IIA study sheds light on curious case of missing dark matter in a distant galaxy

The Hindu

23-04-2025

Astronomers at the Indian Institute of Astrophysics (IIA) have found the reason for the strange deficiency of dark matter in the distant galaxy NGC 1052-DF2. Dark matter is a critical component of galaxy formation.
According to the Department of Science and Technology, earlier models have shown that the Ultra-diffuse galaxy (UDG) NGC 1052-DF2 is deficient in dark matter, which conflicts with the standard galaxy formation and evolution models.
It said that previous studies of NGC 1052-DF2 predict a total 'dynamical mass' within the spatial extent of the galaxy to be less than 340 million solar masses, which is comparable to the estimated mass of the stars of 200 million solar masses.
'This surprising result implies that within the observed extent of the galaxy, the mass is mostly composed of primarily stars that we are familiar with, and that dark matter is significantly less than expected as compared to spiral galaxies like the Milky Way. This contradicts the established paradigm about dark matter, which is needed to explain hierarchical structure formation in the Universe,' the department said.
'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 astronomer K. Aditya, whose research was published in the journal Astronomy & Astrophysics.
To shed light on this problem and to resolve the discrepancies in the mass estimation of NGC 1052-DF2, Mr. Aditya constructed models using the stellar density as an input parameter and constrained the parameters corresponding to the dark matter halo. He then used the observed stellar velocity dispersion profile as a constraint on the model.
'We find that mass models with a 'cuspy' (higher density in the central regions) dark matter halo are comparable to models with no dark matter. Moreover, these cuspy dark matter halo fails to consistently account for the observed velocity dispersion in the inner and outer regions of the galaxy. Consequently, we rule out the possibility of a cuspy dark matter halo for describing the mass models of NGC 1052 - DF2,' said Aditya.