10 How the World Began
213
From Fig. 10.9 we can infer that the scale of the inhomogeneities is much
larger than the dimensions of stars. The stars themselves are subject to gravitational attraction, and group themselves slowly into clusters, or “galaxies”.
Even the galaxies may become clustered. The time scale over which significant changes now manifest themselves is measured in millions (or billions) of
years.
Stars pass through a life cycle of their own, converting their hydrogen
into deuterium and helium, and depending on their mass, may commence
burning their helium, converting it into heavier elements, up to iron and
nickel. During this phase of nuclear fusion inside a star, a balance is achieved
between the outwards radiation pressure from the fusion process, and the
gravitational collapse of the outermost layers of matter. Following the exhaustion of the nuclear fuel in heavier stars, the radiation pressure falls until it can
no longer oppose the gravitational forces. The core collapses, and there is a
resultant huge release of energy. During this period of core collapse, nuclei
heavier than iron are synthesised. A supernova, a star of immense brightness,
appears in the sky for several days, or weeks. The outer layers of the star,
containing traces of the heavier elements, are blown away into space, and the
core collapses further into either a neutron star or a black hole. (Neutron stars
and black holes have been discussed in Chap. 7.)
From the beginnings that we have outlined above, the universe has evolved
into the amazing variety of objects, including planets and life-forms, that
abound today. It is humbling to realise that the atoms, other than the very
lightest, from which our bodies are constructed, were forged in the furnace
of a star. This is the domain of astrophysics and astronomy.
What we have presented above is the standard picture of the universe as it
was two decades ago. As often happens in physics, when physicists believe
they are consolidating their theories and obtaining a glimmer of understanding, new discoveries occur that bring everything into question once
more. In the next Chapter we will discuss some of these new observations and
ideas, and the grey areas and open puzzles that require further investigation.
References
1. West M (2003) The last confession. Toby Press
2. Weinstein G, George Gamow and Albert Einstein: Did Einstein say the cosmological constant was the “biggest blunder” he ever made in his life? (October 3,
2013) https://arxiv.org/ftp/arxiv/papers/1310/1310.1033.pdf. Accessed 14 June
2020
213
From Fig. 10.9 we can infer that the scale of the inhomogeneities is much
larger than the dimensions of stars. The stars themselves are subject to gravitational attraction, and group themselves slowly into clusters, or “galaxies”.
Even the galaxies may become clustered. The time scale over which significant changes now manifest themselves is measured in millions (or billions) of
years.
Stars pass through a life cycle of their own, converting their hydrogen
into deuterium and helium, and depending on their mass, may commence
burning their helium, converting it into heavier elements, up to iron and
nickel. During this phase of nuclear fusion inside a star, a balance is achieved
between the outwards radiation pressure from the fusion process, and the
gravitational collapse of the outermost layers of matter. Following the exhaustion of the nuclear fuel in heavier stars, the radiation pressure falls until it can
no longer oppose the gravitational forces. The core collapses, and there is a
resultant huge release of energy. During this period of core collapse, nuclei
heavier than iron are synthesised. A supernova, a star of immense brightness,
appears in the sky for several days, or weeks. The outer layers of the star,
containing traces of the heavier elements, are blown away into space, and the
core collapses further into either a neutron star or a black hole. (Neutron stars
and black holes have been discussed in Chap. 7.)
From the beginnings that we have outlined above, the universe has evolved
into the amazing variety of objects, including planets and life-forms, that
abound today. It is humbling to realise that the atoms, other than the very
lightest, from which our bodies are constructed, were forged in the furnace
of a star. This is the domain of astrophysics and astronomy.
What we have presented above is the standard picture of the universe as it
was two decades ago. As often happens in physics, when physicists believe
they are consolidating their theories and obtaining a glimmer of understanding, new discoveries occur that bring everything into question once
more. In the next Chapter we will discuss some of these new observations and
ideas, and the grey areas and open puzzles that require further investigation.
References
1. West M (2003) The last confession. Toby Press
2. Weinstein G, George Gamow and Albert Einstein: Did Einstein say the cosmological constant was the “biggest blunder” he ever made in his life? (October 3,
2013) https://arxiv.org/ftp/arxiv/papers/1310/1310.1033.pdf. Accessed 14 June
2020