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The Whirlpool galaxy, M51, has been one of the most photogenic galaxies in amateur and professional astronomy. Easily photographed and viewed by smaller telescopes, this celestial beauty is studied extensively in a range of wavelengths by large ground- and space-based observatories. This Hubble composite image shows visible starlight as well as light from the emission of glowing hydrogen, which is associated with the most luminous young stars in the spiral arms.

M51, also known as NGC 5194, is having a close encounter with a nearby companion galaxy, M51B (NGC 5195), just off the upper edge of this image. The companion's gravitational pull is triggering star formation in the main galaxy, as seen in brilliant detail by numerous, luminous clusters of young and energetic stars. The bright clusters are highlighted in red by their associated emission from glowing hydrogen gas.

This Wide Field Planetary Camera 2 image enables a research group, led by Nick Scoville (Caltech), to clearly define the structure of both the cold dust clouds and the hot hydrogen and link individual clusters to their parent dust clouds. Team members include M. Polletta (U. Geneva); S. Ewald and S. Stolovy (Caltech); R. Thompson and M. Rieke (U. of Arizona).

Intricate structure is also seen for the first time in the dust clouds. Along the spiral arms, dust "spurs" are seen branching out almost perpendicular to the main spiral arms. The regularity and large number of these features suggests to astronomers that previous models of "two-arm" spiral galaxies may need to be revisited. The new images also reveal a dust disk in the nucleus, which may provide fuel for a nuclear black hole.

The team is also studying this galaxy at near-infrared wavelengths with the NICMOS instrument onboard Hubble. At these wavelengths, the dusty clouds are more transparent and the true distribution of stars is more easily seen. In addition, regions of star formation that are obscured in the optical images are newly revealed in the near-infrared images.

This image was composed by the Hubble Heritage Team from Hubble archival data of M51 and is superimposed onto ground-based data taken by Travis Rector (NOAO) at the 0.9-meter telescope at the National Science Foundation's Kitt Peak National Observatory (NOAO/AURA) in Tucson, AZ.

Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: N. Scoville (Caltech) and T. Rector (NOAO), and NASA STScI PRC 01-10

Hubble Heritage M51 page

Center of M51 in the Near-Infrared, as taken by HST's NICMOS instrument, with the following filters: Red, Continuum-subtracted Paschen Alpha + F222M; Green, F160W (K); Blue, F1110W (J).

Center of M51 in the Optical, taken by HST's WFPC2 camera. Filters: Red, Continuum-subtracted H Alpha + F814W (I); Green, F555W (V); Blue, F439W (B).

This image is displayed at same scale as above NICMOS photo. As the dust clouds in M51 are more transparent in the near-IR, the NICMOS image appears to be sharper, and shows the true stellar distribution more clearly than the optical WFPC2 image. Also, regions of star formation that are obscured in the optical image are newly revealed in the near-infrared image.

The central region of M51, as taken with the central chip of the WFPC2. The resolution of this close-up image allows one to peer right into the core of the nucleus and should help to understand what is going on at the very center of this galaxy.

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Location of the HST field within the galaxy M51, shown here in a CCD image obtained with the National Science Foundation's 0.9-meter telescope located at Kitt Peak National Observatory near Tucson, AZ. This CCD image was taken by Travis Rector and Monica Ramirez.

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Hubble View of the Supernova 1994I in M51

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Hartmut Frommert
Christine Kronberg
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Last Modification: April 19, 2001