How a galaxy grows

30 March 2006

Where did our galaxy come from? A new computer simulation is revealing that tiny clumps of gas and dust can grow into giant galaxies - and could develop
life-supporting chemicals much faster than we thought.

Antenna goes starry-eyed...

This story was published in Nature on 30 March 2006.

The new simulation shows how bubbles of gas like this can grow into giant galaxies.

Image: Masao Mori

One of the great mysteries for cosmologists is how a galaxy begins its life. But a new computer simulation is showing how galaxies grow - with some astonishing results.
'Understanding where we came from has been a long-standing question since the beginning of human civilisation. We performed simulations of the chemical evolution of a galaxy which will help to understand the whole history of the universe.'
Masao Mori, computing expert, University of California and Senshu University, Japan

Masao Mori, computing expert, University of California and Senshu University, Japan

Image: Masao Mori

With ultra-hi-tech telescopes, scientists can peer out to distant galaxies - so far away that we see them as they were at a time when the universe was very young.
'The recent advances in observational techniques allow us to directly observe the universe 10 billion years ago to find bright young galaxies there.'
Masao Mori

This snapshot of nearly 10,000 galaxies is the deepest visible-light image of our universe.

Image: NASA, ESA, S Beckwith (STScL) and the HUDF Team

How do these bright young galaxies become the huge galaxies we see today?
'There are two types of galaxies in the present-day universe - elliptical galaxies and spiral galaxies. But the ancestors of these galaxies are unknown.'
Masayuki Umemura, galaxy expert, University of Tsukuba, Japan

Masayuki Umemura, galaxy expert, University of Tsukuba, Japan

Image: Masayuki Umemura

Because we are stuck inside our galaxy, we can't take pictures of it from a distance. This artist's drawing is what scientists think it looks like. Hot young stars make the spiral arms glow very brightly.

Image: NASA/JPL-Caltech


Our own galaxy, the Milky Way, is a spiral galaxy. Most scientists think it formed 13.6 billion years ago. The long swirling arms are areas where stars are still forming.

The giant elliptical galaxy M87 is one of the biggest known galaxies. Elliptical galaxies appear yellow or red because they contain mostly older stars.

Image: NASA


Elliptical galaxies don't create new stars - and most of the stars within them are getting old.

Two galaxies collide. Eventually, billions of years from now, they will merge into a single, more massive galaxy. The new model suggests a different path for galaxy formation.

Image: NASA

Most scientists thought that smaller galaxies collide to form giant galaxies. But this simulation shows that young galaxies can actually spontaneously evolve from one form to another.

But how?
By using their computer simulation, the team showed how clumps of dust and gas evolve to become bubbles of gas - very like primitive galaxies. The hot bubbles of gas collide with each other producing super-bubbles.

Between the bubbles, exploding stars shoot out elements such as carbon and oxygen, which enrich the intergalactic space like a fertiliser.

Broadband Version

Watch this animation to see how gas bubbles build up in the infant galaxy. Supernova explosions blow gas bubbles out, and new stars form in the enriched gas.

Video: Masao Mori

What does this mean for our understanding of life in our Solar System?
'The Earth and the life on it are largely composed of heavy elements, which come mainly from supernova explosions of massive stars.'
Masao Mori
And startlingly, the simulation showed that most of the heavy elements we have on planet Earth were generated in the first billion years of the model galaxy's life.
This is much faster than expected. Until now we thought it took 10 billion years for a galaxy to become rich in the chemicals that support life on Earth.
'This is a significant finding for the whole history of the universe. In addition, it is relevant to the origin of the Earth, organic matter and life in the universe.'
Masao Mori

The Earth and Moon seen from the Galileo spacecraft on its way to explore the Jupiter system.

Image: NASA

Our Solar System was born around 5 billion years ago - 8 billion years after we think our galaxy formed.

But were the ingredients for planets present long before then?
'Our simulation suggests that the first planetary system could have formed much earlier than we thought. So there could be a planetary system out there much more evolved than our Solar System.'
Masao Mori

Could another planetary system have evolved faster than the Solar System?

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