Ruprecht-Karls-Universität Heidelberg

The longest star-cradle in the Milky Way

On this false-color image, the distribution of atomic hydrogen in the newly discovered structure below the Milky Way plane. The red dashed line marks the course of the "Maggie" filament. Image: J. Syed/MPIA

In the Milky Way, a 3900 light-year-long structure  has been identified that consists almost entirely of atomic hydrogen. This structure gives us a unique new view of matter right at the beginning of the star-formation process. The research results, to which ZAH scientists have also contributed, have been published in the journal "Astronomy & Astrophysics".

The formation and evolution of stars from cosmic matter is one of the most complex processes to take place in the universe since it was born in the Big Bang about 13 billion years ago. For this reason, numerous research groups around the world are busy investigating all conceivable aspects of this process. As many circumstances and periods of time as possible in the life of stars long before their birth as glowing balls of gas until their decay to a stellar remnant or spectacular supernova are in focus.

A team of astronomers led by researchers from the Max Planck Institute for Astronomy (MPIA) has now identified a 3900 light-year-long structure  in the Milky Way  that consists almost exclusively of atomic hydrogen and is in the state of matter before the onset of star formation. The discovery was made possible by an observing program called THOR, carried out between 2012 and 2015 with the "Very Large Array (VLA)", an radio interferometer for astronomical observations in New Mexico, USA.  THOR stands for "The HI/OH/Recombination line survey of the Milky Way".

Ralf Klessen and Simon Glover from the Institute of Theoretical Astrophysics at the Center for Astronomy at Heidelberg University were also involved in the planning  of the observing program. Their expertise lies primarily in the theoretical modelling of star formation. Both are therefore enthusiastic about the new discovery. "Through our models, we were able to make a significant contribution to the interpretation of the data as a coherent gas filament that has almost just decided to create stars." Klessen sums up. Simon Glover, a specialist in astrochemistry and the processes associated with the formation of stars, particularly appreciates the richness of the data, with the help of which his theoretical predictions can be tested very well. "THOR has provided us with measurements of a number of important atomic recombination and emission lines that we will use to adapt our models." explains the astrophysicist. The measurements indicate atomic gas combines to form molecular hydrogen. This accompanies gravitational collapse and subsequent star formation. In fact, the researchers found that the gas is running towards itself in some places along the filament. They conclude that hydrogen accumulates in these places, condenses, and the atomic gas there gradually transforms into its molecular form.

Hydrogen is by far the most abundant element in the universe and is the main ingredient in the formation of stars.  Nevertheless, clouds of hydrogen gas are difficult to detect, which makes it challenging to study the earliest phases of star formation.  Therefore, the discovery of this surprisingly long structure of hydrogen - also called a "filament" - is quite sensational.

"The location of this filament contributed to this," explained Jonas Syed, doctoral student at MPIA and first author of the  article published in the journal Astronomy & Astrophysics. "We don't yet know exactly how it got there. But the filament runs about 1600 light years below the Milky Way plane." As a result, the radiation of the hydrogen stands out clearly against the background and makes the filament visible. The co-author of the  study, Juan D. Soler, found a first indication of this filament a year ago. He named the filament "Maggie" after the with 1600 km longest river in his native Colombia, called Río Magdalena.

Since the transition from atomic to molecular hydrogen is still largely unknown, this extraordinarily long filament  will certainly be studied much more intensively in the future and suggests a large number of new findings.


J. Syed, J. D. Soler, H. Beuther, et al. , The "Maggie" filament: Physical properties of a giant atomic cloud, Astronomy & Astrophysics (2021), DOI

Homepage of the THOR project:

Homepage of Ralf Klessen:

Dr Guido Thimm
Center for Astronomy at Heidelberg University

Prof. Dr Ralf Klessen
Center for Astronomy at Heidelberg University
Institute of Theoretical Astrophysik

apl. Prof. Dr Simon Glover
Center for Astronomy at Heidelberg University
Institute of Theoretical Astrophysics


zum Seitenanfang/up