Proof of darkish matter-free dwarf galaxy challenges typical galaxy formation fashions

Astronomers utilizing W. M. Keck Observatory on Maunakea, Hawaiʻi Island have discovered compelling proof of a darkish matter-deficient dwarf galaxy, FCC 224. This ultra-diffuse galaxy is positioned on the outskirts of the Fornax Cluster, roughly 60–65 million light-years from Earth.

The invention challenges the standard cosmological paradigm, which assumes darkish matter is a basic element in galaxy formation. Beforehand, darkish matter-deficient galaxies with none ongoing star formation had solely been claimed in a single different place, the NGC 1052 group, and the brand new observations counsel such objects could also be extra widespread than beforehand thought.

The bizarre galaxy was profiled in two complementary research. The primary examine, led by Doctoral Candidate Yimeng Tang of the College of California, Santa Cruz and published within the Astrophysical Journal, analyzes FCC 224’s distinctive globular star cluster system.

The second, led by Doctoral Candidate Maria Luísa Buzzo of Swinburne College and of the European Southern Observatory, and published in Astronomy & Astrophysics, explores the darkish matter content material of the galaxy and potential eventualities for its formation.

“Globular clusters are sometimes used as a proxy to estimate the quantity of darkish matter a galaxy incorporates,” mentioned Buzzo. “For some cause this galaxy (FCC 224) has an uncommon variety of luminous clusters and no darkish matter, at the very least inside its interior areas. No present galaxy formation mannequin inside our commonplace cosmological paradigm can at the moment clarify how this galaxy got here to be.”

Buzzo’s analysis investigated the darkish matter content material of FCC 224 utilizing high-resolution spectroscopy from Keck Observatory’s Keck Cosmic Internet Imager (KCWI). She explored its similarities to beforehand claimed darkish matter-free dwarf galaxies DF2 and DF4, positioned throughout the NGC 1052 galaxy group, to find out whether or not or not FCC 224 belongs to the identical class of galaxies.

Buzzo’s analysis builds upon the preliminary findings of Tang, who, utilizing imaging from NASA’s Hubble House Telescope (HST), discovered that FCC 224 has star clusters just like different darkish matter-deficient galaxies. Their analysis means that a lot of these star clusters could also be linked to a scarcity of darkish matter, difficult typical fashions of galaxy formation. The Keck Observatory/KCWI knowledge was obtained by a Swinburne College proposal below Principal Investigator (PI) Duncan Forbes, whereas the HST knowledge was acquired by a program led by PI Aaron Romanowsky.

“The brand new high-resolution purple arm of KCWI enabled us to measure very exactly the motions throughout the galaxy, which can be utilized to hint its darkish matter content material,” defined Buzzo. “KCWI’s excessive spectral decision allowed us to exactly measure the motions (velocity dispersion) inside FCC 224’s stars and globular clusters,” mentioned Tang. “These measurements confirmed that the galaxy displays an especially low velocity dispersion—an indicator of darkish matter deficiency.”

Each groups spotlight the necessity for additional observations to know the mechanisms behind FCC 224’s formation. One main speculation is that an exterior interplay, corresponding to a high-velocity collision, could have separated the galaxy’s darkish and visual matter, a formation situation often known as ‘the bullet-dwarf mannequin.” Nevertheless, extra knowledge is required to check this principle.

“FCC 224 serves as a vital knowledge level in our effort to establish and examine different darkish matter-deficient galaxies,” Buzzo added. “By increasing the pattern measurement, we are able to refine our understanding of those uncommon galaxies and of the function of darkish matter in dwarf galaxy formation.”

The invention of FCC 224 exterior the NGC 1052 group means that darkish matter-deficient galaxies could also be extra widespread than beforehand believed, elevating basic questions in regards to the necessity of darkish matter in shaping galaxies. As observational capabilities enhance, astronomers goal to conduct bigger surveys to establish comparable galaxies and examine their origins.