Personal tools
Log in
You are here: Home Research Activities Galaxies and Cosmology

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.

We’re all astronauts on a public health mission: Ten tips for completing the quarantine successfully

Mar 27, 2020

We’re all astronauts on a public health mission: Ten tips for completing the quarantine successfully Debora Penco, Occupational psychologist, workplace health and safety expert, deals with the theme of our life in the times of quarantine and others ideas and suggestions to manage problems and tensions connected to it.

Where's there's one, there's one hundred more

Mar 06, 2020

Where's there's one, there's one hundred more PSO J030947.49+271757.31 is the most distant Blazar observed to date. The light we see from it began its journey when the Universe was less than 1 billion years old, almost 13 billion years ago. The blazar was discovered by a team of researchers led by Silvia Belladitta, a PhD student at the University of Insubria, working for the Italian National Institute for Astrophysics (INAF) in Milan

The New Year’s Day meteorite has been found

Jan 07, 2020

The New Year’s Day meteorite has been found For the first time in Italy a meteorite is recovered through systematic monitoring, thanks to the PRISMA network, promoted and coordinated by INAF