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Spiral Galaxy

The Development Of Galactic Structure



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Today our universe is filled with structure.  This structure is quite uniform on the largest of scales and is the result of galaxy formation.  There may be over 100 billion galaxies in the observable universe.

But this was not always the case.  The cosmic microwave background radiation has shown us that 380,000 years after the Big Bang our universe was a structureless soup of hydrogen atoms and photons.  What happened?

The current consensus is that dark matter formed the gravitational substrate for baryonic matter to aggregate in ever larger “clumps”.  These clumps would form the gaseous seeds for the first stars, and later, solar systems.  The question now becomes: when did this occur?  Are galaxies relatively “new” features of our universe, or have they been around from the beginning.

The question is harder to answer than it originally seems because the enormous expanse of spacetime makes it difficult to observe the development of the early universe.  But, as usual, it is the Hubble Space Telescope to the rescue.  A team of astronomers analyzed data from the Hubble’s Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS).  It’s a mouth full.  The data included information on the structure and colour of galaxies from 2.5 billion years after the Big Bang.

Currently, astronomers know that galaxies first started to form as early as 500 million years after the Big Bang.  But it is currently unknown whether these early galactic structures conform to the types of galaxies we observe in our universe today.  Their analysis showed that by 2.5 billion years after the Big Bang galaxies had, more or less, formed into the three different types of galaxies we observe today: elliptical, spiral, and irregular.

This is an interesting discovery, not just for astronomy, but for all science.  We now have a better understanding of how the universe developed, and consequently, this information can help us hypothesize about many different aspects of cosmic evolution (e.g., formation of complex chemistry and planets, origin of life, complex life, etc.).

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