ASTRONOMY Number of stars in sky is declining, study finds

Astronomers analyzed the light history of more than 96,000 nearby galaxies.
SCRIPPS HOWARD
Not so we would notice night-to-night, but the number of stars in the universe is declining, and has been for about 5 billion years, according to a new study based on a digital survey of the heavens.
The peak of star births is 3 billion years more recent than had been estimated before, based on observations of young stars in distant galaxies.
By the time our own sun was formed some 4.7 billion years ago, almost half of the stellar mass in the universe since the big bang had been created. Star formation has drastically dropped since, and new stars are not being created faster than old stars are dying. The result will be a gradual dimming of the night skies.
Astronomers from the University of Edinburgh and the University of Pennsylvania analyzed the light history of more than 96,000 nearby galaxies to chronicle star formation over the course of the universe's estimated 14 billion-year history.
"Our analysis confirms that the age of star formation is drawing to a close," said Alan Heavens, of the Institute for Astronomy, "and has been roughly since the time our own sun came into being."
Change in estimate
Heavens and Raul Jimenez, an assistant professor of physics at the University of Pennsylvania, had earlier estimated that star formation peaked 6 million years ago, based on a survey of 40,000 galaxies.
But their latest effort, reported today in the journal Nature, refined the calculation using more data from the Sloan Digital Sky Survey, an international collaboration of observatories that aims to map a quarter of all visible objects in the sky.
"Our method takes into account all the stars that are present in the observed galaxies today and allows us to create the most complete history of star formation yet assembled," Jimenez said.