Facing Galaxies Head-On; 'Deprojecting' Images of Galaxies Enables Scientists to View Them Face-to-Face for the First Time

By Thomsen, Dietrick E. | Science News, March 22, 1986 | Go to article overview

Facing Galaxies Head-On; 'Deprojecting' Images of Galaxies Enables Scientists to View Them Face-to-Face for the First Time


Thomsen, Dietrick E., Science News


FACING GALAXIES HEAD-ON

Nature has strewn galaxies around the universe. According to the latest observational results, that scattering is probably not random, but the attitudes in which the galaxies are found seem to be. Only some of the galaxies present themselves face-on to an observer from earth. Most are at angles; many are edge-on.

Astronomers often would like to get a face-on view of galaxies they see at angles. This would be especially useful in attempts to gather statistics about particular astrophysical processes--for example, the way new stars form.

It was precisely such an interest that motivated Philip E. Seiden, Debra M. Elmegreen, Bruce G. Elmegreen and Ayman Mobarak of the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y., to devise a computer program to "deproject" the images of galaxies and turn them face-on.

According to Seiden, the deprojector and the image stretcher are all part of the standard processing package. It took just a little custom work to get the system to interpret properly what it was doing. "The one major block," he says, "is that you have to have the money to buy a good imager, one with the resolution and color capabilities to show you what you've got."

With this mostly off-the-shelf system, Seiden says, observers can concentrate on astronomy. In previous work of this kind, people had to start from scratch, building up the whole computer system themselves. The present arrangement should be practical for many astronomers, he believes. Any of several brands of computer ware could be used, he says.

To deproject the oblique image of a galaxy, the system must know the angle at which the image is projected. This information comes from photometric studies. By comparing galaxies seen face-on with those seen obliquely, astronomers have a good idea what projection at different angles does to the light of a galaxy. With the angular information, the computer system can then do a basically trigonometric procedure for turning the image face-on. It can work with inclination angles up to 55[deg.] or 60[deg.]. Beyond that, too much information is lost.

The system also adjusts contrast and color. In searching for regions where new stars are forming, astronomers are looking for relatively faint and blue areas. Such regions tend to be washed out by bright areas, particularly near the center of a galaxy, and by the overall redness of the brighter and older stars. …

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