Astronomer Kári Helgason Contributes to New Discovery Skip to content
Starburst NGC 4449
Photo: Starburst NGC 4449.

Astronomer Kári Helgason Contributes to New Discovery

An international team of astronomers, including Icelander Kári Helgason, have measured all of the light from all of the stars that have ever existed, RÚV reports. The results of the report, “A gamma-ray determination of the Universe’s star formation history” were published in the journal Science at the end of November and have incited much interest both within and outside of the scientific community.

“How many stars have formed in the Universe, and when did they do so? These fundamental questions are difficult to answer because there are systematic uncertainties in converting the light we observe into the total mass of stars in galaxies,” reads the report abstract. However, as The Guardian explains, researchers were able to answer these questions by measuring “…the extragalactic background light (EBL), a cosmic fog of radiation that has been accumulating since stars first illuminated the dark, vast expanse of space. More than 90% of starlight ends up surviving in this dim backdrop of radiation.”

And today, Kári told The Guardian, “we are sitting in this sea of light.”

Researchers know that star formation peaked around ten million years ago and has been declining steadily since. “You could say that we missed the biggest party in the universe and it’s coming to an end,” Kári told RÚV. “But,” he continued, “we managed to get a look really far back – or 90% back in the history of the life of the universe,” and to isolate the light that existed one billion years after the Big Bang.

Over the course of nine years, the researchers collected data using NASA’s Fermi telescope, which takes measurements in gamma rays. “We found 740 massive black holes throughout the universe,” Kári continued. “These black holes emit incredibly bright gamma rays and they light up the background light from all the galaxies and stars. It is a bit like car lights shining through a thick fog. We were then able to measure the characteristics of the fog, which is the starlight that has accumulated in the universe.”

The result? Since the first stars came into being, they have radiated 4×1084 photons of light. Or, if you wanted to write it all the way out, that’s:

4,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons.

“Maybe that’s not that much when you consider how big the universe is,” said Kári. “It is enormous – our visible universe is, at any rate. We don’t know how big it is as a whole, but if you divide it up by volume, then you end up with just ten thousand photons in every cubic meter of the visible universe.”

At any rate, Kári says, the enormous figure is still just “numbers on a page” for astrologers, no less than for everyone else. “We astronomers maybe don’t understand the magnitude much better than anyone else.”

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