Gas is the raw material from which stars are made and the one Galaxies replenished. But the galaxies also give off huge gas clouds – material that is ejected by supernovae, among other things. Astronomers have now shown for the first time that this “exhaust gas” is actually significantly “dirtier” than the inflow: While the latter consists primarily of hydrogen and helium, the researchers found numerous heavy elements including oxygen, iron and carbon in the outflow of a galaxy 500 million light years away after.
Galaxies are the star factories of the cosmos, in them innumerable new stars grow in star formation regions. But to do this, the star cradles constantly need new supplies of hydrogen and helium – the elements that stars primarily consist of. Only through the nuclear fusion in their interior then further, heavier elements are formed. For galaxies this means that their star formation can only last as long as they have fresh gas available or can attract them. “To do this, enormous gas clouds are sucked into the galaxies,” explains co-lead author Deanne Fisher from Swinburne University in Australia.
A “Frisbee” with gas clouds
However, this influx of gas into a galaxy – also known as accretion – is not a one-way street: a galaxy that is actively forming stars also emits gases. The balance of accretion and outflow is an important factor influencing the growth, mass and size of a galaxy. But until now, astronomers could only guess whether and how the composition of the gases flowing in and out differed in a galaxy. Most galaxies lie so unfavorably in our line of sight that their gas flows are only partially clearly distinguishable and can be examined with spectral analyzes.
The research team has now given the research team a first chance to examine the “exhaust plume” of a galaxy more closely. Unlike most other galaxies, Mrk 1486 turns its narrow side towards us. This enabled the astronomers to clearly see the inflows and outflows. “Think of the galaxy as a spinning Frisbee,” explains co-lead author Alex Cameron of the University of Oxford. “The inflowing gas enters the galaxy at the side of the disk and condenses to form new stars. When these stars then explode again, they hurl new gases out of the galaxy above and below. “
Leaking gas is rich in heavier elements
The astronomers were able to observe these gases, which emerge perpendicular to the main plane of the galaxy, for the first time precisely at Mrk 1486 and determine their elemental composition with the help of an instrument on the telescopes of the Keck Observatory in Hawaii. “By using what is known as the Keck Cosmic Web Imager, we were able to confirm that the incoming gas consists of hydrogen and helium,” says Fisher. “We were also able to observe that the stars that emerge from this fresh gas later hurl enormous amounts of material out of the system again – above all through supernovae.” At Mrk 1486, this ejected material clearly emerges upwards and downwards and exists a mixture of numerous heavier elements, including oxygen, carbon and iron. The team was able to detect the spectral signatures of half the periodic table in this gas.
This is the first time that astronomers have succeeded in examining the exhaust gas flow of a galaxy in more detail. “This is important for astronomy because it also allows us to limit the forces and influencing factors that affect how galaxies produce their stars,” explains Fisher. “It takes us one step closer to understanding how and why galaxies look the way they do – and how long they persist.”
Source: Deanne Fisher (Swinburne University, Australia) et al., The Astrophysical Journal, doi: 10.3847 / 2041-8213 / ac18ca