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The study of galaxies

A galaxy is a massive, gravitationally bound system consisting of stars, gas and dust (that make up the interstellar medium), and a dynamically important but poorly understood component commonly called dark matter. The word galaxy is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way galaxy. Galaxies range from dwarfs with as few as ten million stars to giants with a hundred trillion stars, each orbiting the centre of mass of their host galaxy.

Galaxies vary in their relative amounts of stars and interstellar medium but the mass of most galaxies is dominated by dark matter, 90% being typical. It is now thought that most, if not all, galaxies contain a super-massive black hole at their centre.

As far as their optical appearance goes, galaxies have historically been classified into one of three broad classes. Elliptical galaxies have a smooth, elliptical light distribution that shows little or no detail and are characterised by having relatively little interstellar medium. Spiral galaxies are flattened disk-like systems showing beautiful, curving spiral arms, and have much more interstellar medium than the ellipticals. The third class is the irregular galaxies, generally less massive than either the ellipticals or spirals, and having an amorphous appearance. These galaxies are normally very rich in interstellar medium.

Galaxies sometimes collide and interact with each other and this can both induce very rapid bursts of star formation and transform galaxies from one type into another. Mergers of galaxies in the distant past are thought to have been fundamental in shaping their present-day appearance.

Most galaxies are 1,000 to 100,000 parsecs in diameter and usually separated by distances on the order of millions of parsecs (or megaparsecs). Intergalactic space is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations known as groups and clusters, which, in turn usually form larger superclusters. At the largest scale, these associations are generally arranged into sheets and filaments, which are surrounded by immense voids.

AN UNEXPECTED GAMMA-RAY BURST

Jun 08, 2022

AN UNEXPECTED GAMMA-RAY BURST An international group led by INAF researchers have confirmed that the gamma-ray burst GRB 200826A, which lasted less than two seconds – typical of short bursts – is associated with the explosion of a massive star, which is typical of long gamma-ray bursts

Announcing the new Director of the Large Binocular Telescope

May 31, 2022

Announcing the new Director of the  Large Binocular Telescope The Large Binocular Telescope Observatory, one of the largest and most advanced optical telescopes in the world, is proud to announce the appointment of its new Director, Prof. Joseph Shields, who will assume the position effective June 06, 2022

The final catalogue of the Gaia-ESO Survey is public

May 25, 2022

The final catalogue of the Gaia-ESO Survey is public ESO has just released the final catalogue of the Gaia-ESO Survey (GES), a large public spectroscopic survey carried out with the Very Large Telescope (VLT) of the European Southern Observatory in Chile. INAF has played a key role in all the aspects of the survey.