Johns Hopkins Gazette: June 24, 1996

On Research:
Dazzling Cosmic
Display Mystifies

Emil Venere
News and Information
Astronomers have captured a spectacular image of a nearby galaxy, complete with huge filaments, loops and "bubbles" of ionized hydrogen gas that extend thousands of light-years from the plane of the galaxy.

The features probably are manifestations of the evolution and deaths of many massive stars.

The observations were made in September 1994 and September 1995 by Johns Hopkins University graduate student Annette Ferguson; Rosemary Wyse, a Johns Hopkins professor of astronomy and physics; and Jay Gallagher, a professor of astronomy at the University of Wisconsin-Madison. The astronomers used a 1.5-meter telescope at the Cerro Tololo Inter-American Observatory in Chile.

Ferguson presented a scientific paper about the work during this month's meeting of the American Astronomical Society at the University of Wisconsin.

The galaxy, NGC 55, is an irregular galaxy similar to the Large Magellanic Cloud, a companion to the Milky Way. It resides in a group of galaxies known as the Sculptor Group, located about 5 million light-years from Earth. NGC 55 is seen nearly edge-on from Earth, providing a much different perspective than the Large Magellanic Cloud, which presents a more face-on view.

The edge-on orientation allows for a clear view of the structures seen in images made by the team, as they protrude above and below the plane of the galaxy, Ferguson said.

Astronomers aren't certain what the structures are, but a popular theory is that material flowing out from massive stars, as they evolve, shapes the hydrogen gas surrounding the stars into filaments, bubbles and loops, Ferguson said. The stars, which are more than 10 times the mass of the sun, spew out material in stellar winds and from their explosive deaths, known as supernovas.

Energetic photons from the stars can ionize the hydrogen, removing each atom's single electron. These loose electrons soon "recombine" with bare hydrogen nuclei, releasing energy in the process. Radiation from this recombination can be seen in the form of light in a specific wavelength, measured at 6,563 angstroms, which falls within the visible spectrum. That is the radiation that the astronomers were able to observe, by using a special filter, limiting their observations to a narrow band of the spectrum.

The observations demonstrate the complex interplay between outflows of energy and material from young massive stars and the surrounding gas. The gas is the raw material for successive generations of new stars, said the astronomers, who believe they are seeing the influence of massive stars on future star formation processes, and the evolution of a galaxy.

A photographic image, like the one pictured here, may be downloaded from the World Wide Web by pointing your browser to

A tif version may be downloaded by substituting "tif" for "gif" at the end of the URL.

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