According to University of Oslo cosmology professor Sijing Shen, the European Space Agency’s ARRAKIHS mission will observe roughly 70 to 80 nearby galaxies resembling the Milky Way to study faint stellar structures and map elusive dark matter. The initiative relies on small, fast-turnaround space telescope technology to examine cosmic fossils and test standard cosmological models.
Understanding Galactic Halos and Dark Matter
Dark matter accounts for roughly 27 percent of the universe’s total energy content, according to standard cosmological models cited by Shen. By contrast, all ordinary matter—including hydrogen, helium, stars, and planets—makes up only about five percent.
Galactic halos form where cosmic filaments meet in the large-scale structure of the universe. Gas streams along these filaments into massive dark matter halo structures, cooling and condensing at their centers to spark star and planet formation. When smaller galaxies approach larger ones, gravitational tidal forces tear stars and globular clusters away, producing distinct stellar streams and diffuse outer halos.
Did you know? Tidal forces from massive galaxies can rip apart ancient clusters containing up to millions of stars, scattering them into long stellar streams across the cosmos.
The ARRAKIHS Telescope Mission Goals
The European Space Agency developed the ARRAKIHS mission as a fast-class scientific space project designed to be smaller, cheaper, and faster to execute than traditional flagship missions. Shen coordinates Norway’s contribution to the international consortium building the telescope.
ARRAKIHS will target approximately 70 to 80 nearby galaxies to capture extremely faint surface brightness levels. Traditional observations focus primarily on the bright central regions of galaxies. Reaching down to lower brightness thresholds reveals dwarf galaxies, remnants of swallowed systems, and diffuse stellar halos that act as fossils of galactic evolution.
Testing the Standard Model of Cold Dark Matter
Standard cosmology relies on a cold dark matter model where particles do not collide or interact with normal matter. While this framework successfully explains large-scale cosmic structures, discrepancies emerge at smaller scales.
Simulations based on cold dark matter predict significantly more satellite dwarf galaxies around large systems than astronomers actually observe. Furthermore, models suggest that dark matter density should spike sharply at the centers of galaxies, whereas real observations often display much flatter distributions, according to Shen. Researchers plan to use computer simulations running from the Big Bang to the present day to test alternative theories, such as warm dark matter or self-interacting dark matter.
Frequently Asked Questions
What is dark matter?
According to cosmological models outlined by Professor Sijing Shen, dark matter makes up roughly 27 percent of the universe’s total energy content.
What is the ARRAKIHS mission?
ARRAKIHS is a European Space Agency fast-class science mission designed to observe very faint structures and stellar halos around nearby galaxies.
Why are stellar streams important to cosmologists?
Stellar streams act as cosmic fossils, preserving physical evidence of ancient galactic mergers and helping scientists understand how galaxies form and evolve over time.
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