WASHINGTON - The universe may glitter with far more stars than even Carl Sagan imagined when he rhapsodized about "billions upon billions."
A new study suggests there are 300 sextillion of them, three times as many as previously calculated. That is a 3 followed by 23 zeros. Or 3 trillion times 100 billion.
The estimate, in a study published online Wednesday in the journal Nature, is based on findings that there are many more red dwarf stars - the most common type - than once thought.
But the research goes deeper than that. The study by Yale University astronomer Pieter van Dokkum and Harvard astrophysicist Charlie Conroy questions a key assumption that astronomers often use: that most galaxies have the same properties as our Milky Way.
When scientists previously estimated the total number of stars, they assumed that all galaxies had the same ratio of dwarf stars as the Milky Way, which is spiral-shaped. Much of our understanding of the cosmos is based on observations inside our galaxy and then extrapolated to others.
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But about one-third of the galaxies in the universe are elliptical, not spiral, and van Dokkum found they aren't really made up the same way as ours.
Using the Keck telescope in Hawaii, van Dokkum and a colleague gazed into eight elliptical galaxies and looked at their hard-to-differentiate light signatures. The scientists calculated that elliptical galaxies have far more red dwarf stars than predicted.
"We're seeing 10 or 20 times more stars than we expected," van Dokkum said.
Scientists generally believe there are 100 billion to a trillion galaxies in the universe. And each galaxy was thought to have 100 billion to a trillion stars.
Sagan, the Cornell University scientist and best-selling author who was often impersonated by comedians as saying "billions and billions," usually said there were 100 billion galaxies, each with 100 billion stars.
Van Dokkum's work takes these numbers and adjusts them. That's because some of those galaxies - the elliptical ones, which account for about a third of all galaxies - have as many as 1 trillion to 10 trillion stars, not a measly 100 billion. When van Dokkum and Conroy crunched the incredibly big numbers, they found that it tripled the estimate of stars in the universe from 100 sextillion to 300 sextillion.
The number of stars in the universe "is equal to all the cells in the humans on Earth - a kind of funny coincidence," Conroy said.
