{"id":251512,"date":"2025-09-24T16:47:09","date_gmt":"2025-09-24T16:47:09","guid":{"rendered":"https:\/\/www.europesays.com\/us\/251512\/"},"modified":"2025-09-24T16:47:09","modified_gmt":"2025-09-24T16:47:09","slug":"observations-investigate-a-compact-stellar-system-around-nearby-galaxy","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/us\/251512\/","title":{"rendered":"Observations investigate a compact stellar system around nearby galaxy"},"content":{"rendered":"

\"Observations<\/p>\n

Amateur image of NGC 7531 (left). DESI Legacy Imaging Survey image of NGC 7531 (right). Sky-subtracted image of NGC 7531 as processed by Gnuastro’s NoiseChisel program was used as a basis for photometry measurements. Features are labeled: (a): main shell; (b): faint outer shell; (c): counter plume. Credit: arXiv (2025). DOI: 10.48550\/arxiv.2509.14038<\/p>\n

An international team of astronomers has performed photometric and spectroscopic observations of a compact stellar system around a nearby spiral galaxy known as NGC 7531. Results of the observational campaign, published<\/a> September 17 on the arXiv preprint server, indicate that the investigated stellar system is an ultra-compact dwarf galaxy.<\/p>\n

The outer regions of galaxies<\/a> may contain stellar substructures formed when satellite galaxies merge with their hosts and break apart into debris. Studies suggest that many of the disrupted satellite dwarf galaxies once harbored nuclear star clusters (NSCs) and tend to survive the tidal disruption of their host galaxy and morphologically evolve into\u2014for instance\u2014ultra-compact dwarf galaxies (UCDs).<\/p>\n

NGC 7531 is an intermediate spiral galaxy located some 72.4 million light years away in the constellation Grus. The galaxy, which was discovered in 1836, has a size of about 95,000 light years. Previous observations of NGC 7531 have found that it hosts an enormous cloud of shell-like tidal stellar debris and a compact stellar system (CSS) embedded within it.<\/p>\n

Now, a new study by a group of astronomers led by David Mart\u00ednez-Delgado of the Aragon Center for Physics of the Cosmos in Spain sheds more light on the nature of this stellar system around NGC 7531. The new findings are based on the analysis of data mainly from the DESI Legacy Imaging Survey and from the Keck Observatory.<\/p>\n

“Our goals are to determine the nature of the CSS, reconstruct its accretion history, and understand how the large, diffuse shell-like structure formed,” the researchers explain.<\/p>\n

The study found that the CSS around NGC 7531 has a stellar mass of about 3.7 million solar masses<\/a> and a half-light radius of 45.6 light years<\/a>. The age of the system was estimated to be around 3.7 billion years, while its metallicity was measured to be approximately 0.13 dex.<\/p>\n

Furthermore, it turned out that the CSS experienced a burst of star formation some one billion years ago. It appears that the system was likely an NSC that experienced and may still be experiencing tidal stripping.<\/p>\n

According to the authors of the paper, the findings strongly suggest that the investigated CSS is an ultra-compact dwarf galaxy. Therefore, they designated it NGC 7531-UCD1. They added that NGC 7531-UCD1 is a crucial addition to the list of objects confirming the NSC-UCD formation pathway.<\/p>\n

“Our findings agree with theoretical predictions about the NSC to UCD formation pathway via tidal stripping, and further confirm the presence of these objects outside of our Milky Way,” the researchers conclude.<\/p>\n

The collected data also allowed the astronomers to reproduce the merger event, finding that two pericentric passages are needed to create the observed shell and the trailing stream. The timing of the first pericenter passage coincides with the star formation burst that took place one billion years ago.<\/p>\n

\n Written for you by our author Tomasz Nowakowski<\/a>, edited by Stephanie Baum<\/a>, and fact-checked and reviewed by Robert Egan<\/a>\u2014this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive.
\n If this reporting matters to you,
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More information:<\/strong>
\n\t\t\t\t\t\t\t\t\t\t\t\tDavid Mart\u00ednez-Delgado et al, A Pearl in the Shell: an ultra-compact dwarf within the tidal debris surrounding spiral galaxy NGC 7531, arXiv (2025). DOI: 10.48550\/arxiv.2509.14038<\/a><\/p>\n

\n\t\t\t\t\t\t\t\t\t\t\t\t\tJournal information:<\/strong>
\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\tarXiv<\/a>
\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/p>\n

\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/p>\n

\n\t\t\t\t\t\t\t\t\t\t\t\t \u00a9 2025 Science X Network\n\t\t\t\t\t\t\t\t\t\t\t <\/p>\n

\n\t\t\t\t\t\t\t\t\t\t\t\tCitation<\/strong>:
\n\t\t\t\t\t\t\t\t\t\t\t\tObservations investigate a compact stellar system around nearby galaxy (2025, September 24)
\n\t\t\t\t\t\t\t\t\t\t\t\tretrieved 24 September 2025
\n\t\t\t\t\t\t\t\t\t\t\t\tfrom https:\/\/phys.org\/news\/2025-09-compact-stellar-nearby-galaxy.html\n\t\t\t\t\t\t\t\t\t\t\t <\/p>\n

\n\t\t\t\t\t\t\t\t\t\t\t This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
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