November 12, 2000
The same gravity that holds galaxies together and keeps planets in their orbits also held you to the Earth on the day you were born.
The Lyman Alpha Forest
Birthday · November 12, 2000
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APOD published November 12, 2000. Credit: J. Shalf, Y. Zhang (UIUC) et al., GCCC. A publication-date match, not a photo taken on your date. Independent of NASA.
We live in a forest. Strewn throughout the universe are "trees" of hydrogen gas that absorb light from distant objects. These gas clouds leave numerous absorption lines in a distant quasar's spectra, together called the Lyman-alpha forest. Distant quasars appear to be absorbed by many more Lyman-alpha clouds than nearby quasars, indicating a Lyman-alpha thicket early in our universe. The above image depicts one possible computer realization of how Lyman-alpha clouds were distributed at a redshift of 3. Each side of the box measures 30 million light-years across. Much remains unknown about the Lyman-alpha forest, including the real geometry and extent of the clouds, and why there are so many fewer clouds today.
Image credit: J. Shalf, Y. Zhang (UIUC) et al., GCCC