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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.

Studying the birth of exoplanets with chemistry

Sep 23, 2022

Studying the birth of exoplanets with chemistry A new study led by Elenia Pacetti, PhD student at La Sapienza University and INAF, jointly uses ultra-volatile, volatile, and refractory elements in the atmospheres of giant planets to develop a unified method to shed light on how and where giant planets form. The new work, published in The Astrophysical Journal, paves the road to the exoplanetary studies of the ESA mission Ariel

Stellar evolution along the HR diagram with Gaia

Sep 21, 2022

Stellar evolution along the HR diagram with Gaia The hybrid workshop started its activities in the INAF National Auditorium “Ernesto Capocci” of the Capodimonte Astronomical Observatory in Naples

The discovery of an extremely energetic gamma-ray burst from the infant Universe

Sep 21, 2022

The discovery of an extremely energetic gamma-ray burst from the infant Universe An international effort led by INAF researcher Andrea Rossi discovered and followed up the gamma-ray burst GRB 210905A, one of the most luminous events ever recorded that exploded when our Universe was just less than 900 million years old