X -ray image coded by the energy of Chandra de NGC 6528 with fusion of two Chandra ACI observations. The exterior and interior circles represent the half-light radius (0.91 arcmin) and the central radius (3.05 Arcsec) respectively. The color image consists of red (soft: 0.5 – 1.0 kev), green (medium: 1.0 – 2.0 kev) and blue (hard: 2.0 – 7.0 kev). A total of 18 sources> 3𝜎 were detected, represented by the green circles. Credit: arxiv (2025). DOI: 10.48550 / Arxiv.2508.10105
By analyzing data from the Chandra space vessels of NASA, astronomers conducted the first X -ray study of a globular group known as NGC 6528. Results of the study, published on August 13 on the arxivPre -printed server, give important information concerning the population of X -ray sources in this cluster.
The globular clusters (GC) are spherical collections of stars closely linked to gravitation. They contain tens of thousands to millions of stars and studying could help us better understand the training, history and evolution of start -up galaxies, because the origin of GCs seems to be closely linked to periods of stars’ intensity formation.
Located at around 25,800 light years, NGC 6528 is a galactic globular group with an estimated age of around 11 billion years. With a metallicity at a level of -0.1, NGC 6528 is one of the GCs richest in metals in our galaxy.
In order to shed light on the properties of NGC 6528, a team of astronomers, led by Bernard Leal of Michigan State University, decided to explore this cluster on X -rays using data from the Advanced CCD Imagery Spectrometer (ACIS). Their study was supplemented by data from the Hubble (HST) and Satellite Gaia space telescope.
“This article presented the first NGC 6528 X -ray study, one of the galaxy metal GCs,” write the researchers.
The relatively deep archival imagery of Chandra allowed the Leal team to identify 18 X-ray sources (designated S01-S018) within the ngc 6528 half-light radius. Two of these sources, designated S01 and S08, seem to be located in the central radius of the cluster.
The most brilliant x-ray source of this sample is S01, with an uncommon X-Luminosity at a level of 100 erg / s not changed. The source has long -term variability and astronomers assume that it is most likely a compact binary system separate in mass.
The second most brilliant X-ray source reported in the document is S14, having an uncommon brightness of approximately 46 non-Villaire Erg / s. The X-ray emission of this source has proven to be relatively soft, and since it is located near the ngc 6528 half-light radius, it can be a field star.
In general, the authors of the article stressed that the identified X -rays sources are mainly cataclysmic variables (CV) and active binary (ABS). However, they noted that one or more of the brighter sources could be binary X -ray with low mass with low mass (LMXB).
Other observations, mainly focused on optical or close infrared photometry, could improve the classification of X -ray sources detected.
Summarizing the results, astronomers have stressed what their results can tell us about the general properties of NGC 6528.
“For this cluster, it appears that the effects of improvement in X -rays of high metallicity are compensated by the advanced dynamic evolution of the cluster, leading to a relatively modest X -ray population”, conclude scientists.
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More information:
Bernard Leal et al, the population source of X -ray of the globular cluster rich in NGC 6528 metals, arxiv (2025). DOI: 10.48550 / Arxiv.2508.10105
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