MPIA: How Galaxies Have Produced Their Stars

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MPIA: How Galaxies Have Produced Their Stars

Post by bystander » Thu Sep 24, 2020 5:55 pm

How Galaxies Have Produced Their Stars
Max Planck Institute for Astronomy | 2020 Sep 24

ASPECS survey provides key chapter of cosmic history

Astronomers have used the ALMA observatory to trace the fuel for star formation – molecular hydrogen gas – in the iconic Hubble Ultra-Deep Field, one of the best-studied regions of the sky. The observations ... track how the universe’s inventories of gas and dust have changed over time from just two billion years after the big bang to the present. Comparing their own observations with additional observational data and modern simulations, the astronomers were able to characterize and quantify the gas flows that are necessary prerequisites for the formation of stars within galaxies. The result is a broad-brush history of cosmic star formation that includes all the important pieces: the history of star production itself as well as information about the supply chain that enables stars to be produced in the first place.

Tracing the origin of a common household item, like an appliance, amounts to reconstructing a supply chain: the raw materials transformed into more elaborate components, and those components assembled into a finished product. If supplies are missing, production will slow down, or might even grind to a halt. Documenting the factory's inventory of the necessary components or raw material is a useful way of learning about the production history.

When galaxies form stars, there is of course no planning behind it, economic or otherwise. Stars form whenever the conditions are right for them to form, whenever the right material is available. In order to produce stars, we need cool gas made of hydrogen molecules. Such cool gas is produced when a sufficiently dense cloud of warmer gas made of hydrogen atoms cools down – under the right conditions, the hydrogen atoms pair off, each pair forming a hydrogen molecule H2.

The atomic hydrogen inventory can be replenished as well. There is a huge reservoir of ionized hydrogen in the vast spaces between galaxies, warm intergalactic plasma that contains more than 90% of all hydrogen in the universe. Keep track of how those inventories change over time, reconstruct the supply chain, and you can learn about the production history of stars. Keeping track of change is possible because astronomers always look into the past. ...

The Evolution of the Baryons Associated with Galaxies
Averaged over Cosmic Time and Space
~ Fabian Walter et al
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