Planets in our galaxy.
With the help of the European Space Agency (ESA) INTEGRAL-INTErnational Gamma Ray Astrophysics Laboratory, launched on October 17, 2002 from Baikonur by the Russian Proton rocket carrier, an international team of researchers was able to confirm the predicted intensity of the birth of radioactive aluminum (26 Al) in massive stars and supernovae throughout our Galaxy and thus estimate the number of supernovae per the number of ordinary stars – this is one of the key parameters that influence the development of the galaxy (the work is published in the journal Nature on January 5, 2005).
The environment around us, as we know, consists mainly of chemical elements formed in ancient times inside stars during nuclear fusion reactions and during supernova outbreaks. These processes of nucleosynthesis are accompanied by the emission of high – energy photons-gamma rays – which easily reach us from all regions of our Galaxy.
Since its birth from a cloud of hydrogen and helium about 12 billion years ago, the Milky Way has gradually accumulated heavier chemical elements. At some stage, planets were able to form from them and, eventually, life appeared on Earth. More than 100 types of atoms or elements are now known in nature, such as iron, oxygen, hydrogen, etc.Nuclear fusion reactions occurring inside stars and during supernova explosions lead to the formation of new elements when lighter elements are combined into heavier ones. In most stars, including our Sun, hydrogen is continuously melted into helium. After the complete burning out of hydrogen, the fuel for the combustion process becomes helium itself.Gorenje. Gorenje: This is where the burning process in most stars ends, and the star sheds its outer layers into the surrounding space, so that this enriched gas can become the raw material for the next generation of stars and planets. A star with a mass several times that of the Sun can go further, producing carbon, oxygen, silicon, sulfur, and iron within itself. If up to this point the process was carried out with the release of energy, now for the formation of elements heavier than iron and nickel, in conditions when all the fuel available in the core of the star has already burned out, a new supply of energy is required. Such heavier elements, such as gold, lead, and uranium, are formed in supernova explosions and are released into outer space, where they can become the building material for new celestial objects.
The team, led by Roland Diehl of the Max-Planck-Institut für extraterrestrische Physik – MPE, Germany, investigated the emission of gamma-ray radiation from decaying aluminum-26 (a by-product of the fusion reaction of nuclei inside stars and during supernova outbreaks; its half-life is 720 thousand years, eventually it gives magnesium). They were looking for variations in the energy lines that could reveal the location of sources within the galactic plane. Scientists assumed that the gamma rays from the decaying aluminum-26 come to us mainly from the central regions of our Galaxy, since modern processes of production of new atomic nuclei are primarily associated with the galactic regions of active star formation.
Due to the fact that the galactic disk rotates around its central axis all the time, the observed wavelengths of gamma radiation from the decaying aluminum-26 (the decay corresponds to the value of 1808.65 kiloelectrons-volts) from the inner regions (the stars there rotate in their orbits much faster, since they are forced to compensate for the more powerful attraction of the galactic center) must change in a characteristic way under the influence of the Doppler effect. It is this characteristic pattern that was revealed by the “Integral”. It turned out that the gamma rays from the decaying aluminum-26 actually come to us more from the inner, rather than from the outer regions of the Galaxy, which is most likely caused by the local and specific production of 26 Al (otherwise, these radiation sources would not be characterized by the recorded high relative velocity).
Based on these new observations, it was possible to estimate the total amount of radioactive aluminum-26 in our Galaxy – it is equivalent to three solar masses. This is quite a lot, considering that aluminum-26 is an extremely rare isotope, and even in the conditions of the early Solar system (4.5 billion years ago), its ratio to the stable isotope aluminum-27 ( 27 Al) was 5 to 100 thousand.
Since astrophysicists have already identified possible sources of radioactive aluminum-mainly massive stars (red giants or hot blue stars) that end their lives as supernovae – it is possible to make a rough estimate of the frequency of such events: it turns out about one supernova outbreak in 50 years, which is compatible with the values found by indirect methods – in the course of observations of other galaxies and by comparing them with the Milky Way.
Since the study of gamma rays by the Integral will continue in the coming years, there is still hope for improving the accuracy of such measurements. Roland Dichl, who led the project, said that ” studying gamma rays will allow us to better understand the processes occurring in our home Galaxy, which are sometimes very difficult to study at other wavelengths due to the absorbing effects of the interstellar medium.”