There's a zoo of galaxies out there. Understanding exactly how they formed has been a notoriously difficult problem. But including details of 'dark energy' and each galaxy's dark matter halo in calculations now seems to do the trick.
Credit: NASA
SYDNEY: Using a detailed cosmological model that includes dark energy and dark matter, two American astrophysicists have been able to correctly predict the shapes and proportions of the different types of galaxies in the universe and discover the Milky Way’s past.
The shape of galaxies depends on their turbulent history, and understanding how they evolve is a major task.
Astrophysicists Nick Devereux of Embry-Riddle University in Arizona and Andrew Benson of the California Institute of Technology used a sophisticated computer model called GALFORM, combined with data from the infrared Two Micron All Sky Survey, which scanned 70% of the sky between 1997 and 2001.
Researchers were ”completely astonished”
GALFORM simulates galaxy formation in a universe dominated by the enigmatic dark energy and dark matter. It’s based on a cosmological model of the universe called the Lambda Cold Dark Matter (LCDM) that predicts how matter flows and lumps together. The Lambda component is represents ‘dark energy’, which drives the expansion of the universe.
The model was able to reproduce the evolutionary history of the universe over its 13.7 billion years. Moreover it not only got the shapes but also the numbers of various galaxies right and the rate at which galaxy mergers occur.
“We were completely astonished that our model predicted both the abundance and diversity of galaxy types so precisely,” said astrophysicist Nick Devereux of Embry-Riddle University in Arizona.
“It really boosts my confidence in the model,” said Benson.
Shapely galaxies
If galaxies are close enough together, then gravity can cause them to merge, with spiral galaxies morphing to elliptical galaxies. The Milky Way and its neighbour Andromeda are close enough that this will happen,.
Benson and Devereaux said that their model, published in the Monthly Notices of the Royal Astronomical Society shows that the Milky Way has a complex past but so far has only undergone minor collisions and the gravitational collapse of its inner disk to form the central bar.
A galaxy’s shape depends on how it formed – and can vary from elliptical and lens shapes to spirals. Our own Milky Way galaxy is classified as a barred spiral.
American astronomer Edwin Hubble defined these ranges of galactic shapes as the ‘Hubble sequence’. They appear as elliptical blobs, or spiral disks with circles or bars at the centre. Our own Milky Way is classified as a barred spiral.
