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The Cocytos Stream - A Disrupted #GlobularCluster from our Last Major Merger? arxiv.org/abs/2504.11687 -> Determining The Origin of The Cocytos Stream: astrobites.org/2025/05/02/cocy

arXiv.orgThe Cocytos Stream: A Disrupted Globular Cluster from our Last Major Merger?The census of stellar streams and dwarf galaxies in the Milky Way provides direct constraints on galaxy formation models and the nature of dark matter. The DESI Milky Way survey (with a footprint of 14,000$~deg{^2}$ and a depth of $r<19$ mag) delivers the largest sample of distant metal-poor stars compared to previous optical fiber-fed spectroscopic surveys. This makes DESI an ideal survey to search for previously undetected streams and dwarf galaxies. We present a detailed characterization of the Cocytos stream, which was re-discovered using a clustering analysis with a catalog of giants in the DESI year 3 data, supplemented with Magellan/MagE spectroscopy. Our analysis reveals a relatively metal-rich ([Fe/H]$=-1.3$) and thick stream (width$=1.5^\circ$) at a heliocentric distance of $\approx 25$ kpc, with an internal velocity dispersion of 6.5-9 km s$^{-1}$. The stream's metallicity, radial orbit, and proximity to the Virgo stellar overdensities suggest that it is most likely a disrupted globular cluster that came in with the Gaia-Enceladus merger. We also confirm its association with the Pyxis globular cluster. Our result showcases the ability of wide-field spectroscopic surveys to kinematically discover faint disrupted dwarfs and clusters, enabling constraints on the dark matter distribution in the Milky Way.

✨ New selected research highlight ✨

Towards a deeper understanding of black hole origins

Research team studies the impact of remnant kicks on spin distributions of black holes from hierarchical mergers

A new study revisits modelling of the spin distributions from hierarchical binary black hole mergers in dense stellar environments, such as globular clusters. It finds clear deviations from the unique spin distribution described in previous studies, and shows a way to identify black holes from repeated mergers, which could help shed light on black hole formation through precise spin measurements in future observing runs.

Read more ➡️ aei.mpg.de/1244528/towards-a-d

📄 arxiv.org/abs/2503.21278

Messier 13, der große Kugelsternhaufen im Herkules, wurde 1714 von Edmund Halley entdeckt. Mit einer Flächenausdehnung von 20,0' (wahrer Durchmesser 145 Lichtjahre) und einer Helligkeit von 5,7 mag ist er unter einem dunklen Himmel bereits mit dem bloßen Auge zu sehen. Er umkreist unsere Heimat­milch­straße in einer Entfernung von 25 000 Lichtjahren.

Aufnahmedaten:
Kamera: ZWO ASI 1600 MMP
Optik: 102/920 mm Fluorit Apo bei f/7
Belichtung: 10x300s L, 24x240s RGB,
gesamte Belichtungszeit: 2h 26 m
Korrekturen: Bias, Dark- und Flatframes
EBV: PixInsight, Fitswork

#astronomie #astronomy #astrophotography #deepsky #deepskyphotography #globularcluster #sternfreundemünster

ω Centauri - a MUSE discovery of a counter-rotating core: arxiv.org/abs/2401.15149 -> "data near the center reveal for the first time that stars within the inner 20" (∼0.5 pc) counter-rotate relative to the bulk rotation of the cluster." #GlobularCluster

arXiv.org$ω$ Centauri: A MUSE discovery of a counter-rotating core$ω$ Centauri is considered the most massive globular cluster of the Milky Way and likely the former nuclear star cluster of a galaxy accreted by the Milky Way. It is speculated to contain an intermediate-mass black hole (IMBH) from several dynamical models. However, uncertainties regarding the location of the cluster center or the retention of stellar remnants limit the robustness of the IMBH detections reported so far. In this paper, we derive and study the stellar kinematics from the highest-resolution spectroscopic data yet, using the Multi Unit Spectroscopic Explorer (MUSE) in the narrow field mode (NFM) and wide field mode (WFM). Our exceptional data near the center reveal for the first time that stars within the inner 20" ($\sim$0.5 pc) counter-rotate relative to the bulk rotation of the cluster. Using this dataset, we measure the rotation and line-of-sight velocity dispersion (LOSVD) profile out to 120$''$ with different centers proposed in the literature. We find that the velocity dispersion profiles using different centers match well with those previously published. Based on the counter--rotation, we determine a kinematic center and look for any signs of an IMBH using the high-velocity stars close to the center. We do not find any significant outliers $>$60 km/s within the central 20$''$, consistent with no IMBH being present at the center of $ω$ Centauri. A detailed analysis of Jeans' modeling of the putative IMBH will be presented in the next paper of the series.

Ultra-deep ATCA imaging of 47 Tucanae reveals a central compact radio source: arxiv.org/abs/2401.09692 -> A global team of astronomers have created the most sensitive radio image ever of a #GlobularCluster, an ancient ball of tightly-packed stars: icrar.org/47tuc/

arXiv.orgUltra-deep ATCA imaging of 47 Tucanae reveals a central compact radio sourceWe present the results of an ultra-deep radio continuum survey, containing $\sim480$ hours of observations, of the Galactic globular cluster 47 Tucanae with the Australia Telescope Compact Array. This comprehensive coverage of the cluster allows us to reach RMS noise levels of 1.19 $μJy~\textrm{beam}^{-1}$ at 5.5 GHz, 940 $nJy~\textrm{beam}^{-1}$ at 9 GHz, and 790 $nJy~\textrm{beam}^{-1}$ in a stacked 7.25 GHz image. This is the deepest radio image of a globular cluster, and the deepest image ever made with the Australia Telescope Compact Array. We identify ATCA J002405.702-720452.361, a faint ($6.3\pm1.2$ $μJy$ at 5.5 GHz, $5.4\pm0.9$ $μJy$ at 9 GHz), flat-spectrum ($α=-0.31\pm0.54$) radio source that is positionally coincident with the cluster centre and potentially associated with a faint X-ray source. No convincing optical counterpart was identified. We use radio, X-ray, optical, and UV data to show that explanations involving a background active galactic nucleus, a chromospherically active binary, or a binary involving a white dwarf are unlikely. The most plausible explanations are that the source is an undiscovered millisecond pulsar or a weakly accreting black hole. If the X-ray source is associated with the radio source, the fundamental plane of black hole activity suggests a black hole mass of $\sim54-6000$ M$_{\odot}$, indicating an intermediate-mass black hole or a heavy stellar-mass black hole.