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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.

Thanks to the HARPS-N spectrograph, the TNG can see Venus

Feb 10, 2017

Thanks to the HARPS-N spectrograph, the TNG can see Venus TThe HARPS-N spectrograph succeeded in measuring from the Earth the velocity of the clouds in the atmosphere of Venus thanks to its high precision, competing with the Japanese Akatsuki probe, which has recently begun to study the atmosphere of the second planet.

The X-ray Universe 2017

Feb 03, 2017

The X-ray Universe 2017 The symposium (Rome, 6-9 June 2017) is the fifth meeting in the series of the international symposia "The X-ray Universe". The intention is to gather a general collection of research in high energy astrophysics. The symposium will provide a showcase for results, discoveries and expectations from current and future X-ray missions.

IXPE mission: Italy and NASA for new X-ray astronomy

Jan 21, 2017

IXPE mission: Italy and NASA for new X-ray astronomy NASA has announced that it is funding a new mission to study the high-energy Universe: it will be called IXPE (Imaging X-Ray Polarimetry Explorer) and will allow astronomers to explore with unprecedented details some of the most extreme astronomic objects, including stellar and supermassive black holes, neutron stars and pulsars. The mission, scheduled for the end of 2020, will count on a considerable Italian contribution through the Italian Space Agency(ASI), the National Institute for Nuclear Physics (INFN) and the National Institute of Astrophysics (INAF).