The magnetic fields of the jellyfish galaxy JO206

An international team of astronomers has gained new insights into the physical conditions prevailing in the gas tail of so-called jellyfish galaxies. They are particularly interested in the parameters that lead to the formation ...

New CubeSat will observe the remnants of massive supernovas

Scientists at CU Boulder are developing a satellite about the size of a toaster oven to explore one of the cosmos' most fundamental mysteries: How did radiation from stars punch its way out of the first galaxies to fundamentally ...

James Webb Telescope will reveal hidden galaxies

Two new studies from the University of Melbourne will help the largest, most powerful and complex space telescope ever built to uncover galaxies never before seen by humanity.

New M92 stellar stream discovered

A team of astronomers using the Canada-France-Hawaii Telescope discovered a new stellar stream emanating from the M92 globular cluster. This new stream suggests that M92 is actively being disrupted by tidal forces caused ...

The spin of the supermassive black hole in the Milky Way

Once a black hole forms, its intense gravitational field produces a surface beyond which even light cannot escape, and it appears black to outsiders. All the details of the complex mix of matter and energy in its past are ...

Astronomers discover metal-poor globular cluster by chance

An international team of astronomers led by Soren Larsen (Radboud University, Nijmegen, The Netherlands) has accidentally discovered a globular cluster that contains extremely few metals, those elements heavier than hydrogen ...

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Galaxy

A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with one trillion (1012) stars, all orbiting the galaxy's center of mass. Galaxies can also contain many multiple star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.

Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with curving, dusty arms. Galaxies with irregular or unusual shapes are known as peculiar galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies.

There are probably more than 100 billion (1011) galaxies in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs). Intergalactic space (the space between galaxies) 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 called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.

Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object within its nucleus.

This text uses material from Wikipedia, licensed under CC BY-SA