Swinburne: Giant galaxies akin to snowflakes in space

[bystander]

Giant galaxies akin to snowflakes in space
Swinburne University of Technology
Crystal Ladiges | 2011 Feb 21

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Giant galaxies that contain billions of stars are born in much the same way as delicate snowflakes, new research from Swinburne University of Technology has shown.

In a paper accepted for publication in the Monthly Notices of the Royal Astronomical Society, Professor Duncan Forbes has provided the first direct evidence to support a theory of galaxy formation that he has likened to the birth of a snowflake.

Forbes, with the help of international collaborators, analysed data from three different telescopes in order to help confirm this galaxy formation theory proposed last year by German astronomer Ludwig Oser and his colleagues.

“What we’ve found is that galaxies form in two phases. Firstly, an inner region of stars is formed from collapsing gas. This region then acts as a core, or ‘seed’, around which the galaxy grows as the result of stars which are acquired from other smaller galaxies,” he said.

According to Professor Jean Brodie from the University of California, “our work provides some of the best evidence for this inside-out build up of giant galaxies.”

“Snowflake formation requires a ‘seed’ to get it started. In the case of snowflakes, that ‘seed’ is a microscopic dust grain. Having a core from which to build upon is comparable to the formation of a giant galaxy,” Forbes said.

“Then, in much the same way as water vapour accumulates to grow the snowflake, small galaxies and their stars are accreted onto the galaxy core.”

The astronomers based their conclusions on observations of the massive elliptical galaxy NGC1407, one of the largest galaxies in the southern skies with over 10 billion stars.

They made their observations using two giant telescopes in Hawaii – the 8.2 metre Subaru and the 10 metre Keck, the largest optical telescope in the world. They also included data collected from the Hubble Space Telescope.

“Our data came from three of the world’s premier telescopes, and in each case it supported the ‘snowflake theory’ of galaxy formation,” Forbes said. “This means we can be very confident in our findings.”

Evidence for Two Phases of Galaxy Formation from Radial Trends in the Globular Cluster System of NGC 1407 - D Forbes et al

• Monthly Notices of the Royal Astronomical Society 413(4) 2943 (June 2011) DOI: 10.1111/j.1365-2966.2011.18373.x
  arXiv.org > astro-ph > arXiv:1101.3575 > 18 Jan 2011

[bystander]

Building Galaxies
Smithsonian Astrophysical Observatory
Weekly Science Update | 2011 Jul 08

[attachment=0]NGC1407.jpg[/attachment][/i]

Galaxies frequently collide with one another. Our own Milky Way galaxy, for example, and its nearest giant neighbor, the Andromeda galaxy, are heading towards each other at a rate of about 120 kilometers per second; predictions claim the two will merge together in another four billion years or so. It is not only the future of our home galaxy that interests scientists. These powerful interactions are thought to help produce stars, feed the massive black holes that sit at the cores of galaxies, and in general influence in fundamental ways the development and evolution of galaxies. According to theory, the later stages of a galaxy's growth are the ones dominated by sporadic collisions; in the earlier stages a galaxy steadily accumulates material from its surroundings. These early phases should dominate the nature of stars in the older, inner regions of a galaxy, whereas interactions dominate the stars in the outer regions. The two sets of stars are demonstrably different, distinguished by the relative abundances of their elements in the sense that heavier elements signal older, evolved stars.

A galaxy's globular clusters can provide a measure of a galaxy's element abundances, and how they vary. A globular cluster is a roughly spherical ensemble of stars (as many as several million) that are gravitationally bound together and typically located in the outer regions of galaxies. CfA astronomer Jay Strader, together with five colleagues, has examined the family of about 2600 globular clusters around the giant elliptical galaxy NGC1407, which is interacting with its neighbor, NGC1400. The team reports finding a strong variation in the elemental abundances of the globular clusters, with those closer to the galaxy having more heavier elements. The evidence provides strong confirmation of the overall model in which the inner regions formed earlier, by steady accumulation, whereas the more distant, outer regions, which were involved in more recent interactions, are younger.

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[Ann]

Crystal Ladiges wrote:

Giant galaxies that contain billions of stars are born in much the same way as delicate snowflakes, new research from Swinburne University of Technology has shown.

Click to view full size image

There are sure a lot of galaxies out there! Photo: Chris Devaney.

Ann