- 4358 - GALAXY EVOLUTION - and the cosmic web? How does the cosmic web drive galaxy evolution? Galaxies experience a long strange trip through the cosmic web as they grow and evolve. The neighborhoods galaxies spend time in on the journey change their evolution, and that affects their star formation activity and alters their gas content.
-------------- 4358 - GALAXY EVOLUTION - and the cosmic web?
- Galaxies are giant
stellar cities are spread throughout the Universe. They tend to cluster together into large
conglomerations. Hundreds of thousands of them group together in the largest
ones, while smaller ones have only a few. They can also be part of the filament
structure called the “cosmic web”. Or, some can be relatively isolated in
“low-density” galactic neighborhoods.
-
- In shaping the
Universe, gravity builds a vast cobweb-like structure of filaments tying
galaxies and clusters of galaxies together along invisible bridges hundreds of
millions of light-years long. A galaxy can move into and out of the densest
parts of this web throughout its lifetime.
-
- How do they get
clumped together, and what do they experience as they gather together? How do these behemoths evolve and grow? A
quick look at the history of our Milky Way gives us a good idea of the general
story. It began forming as a cloud of hydrogen gas some 13 billion years ago.
-
- Gravity pushed the
clouds together, which began the process of star formation. Other structures in
the galaxy, the core, the flat disk, the halo, formed in quick succession. The
infant Milky Way experienced multiple collisions with other galaxies throughout
its history. It’s still cannibalizing some today.
-
- Our Galaxy is part
of a larger collection called the “Local Group”, which is itself part of the
“Virgo Supercluster”. The Virgo collection is also part of a suspected larger
grouping called “Laniakea”. And, all of this is part of the cosmic web that
defines large-scale cosmic structure.
-
- Galaxies follow a
path into these filaments, experiencing a dense environment for the first time
before progressing into groups and clusters. Studying galaxies in filaments
allows us to examine the initial encounters of galaxies with dense
environments.
-
- The majority of
galaxies entering the ‘urban centers’ of clusters do so along these
‘superhighways,’ with only a minimal number taking rural routes that bring them
into the clusters and groups without interacting much with their surroundings.
-
- Filaments,
fields, groups, and clusters all have different environments. Each of these
neighborhoods affects gas behavior. Astronomers think of these changes in terms
of a “baryon cycle”. That’s a complex phenomenon. It describes all the ways
that gas is processed in dense clusters and filaments of the cosmic web.
-
- The space between
galaxies contains gas. Most of the atoms
in the universe are in this gas, and that gas can create the galaxies. This intergalactic gas undergoes a
transformation into stars, although the efficiency of this process is
relatively low, with only a small percentage contributing to star formation.
The majority is expelled in the form of large winds.
-
- Think of galaxies
as baryon processing engines, drawing gas from the intergalactic medium and
converting some of it into stars. Stellar populations produce heavier elements
as they evolve. Eventually all material ends up in space, along with the gas,
forming a fountain that eventually falls back to the galaxy.
-
- When they move
into a denser environment, the pressure of their passage disrupts the baryon
cycle. It removes galactic gas or in some way deprives it of the “stuff” it
needs to make new stars. This has happened in the centers of clusters. The disruption affects the intake and
expulsion of gas by galaxies, leading to alterations in their star formation
processes. It eventually results in a
decline in star formation.
-
- Astronomers hope to
uncover more about the long-term evolution of galaxies, starting in the early
Universe and extending to the modern cosmos.
This will reveal more about the cosmic web and filaments that make up
the large-scale structure that defines the Universe.
-
-
February 17, 2024 GALAXY EVOLUTION -
and the cosmic web? 4358
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Sunday, February 18, 2024 ---------------------------------
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