New images from NASA's Hubble Space Telescope are helping researchers view in unprecedented detail the spiral arms and dust clouds of a nearby galaxy, which are the birth sites of massive and luminous stars.

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, 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)

NASA's Hubble Space Telescope has returned the most detailed images ever of supernova 1994I which is in the "Whirlpool Galaxy" (M51) located 20 million light-years away in the constellation Canes Venatici.

The view in this picture encompasses the inner region of the galaxy's grand spiral disk, which extends all the way to the bright nucleus.

An arrow points to the location of the supernova, which lies approximately 2,000 light-years from the nucleus. The supernova appears to be superposed on a diffuse background of starlight. The Hubble Space Telescope was also used to measure the spectrum of the supernova in the ultraviolet light, which can be used to analyze the chemical composition and the motion of the gas ejected in the explosion.

A supernova is a violent stellar explosion which destroys a star, while ejecting the products of nuclear burning into the gas between stars. The energy for some supernova explosions comes from the collapse of a massive star to a compact neutron star, with the mass of the Sun, but the size of a city. Elements out of which the Earth is formed had their origin in ancient supernova explosions in our own Milky Way Galaxy.

This supernova was discovered on April 2, 1994 by amateur astronomers and has been the target of investigations by astronomers using ground-based optical and radio telescopes and NASA's International Ultraviolet Explorer satellite. Because a supernova explosion is a billion times as bright as a star like the Sun, they can be seen to great distances and may prove useful in charting the size of the universe. These previous observations show that SN 1994I is a very unusual supernova, called "Type Ic," for which very few examples have been studied carefully. The ultraviolet observations made with HST will help astronomers understand what type of stellar explosion led to supernova 1994I.

Further observations of SN 1994I with the Hubble Space Telescope will be able to see more deeply into the interior of the exploded star, as it ages. Although the supernova is now 10 times dimmer than when it was discovered, HST will be able to observe the light from SN 1994I well into 1995, when it is impossible to observe from the ground. This will allow astronomers to probe the chemical composition of the debris and to learn more about the type of star that exploded.

The HST image was taken with the Wide Field Planetary Camera on May 12, 1994.

Credit: Robert P. Kirshner/Harvard-Smithsonian Center for Astrophysics, NASA