Multi-spectrum viewer of M94 (NGC 4736)

Electromagnetic radiation is the primary method for transferring energy throughout the Universe. It's composed of particles, called photons, arranged in waves moving outward like ripples in a pond, traveling at a constant speed in all directions from its source. The distance between the crest of each wave can be less than a billionth of a centimeter (gamma rays) to more than a thousand kilometers in length (radio waves). Our eyes are sensitive to only a small portion of all possible wavelengths- those that the Sun releases in greatest quantity. We call this White Light. But, white light is nothing of the kind; it's a mixture of all visible wavelengths, each of which produces a different color when isolated. The shorter wavelengths yield violet and blue, the longer ones create orange and red. On either side of these familiar rainbow colors extend other forms of radiation our eyes cannot perceive: gamma, X-rays and ultraviolet rays have wavelengths that are too short while infrared and radio waves are too long.

The space between the stars is not empty- it's filled with very thin amounts of molecular gas and dust. But, even a few molecules of this material per cubic centimeter can create a dense, opaque cloud when viewed from a distance of a hundred or more light years. These clouds can absorb the white light released by stars that lie further beyond making it difficult or impossible for us to see them visually. But, ultraviolet and infrared radiation often provides a different perspective. This enables astronomers to pierce otherwise obscuring haze with images taken through filters that only pass these wavelengths. For example, ultraviolet images can reveal active star forming regions where the gas and dust is thin. Mid and far infrared pictures can capture gas and dust structures heated by stars in relative close proximity.

In 2006, this ground based optical (white light) image attracted the attention of an international team of astrophysicists who launched a three year investigation that probed M94(NGC 4736) in multiple wavelengths. Optical images typically display this star system as an active central region surrounded by an amorphous circular band of gas, dust and stars classically described as a closed stellar ring. Modern astronomical CCD cameras possess an incredible tonal range- far more than photographs produced with film emulsions. If great care is exercised with digital dark room techniques, it's possible to preserve and enhance small contrast variances captured by modern electronic imaging chips that are often overlooked. For M94(NGC 4736), the result is an optical image that offers a tantalizing glimpse of a classic spiral pattern hidden within the surrounding ring.

Our investigation detected furious stellar formation (about twice that occurring in the central disk), confirmed the existence of an impressive set of spiral arms extending throughout the surrounding ring and provided an explanation about their origin when M94(NGC 4736) was studied through mid-infrared, near and far ultraviolet wavelengths. More...