Beyond the brim, Sombrero Galaxy's halo suggests turbulent past

Surprising new data from NASA's Hubble Space Telescope suggests the smooth, settled "brim" of the Sombrero galaxy's disk may be concealing a turbulent past. Hubble's sharpness and sensitivity resolves tens of thousands of ...

Galaxy Cruise—Your galactic journey as a citizen scientist

The Universe is full of galaxies of various shapes; some galaxies have spiral arms and others don't. Why do galaxies show such diversity? Galaxies are thought to grow by interacting and merging with other galaxies; and the ...

Image: Hubble embraces spiral with open arms

The spiral galaxy NGC 2008 sits center stage, its ghostly spiral arms spreading out toward us, in this image captured by the NASA/ESA Hubble Space Telescope.

Globular cluster system of NGC 4546 studied in detail

Using the Gemini-South telescope, astronomers have performed a photometric study of the lenticular galaxy NGC 4546. Results of the new research provide more clues about the structure and nature of the galaxy's globular cluster ...

Fast radio burst with steady 16-day cycle observed

A large team of space scientists working in Canada has found evidence of a fast radio burst with a steady 16-day cycle. The team has published a paper describing their findings on the arXiv preprint server.

Galaxy formation simulated without dark matter

For the first time, researchers from the Universities of Bonn and Strasbourg have simulated the formation of galaxies in a universe without dark matter. To replicate this process on the computer, they have instead modified ...

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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