Cosmic timeline 13

Did the First Stars Shine Light ?

Recent studies show they might have not. Powered with energy, resulted from the interaction between ordinary matter and dark matter, and having masses between 400 to 200,000 times that of the Sun, these so-called “dark stars” could have been the first structures to ever populate the universe.

The first stars began to shine maybe 100 million years after the big bang.

The Hubble Ultra Deep Field shows a number of small galaxies merging to form larger ones, at 13 billion light years, when the Universe was only 5% its current age.

Formation of galaxies
The formation of the first galaxy probably occurred around 600 million years after the big bang and it is the era of stars that leads to the formation of these structures we call the galaxies. Large volumes of matter in the early part of the stelliferous epoch collapse to form a galaxies. Population II stars are formed early on in this process, with Population I stars formed later.

The globular cluster M80. Stars in globular clusters are mainly older metal-poor members of Population II.

Star populations are categorized as I, II, and III, according to the order in which the groups were first recognized, so stars astronomers have known about the longest are Population I stars followed by discovering Population II stars and lastly by Population III stars. Each of these succeeding groups seem to have a decreasing metal content. The oldest stars are the Population III stars and Population I the more recent stars, so astronomers have been on an amazing journey of discovery looking at stars that takes us right back to the first stars that began to shine

While older stars do have fewer heavy elements, the fact that all stars observed have some heavier elements poses something of a puzzle, and the current explanation for this proposes the existence of hypothetical metal-free Population III stars in the early universe. Soon after the Big Bang, without metals, it is believed that only stars with masses hundreds of times that of the Sun could be formed; near the end of their lives these stars would have created the first 26 elements up to iron in the periodic table via nucleosynthesis.

Because of their high mass, current stellar models show that Population III stars would have soon exhausted their fuel and exploded in extremely energetic pair-instability supernovae.
Those explosions would have thoroughly dispersed their material, ejecting metals throughout the universe to be incorporated into the later generations of stars that are observed today.

An infant galaxy

Another Hubble image shows an infant galaxy forming. This happened very recently on the cosmological timescale, so, the Universe is not quite finished with galaxy formation yet.

The most accepted theory of how these structures came to be is that all the structure we observe today was formed as a consequence of the growth of the primordial fluctuations, which are small changes in the density of the universe in a confined region. As the universe cooled clumps of dark matter began to condense, and within them gas began to condense. The primordial fluctuations gravitationally attracted gas and dark matter to the denser areas, and thus the seeds that would later become galaxies were formed. These structures constituted the first galaxies. At this point the universe was almost exclusively composed of hydrogen, helium, and dark matter.

The universe was very violent in its early epochs, and galaxies grew quickly, evolving by accretion of smaller mass galaxies. The result of this process is left imprinted on the distribution of galaxies in the nearby universe.

Gravitational attraction pulls galaxies towards each other to form groups, clusters and superclusters.

Galaxies are not isolated objects in space, but rather galaxies in the universe are distributed in a great cosmic web of filaments. The locations where the filaments meet are dense clusters of galaxies, that began as the small fluctuations to the universe. Hence the distribution of galaxies is closely related to the physics of the early universe.

The earliest Population I stars appear 4 billion years after the big bang.


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