The great galactic recession

The great galactic recession

The density of gas in and around a simulated galaxy just
over a billion years after the Big Bang. New gas is arriving at
too great a rate for the galaxy to convert it into stars and
the gas piles up.

A simulated universe created by Swinburne University of
Technology and The University of Melbourne has revealed
galaxies emerging in the first billion years after the Big
Bang were experiencing a recession.

It has long been imagined that the first galaxies formed after
the Big Bang were rapidly growing, turning huge clouds of
pristine gas into stars at rates thousands of times greater
than what we see in the Milky Way today.

However, new modelling inspired by economics theory has instead
revealed the galaxies weren’t forming as fast as they could

Swinburne astronomer Associate Professor Alan Duffy created
supercomputer simulations of the early universe treating the
complex forming galaxies as a simple economical model with raw
materials arriving (under gravity) and being processed (into

What surprised Associate Professor Duffy and colleagues was
that not all the gas that could form stars was being turned
into stars.

“In the universe around us today, we think of galaxies in
balance, raising their internal rate at which they form
until it reaches the rate at which gas
arrives,” says co-author Professor Stuart Wyithe, from The
University of Melbourne.

“If the internal consumption rate is too high then the gas is
used up and the galaxy starves until enough new material
arrives to replenish their supply. We thought that would occur
in the too, but the picture
was totally wrong.

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Credit: Swinburne University of Technology

Associate Professor Duffy explains that first galaxies have
such a torrent of cold gas flowing into them that they simply
can’t keep up.

“The internal gas consumption can’t rise fast enough with
supply outstripping demand or in economics terms the galaxy is
in recession. It’s only when the expands over billions of years do the
rates of material falling into these growing slow enough to allow the galaxy to find
that balance we see today,” Associate Professor Duffy says.

Collectively known as Smaug the gas simulations featured in
this work are part of the larger series DRAGONS (Dark-ages,
Reionization And Galaxy-formation Observables Numerical
Simulation) led by University of Melbourne’s Professor Stuart
Wyithe and funded by Professor Wyithe’s Australian Research
Council Laureate Fellowship.

The research has been published in the Monthly Notices of
the Royal Astronomical Society

Explore further:

Discovered: Fast-growing galaxies from early universe

More information: Alan R. Duffy et al. Dark-ages
reionization and galaxy formation simulation – IX. Economics of
reionizing galaxies, Monthly Notices of the Royal
Astronomical Society
(2017). DOI:

Journal reference:
Monthly Notices of the Royal Astronomical Society

Provided by:
Swinburne University of Technology