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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 INAF study provides new assumptions on oscillation in star layers

Mar 21, 2017

An INAF study provides new assumptions on oscillation in star layers A team of researchers led by Enrico Corsaro, fellow of the AstroFIt2 programme at INAF in Catania, has recently published a study in Nature Astronomy which shows the relationship between the orientation of the stellar-spin axis and the environment where they formed.

INAF researchers participate in the discovery of two Super Earths

Mar 21, 2017

INAF researchers participate in the discovery of two Super Earths Two massive rocky planets 21 light-years from us, the closest known among those transiting in front of their parent star, have been detected and studied thanks to TNG Galileo National Telescope observations.

Risparmio e vedo il cielo. INAF joins the “M’illumino di meno” campaign

Feb 26, 2017

Risparmio e vedo il cielo. INAF joins the “M’illumino di meno” campaign On 24 February, on the occasion of the Energy Saving Day 2017, the National Institute for Astrophysics – INAF has joined the M’illumino di Meno campaign launched by Radio Rai 2 show Caterpillar, now in its thirteenth year, which renews the invitation to turn off the lights in squares, private and public lightings across Italy.