by Sarah Perrin
Polytechnique Federale de Lausanne
February 25, 2022
The shape of galaxies and how they evolve depend on a web of
cosmological filaments that run across the universe.
According to a recent
study headed by EPFL's Laboratory of Astrophysics, this cosmic web
plays a much bigger role than previously thought.
Across the universe, galaxies are distributed along what's called
Cosmic Web, a complex network
of filaments made up of ordinary and
And where those filaments
galaxy clusters - collections of
hundreds or even thousands of galaxies bound to each other by the
force of gravity - tend to form.
They are the biggest and
densest clusters in the universe and are the subject of much
research by astrophysicists. But precisely how filaments contribute
to galactic evolution is still poorly understood.
To get deeper insight, an international team of scientists led by
Prof. Pascale Jablonka and Gianluca Castignani from
EPFL's Laboratory of Astrophysics (LASTRO)
examined the vast environment surrounding
Virgo, a representative cluster in
the local universe.
It contains some
1,500 galaxies and is located around 65 million light-years away
from our own galaxy, the Milky Way.
The team's findings have
been published in two articles:
"Many properties of
galaxies, like their morphology, gas content and star formation
rate, are directly influenced by their environment," says
"We know that
galaxies form fewer stars in very dense environments and adopt a
more elliptical shape. But the exact role that filaments play in
this transformation is still not clear.
That's what we wanted
to investigate with our research."
The scientists analyzed
the properties of galaxies located around the Virgo cluster, across
a region spanning 12 times the radius of the main cluster.
Theirs is the largest
study conducted to date on this topic and covers a sample size of
some 7,000 galaxies, including 250 that are big enough for
scientists to be able to precisely estimate their gas content - and
especially the amount of cold, dense atomic hydrogen that stars are
made out of.
Measurements were taken
using the decametric telescope in
Nanšay Radio Observatory, France,
IRAM-30m telescope in Pico Veleta,
By combining the new data they collected with measurements from the
literature, the scientists found that the properties of galaxies,
their shape, star
formation rate, gas content, and the age and metal content of
...clearly change as the
galaxies progress from more isolated positions towards
filaments and eventually
Filaments therefore seem to serve as a transitional environment
where galaxies are pre-processed before falling into a cluster.
In this environment, star
formation slows or even stops altogether, elliptical shapes appear
more frequently, and there is less atomic and molecular hydrogen,
indicating that the galaxies are reaching the end of their active
The scientists observed
that a galaxy's evolution through its life cycle corresponds to the
local galaxy density:
few or no stars made up less than 20% of the sample of isolated
galaxies, but they accounted for 20-60% of galaxies in the
filaments and some 80% of galaxies in the Virgo cluster.
These findings open up
new avenues of research on theories to explain galaxy formation and
how galaxies evolve in tandem with major cosmic bodies.