Milky Way halo gas turns out to be 10 times hotter than scientists thought

Milky Way halo gas turns out to be 10 times hotter than scientists thought
Milky Way halo gas turns out to be 10 times hotter than scientists thought
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New observations of the halo gas in the Milky Way, carried out by the European Space Agency's XMM-Newton space observatory, have shown that the gas is much higher than expected, and in addition, the chemical composition of this gas also does not correspond to forecasts. These results may change our understanding of the evolution of the Galaxy, according to the authors of the work.

A halo is a vast region of space around a galaxy filled with gas, stars, and invisible dark matter. The halo is a key component of the galaxy's structure, linking it to the vast intergalactic space, and therefore plays an important role in the evolution of the galaxy.

Until now, it was believed that the halo of the Milky Way contains hot gas at temperatures from 10,000 to 1 million degrees (according to theory, the temperature of the gas that is part of the halo is determined by the total mass of the galaxy). However, new X-ray observations from the XMM-Newton observatory by researchers led by Sanskriti Das, a graduate student at Ohio State University, USA, have shown that in some areas of the Milky Way's halo, gas temperatures can reach 10 million degrees. The XMM-Newton's onboard Reflection Grating Spectrometer (RGS) and European Photon Imaging Camera (EPIC) instruments made it possible to observe, respectively, the absorption of transmitted light and the emission of scattered light by the halo gas. To observe the parameters of the scattering of transmitted light by this gas, the team used a distant blazar - a very active galactic nucleus that emits jets directed towards the Earth.

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In addition, studying the spectra of the halo gas allowed the team to figure out new details about its chemical composition. It is known that this gas is enriched in heavy elements that form in the last stages of the life cycle of stars. Until now, astronomers have mainly looked for oxygen (blue dots in the photo) in the halo of the Milky Way, as it is easiest to detect, but in the new work, the researchers also analyzed the contents of nitrogen (black dots), neon (yellow dots) and iron (red dots) and found interesting patterns. Observations have revealed lower iron and oxygen concentrations compared to the material in the sun. According to the authors, the lack of iron in the material of the halo gas can be explained by the fact that the enrichment of this material with heavy elements occurred at the expense of massive stars. The authors explain the observed lack of oxygen by the concentration of this element in the dust particles of interstellar space, due to which the oxygen depletion of the gas occurs. These results came as a surprise to scientists and could change the current understanding of the evolution of the Milky Way, the researchers said.

The work was published in the Astrophysical Journal.

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