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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.

A farewell to BepiColombo after the flyby with the Earth

Apr 17, 2020

A farewell to BepiColombo after the flyby with the Earth The picture was taken by Liverpool Telescope on the Canary Island of La Palma when the spacecraft was more than 2 million kilometres far from our planet

Unexpected magnetic channels in a distant galaxy

Apr 08, 2020

Unexpected magnetic channels in a distant galaxy An international team of astronomers has uncovered unusual structures and a probable magnetic connection between the two lobes of the radio galaxy ESO 137-006 using the MeerKAT telescope, a precursor to the Square Kilometre Array (SKA). The study, led by Mpati Ramatsoku, was published in the Astronomy and Astrophysics journal

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.