Classroom Aid - Reionization Discovery

The Intergalactic medium contains roughly half of the normal matter in the universe the average density is about 1 atom per cubic meter that would be 1 atom per 35 cubic feet but the universe is so vast that this accounts for around half of the total bionic matter the other half is in the hundreds of billions to trillions of galaxies that populate the universe following Martin Schmidt's discovery of quazer 3 c273 astronomers around the world began searching for and studying quazer Spectra in 1965 astronomers James Gunn and Bruce Peterson used quazar 3 C9 Spectra provided by Schmidt to calculate how much molecular hydrogen the light went through as it traveled 10.4 billion light years through the intergalactic medium to get here to do the measurements gun and Peterson used the base hydrogen energy level transitions in the how small is it video book we covered how light is created and absorbed when electrons change energy levels in an atom for example when an electron and a hydrogen atom drops from energy level two to the base energy level one a photon is emitted with a wavelength small enough to carry away exactly the amount of energy lost by the atom this is called a Lyman Alpha Photon after Theodore Lyman the American physicist who discovered this series of spectral lines it's in the ultraviolet range of the electromagnetic spectrum and in large numbers they create the Lyman Alpha emission line in the Spectra in the other direction such a photon would be absorbed when it encounters a hydrogen atom in its ground state driving the electron to the higher energy level light passing through a large number of hydrogen atoms in the ground state would create ly and Alpha absorption dips in the light Spectra gun and Peterson reasoned that as light Bluer Than Lyman Alpha is stretched with the expansion of the space it is passing through it will reach the Lyman Alpha wavelength and also be absorbed by hydrogen they calculated that even as few as one atom for every 100,000 ionized would have enough of an effect to create a trough in the light Spectra they predicted this trough now named after them would show up for quazars far enough away to be radiating through molecular hydrogen they never got to see one the light from 3 C9 that traveled over 10 billion light years did not encounter enough molecular hydrogen to create the trough they concluded that the IGM had already changed from molecular hydrogen to ionized hydrogen by the time the light left 3 C9 10 billion years ago it wasn't until the summer of 2001 when Robert Becker from the Lawrence Livermore National Laboratory in California led a team of astronomers that examined the spectrum of this distant quazar located by the Sloan digital Sky survey its light traveled 12.8 billion light years to get here they found an unmistakable gun Peter trough in the quazar Spectra its trough was shifted from the ultraviolet into the infrared gun Peterson analysis shocked the world of astronomy and created two longstanding Mysteries one how did this transformation of the entire universe happen and two how is it possible that any Lyman Alpha photons created when the universe was still filled with molecular hydrogen ever reach Earth to probe these Mysteries the world was going to need space-based telescopes with infrared capabilities