Interstellar dust allowed scientists to look at the Milky Way from distant galaxies
Scientists from the Moscow Institute of Physics and Technology (MIPT), the P.N. Lebedev Physical Institute of the Russian Academy of Sciences (LPI) and the Crimean Astrophysical Observatory looked at the Milky Way from distant galaxies. They were helped by quasars, beacons of the Universe, some of the brightest objects in space that are billions of light years from Earth.
According to a paper published in the journal Monthly Notices of the Royal Astronomical Society, it is impossible to see the full structure of our Galaxy from Earth, because we are inside it. We need “photographs” of the Milky Way “outside”. Astrophysicists use radio images from distant galaxies as such “photographs. These images are influenced by the clouds of dust and gas that fill all the space between the stars in our Galaxy.
Passing through them, the radio emissions are scattered and the images are “smeared”. But: “who prevents us, he helps us”, decided the Russian scientists and formed the most complete map to date of the distribution of large-scale scattering screens in the interstellar medium of the Galaxy. Distant quasars helped them do this.
“Our task was to investigate how strong is the scattering of radio waves in different directions in the sky, and to build the first detailed map of the spatial distribution of such areas – powerful scattering screens of the Milky Way,” Alexander Pushkarev, professor of the Russian Academy of Sciences, a leading researcher at the Crimean Astrophysical Observatory and the PhIAN, said about the study.
The interstellar medium may have high turbulence caused by explosive processes due to the evolution of stars in the Galaxy, as well as the influence of cosmic rays. The passage of radio waves through turbulent plasma leads to scattering of radiation and, as a consequence, distortion of the source image. Studying the effects of radio wave scattering makes it possible to reconstruct a true image of distant space objects.
“In our work, we have shown that scattering screens are concentrated to the plane of the Galaxy in the directions towards its center, as well as the areas of supernova flares – the strongest explosions at the final stages of stellar evolution,” explained Tatiana Koryukova, a graduate student at PhIAN.
Pulsars of our stellar system were traditionally used as translucent beacons because of their extremely small size, only about 10 km in diameter. But quasars are more numerous, and in addition their radiation passes through the whole depth of the Galaxy.
“Astronomers are always interested in understanding how matter is distributed in our Milky Way Galaxy, and we are here shining a light on it with distant beacons – the nuclei of other galaxies. By the way their radiation changes, we understand the composition and location of the interstellar medium, and this allows us to study our cosmic home even better,” said Alexander Plavin, a researcher at the Laboratory of Basic and Applied Research of Relativistic Objects of the Universe at MIPT.
Thus, the study has important applications: a new detailed map of galactic scattering power will allow scientists to take this effect into account for a wide range of modern astrophysics problems. “I will add one specific example that many people have heard of – the shadow of a black hole, the very “orange bagel” at the center of our Galaxy, which astrophysicists made public at the end of May 2022. The distance to this black hole is 27 thousand light-years, its mass – about four million solar masses.
So why did it take astronomers years to reconstruct this picture? Sadly, the black hole is hidden from observers by a very dense cloud of interstellar plasma; astronomers have only seen a blurred spot there for years. In order to see anything at all, they had to work hard and make observations on a very short wave: 1.3 mm,” summarized Yuri Kovalev, corresponding member of the Russian Academy of Sciences, chief scientist of the MIPT and PhIAN.
