image: Approximately 400 million years after the big bang, the first stars and galaxies were formed which ended the so-called 'Dark Ages'. During the Dark Ages the matter that fills the space between the galaxies was in the neutral state, but the intense ultraviolet light of the first stars and galaxies started to ionize it. The process of ionization continued for another 550 million years leading to the complete ionization of the intergalactic hydrogen in the universe. This crucial period in the life of the universe is known as the epoch of reionization. While we know that star-forming galaxies reionized the universe, the exact process has eluded astronomers for decades. Part of the problem is that the radiation produced by the stars that can ionize hydrogen gets absorbed in the gas cocoons where stars are formed. This results in very little radiation escaping the parent galaxies. This material relates to a paper that appeared in the Oct. 10, 2014, issue of Science, published by AAAS. The paper, by Sanchayeeta Borthakur at Johns Hopkins University in Baltimore, MD, and colleagues was titled, 'A local clue to the reionization of the universe.' view more
Credit: [Credit: Sanchayeeta Borthakur (JHU), SDSS)]