Astronomers shed light on different galaxy types

September 14, 2016, Australian Astronomical Observatory
Classification of several of the 488 galaxies observed in this study using the Hubble Sequence and the proposed Angular Momentum based system. Credit: L. Cortese (ICRAR/UWA) and Sloan Digital Sky Survey

In research published today, Australian scientists have taken a critical step towards understanding why different types of galaxies exist throughout the Universe.

The research, made possible by cutting-edge AAO instrumentation, means that astronomers can now classify according to their rather than human interpretation of a galaxy's appearance.

For the past 200 years, telescopes have been capable of observing galaxies beyond our own galaxy, the Milky Way.

Only a few were visible to begin with but as telescopes became more powerful, more galaxies were discovered, making it crucial for astronomers to come up with a way to consistently group different types of galaxies together. 

In 1926, the famous American astronomer Edwin Hubble refined a system that classified galaxies into categories of spiral, elliptical, lenticular or irregular shape. This system, known as the Hubble sequence, is the most common way of classifying galaxies to this day.

Despite its success, the criteria on which the Hubble scheme is based are subjective, and only indirectly related to the physical properties of galaxies. This has significantly hampered attempts to identify the evolutionary pathways followed by different types of galaxies as they slowly change over billions of years.  

Amanda Bauer configuring the SAMI instrument for a night of observing with the AAT. Credit: Amanda Bauer/AAO

Dr Luca Cortese, from The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), said the world's premier astronomical facilities are now producing surveys consisting of hundreds of thousands of galaxies rather than the hundreds that Hubble and his contemporaries were working with.

"We really need a way to classify galaxies consistently using instruments that measure physical properties rather than a time consuming and subjective technique involving human interpretation," he said.

In a study led by Dr Cortese, a team of astronomers has used a technique known as Integral Field Spectroscopy to quantify how gas and stars move within galaxies and reinterpret the Hubble sequence as a physically based two-dimensional classification system.

"Thanks to the development of new technologies, we can map in great detail the distribution and velocity of different components of galaxies. Then, using this information we're able to determine the overall angular momentum of a galaxy, which is the key physical quantity affecting how the galaxy will evolve over billions of years.

"Remarkably, the galaxy types described by the Hubble scheme appear to be determined by two primary properties of galaxies–mass and angular momentum. This provides us with a physical interpretation for the well known Hubble sequence whilst removing the subjectiveness and bias of a visual classification based on human perception rather than actual measurement."

The 3.9 metre Anglo-Australian Telescope located at Siding Spring Observatory in NSW. Credit: Angel Lopez-Sanchez/AAO

The new study involved 488 galaxies observed by the 3.9m Anglo Australian Telescope in New South Wales and an instrument attached to the telescope called the Sydney-AAO Multi-object Integral-field spectrograph or 'SAMI'.

The SAMI project, led by the University of Sydney and the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), aims to create one of the first large-scale resolved survey of galaxies, measuring the velocity and distribution of gas and stars of different ages in thousands of systems.

"Australia has a lot of expertise with this type of astronomy and is really at the forefront of what's being done," said Professor Warrick Couch, Director of the Australian Astronomical Observatory and CAASTRO Partner Investigator.

"For the SAMI instrument we succeeded in putting 61 optical fibres within a distance that's less than half the width of a human hair.

"That's no small feat, it's making this type of work possible and attracting interest from astronomers and observatories from around the world."

Galaxies of Stephan’s Quintet in the constellation Pegasus, observed by the Hubble Space Telescope. Credit: NASA, ESA, and the Hubble SM4 ERO Team

Future upgrades of the instrument are planned that will allow astronomers to obtain even sharper maps of galaxies and further their understanding of the physical processes shaping the Hubble sequence.

"As we get better at doing this and the instruments we're using are upgraded, we should be able to look for the physical triggers that cause one type of galaxy to evolve into another—that's really exciting stuff," Dr Cortese said.

Explore further: Hubble spots a lopsided Lynx

More information: The SAMI Galaxy Survey: the link between angular momentum and optical morphology. arxiv.org/abs/1608.00291

Related Stories

Hubble spots a lopsided Lynx

August 15, 2016

This galaxy, known as NGC 2337, resides 25 million light-years away in the constellation of Lynx. NGC 2337 is an irregular galaxy, meaning that it—along with a quarter of all galaxies in the universe—lacks a distinct, ...

Hubble spots an irregular island in a sea of space

August 29, 2016

This image, courtesy of the NASA/ESA Hubble Space Telescope's Advanced Camera for Surveys (ACS), captures the glow of distant stars within NGC 5264, a dwarf galaxy located just over 15 million light-years away in the constellation ...

Hubble peers at a distinctly disorganized dwarf galaxy

April 4, 2016

Despite being less famous than their elliptical and spiral galactic cousins, irregular dwarf galaxies, such as the one captured in this NASA/ESA Hubble Space Telescope image, are actually one of the most common types of galaxy ...

Hubble sees galaxy hiding in the night sky

May 2, 2016

This striking NASA/ESA Hubble Space Telescope image captures the galaxy UGC 477, located just over 110 million light-years away in the constellation of Pisces (The Fish).

Hubble uncovers a galaxy pair coming in from the wilderness

August 11, 2016

NASA's Hubble Space Telescope has uncovered two tiny dwarf galaxies that have wandered from a vast cosmic wilderness into a nearby "big city" packed with galaxies. After being quiescent for billions of years, they are ready ...

Image: Hubble gets in on a galactic gathering

May 30, 2016

Nearly as deep as the Hubble Ultra Deep Field, which contains approximately 10,000 galaxies, this incredible image from the Hubble Space Telescope reveals thousands of colorful galaxies in the constellation of Leo (The Lion). ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

NASA instruments image fireball over Bering Sea

March 22, 2019

On Dec. 18, 2018, a large "fireball—the term used for exceptionally bright meteors that are visible over a wide area—exploded about 16 miles (26 kilometers) above the Bering Sea. The explosion unleashed an estimated 173 ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

wduckss
1 / 5 (3) Sep 14, 2016
"The research, made possible by cutting-edge AAO instrumentation, means that astronomers can now classify galaxies according to their physical properties rather than human interpretation of a galaxy's appearance."

The basic error of working with instruments. From the whole extract similar patterns and draw conclusions, strictly respecting the old misconceptions.
Seems, more data means that the further away from reality. Nobody today not respect the law of universality ...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.