Asymmetrical tidal tails of open star clusters: stars crossing their cluster’s práh† challenge Newtonian gravitation

Kroupa, Pavel; Jeřabková, Tereza; Thies, Ingo; Pflamm-Altenburg, Jan; Famaey, Benoît; Boffin, H. M. J.; Dabringhausen, J.; Beccari, G.; Prusti, T.; Boily, C. M.; Haghi, Hosein; Wu, Xufen; Haas, Jaroslav; Zonoozi, Akram Hasani; Thomas, Guillaume; Šubr, Ladislav; Aarseth, Sverre J.

doi:10.1093/mnras/stac2563

Cited by 28 publications

(52 citation statements)

References 240 publications

(349 reference statements)

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“…Since the Galactic latitude of each of these clusters is negative, their counterclockwise rotation opposes the Galactic disk angular momentum. This is consistent with the theoretical prediction of Kroupa et al (2022). Since the inclination distributions of these clusters are either unconstrained or potentially isotropic, we cannot definitively compare the mean inclination of their spin-axis distributions to the orientation of their bulk rotation.…”

Section: Kinematicssupporting

confidence: 77%

A Study of Stellar Spins in 15 Open Clusters

Healy

McCullough

Schlaufman

et al. 2023

ApJ

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We analyze spectroscopic and photometric data to determine the projected inclinations of stars in 11 open clusters, placing constraints on the spin-axis distributions of six clusters. We combine these results with four additional clusters studied by Healy & McCullough and Healy et al. to perform an ensemble analysis of their spins. We find that eight out of 10 constrained clusters (80%) have spin-axis orientations consistent with isotropy, and we establish a lower limit of four out of 10 (40%) isotropic clusters at 75% confidence, assuming no correlation of spins between clusters. We also identify two clusters whose spin-axis distributions can be better described by a model consisting of an aligned fraction of stars combined with an isotropic distribution. However, the inclination values of these stars may be influenced by systematic error, and the small number of stars modeled as aligned in these two clusters precludes the interpretation that their stellar subsets are physically aligned. Overall, no cluster displays an unambiguous signature of spin alignment, and 97% of the stars in our sample are consistent with isotropic orientations in their respective clusters. Our results offer support for the dominance of turbulence over ordered rotation in clumps and do not suggest the alignment of rotation axes and magnetic fields in protostars.

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Section: Kinematicssupporting

confidence: 77%

A Study of Stellar Spins in 15 Open Clusters

Healy

McCullough

Schlaufman

et al. 2023

ApJ

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“…If the asymmetric evaporation probabilities have an internal origin, then larger asymmetries in the star cluster potential and the kinematics of the evaporation process is required than New-tonian dynamics can provide (Kroupa et al 2022). On the other hand the asymmetry might be due to an external perturbation, for example through the encounter with a molecular cloud (Jerabkova et al 2021).…”

Section: Discussionmentioning

confidence: 99%

“…As a consequence, a fraction of the initial set of stars have positive energy with respect to the Lagrange points and lead to a continuous stream of escaping stars across the clusters's tidal threshold (or práh according to Kroupa et al 2022), with individual escape time scales up to a Hubble time. This method has been successfully tested in Fukushige & Heggie (2000).…”

Section: Numerical Modelmentioning

confidence: 99%

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On the degree of stochastic asymmetry in the tidal tails of star clusters

Pflamm-Altenburg¹,

P.²,

Thies³

et al. 2023

Preprint

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Context. Tidal tails of star clusters are commonly understood to be populated symmetrically. Recently, the analysis of Gaia data revealed large asymmetries between the leading and trailing tidal tail arms of the four open star clusters Hyades, Praesepe, Coma Berenices and NGC 752. Aims. As the evaporation of stars from star clusters into the tidal tails is a stochastic process, the degree of stochastic asymmetry is quantified in this work. Methods. For each star cluster 1000 configurations of test particles are integrated in the combined potential of a Plummer sphere and the Galactic tidal field over the life time of the particular star cluster. For each of the four star clusters the distribution function of the stochastic asymmetry is determined and compared with the observed asymmetry. Results. The probabilities for a stochastic origin of the observed asymmetry of the four star clusters are: Praesepe ≈1.7 σ, Coma Berenices ≈2.4 σ, Hyades ≈6.7 σ, NGC 752 ≈1.6 σ. Conclusions. In the case of Praesepe, Coma Berenices and NGC 752 the observed asymmetry can be interpreted as a stochastic evaporation event. However, for the formation of the asymmetric tidal tails of the Hyades additional dynamical processes beyond a pure statistical evaporation effect are required.

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“…The present-day stellar distributions have been obtained by the Jerabkova et al (2021) compact convergent point (CCP) method, which allows the tidal tails to be mapped to their tips. Table 1 summarises the observed values of the star clusters that are of interest for this work (see Kroupa et al 2022 for details).…”

Section: Observed Open Star Clustersmentioning

confidence: 99%

Degree of stochastic asymmetry in the tidal tails of star clusters

Pflamm-Altenburg

Kroupa

Thies

et al. 2023

A&A

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Context. Tidal tails of star clusters are commonly understood to be populated symmetrically. Recently, the analysis of Gaia data revealed large asymmetries between the leading and trailing tidal tail arms of the four open star clusters Hyades, Praesepe, Coma Berenices, and NGC 752. Aims. As the evaporation of stars from star clusters into the tidal tails is a stochastic process, the degree of stochastic asymmetry is quantified in this work. Methods. For each star cluster, 1000 configurations of test particles were integrated in the combined potential of a Plummer sphere and the Galactic tidal field over the lifetime of the particular star cluster. For each of the four star clusters, the distribution function of the stochastic asymmetry was determined and compared with the observed asymmetry. Results. The probabilities for a stochastic origin of the observed asymmetry of the four star clusters are ≈1.7σ for Praesepe, ≈2.4σ for Coma Berenices, ≈6.7σ for Hyades, and ≈1.6σ for NGC 752. Conclusions. In the case of Praesepe, Coma Berenices, and NGC 752, the observed asymmetry can be interpreted as a stochastic evaporation event. However, for the formation of the asymmetric tidal tails of the Hyades, additional dynamical processes beyond a pure statistical evaporation effect are required.

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Asymmetrical tidal tails of open star clusters: stars crossing their cluster’s práh† challenge Newtonian gravitation

Cited by 28 publications

References 240 publications

A Study of Stellar Spins in 15 Open Clusters

A Study of Stellar Spins in 15 Open Clusters

On the degree of stochastic asymmetry in the tidal tails of star clusters

Degree of stochastic asymmetry in the tidal tails of star clusters

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