Structure of Early Stars
Due to the lack of metals in the early universe, it is believed that it would be much easier to form incredibly massive stars of well over 100 solar masses, well over the average stellar mass today.
Although these stars were considerably different in mass and composition (in the sense that they were devoid of the traces of elements heavier than hydrogen we would expect to find in the core) they are believed to have been of similar structure.
As with all stars the early stars would have layers of varying temperature depending on distance from the core. Starting from the inside we would find the core of one of these massive stars where temperatures are such that fusion of hydrogen into helium can occur in order to produce the energy necessary to maintain dynamic equilibrium and therefore stave off collapse from its own gravity. Out from the core we find the radiation zone, where temperatures and pressures are less great than in the core and transfer of energy from the core in the form of photons and light occurs. The churning surface of any star would be caused by the activity in the next layer, known as the convection zone. Here transfer of heat causes plasma to rise and fall creating pockets of relatively warm and cool plasma. Beyond the convection zone we find the photosphere which consists of decreasingly dense gas and relatively cool temperatures compared with the rest of the star. As we extent into the atmosphere the temperatures of the star would actually begin to rise as we rise through the chromo sphere and into the outermost layers of its atmosphere where we would find the emission of the highest energy radiation.
While the structure of these early stars is familiar to us through the study of modern stars and processes such as dynamic equilibrium would be very much the same the much greater mass and varying composition due to the makeup of the early universe would cause the temperatures and rate of fusion to be greatly increased. These early stars would rapidly burn through both their hydrogen and helium supplies and turn to fusing even heavier elements. These elements would then be spread throughout the universe to comprise later generations of stars and help to shape the universe we know today.
Study of these early stars is very difficult as they were so massive that it is hardly conceivable for them to be in existence today. However some light from the farthest corners of the universe is nearly as old as the universe itself due to the rapidity of its expansion and therefore with advanced telescopes it may be possible to look back into time and study these now long dead stars.
This picture shows the distribution of elements in a high mass star as it fuses heavier elements near the end of its life
This illustration shows a diagram of the structure of our own star, the sun, which although considerably less massive has a structure in common with other stars during their hydrogen burning years.