Original | Matt Williams
Translate | Linvo
About 13.8 billion years ago, our universe was born in a big bang and spawned the first subatomic particles and the laws of physics as we know it. About 370,000 years later, hydrogen formed, which is the building block that makes up stars, and inside the star hydrogen and helium fuses to create all the heavier elements. (Translator's note: Not all of the heavier elements are actually available.) Stellar fusion mostly goes to iron, and elements heavier than iron come from supernova explosions and neutron star collisions. While hydrogen is still the most ubiquitous element in the universe, it is difficult to detect a single cloud of hydrogen in the interstellar medium (ISM).
This makes it difficult to study the early stages of star formation, which will provide clues to the evolution of galaxies and the universe. An international team of astronomers led by the Max Planck Institute for Astronomy (MPIA) recently noticed that there is a huge filament of gas made of hydrogen atoms in our galaxy. The structure, named "Maggie," is located about 55,000 light-years away (on the other side of the Milky Way) and is one of the longest structures in the Milky Way ever observed.
The study, describing their findings, was published recently in the journal Astronomy and Astrophysics. The study is based on data obtained by THOR, and the observation program relies on the Carl G. Jansky Very Large Array (VLA) in New Mexico. This project uses VLA's centimeter-wave antenna to study molecular cloud formation, atom-to-molecular hydrogen conversion, galactic magnetic fields, and other problems related to ISM and star formation.
The ultimate goal of the study was to determine how the two most common hydrogen isotopes come together to form dense clouds until new stars form. Isotopes include atomic hydrogen (H), which consists of a proton and an electron; and molecular hydrogen (H2), or deuterium, consisting of a proton, a neutron, and an electron. Only the latter condenses into relatively compact clouds, forming frost zones, and eventually new stars are born.
The process of how atomic hydrogen is converted into molecular hydrogen is still unknown, making this very long "filament" a particularly exciting discovery. The largest known cloud of molecular gas is generally around 800 light-years long, while Maggie is 3900 light-years long and 130 light-years wide. As Syed explained in a recent MPIA press release:
"The location of the silk thread determines its formation. We don't yet know how it got there. But this thread extends another 1600 light-years under the silver plate. These observations give us an idea of the speed of hydrogen, which can prove that there is little difference in the speed along the silk line. (Translator's note: It is a whole structure)"
A partial map of the Milky Way measured by ESA's Gaia satellite (above) with squares indicating Maggie's position; an image of the atomic hydrogen distribution (bottom), with red lines representing Maggie
The team's analysis showed that the average velocity of the substance in the silk thread was 54 km/s, which was determined primarily by measuring its rotational speed with the silver disc. This means that the 21 cm wavelength radiation of this silk thread is visible in the cosmic context and the structure is clearly recognizable. "These observations also allowed us to determine the speed of hydrogen," said Henrik Beuther, head of THOR and co-author of the study. "This allows us to show that there is almost no difference in the speed along the silk thread."
From this, the researchers concluded that Maggie was a coherent structure. The findings confirm what Juan D. Soler, an astrophysicist and co-author of the paper at the University of Vienna, made a year ago. When he observed the silk thread, he named it after the longest river in their country, Colombia: "Maggie." While Maggie can be identified in an early assessment of the solar system from THOR data, only current research has unquestionably demonstrated that it is a coherent structure.
Based on previously published data, the team also estimated that Maggie contained 8 percent of the molecule hydrogen. After looking more closely, the team noticed that the gases were gathering along the silk lines at different points, which led them to conclude that hydrogen would accumulate in these places into large clouds. They further speculate that in these environments, atomic gases will gradually condense into sub-forms.
"Yet many questions remain unanswered," Said added. "We hope that more data will give us more clues about the composition of molecular gases, which are already waiting to be analyzed." Fortunately, some space and ground-based observatories will soon be put into use, and in the future telescopes will be equipped to study these filaments. These include the James Webb Space Telescope (JWST), as well as radio observations like the Square Kilometre Array (SKA), which will allow us to see the earliest period of the universe ("cosmic dawn") and the first stars in our universe.
Original: https://www.universetoday.com/153899/astronomers-find-the-biggest-structure-in-the-milky-way-a-filament-of-hydrogen-1600-light-years-long/