Galaxy Formation: IIA study decodes the curious case of missing dark matter from distant galaxy | India News

Image of ultra diffuse galaxy “NGC 1052 – DF2”, taken by the ACS/WFC instrument on the Hubble Space Telescope. (Picture credit: DST)

A distant galaxy once thought to lack a key ingredient in galaxy formation may now be better understood, thanks to new research from Bengaluru’s Indian Institute of Astrophysics (IIA).
Their recent study, published in Astronomy & Astrophysics, revisits the puzzling case of “NGC 1052-DF2” — a galaxy 62 million light years away and offers a fresh explanation for its apparent shortage of dark matter.
“NGC 1052-DF2” belongs to a class of galaxies called ultra-diffuse galaxies (UDGs). These are faint, spread-out collections of stars with relatively few of them for their size. Unlike the dense spiral arms of our Milky Way, UDGs such as “NGC 1052-DF2” appear ghostly and sparse, almost translucent against the backdrop of space.
What made DF2 particularly intriguing was its seemingly low content of dark matter. Earlier studies estimated the total ‘dynamical mass’ — the sum of all matter influencing its gravitational behaviour — to be around 340 million times the mass of the Sun.
“That figure was not far off from the estimated 200 million solar masses contained in visible stars alone, implying that dark matter, which usually makes up the bulk of a galaxy’s mass, was largely absent. This finding challenged prevailing theories, as dark matter is thought to play a central role in galaxy formation and structure,” the department of science and technology (DST) said.
But the new study led by K Aditya from IIA, which is an autonomous institute under DST, offers a different take.
“We find that “NGC 1052-DF2” poses interesting questions regarding the formation of galaxies with minimal dark matter content, the astrophysical processes regulating the formation of such galaxies, as well as the potential nature of dark matter itself,” said Aditya.
To investigate, Aditya developed detailed models of the galaxy’s mass using the distribution of its stars and their observed velocities. These models tested different assumptions about the structure of the galaxy’s dark matter halo—the vast, invisible cloud of matter thought to surround galaxies and affect their dynamics.
Interestingly, the study found that models with a concentrated, or “cuspy”, dark matter halo could not explain the observed movements of stars in both the inner and outer parts of “NGC 1052-DF2”.
“We rule out the possibility of a cuspy dark matter halo for describing the mass models of NGC 1052 – DF2,” Aditya said. Instead, the research supports a “cored” model—one where dark matter is spread more evenly through the galaxy’s centre.
According to the findings, a cored halo with a total mass of about 32 billion solar masses fits the observed data, though it would require an unusually extended structure: 65,000 light years in scale length, with a cutoff at around 85,000 light years.
“Our results suggest that ‘NGC 1052 – DF2’ may not only have an ultra-diffuse stellar distribution but that it can, within known uncertainties in the data, potentially host an ultra-diffuse dark matter distribution compatible with the standard galaxy formation and evolution models,” said Aditya.
The work helps clarify a long-standing mystery and shows how even galaxies that look like outliers might still fit into our broader understanding of the cosmos—once we model them carefully enough.