Astronomers: average distance between stars in universe: about 4,150 light years.

By | November 5, 2012

[optional image description]… This afternoon, NASA made an announcement: Astronomers, using data from the Fermi Gamma-ray Space Telescope, have developed a new way to understand the most ancient light of the universe.

And: all the light. Or, as NASA sums it up, appropriately pragmatically and appropriately poetically: “the total amount of light from all of the stars that have ever shone.”

That light — photons from primordial stars, formed some 400 million years after the big bang — is still extant in the universe. It is more commonly known as extragalactic background light, or EBL — which is an accumulation of all the radiation in the universe …

… distant sources are blazars — compact quasars, or galactic nuclei — that boast more than a billion times the energy of visible light. Ajello and his team, for this project, studied 150 of them. Blazars are powered by massive black holes that emit jets of energy. And those jets include gamma rays. Gamma rays were the keys to the EBL project: When those rays collide with ancient photons, they’re converted into electrons and their antimatter (positrons). That collision effectively dims their light — meaning that gamma rays, when they finally hit our Fermi telescope, have an energy that belies their path through the universe. Using measures of that energy, Ajello and his colleagues were able to determine the amount of photons between Earth and the blazars. …

So, using this method, what’s the scientists’ best guess for the makeup of the universe’s ancient, photonic fog? The average stellar density in the cosmos, they estimate, is about 1.4 stars per 100 billion cubic light years. Which means that the average distance between stars in the universe is about 4,150 light years.  …

via Astronomers Read the Shadows of the Universe’s Earliest Stars – Megan Garber – The Atlantic.

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