White image of Messier 74 obtained from the cropped MUSE data cube of the central arcmin, combining the light in the full MUSE wavelength range. Credit: arXiv (2025). DOI: 10.48550/arxiv.2512.03999

By analyzing the data from the PHANGS-MUSE survey, an international team of astronomers has inspected a nuclear star cluster of the nearby large spiral galaxy Messier 74. The new study presented Dec. 3 on the arXiv pre-print server, provides essential information regarding the properties and nature of this cluster.

Peeking into the densest stellar systems

Nuclear star clusters (NSCs) are massive, dense and compact stellar systems found in all types of galaxies, from dwarfs to massive galaxies. With masses between 10,000 and 100 million solar masses and effective radii within the range of three to 65 light years, they are the densest stellar systems in the universe.

Messier 74, also known as NGC 628, is a large spiral star-forming galaxy located some 32 million light years away from Earth. It has a size of approximately 85,300 light years, a stellar mass of about 22 billion solar masses, and a star-formation rate at a level of 1.74 solar masses per year.

In 2009, a nuclear star cluster was identified in Messier 74 with the Hubble Space Telescope (HST). It has an effective radius of 39 light years and subsolar metallicity. Its age of around 8 billion years suggests that it was not involved in relatively recent star formation in the galaxy (within a few billion years).

A group of astronomers led by Francesca Pinna of the University of La Laguna in Spain decided to take a closer look at the NSC in Messier 74, hoping to shed more light on the properties of this cluster. For this purpose, they combed through the PHANGS data from the Very Large Telescope’s (VLT) Multi Unit Spectroscopic Explorer (MUSE).

PHANGS (Physics at High Angular resolution in Nearby GalaxieS) is a multiwavelength survey aimed at tracing the smallscale physics of star formation through different phases of the interstellar medium.

Old, inactive and metal-poor

The study found that Messier 74’s NSC has an age of about 11 billion years and a total metallicity at a level of -0.5 dex. The star-formation history of the NSC indicates that it is made up exclusively of old stellar populations.

"These results indicate that NSC stars formed during the earliest stages of the evolution of Messier 74, probably spanning 2–3 distinct episodes," the astronomers explained.

According to the paper, the NSC in Messier 74 appears to have remained inactive for a long time, in terms of star formation and chemical evolution. It turned out that this NSC lives in a cavity (with a size of about 1,000 light years) devoid of gas and dust, while the rest of the galaxy shows a complex web of gas and dust filaments, where star formation is currently taking place.

The study also found that the NSC in Messier 74 is much more metal poor not only than its host galaxy, but also than other NSCs hosted by early-type galaxies of the same mass as Messier 74. Moreover, this NSC is more metal poor than other such clusters in slightly lower-mass late-type galaxies.

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More information: Francesca Pinna et al, The Nuclear Star Cluster of M 74: A fossil record of the very early stages of a star-forming galaxy, arXiv (2025). DOI: 10.48550/arxiv.2512.03999

Journal information: arXiv

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Citation: Astronomers examine nuclear star cluster of nearby galaxy Messier 74 (2025, December 11) retrieved 11 December 2025 from https://phys.org/news/2025-12-astronomers-nuclear-star-cluster-nearby.html

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