Astronomers 'Now Have Constraints on the Total Number of Stars Ever Formed': Astronomer

Thanks to NASA's Fermi Space Telescope, astronomers are now able to accurately measure the amount of starlight in the universe and used it to determine the sum of all light ever shone from every star that ever existed.

Astronomers have been able to observe the photons from the earliest stars, which are caught by distant galaxies shining in the cosmos that have attracted the photons within their gamma rays. However, as Science News.com points out, it's not only the earliest stars that can be observed-astronomers can also observed the captured photons of every star that has ever been.

 "We now have constraints on the total number of stars that ever formed," Volker Bromm, an astronomer at the University of Texas at Austin, says of the new way to see old light, described online November 1 in Science, according to Science News.com. "It provides us with a review of the entire history of cosmic star formation, including the very first epochs of star formation in the very early universe."

Gamma rays, the most energetic form of light, are observed every three hours by NASA's Fermi. Since Fermi was launched in 2008, its Large Area Telescope (LAT) observes the entire sky in high-energy gamma rays, which allows astronomers to view the most detailed map of the universe ever known as mapped out by the gamma rays, Phys.org reports.

The total amount of starlight in the universe, known to astronomers as the extragalactic background light (EBL), act as sort of a "cosmic fog" to gamma rays. A team led by Marco Ajello, the lead scientist on the project and researcher at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University in California, examined the EBL by studying gamma rays from 150 blazars, or galaxies powered by black holes, that were detected at energies greater than 3 billion electron volts-more than a billion times the energy of visible light.
Researchers eventually determined that the amount of gamma-radiation emanating from those blazers ranged from 4 billion years old to as old as 11.2 billion years, the Los Angeles Times reported.
"With more than a thousand detected so far, blazars are the most common sources detected by Fermi, but gamma rays at these energies are few and far between, which is why it took four years of data to make this analysis," team member Justin Finke, an astrophysicist at the Naval Research Laboratory in Washington, told Phys.org.

A copy of the research findings can be found in this month's Science Xpress magazine.