Image: Hubble traces a galaxy's outer reaches

Believe it or not, this long, luminous streak, speckled with bright blisters and pockets of material, is a spiral galaxy like our Milky Way. But how could that be? 

Image: Hubble snaps a galactic potpourri of particles

Every now and then, the NASA/ESA Hubble Space Telescope glimpses a common object—say, a spiral galaxy—in an interesting or unusual way. A sharply angled perspective, such as the one shown in this Hubble image, can make ...

Image: Hubble spots a stunning spiral

Galaxies come in many shapes and sizes. One of the key galaxy types we see in the universe is the spiral galaxy, as demonstrated in an especially beautiful way by the subject of this Hubble Space Telescope image, NGC 2985. ...

Hubble sets sights on an explosive galaxy

When massive stars die at the end of their short lives, they light up the cosmos with bright, explosive bursts of light and material known as supernovae. A supernova event is incredibly energetic and intensely luminous—so ...

Citizen scientists re-tune Hubble's galaxy classification

Hundreds of thousands of volunteers have helped to overturn almost a century of galaxy classification, in a new study using data from the longstanding Galaxy Zoo project. The new investigation, published in the journal Monthly ...

Image: Mature galaxy mesmerizes in new Hubble view

This striking image was taken by the NASA/ESA Hubble Space Telescope's Wide Field Camera 3 (WFC3), a powerful instrument installed on the telescope in 2009. WFC3 is responsible for many of Hubble's most breathtaking and iconic ...

Galaxies as 'cosmic cauldrons'

Star formation within interstellar clouds of gas and dust, so-called molecular clouds, proceeds very rapidly yet highly inefficiently. Most of the gas is dispersed by stellar radiation, revealing galaxies to be highly dynamic ...

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Spiral galaxy

A spiral galaxy is a galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the Nebulae” and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are surrounded by a much fainter halo of stars, many of which reside in globular clusters.

Spiral galaxies are named for the (usually two-armed) spiral structures that extend from the center into the disk. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disk because of the young, hot OB stars that inhabit them. Roughly half of all spirals are observed to have an additional component in the form of a bar-like structure, extending from the central bulge, at the ends of which the spiral arms begin. Our own Milky Way has been recently (in the 1990s) been confirmed to be a barred spiral, although the bar itself is difficult to observe from our position within the Galactic disk. The most convincing evidence for its existence comes from a recent survey, performed by the Spitzer Space Telescope, of stars in the Galactic center.

Together with irregulars, spiral galaxies make up approximately 60% of galaxies in the local Universe. They are mostly found in low-density regions and are rare in the centers of galaxy clusters.

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