Spitzer
Snaps Beautiful Image of Messier 81
This infrared image taken by NASA’s Spitzer Space Telescope shows a spiral galaxy called Messier 81. Image credit: NASA / JPL-Caltech. |
This
infrared image taken by NASA’s Spitzer Space Telescope shows a spiral galaxy
called Messier 81. Image credit: NASA / JPL-Caltech.
Messier 81 was
discovered on December 31, 1774 by the German astronomer Johann Elert Bode.
Also
known as M81, LEDA 28630 or NGC 3031, this galaxy is located 11.6 million
light-years from Earth and has an apparent magnitude of 6.9.
Messier
81 has a diameter of 90,000 light-years,
about half the size of our own Milky Way Galaxy.
It
is the largest galaxy in the M81 Group, a gathering of 34 galaxies located in
the northern constellation of Ursa Major.
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.
The
galaxy’s central bulge contains much older, redder stars. It is significantly
larger than the Milky Way’s bulge.
A
supermassive black hole of 70 million solar masses resides at the center of Messier
81 and is about 15 times the mass of the Milky Way’s central black hole.
“The
Spitzer infrared image of Messier 81 is a composite mosaic combining data from
the Infrared Array Camera at wavelengths of 3.6/4.5 microns (blue/cyan) and 8
microns (green) with data from the Multiband Imaging Photometer at 24 microns
(red),” NASA astronomers said.
“The
3.6-micron near-infrared data (blue) traces the distribution of stars, although
the image is virtually unaffected by obscuring dust and reveals a very smooth
stellar mass distribution, with the spiral arms relatively subdued.”
“As
one moves to longer wavelengths, the spiral arms become the dominant feature of
Messier 81.”
“The
8-micron emission (green) is dominated by infrared light radiated by hot dust
that has been heated by nearby luminous stars.
”
”
“Dust
in the galaxy is bathed by ultraviolet and visible light from nearby stars.”
“Upon
absorbing an ultraviolet or visible-light photon, a dust grain is heated and
re-emits the energy at longer infrared wavelengths.”
“The
dust particles are composed of silicates, carbonaceous grains and polycyclic
aromatic hydrocarbons and trace the gas distribution in Messier 81.”
“The
well-mixed gas and dust provide a reservoir of raw materials for future star
formation.”