One of the largest hydrogen filaments ever seen in the Milky Way is discovered

The Milky Way has a large filament of gaseous atomic hydrogen. The structure, nicknamed "Maggie", is about 55,000 light-years from us, and is one of the largest ever observed in our galaxy. This discovery was made by an international team of scientists, led by astronomers from the Max Planck Institute of Astronomy (MPIA).

 The authors worked with data collected during the observation program HI/OH/Recombination line survey of the Milky Way (or just "THOR"), carried out with the Very Large Array (VLA) observatory, in New Mexico. With the VLA's radio antennas, the project analyzes processes such as the formation of molecular clouds, the conversion of atomic to molecular hydrogen, the magnetic fields of galaxies, among others.

The main purpose of this is to determine how atomic hydrogen (made up of a proton and an electron) and molecular hydrogen (the latter, with a proton, a neutron and an electron) transform to create dense clouds, which give rise to new stars. In this case, only deuterium (molecular hydrogen) condenses into relatively compact clouds, from which stars emerge at some point.

As the transformation process from atomic to molecular hydrogen is a great mystery, the discovery of the filament was a pleasant surprise to the team. After all, the largest clouds of molecular gas don't usually exceed 800 light years, but the Maggie is 3,900 light years across and 130 light years across.

Jonas Syed, lead author of the study, commented that they are still not sure how the structure ended up in our galaxy. “The filament extends about 1,600 light years below the plane of the Milky Way,” he explained. The result of this is that the molecule's radiation, with a wavelength of 21 cm, stood out from the background and made it possible for Maggie to be observed.

The authors' analysis showed that the filament matter had a velocity of 54 km/s-1. From the observations, they determined the velocity of the hydrogen gas, finding that there are almost no velocity variations in the structure. Therefore, they concluded that Maggie is a coherently structured filament.

From data published in previous studies, the team estimated that Maggie has about 8% molecular hydrogen by mass fraction, and observed that the gas converges at different points along its structure. Hence, they believe that hydrogen gas accumulates in large pockets at these locations, and speculate that the atomic gas will gradually condense there into molecular form.

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