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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.

Radio evidence of a minor merger in the Shapley supercluster

Jan 17, 2022

Radio evidence of a minor merger in the Shapley supercluster A group of radio astronomers led by INAF has conducted a multi-frequency and multi-band study of the Shapley Supercluster, where the formation of large structures is ongoing at the present cosmological age. Radio astronomers have discovered a radio emission that acts as a "bridge" between a cluster of galaxies and a group of galaxies

Multiwavelength snapshot of a repeating fast radio burst

Dec 09, 2021

Multiwavelength snapshot of a repeating fast radio burst With a multiwavelength campaign, a group of astronomers led by the Italian National Institute for Astrophysics (INAF) studied a repeating fast radio burst (FRB). The object FRB20201124A, discovered in November 2020, reactivated in March 2021, emitting a series of radio bursts

Classifying Seyfert Galaxies with Deep Learning

Sep 28, 2021

Classifying Seyfert Galaxies with Deep Learning Scientist uses deep learning to identify low luminous Seyfert 1.9 galaxies that are usually missed by human inspection among ten thousands of spectra. These results are published in the Astrophysical Journal Supplement Series by Yen Chen Chen, in the department of physics at Sapienza University of Rome and ICRANet