HUBBLE PHOTOGRAPHS GRAND DESIGN SPIRAL GALAXY M81
The Hubble Space Telescope has taken the sharpest image ever of the large "grand design" spiral galaxy M81. This beautiful galaxy is tilted at an oblique angle on to our line of sight, giving a "birds-eye
view" of the spiral structure. The galaxy is similar to our Milky Way, but our favorable view
provides a better picture of the typical architecture of spiral galaxies. Though the galaxy is
11.6 million light-years away, NASA Hubble Space Telescope's view is so sharp that it can
resolve individual stars, along with open star clusters, globular star clusters, and even
glowing regions of fluorescent gas.
The spiral arms, which wind all the way down into the 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. The
greenish regions are dense areas of bright star formation. The ultraviolet light from hot
young stars are 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. The central black hole is 70 million solar masses, or 15 times the
mass of the Milky Way's black hole. Previous Hubble research shows that the size of the
central black hole in a galaxy is proportional to the mass of a galaxy's bulge.
M81 may be undergoing a surge of star formation along the spiral arms due to a close
encounter it may have had with its nearby spiral galaxy NGC 3077 and a nearby starburst
galaxy (M82) about 300 million years ago. Astronomers plan to use the Hubble image to
study the star formation history of the galaxy and how this history relates to the neutron
stars and black holes seen in X-ray observations of M81 with NASA's Chandra X-ray
M81 is one of the brightest galaxies that can be seen from the Earth. It is high in the
northern sky in the circumpolar constellation Ursa Major, the Great Bear. At an apparent
magnitude of 6.8 it is just at the limit of naked-eye visibility. The galaxy's angular size is
about the same as that of the Full Moon.
The Hubble data was taken with the Advanced Camera for Surveys in 2004 through 2006.
This color composite was assembled from images taken in blue, visible, and infrared light.
Credit: NASA, ESA, and The Hubble Heritage Team
Acknowledgment: A. Zezas and J. Huchra (Harvard-Smithsonian
Center for Astrophysics)