Ionized Hydrogen Gas

1
Ionized Hydrogen Gas
The Intergalactic Medium

• While looking inside galaxies for the the main
  constituent of mass, we can not account for more
  than half of all normal baryonic matter.

• The answer lies outside of the galaxy in the form
  of ionized hydrogen gas the Intergalactic
  Medium

2
Formation of Protons

• The Hadron Epoch One second after the big bang
• The universe cools down enough for protons and
  neutrons to form

• Nucleosyntheseis 100 Seconds after the Big Bang
• The universe cools down enough for protons and
  neutrons to fuse to create heavier elements such
  as Hydrogen and Helium

• Three minutes after nucleosynthesis began, the
  temperature cooled down so much that nuclear
  fusion could no longer take place. The relative
  abundances of matter were 75 of matter was
  Hydrogen, 25 of matter was Helium, 1/10 of
  deuterium, and traces of lithium and beryllium

3
Large Scale Structures

• In the early universe, matter was spread mostly
  uniformly.

• Density enhancements led to matter condensing.

• This condensing is what led to galaxy formation.
  This took place 10 million years after the Big
  Bang.

4
Determining the Amount of Baryons in the Universe

• Recall that in the Big Bang nucleosynthesis,
  deuterium, a heavy isotope of hydrogen was formed.

• Deuterium is very easy to destroy.

• A certain amount of energy is needed by a photon
  to destroy the deuterium

5
What this means

• Deuterium will cease to be destroyed once the
  universe expands to a certain point.

• Recall that light seems to interact only with
  baryonic matter.

• Astronomers can calculate the baryon to photon
  ratio from observing the abundance of deuterium
  in the universe.

6
What is found
Type of Material
Percentage of Baryonic Matter
Stars 10
Gas in Galaxy Clusters 6
Cold Intergalactic Gas 24
Cold Gas in Galaxies 2
TOTAL MASS 42

• This implies that over half of all baryonic
  matter is unaccounted for with just stars, gas in
  galaxy clusters, cold intergalactic gas, and cold
  gas in galaxies

• Astronomers continue to this day to increase
  precision of such calculations

7
Efficiency of Structure Formation

• Simulations have shown that galaxy formation does
  not efficiently consume all primordial material.

• Not all material around galaxy formation is
  accreted into the galaxy

• During galaxy formation, as matter falls into the
  galaxy, a shock wave is sent outward. This shock
  wave will carry enough energy to shock heat any
  material that may lie outside of the galaxy.

• It is now suspected that a majority of the
  primordial matter exists outside of galaxies and
  has been ionized by this shock wave.

The Intergalactic Medium
Shock heating should heat the intergalactic
medium to 105 107 Kelvin.
8
Ionized Hydrogen Gas

• An atom has a nucleus where protons and neutrons
  reside.

• In the case of a hydrogen atom, there is simply a
  proton in the nucleus of the atom

• A single electron is bound to the atom.

• Ionized hydrogen is hydrogen that has had the
  electron stripped away from the atom.

9
Ionization of Hydrogen
10
Detection

• Once hydrogen has been ionized, there is no
  longer any electrons to absorb or release energy
  (no way to emit or absorb photons).

• This makes detecting ionized hydrogen in the
  intergalactic medium nearly impossible.

Solution

• Recall that there were other elements that were
  created early in the universe that should be
  present in the intergalactic medium.

• Using other constituents of the intergalactic
  medium, astronomers are finally detecting this
  mass of material outside of galaxies.

11
Quasars and Absorption

• Helium requires higher temperatures than hydrogen
  to be ionized.

• FUSE Far Ultraviolet Spectroscopic Explorer

• FUSE uses distant quasars as a background source
  against the IGM, to look for absorption of the
  quasars light by helium, the second most abundant
  element of the IGM

• Other material is suspected to exist in the IGM
  as a result of supernovae explosions sending
  heavy elements off with enough energy to escape
  the galaxy.

12
Stats

• Amount of mass of HII suspected to exist
• 5.4E10 Solar Masses 1.0692E41 kg
• If dark matter were all HII
• We would expect a mass of 9E10 Solar Masses
• Thats 1.07E68 atoms.
• A density of 5E55 pc-3, 1.7E06 m-3
• 5.96E36 atoms would pass through the Solar
  System each second
• 3.83E24 Atoms would pass through the Earth each
  second!

13
References

• Burles, Scott . "Sharpening the Predictions of
  Big-Bang Nucleosynthesis." . 14 01. 1999.
  American Physics Society. 18 04. 2007
  lthttp//prola.aps.org/abstract/PRL/v82/i21/p4176_1
  gt.
• Fukugita, M.. "The History of Galaxies." Nature
  06 06. 1996 489 - 495.
• Krauss, Lawrence M. . "Cosmological Antigravity."
  Scientific American 01. 1999 53 - 59.
• Kriss, Gerard . "FUSE Observes the Intergalactic
  Medium." FUSE Science Summaries. 15 02. 2005.
  NASA. 18 04. 2007 lthttp//fuse.pha.jhu.edu/wpb/sci
  _h2347.htmlgt.
• Nath, Biman B. . "Heating of the Intergalactic
  Medium as a Result of Structure Formation." . 10
  05. 2001. Royal Astronomical Society. 18 04.
  2007 lthttp//articles.adsabs.harvard.edu/cgi-bin
  /nph-iarticle_query?2001MNRAS.327L...5Ngt.
• Romeel, Davé. "Baryons In The Warm-Hot
  Intergalactic Medium." . 10 05. 2001. The
  Astrophysical Journal. 18 04. 2007
  lthttp//www.journals.uchicago.edu/ApJ/journal/issu
  es/ApJ/v552n2/52296/52296.web.pdfgt.