Spiral Galaxy Messier 81

Spitzer_ssc2003-06c1_1024

spitzer_ssc2003-06c1 December 18th, 2003

Credit: NASA/JPL-Caltech/S. Willner (Harvard-Smithsonian Center for Astrophysics)

The magnificent spiral arms of the nearby galaxy Messier 81 are highlighted in this NASA Spitzer Space Telescope image. Located in the northern constellation of Ursa Major (which also includes the Big Dipper), this galaxy is easily visible through binoculars or a small telescope. M81 is located at a distance of 12 million light-years.

Because of its proximity, M81 provides astronomers with an enticing opportunity to study the anatomy of a spiral galaxy in detail. The unprecedented spatial resolution and sensitivity of Spitzer at infrared wavelengths show a clear separation between the several key constituents of the galaxy: the old stars, the interstellar dust heated by star formation activity, and the embedded sites of massive star formation. The infrared images also permit quantitative measurements of the galaxy's overall dust content, as well as the rate at which new stars are being formed.

The infrared image was obtained by Spitzer's infrared array camera. It is a four-color composite of invisible light, showing emissions from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (yellow) and 8.0 microns (red). Winding outward from the bluish-white central bulge of the galaxy, where old stars predominate and there is little dust, the grand spiral arms are dominated by infrared emission from dust. Dust in the galaxy is bathed by ultraviolet and visible light from the surrounding 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, composed of silicates (which are chemically similar to beach sand) and polycyclic aromatic hydrocarbons, trace the gas distribution in the galaxy. The well-mixed gas (which is best detected at radio wavelengths) and dust provide a reservoir of raw materials for future star formation.

The infrared-bright clumpy knots within the spiral arms denote where massive stars are being born in giant H II (ionized hydrogen) regions. The 8-micron emission traces the regions of active star formation in the galaxy. Studying the locations of these regions with respect to the overall mass distribution and other constituents of the galaxy (e.g., gas) will help identify the conditions and processes needed for star formation. With the Spitzer observations, this information comes to us without complications from absorption by cold dust in the galaxy, which makes interpretation of visible-light features uncertain.

The white stars scattered throughout the field of view are foreground stars within our own Milky Way galaxy.

Provider: Spitzer Space Telescope

Image Source: http://www.spitzer.caltech.edu/images/1072-ssc2003-06c1-Spiral-Galaxy-Messier-81

Curator: Spitzer Space Telescope, Pasadena, CA, USA

Image Use Policy: http://www.spitzer.caltech.edu/info/18-Image-Use-Policy

Image Details

Image Type
Observation
Object Name
Bode's Galaxy Messier 81 M81 NGC 3031 UGC 5318
Subject - Local Universe
Galaxy > Type > Spiral

Distance

Universescale2
12,000,000 light years
Spitzer_ssc2003-06c1_128
 

Position Details

Position (ICRS)
RA = 9h 55m 34.0s
DEC = 69° 3’ 54.9”
Orientation
North is 268.7° CCW
Field of View
23.5 x 17.9 arcminutes
Constellation
Ursa Major

Color Mapping

  Telescope Spectral Band Wavelength
Arrow_left_blue Spitzer (IRAC) Infrared (Near-IR) 3.6 µm
Arrow_left_green Spitzer (IRAC) Infrared (Near-IR) 4.5 µm
Arrow_left_red Spitzer (IRAC) Infrared (Mid-IR) 5.8 µm
Arrow_left_red Spitzer (IRAC) Infrared (Mid-IR) 8.0 µm
The contribution from starlight has been subtracted from the 5.8 and 8.0 micron channels to enhance the visibility of dust features.
Spectrum_base
Arrow_top_blue
Arrow_top_green
Arrow_top_red
Arrow_top_red
Spitzer_ssc2003-06c1_1280
×
ID
ssc2003-06c1
Subject Category
C.5.1.1.  
Subject Name
Bode's Galaxy, Messier 81, M81, NGC 3031, UGC 5318
Credits
NASA/JPL-Caltech/S. Willner (Harvard-Smithsonian Center for Astrophysics)
Release Date
2003-12-18
Lightyears
12,000,000
Redshift
-0.000113
Reference Url
http://www.spitzer.caltech.edu/images/1072-ssc2003-06c1-Spiral-Galaxy-Messier-81
Type
Observation
Image Quality
Good
Distance Notes
Distance taken from Fast Facts and NED
Facility
Spitzer, Spitzer, Spitzer, Spitzer
Instrument
IRAC, IRAC, IRAC, IRAC
Color Assignment
Blue, Green, Red, Red
Band
Infrared, Infrared, Infrared, Infrared
Bandpass
Near-IR, Near-IR, Mid-IR, Mid-IR
Central Wavelength
3600, 4500, 5800, 8000
Start Time
Integration Time
50, 50, 50, 50
Dataset ID
Notes
T
Coordinate Frame
ICRS
Equinox
J2000
Reference Value
148.891519342434, 69.065246176994862
Reference Dimension
1158, 878
Reference Pixel
579, 439
Scale
-0.00033889738260893987, 0.00033889738260893987
Rotation
268.70316683549561
Coordinate System Projection:
TAN
Quality
Full
FITS Header
Notes
Creator (Curator)
Spitzer Space Telescope
URL
http://www.spitzer.caltech.edu
Name
Spitzer Space Telescope
Email
Telephone
Address
1200 E. California Blvd.
City
Pasadena
State/Province
CA
Postal Code
91125
Country
USA
Rights
http://www.spitzer.caltech.edu/info/18-Image-Use-Policy
Publisher
Spitzer Science Center
Publisher ID
spitzer
Resource ID
ssc2003-06c1.tif
Metadata Date
2012-10-11
Metadata Version
1.1
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Detailed color mapping information coming soon...

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Universescalefull
12,000,000 light years