Hubble2005-01-barred-spiral-galaxy-NGC1300

The corotation circle is the circle around the

galactic center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ...

of a

spiral galaxy Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

s move at the same speed as the

spiral arms Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

of this circle is called the corotation radius. Inside the circle the stars move faster and outside they move slower than the spiral arms. The

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared rad ...

is located near the corotation circle of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked ey ...

Influence of dark matter

The corotation circle can be used to probe

dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...

in a galaxy. In

barred spiral galaxies A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies, and generally affect both the motions of stars and interstellar gas within spiral galaxies ...

, such as the

, the stars in the bar rotate faster than the stars in the

spiral arm Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''dark matter haloes According to modern models of physical cosmology, a dark matter halo is a basic unit of cosmological structure. It is a hypothetical region that has decoupled from cosmic expansion and contains gravitationally bound matter. A single dark mat ...

slow the rotation, causing the corotation radius to be greater than 1.4 times the length of the bar. Most measurements have found that the corotation radius is always less than 1.4 times the bar length, leading to the conclusion that dark matter does not significantly influence galactic rotation. However, a 2017 study found that the arms of galaxies rotate more slowly than previously thought, implying that dark matter does sometimes influence the rotation of a galaxy even when the corotation radius is less than 1.4 times the bar length.{{Cite journal, last1=Font, first1=J., last2=Beckman, first2=J. E., last3=Martínez-Valpuesta, first3=I., last4=Borlaff, first4=A. S., last5=James, first5=P. A., last6=Díaz-García, first6=S., last7=García-Lorenzo, first7=B., last8=Camps-Fariña, first8=A., last9=Gutiérrez, first9=L., last10=Amram, first10=P., date=2017-02-02, title=Kinematic Clues to Bar Evolution for Galaxies in the Local Universe: Why the Fastest Rotating Bars are Rotating Most Slowly, journal=The Astrophysical Journal, language=en, volume=835, issue=2, pages=279, doi=10.3847/1538-4357/835/2/279, issn=1538-4357, bibcode=2017ApJ...835..279F, arxiv=1702.01743, s2cid=55782342 , doi-access=free

References

Spiral galaxies