dwarfs that are known to researchers reside within 1,500 light years of the Sun, which astronomically speaking is relatively nearby.
In 2006, Jayawardhana and his collaborators began a new search for young brown dwarfs. After surveying five nearby star-forming regions, they turned their attention to the more distant “RCW 38” star cluster, which has a high density of more massive stars and very different conditions from the other surveyed regions.
The fact that they have found just as many brown dwarfs in RCW 38 suggests that the environment where the stars develop has only a small effect on how brown dwarfs form.
For the current study, the researchers used the European Southern Observatory’s Very Large Telescope in Chile to target the RCW 38 cluster, which is located some 5,500 light years away from the Sun.
The RCW 38 study has been submitted to Monthly Notices of the Royal Astronomical Society. The study is available at https://arxiv.org/abs/1707.00277