It's a cosmic embarrassment of riches – the universe appears to hold three times the number of stars many astronomers might have estimated only a year ago. That's the implication a pair of scientists has drawn after measuring eight huge elliptical galaxies that they selected from two vast galaxy clusters located between 53 million to 321 million light-years from Earth.
With as many as 200 billion galaxies in the observable universe, each with hundreds of billions of stars, the result – if it holds up – implies an enormous number of additional burning gas balls out there, with intriguing implications for explanations of how stars and galaxies form and evolve, researchers say.
The cause of this huge revision of the stellar census are stars known as red dwarfs, literally the dimmest stellar bulbs on the shelf. These stars weigh in at no more than about 30 percent of the sun's mass.
Surveys of our own galaxy, the Milky Way, have found that these dwarfs outnumber sun-like stars by about 100 to 1, explains Pieter van Dokkum, an astronomer at Yale University in New Haven, Conn. But the dwarfs are so dim and other galaxies so distant that red dwarfs fail to appear when astronomers try to account for the stars other galaxies contain.
As a consequence, when estimating how much of a galaxy's mass stars account for – important to understanding a galaxy's life history – astronomers basically had to assume that the relative abundance of red-dwarf stars found in the Milky Way held true throughout the universe for every galaxy type and at every epoch of the universe's evolution, Dr. van Dokkum says.