The Lyman Alpha Forest By Shira Mitchell

Big Bang Star Formation Neutral universe Ionized universe

When did stars form?

Wavelength

What is a Spectrum? The distribution of energy emitted by a radiant source Wavelength Intensity

Atoms n=1 n=2 n=3 n=4 Hydrogen Atom Energy Levels Photon 1216 A Electron excited

Atoms n=1 n=2 n=3 n=4 Hydrogen Atom Energy Levels Electron excited

Absorption Wavelength Wavelength Wavelength Intensity

Redshift z = Observed wavelength - Rest wavelength Rest wavelength The Cosmological Redshift is a redshift caused by the expansion of space.

Hubble’s Law v = H*r. v = recessional velocity r = distance from Earth H = Hubble's constant, km/sec/Mpc (a megaparsec is 3,000,000 light-years) Hubble constant sets the rate at which the Universe is expanding.

Redshift z = 6 farther back to the universe’s beginnings than z = 3 Astronomers speak of the history of the universe in terms of red-shifts

Quasars Short for quasi-stellar radio sources. They are bright active galaxy nuclei with huge red-shifts and therefore, far distances

Quasar Spectrums Wavelength Intensity Neutral hydrogen absorbed this light

Quasar Spectrums

Why is there a forest? If the universe has so much hydrogen, why is there no trough? The hydrogen must be ionized because ionized hydrogen can not absorb light. Why is the hydrogen ionized? The radiation from stars Therefore, to find the trough, one must look at very very distant quasars to look for the trough back towards the universe’s beginnings.

Looking for the Trough 13 Apr 2000 Using the powerful Keck telescope on Mauna Kea in Hawaii, Robert Becker and his colleagues detected the imprint of neutral atoms on light from quasar J , one of the most distant objects yet found. They found that, over a region of the spectrum corresponding to millions of years of cosmic history, no light from the quasar gets through -- it is all absorbed in intergalactic space.

Looking for the Trough

Quasar Spectrums z=5.80 z=6.28 z = 6 means it left the sources less than a billion years after the Big Bang Gun- Peterson Trough

Why is this important? To understand the complex universe we live in today, it is necessary to understand its evolution from an early state of simplicity.

Current Progress Some astrophysicists are not satisfied with the trough in the z=6.28 quasar. A deeper understanding of the physics of reionization may be required Some astrophysicists and cosmologists have turned to computer simulations

Work Cited SPECTRA OF THE MOST DISTANT QUASARS ELUCIDATE THE REIONIZATION OF THE COSMOS, By Schwarztschild, Bertram, Physics Today, , Oct2001, Vol. 54, Issue 10 (Database: MasterFILE select) Cosmic Coincidences: Darkmatter, Mankind and anthropic cosmology, by John Bribbin and Martin Rees