A team of researchers has discovered a complex network of filament structures in the Milky Way. The structures are made of atomic hydrogen gas. And we all know that stars are mostly made up of hydrogen gas.
Not only did the team discover that all of the hydrogen potential is future star stuff, but they also found that its filament structure is also a historical imprint of some events in the Milky Way.
The paper in which this finding is announced is entitled “The history of dynamics and star feedback revealed by the HI filament structure in the disk of the Milky Way”. The lead researcher is Juan Diego Soler from the Max Planck Institute for astronomy (MPIA). The paper was published in the journal Astronomy and Astrophysics.
The authors present their work with the words: “Diffuse neutral atomic hydrogen (HI) is the matrix in which star-forming clouds are located and the medium that absorbs the energy injected by stellar winds, ionizing radiation and supernovae. The observation of its distribution and dynamics provides decisive evidence for an understanding of the energy and matter cycle in the interstellar medium (ISM).
The study is based on an MPIA project called THOR (The HI / OH / Recombination line). THOR is a poll based on the famous H1 line, or hydrogen line. The H1 line is a commonly used part of astronomical observations. It is based on the spectral line created by neutral hydrogen atoms when their energy state changes. The H1 line has a wavelength of 21 cm, which can be easily observed by radio telescopes, and can penetrate interstellar dust that blocks visible light.
"We are reconstructing the history of the Milky Way using the clouds of atomic hydrogen gas."
Juan Diego Soler, Senior Researcher, MPIA
Due to the properties of the H1 line and the VLA radio interferometer (Very Large Array), with which the data for THOR were recorded, the survey provides maps of the gas distribution in the inner Milky Way, "which have the highest spatial resolution to date" for a press release .
"The latest addition to the THOR data set is our data version 2, which contains a count of the neutral atomic hydrogen with an angular resolution of 40 arc seconds," explains Henrik Beuther, who heads the THOR project at MPIA, in the version.
Co-author Yuan Wang was partially responsible for processing the THOR data for this study. "We used the famous spectral line of hydrogen, which is at a wavelength of 21 cm," explains Yuan Wang. “These data also provide the gas velocity in the direction of observation. In combination with a model of how the gas in the Milky Way disk rotates around its center, we can even infer distances, ”added Wang. Thanks to the high resolution in the THOR observations, completely new studies were possible.
The lead author Soler was also responsible for processing the THOR data. He applied an algorithm to the data to better study the hydrogen distribution. The algorithm was the same as that used in satellite image analysis and character recognition. This algorithm revealed the detailed filamentary nature of hydrogen.
Most of the hydrogen filaments run parallel to the disk of the Milky Way. One of the traces of hydrogen that Soler Magdalena named after the longest river in his native Colombia is 3,000 light years long. At this length it could be one of the largest structures in the entire galaxy.
“Maggie (Magdalena) could be the largest known contiguous object in the Milky Way. In the past few years, astronomers have studied many molecular filaments, but Maggie appears to be purely atomic. Because of its fortunate position in the Milky Way, we are fortunate to be able to recognize it, ”said Jonas Syed, Ph.D. Student at the MPIA who is also part of the THOR team.
This number from the study shows the Magdalena filament, a 3,000 light year long filament made of atomic hydrogen. The upper field shows measurements in different speed channels. The middle field shows data from Magdalena's observations, which were processed with a so-called Hessian technique. The lower field shows spectra for the positions indicated by the crosses in the upper field. Photo credit: Wang et al., 2020.
But Maggie didn't get the most of the attention. Instead, the researchers were interested in a group of vertical hydrogen filaments.
The Milky Way is turning. And this rotation should expand the hydrogen filaments parallel and on the same plane as the Milky Way. Why is a group of filaments vertical?
“As with the rotating pizza dough, we expected most of the filaments to be parallel to the plane and stretched by the rotation. But when we found lots of vertical filaments in regions known for their high star formation activity, we knew we were into something. A process must have blown material off the galactic plane, ”Soler explained.
This process was likely massive stars that explode as supernovae at the end of their life.
These massive stars have powerful stellar winds with the power to shape their surroundings, including hydrogen that can be pushed around easily. The ionizing radiation from the stars supports the process. This puts it back on the H1 line.
<img load = "lazy" width = "669" height = "217" src = "https://www.universetoday.com/wp-content/uploads/2020/10/Hydrogen-Filaments-SN-1.png" alt = "This number from the study
The H1 line has been used for all kinds of observations, including finding and identifying the gas shells around stars that have become supernovae. The supernova's powerful shock waves hit hydrogen gas, causing it to clump and sometimes trigger new star formation. But that's not quite what happened to the vertical filaments THOR found.
Most of the vertical filaments of atomic hydrogen are in regions with a known, long history of star formation. Several generations of stars and supernovae have shaped the region, and the research team linked the vertical filaments to events that occurred long before the shells carved out by supernovae.
"Most likely, we are looking at the rest of many older seashells that burst when they reached the edge of the Galactic Disk, accumulated over millions of years, and thanks to the magnetic fields, remain coherent," explains Soler.
Reconstruction of hydrogen gas distribution in part of the Milky Way based on observations from the THOR survey. This is roughly what an observer would see from the top of the galaxy. The colors correspond to the density of atomic hydrogen. The gray bands indicate the spiral arms of the Milky Way. The crosses localize clouds of ionized gas that mark the star-forming regions with high mass. Wang et al., 2020.
This study gives us a fresh look at some of the dynamic processes that go on in galaxies. It links observations to the physical processes that cause gas to accumulate and then form new stars. "Our results show that a systematic characterization of the emission morphology towards the galactic plane creates an unexplored link between the observations and the dynamic behavior of the interstellar medium, from the effect of large-scale galactic dynamics to the galactic wells powered by SNe." The authors write in their work.
“Galaxies are complex dynamic systems and new clues are difficult to come by. Archaeologists reconstruct civilizations from the ruins of cities. Paleontologists assemble ancient ecosystems from dinosaur bones. We are reconstructing the history of the Milky Way using the clouds of atomic hydrogen gas, ”concludes Soler.
The team believes their methodology can be applied to other regions of the galaxy to reveal the nature of neutral hydrogen atomic structures. Will there be more Magdalenas?
"The statistical nature of our study reveals general trends in the structure of atomic gas in the galaxy and motivates additional high-resolution observations of HI emissions in other regions of the galaxy," the authors write in their conclusion. "Our results show that measuring the orientation of filamentary structures in the galactic plane is a promising tool to uncover the imprint of galactic dynamics, star feedback and magnetic fields in the observed structure of the Milky Way and other galaxies."