The Pinwheel Galaxy M101 in UV

Astronomers at the Goddard Space Flight Center in Greenbelt, Md. released today an image of the giant spiral galaxy, M101, as photographed on March 9 with the Ultraviolet Imaging Telescope (UIT) during the Astro-2 mission of Space Shuttle Endeavour. It is the first photograph in far-ultraviolet light ever obtained of M101, a spiral galaxy located about 16 million light years from the Earth in the constellation Ursa Major (the Great Bear). The region shown in the photograph is about 130,000 light years in diameter at the distance of M101. [One light year, the distance that light travels through space during one year, is approximately 5.9 trillion miles.]

"The image reveals regions where new stars are forming at a rapid rate," said Theodore P. Stecher, the principal investigator for the Ultraviolet Imaging Telescope. Stecher is a senior staff scientist in the Laboratory for Astronomy and Solar Physics at NASA's Goddard Space Flight Center. At lower left, outside the main body of the galaxy, the image shows a bright blob called NGC 5471, which is the brightest of all the new-star forming regions. The bright blob may have been produced in an ancient collision of cosmic proportions, according to UIT co-investigator Dr. Morton Roberts, of the National Radio Astronomy Observatory (NRAO) in Charlottesville, Va. (Roberts is a former drector of the NRAO.) "Galaxy M101 has probably collided with another galaxy in the past, which may have produced his bright clump of new stars," Roberts said.

An ultraviolet-sensitive electronic image intensifier was used together with a special photographic film to record the image as a 22-minute time-exposure, taken on the night side of Endeavour's orbit. "This is a fantastic image! I'm like a kid in a candy store scanning the film from this mission," said Dr. Susan Neff, a galaxy researcher at Goddard Space Flight Center and a co-investigator on the UIT team.

Ultraviolet light is blocked by the Earth's atmosphere and therefore must be observed from space. Ultraviolet light, which is invisible to the human eye, is generated predominantly by hot, young massive stars in galaxies such as M101.

The Ultraviolet Imaging Telescope was built at the Goddard Center and was previously flown in space during the Astro-1 mission in December 1990. The image of M101 released today has a diameter of 29 arc minutes, representing an area on the sky nearly as large as the Full Moon as seen from Earth. The image was obtained at a wavelength of 152 nanometers (1520 Angstroms).

The spiral arms of M101 are dotted with bright "beads" that represent massive concentrations of young, very hot stars. These star clusters "are shown to best advantage in the far-ultraviolet image, where vast numbers of older stars are 'screened out' because they emit very little ultraviolet light," according to Stecher. "Our team of scientists will be analyzing this image intensively in the next few months and will have more to say about M101 and many of the more than 200 other objects photographed during the Astro-2 mission," he added. He will present an invited talk on the findings from the UIT images at the American Astronomical Society's national meeting in Pittsburgh, PA, June 11- 15.

Credit: Jim Sahli, Goddard Space Flight Center, Greenbelt, MD. Nasa Press Release No. 95-77 (March 31, 1995)

UIT Science Team's M101 image caption

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Last Modification: June 28, 1998