Barred spiral galaxy

A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure made of stars. Bars are found in many spiral galaxies. They affect how stars and interstellar gas move inside these galaxies. The Milky Way Galaxy, where our Solar System is located, is a barred spiral galaxy.

Edwin Hubble classified these galaxies as "SB" (spiral, barred) in his Hubble sequence. He grouped them based on how spread out their spiral arms are. SBa types have tightly wound arms. SBc types have more loosely wound arms. SBb-type galaxies are in between these two.

Bars

Further information: Density wave theory § Galactic spiral arms

Many spiral galaxies have a special feature called a bar. This bar is a straight group of stars in the middle of the galaxy. Scientists think bars form when a wave of energy moves from the center, changing where stars go and making the bar grow.

Bars help new stars form by pulling material toward the center of the galaxy. They may also help make bright areas in the center, called active galactic nuclei. Bars do not last forever; they can change shape or disappear over billions of years. Most spiral galaxies, including our own Milky Way, have bars sometimes.

Grades

Barred spiral galaxies are called "SB" for short, which means spiral barred. The types differ based on how tightly the galaxy's spiral arms are wrapped. SBa types have arms that are tightly wrapped. SBc types have arms that are loosely wrapped. SBb types are in the middle. SBm describes barred spirals that are a bit irregular. There is also SB0, which is a barred lenticular galaxy.

Example	Type	Image	Information
NGC 2787	SB0		SB0 is a type of lenticular galaxy
NGC 4314	SBa
NGC 4921	SBab
Messier 95	SBb
NGC 3953	SBbc
NGC 1073	SBc
Messier 108	SBcd
NGC 2903	SBbc
NGC 5398	SBdm		SBdm can also be considered a type of barred Magellanic spiral
NGC 55	SBm		SBm is a type of Magellanic spiral (Sm)

Name	Image	Type	Constellation
M58		SBc	Virgo
M91		SBb	Coma Berenices
M95		SBb	Leo
M109		SBb	Ursa Major
NGC 1300		SBbc	Eridanus
NGC 7541		SB(rs)bcpec	Pisces
NGC 1365		SBc	Fornax
NGC 2217		SBa	Canis Major
Magellanic Clouds		SBm	Dorado, Tucana
UGC 12158		SB	Pegasus
NGC 1512		SB(r)ab	Horologium