How galaxies came to be: Astronomers explain Hubble sequence

Galaxies are the collections of stars, planets, gas and dust that make up most of the visible component of the cosmos. The smallest have a few million and the largest as many as a million million (a trillion) stars.

American astronomer Edwin Hubble first developed a taxonomy for galaxies in the 1930s that has since become known as the 'Hubble Sequence'. There are three basic shapes: spiral, where arms of material wind out in a disk from a small central bulge, barred spirals, where the arms wind out in a disk from a larger bar of material and elliptical, where the galaxy's stars are distributed more evenly in a bulge without arms or disk. For comparison, the galaxy we live in, the Milky Way, has between two and four hundred thousand million stars and is classified as a barred spiral.

Explaining the Hubble Sequence is complex. The different types clearly result from different evolutionary paths but until now a detailed explanation has eluded scientists.

Benson and Devereux combined data from the infrared Two Micron All Sky Survey (2MASS) with their sophisticated GALFORM computer model to reproduce the evolutionary history of the Universe over thirteen billion years. To their surprise, their computations reproduced not only the different galaxy shapes but also their relative numbers.

“We were completely astonished that our model predicted both the abundance and diversity of galaxy types so precisely”, said Devereux. “It really boosts my confidence in the model”, added Benson.

The astronomers' model is underpinned by and endorses the 'Lambda Cold Dark Matter' model of the Universe. Here 'Lambda' is the mysterious 'dark energy' component believed to make up about 72% of the cosmos, with cold dark matter making up another 23%. Just 4% of the Universe consists of the familiar visible or 'baryonic' matter that makes up the stars and planets of which galaxies are comprised.

Galaxies are thought to be embedded in very large haloes of dark matter and Benson and Devereux believe these to be crucial to their evolution. Their model suggests that the number of mergers between these haloes and their galaxies drives the final outcome – elliptical galaxies result from multiple mergers whereas disk galaxies have seen none at all. Our Milky Way galaxy's barred spiral shape suggests it has seen a complex evolutionary history, with only a few minor collisions and at least one episode where the inner disk collapsed to form the large central bar.

“These new findings set a clear direction for future research. Our goal now is to compare the model predictions with observations of more distant galaxies seen in images obtained with the Hubble and those of the soon to be launched James Webb Space Telescope (JWST)”, said Devereux.

CONTACTS

Dr Andrew Benson
California Institute of Technology
Tel: +1 626 407 4953
Mob: +1 626 319 0158
E-mail: abenson@its.caltech.edu
Dr Nicholas Devereux
Embry-Riddle University
Arizona
Tel: +1 928 777 3715
Mob: +1 928 273 9069
E-mail: devereux@erau.edu
Dr Robert Massey
Press and Policy Officer
Royal Astronomical Society
Tel: +44 (0)7734 3307
Mob: +44 (0)794 124 8035
E-mail: rm@ras.org.uk

All latest news from the category: Physics and Astronomy

This area deals with the fundamental laws and building blocks of nature and how they interact, the properties and the behavior of matter, and research into space and time and their structures.

innovations-report provides in-depth reports and articles on subjects such as astrophysics, laser technologies, nuclear, quantum, particle and solid-state physics, nanotechnologies, planetary research and findings (Mars, Venus) and developments related to the Hubble Telescope.

Back to home

Comments (0)

Write a comment

Newest articles

Lighting up the future

New multidisciplinary research from the University of St Andrews could lead to more efficient televisions, computer screens and lighting. Researchers at the Organic Semiconductor Centre in the School of Physics and…

Researchers crack sugarcane’s complex genetic code

Sweet success: Scientists created a highly accurate reference genome for one of the most important modern crops and found a rare example of how genes confer disease resistance in plants….

Evolution of the most powerful ocean current on Earth

The Antarctic Circumpolar Current plays an important part in global overturning circulation, the exchange of heat and CO2 between the ocean and atmosphere, and the stability of Antarctica’s ice sheets….

Partners & Sponsors