A new research from the Niels Bohr Institute has shown that massive galaxies were formed by explosive star formation that was set in motion by the collision of galaxies a few billion years after the Big Bang.
It has long puzzled scientists that these enormously massive galaxies were already old and no longer forming new stars in the very early universe, approx. 3 billion years after the Big Bang.
Galaxies are giant collections of stars, gas and dark matter. The smallest galaxies contain a few million stars, while the largest can contain several hundred billion stars.
The first stars already emerged in the very early universe approx. 200 million years after the Big Bang from the gases hydrogen and helium.
Gas is the raw material used to form stars. These giant clouds of gas and dust contract and eventually the gas is so compact that the pressure heats the matter so that glowing gas balls are formed, new stars are born.
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The stars are collected in galaxies, the first of which are a kind of baby galaxies. As long as there is gas in the galaxy, new stars are being formed.
The astronomers' theory is therefore that the structure of the universe was built by baby galaxies gradually growing larger and more massive by constantly forming new stars and by colliding with neighbouring galaxies to form new, larger galaxies.
The largest galaxies in today's universe were therefore believed to have been under construction throughout the history of the universe.
The findings are published in the scientific journal, Astrophysical Journal.
