A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in approximately two-thirds of all spiral galaxies. Bars generally affect both the motions of stars and interstellar gas within spiral galaxies and can affect spiral arms as well.
Edwin Hubble classified these types of spiral galaxies as "SB" (spiral, barred) in his Hubble sequence, and arranged them into three sub-categories based on how open the arms of the spiral are. SBa types feature tightly bound arms, while SBc types are at the other extreme and have loosely bound arms. SBb-type galaxies lie in between. A fourth type, SBm, was subsequently created to describe somewhat irregular barred spirals, such as the Magellanic Cloud galaxies, which were once classified as irregular galaxies, but have since been found to contain barred spiral structures. Among other types in Hubble's classifications for the galaxies are: spiral galaxy, elliptical galaxy and irregular galaxy.
In 2005, observations by the Spitzer Space Telescope backed up previously collected evidence that suggested the Milky Way is a barred spiral galaxy. Observations by radio telescopes had for years suggested the Milky Way is barred, but Spitzer's vision in the infrared region of the spectrum has provided a more definite calculation.
Famous quotes containing the words barred, spiral and/or galaxy:
“Cinema is the culmination of the obsessive, mechanistic male drive in western culture. The movie projector is an Apollonian straightshooter, demonstrating the link between aggression and art. Every pictorial framing is a ritual limitation, a barred precinct.”
—Camille Paglia (b. 1947)
“Year after year beheld the silent toil
That spread his lustrous coil;
Still as the spiral grew,
He left the past years dwelling for the new,
Stole with soft step its shining archway through,
Built up its idle door,
Stretched in his last-found home, and knew the old no more.”
—Oliver Wendell Holmes, Sr. (18091894)
“for it is not so much to know the self
as to know it as it is known
by galaxy and cedar cone,
as if birth had never found it
and death could never end it:”
—Archie Randolph Ammons (b. 1926)