The European Space Agency's gamma-ray observatory Integral is making progress in its effort to map our home galaxy at key gamma-ray wavelengths, officials said yesterday. It is now poised to give astronomers their truest picture yet of recent changes in the Milky Way's chemical composition.

At the same time, it has confirmed an 'antimatter' mystery at the center of the Galaxy.

Gamma radiation is high-energy "light" emitted from powerful but often mysterious space objects and phenomena. Gamma rays are more energetic than X-rays on the electromagnetic spectrum, which also includes visible light and even radio waves.

This false color picture was taken by the spectrometer on board Integral between December 2002 and March 2003. The yellow dots correspond to bright known gamma-ray sources, while the blue areas indicate regions of low emission. Data similar to these, but in a higher energy range, have been used to study where aluminum and iron are produced in the Galaxy.

Since its formation from a cloud of hydrogen and helium gas, around 12 billion years ago, the Milky Way Galaxy has gradually been enriched with heavier chemical elements. This has allowed planets and then life on Earth to form.

Today, one of those heavier elements -- radioactive aluminum -- is spread throughout the galaxy and, as it decays into magnesium, gives out gamma rays with a wavelength known as the '1809 keV line.' Integral has been mapping this emission with the aim of understanding exactly what is producing all this aluminum

Astronomers believe that the most likely sources of the aluminum are supernovas -- exploding high-mass stars. And, since the decay time of the aluminum is around one million years, Integral's map shows how many stars have died in recent celestial history. Other possible sources of the aluminum include red giant stars or hot blue stars that give out the element naturally, without killing themselves.

Credit: ESA/SPI team