The Lyman Alpha Forest
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Transcript of The Lyman Alpha Forest
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=2n=3n=4
Hydrogen Atom Energy Levels
Photon
1216 A
Electron excited
Atoms
n=1
n=2n=3n=4
Hydrogen Atom Energy Levels
Electron excited
Absorption
Wavelength Wavelength Wavelength
Intensity
Redshift
z = Observed wavelength - Rest wavelengthRest wavelength
The Cosmological Redshift is a redshift caused by the expansion of space.
Hubble’s Lawv = H*r.
v = recessional velocityr = distance from EarthH = Hubble's constant, 50-100 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 J1030 0524, 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
• http://nedwww.ipac.caltech.edu/level5/Sept01/Rauch/Rauch4.html
• http://www.seds.org/~rme/cosmol.html
• http://astron.berkeley.edu/~mwhite/darkmatter/bbn.html
• http://astron.berkeley.edu/~john/lya.html
• http://nedwww.ipac.caltech.edu/level5/March01/Barcana/Bar1.html
• http://www.ticam.utexas.edu/CCV/projects/DiDi/cosmo/cosmo.html
• SPECTRA OF THE MOST DISTANT QUASARS ELUCIDATE THE REIONIZATION OF THE COSMOS, By Schwarztschild, Bertram, Physics Today, 00319228, Oct2001, Vol. 54, Issue 10 (Database: MasterFILE select)
• Cosmic Coincidences: Darkmatter, Mankind and anthropic cosmology, by John Bribbin and Martin Rees
• http://www.scienceagogo.com/news/20010710012750data_trune_sys.shtml