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Messier 81

This stately spiral galaxy holds a black hole at its heart that is 70 million times the mass of the Sun.

Distance

11.6 million light-years

Apparent Magnitude

6.9

constellation

Ursa Major

object type

Spiral Galaxy

M81
NASA, ESA and the Hubble Heritage Team (STScI/AURA)

Discovered by the German astronomer Johann Elert Bode in 1774, M81 is one of the brightest galaxies in the night sky. It is located 11.6 million light-years from Earth in the constellation Ursa Major and has an apparent magnitude of 6.9. Through a pair of binoculars, the galaxy appears as a faint patch of light in the same field of view as M82. A small telescope will resolve M81’s core. The galaxy is best observed during April.

This stunning Hubble image was assembled using observations in visible and infrared light. The galaxy’s spiral arms, which wind all the way down into its nucleus, are made up of young, bluish, hot stars formed in the past few million years. They also host a population of stars formed in an episode of star formation that started about 600 million years ago. Ultraviolet light from hot, young stars is fluorescing the surrounding clouds of hydrogen gas. A number of sinuous dust lanes also wind all the way into the nucleus of M81.

The galaxy’s central bulge contains much older, redder stars. It is significantly larger than the Milky Way’s bulge. A black hole of 70 million solar masses resides at the center of M81 and is about 15 times the mass of the Milky Way’s central black hole. Previous Hubble research showed that the size of the black hole in a galaxy’s nucleus is proportional to the mass of the galaxy’s bulge.

Detailed Images of Spiral Galaxy M81
Hubble's high-resolution images of distinct regions contained within M81 illustrate various structures contained within the spiral galaxy. [Left] The inner bulge and nucleus of M81 are relatively structure free, except for fine dust lanes that wind into the center. Several whitish-colored concentrations of stars, known as globular clusters are easily visible. [Middle] A string of star-forming regions show along a spiral arm, their glowing hydrogen gas appears green in color. A denser concentration of dust is visible along the arms. [Right] Interspersed within the active spiral arms are areas of new star formation. Here, associations of hot blue stars have formed. These massive stars' lifetimes are relatively short compared to the overall age of the galaxy. Their existance and inevitable death will help to enrich the surrounding area with heavier elements which will in turn make more robust, longer-living stars.
NASA, ESA and the Hubble Heritage Team (STScI/AURA). Acknowledgment: A. Zezas and J. Huchra (Harvard-Smithsonian Center for Astrophysics)

For more information about Hubble’s observations of M81, see:

locator star chart for M81
This star chart for M81 represents the view from mid-northern latitudes for the given month and time.
Image courtesy of Stellarium

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