An international team of scientists has used data from ESA’s Planck Space Observatory and other telescopes to map the distribution of all light energy in our Milky Way Galaxy.
An all-sky image of the Milky Way Galaxy, as observed by ESA’s Planck Space Observatory in IR. The data contained in this image were used in this research and were essential in calculating the distribution of the light energy of the Galaxy. Image credit: ESA / HFI / LFI consortia.
The research, published in the Monthly Notices of the Royal Astronomical Society (arXiv.org preprint), shows how the stellar photons within the Milky Way control the production of the gamma-rays — the highest energy photons in the Universe.
This was made possible using a new method involving computer calculations that track the destiny of all photons in the Galaxy, including the photons that are emitted by interstellar dust, as infrared (IR) light.
“We have not only determined the distribution of light energy in the Milky Way, but also made predictions for the stellar and interstellar dust content of our Galaxy,” said University of Central Lancashire Professor Cristina Popescu, lead author of the study.
Previous attempts to derive the distribution of all light in the Milky Way based on star counts have failed to account for the all-sky images of the Milky Way, including recent images provided by the Planck observatory, which map out IR light.
By tracking all stellar photons and making predictions for how the Milky Way should appear in ultraviolet (UV), IR, and visual radiation, Professor Popescu and co-authors have been able to calculate a complete picture of how stellar light is distributed throughout the Galaxy.
An understanding of these processes is a crucial step towards gaining a complete picture of our Galaxy and its history.
The modeling of the distribution of light in the Milky Way follows on from previous research that the team conducted on modeling the stellar light from star-forming galaxies in the nearby Universe.
“It has to be noted that looking at galaxies from outside is a much easier task than looking from inside, as in the case of our Galaxy,” said co-author Dr. Richard Tuffs, of the Max Planck Institute for Nuclear Physics.
The authors have also been able to show how the stellar light within our Galaxy affects the production of gamma-ray photons through interactions with cosmic rays.
“Cosmic rays are high-energy electrons and protons that control star and planet formation and the processes governing galactic evolution,” they said.
“They promote chemical reactions in interstellar space, leading to the formation of complex and ultimately life-critical molecules.”
“Working backwards through the chain of interactions and propagations, one can work out the original source of the cosmic rays,” Dr. Tuffs said.
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C.C. Popescu et al. 2017. A radiation transfer model for the Milky Way: I. Radiation fields and application to high-energy astrophysics. Mon Not R Astron Soc 470 (3): 2539-2558; doi: 10.1093/mnras/stx1282
