It's evening in the universe. The stars we have are dying, and we're not making new ones the way we used to. A group of British and U.S. astronomers reported that the birthrate of stars in the universe has declined over the last 11 billion years. The universe is only producing stars one-thirtieth as fast as it was at its peak in the lusty primordial days when protogalaxies were colliding and merging, popping with blazing bright new stars.
"You might say that the universe has been suffering from a long, serious crisis: cosmic GDP output is now only 3 percent of what it used to be at the peak in star production," said astronomer David Sobral of Leiden University in the Netherlands. Sobral and his colleagues published their paper in the Monthly Notices of the Royal Astronomical Society.
They calculated that the current consolidation rate of "starstuff" into stars amounts to about 1 million tons per year per cubic light-year. The sun is about 22 trillion trillion tons.
In a fundamental sense, this cosmic fatigue is not really new. But Sobral and his colleagues said that if this decline goes on, it means the universe has already made 95 percent of the star mass that it will ever make. As eternity goes on, the cosmos will be dominated by older and older stars.
There is no cause for immediate alarm. Stars live for millions or billions of years, depending on their masses; the biggest burn out quickly, while the smaller ones can limp on as red dwarfs for a trillion years or more. The sun, a middle-size and middle-aged star, has another 5 billion years or so to go. Our own Milky Way galaxy -- born near the height of the star baby boom, about 10 billion years ago -- is still busily hatching stars out of dense gas clouds. If you ever agonized about missing out on Paris in the 1920s or Italy in the Renaissance, at least you can take comfort that we live in the Golden Age of the Milky Way.
To paraphrase Bob Dylan, it's not dark yet, but it's getting there.
NEW YORK TIMES
