View Full Version : Reionization in universe

2004-Jul-31, 03:20 PM
I am facing a problem in understanding the reionization time in Universe. Can anybody clarify me when and how the reionization started in Universe? How it can be measured? I shall be very helped if I have some references on this topic.


2004-Jul-31, 04:35 PM
Hi snborah, welcome to the forum,

You'd do well to look it up through web searches, but here's an amateur explanation:

The universe was ionized for the first 380,000 years. After that time, the ions in the plasma cooled off enough that they could form atoms. Light passing through these atoms [plasma is relatively opaque] is what constitutes the cosmic microwave background radiation we see today.

At some point [the time for which is only theorized so far], Supermassive black holes, galaxies, globular clusters, and/or stars began to form. This might have been about 250,000,000 years after the big bang [give or take 250,000,000 million years].

These first stars formed quickly, brightly, and ubiquitously [so goes the theory], and the light from them reionized some or all of the intergalactic media. We generally say that reionaztion ended about z=6 [about 950,000,000 years after the big bang]. This is what is called reionization. We believe that it is difficult to see through the IGM during this period, which is one of the reasons that the topic comes up.