Key points: First stars, assembly of galaxies, role of dark matter in galaxy growth
Era of Galaxies
The gap in time when matter in the Universe was converted from a nearly uniform distribution to its clumpy state at z = 6 is sometimes called the "dark ages" because we know so little (and because the cosmic background cooled to where we could not see it and stars had not yet formed in enough numbers to light it up). We have to leave it largely to theory to probe what might have happened.
| We believe that the stars, galaxies, and
planets formed where the gravity from concentrations of dark matter
attracted them in the early Universe. The artist's concept to the
right shows the Universe shortly after the first stars formed, when their photons are
exciting the gas around them and blowing huge bubbles into the surrounding gas.(From
NASA Origins Theme Roadmap, 2003; http://origins.jpl.nasa.gov/universe/invest02.html) This
animation lets you watch the bubble-like structures grow as the first stars ionize the
surrounding gas and change the very nature of the Universe
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We can probe the same process in more detail in terms of the actual distribution of gas and formation of matter in the simulation below:
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Dark matter places a critical role in
the process of galaxy formation. Galaxies appear to
have huge distributions of dark matter around the visible stars, as we see from
their rotation curves (as discussed earlier). These dark matter halos increase the effective size of the galaxy and
make it far more likely to collide with other galaxies. In fact, computer
simulations of the growth of galaxies like the ones we have just shown do
not work if the dark matter halos are left off the galaxies; the
galaxies grow too slowly without them. With them, it is possible to start with small scraps of
galaxies, and grow large galaxies entirely by collisions and mergers. (from
Jose Wudka, http://phyun5.ucr.edu/~wudka/Physics7/Notes_www/node121.html) |
| Here is a succinct summary of what we have discussed, by one of the originators of our ideas about the nature of the Universe. | The evolution of the world may be compared to a display of fireworks that
has just ended: some few red wisps, ashes, and smoke. Standing on a cooled cinder, we see
the slow fading of the suns, and we try to recall the vanished brilliance of the origin of
the worlds. - G. Lemaitre |
How well do we understand the early stages of the Universe
Cosmology was long in the domain of theology and philosophy because of a
lack of observational data, and perhaps with the incredible recent progress, it is now
acquiring the potential to re-acquire this role in a different way. Nonetheless, shouldn't we be a bit humble about how far
we can understand these issues
For more on these subjects, try http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/CosmosCompHome.html
Test your understanding before going on
Depiction of the epoch of reionization from Loeb, 2006, Scientific American
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Artist's concept drawing of JWST |
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| Click to return to the Recombination and Reionization | hypertext |
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G. H. Rieke