J/A+A/711/A138 Anti-mass-segregated open clusters in MW (Zhang+, 2026)
Anti-mass-segregated open clusters as a statistical population in the Milky Way
revealed by DR3 Gaia.
Zhang S., Huang L., Zhao W., Chi H., Chen J.
<Astron. Astrophys. 711, A138 (2026)>
=2026A&A...711A.138Z 2026A&A...711A.138Z (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, open ; Optical
Keywords: stars: black holes - open clusters and associations: general
Abstract:
Mass segregation, defined as the preferential concentration of massive
stars towards cluster centres, is a well-established outcome of
two-body relaxation in star clusters. It is not yet established
whether the inverse configuration, in which massive stars are
preferentially dispersed to large radii, can survive over dynamical
timescales on a population scale.
We investigate whether anti-mass-segregated open clusters exist as a
statistically significant, dynamically stable population in the Milky
Way.
We used 2800 open clusters from the Gaia DR3 catalogue and identified
mass segregation using two independent diagnostics: the minimum
spanning tree ratio (LambdaMSR) and the centre-of-mass distance
ratio (LambdaCC), evaluated for the five and ten most massive
members. We further performed direct N-body simulations to test the
dynamical stability of anti-segregated configurations.
We identify 706 anti-mass-segregated clusters (25.2% of the sample).
Compared to the normal population, these systems are systematically
more extended (+20% in the half-mass radius), dynamically younger
(∼39% in dynamical age) and have longer relaxation timescales
(+25%). The mass excess of anti-segregated clusters relative to normal
clusters increases monotonically with dynamical age, reaching +109% at
tau=5-10. Direct N-body simulations confirm that anti-segregated
configurations remain stable over multiple relaxation timescales,
while mass-segregated and random clusters develop strong positive
segregation.
Anti-mass segregation is a dynamically stable structural state that
likely reflects primordial cluster conditions. The prevalence of this
configuration provides indirect constraints on the central mass
content of open clusters, as massive central black holes would rapidly
disrupt the anti-segregated state.
Description:
The complete catalogue contains measurements of Lambda_MSR and
Lambda_CC for all 2800 open clusters compiled from Hunt & Reffert
(2024A&A...686A..42H 2024A&A...686A..42H, Cat. J/A+A/686/A42), together with the half-mass
relaxation timescale (trelaxMyr) and the dimensionless dynamical age
(Dynamical_Age) derived in this work.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
clusters.dat 1182 2800 Full parameter catalogue with dynamical ages
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See also:
J/A+A/686/A42 : Improving the open cluster census. III. (Hunt+, 2024)
Byte-by-byte Description of file: clusters.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 20 A20 --- Name Cluster designation name (Name)
22- 25 I4 --- Ntotal Total number of member stars (N_total)
27- 38 F12.9 --- LambdaMST5 MST segregation ratio evaluated at N=5
(LambdaMST5)
40- 51 F12.9 --- LambdaCC5 Center-of-mass distance ratio at N=5
(LambdaCC5)
53- 63 F11.9 --- LambdaMST10 MST segregation ratio evaluated at N=10
(LambdaMST10)
65- 75 F11.9 --- LambdaCC10 Center-of-mass distance ratio at N=10
(LambdaCC10)
77- 87 F11.9 --- LambdaMST15 MST segregation ratio evaluated at N=15
(LambdaMST15)
89- 99 F11.9 --- LambdaCC15 Center-of-mass distance ratio at N=15
(LambdaCC15)
101- 111 F11.9 --- LambdaMST20 MST segregation ratio evaluated at N=20
(LambdaMST20)
113- 123 F11.9 --- LambdaCC20 Center-of-mass distance ratio at N=20
(LambdaCC20)
125- 128 I4 --- ID Unique cluster identifier ID (ID)
130- 382 A253 --- AllNames Alternative cluster names/cross-matches
(AllNames)
384 A1 --- Type [o] Cluster type classification
(o=open cluster) (Type)
386- 396 F11.8 --- CST Cluster Structural Parameter (CST)
398- 401 I4 --- N Number of stars used in structural fit
(N)
403- 413 F11.8 --- CSTt Tidal structural parameter (CSTt)
415- 418 I4 --- Nt Number of stars used in tidal fit (Nt)
420- 431 F12.8 deg RAdeg Right Ascension (J2000) (RAdeg)
433- 444 F12.8 deg DEdeg Declination (J2000) (DEdeg)
446- 457 F12.8 deg GLON Galactic longitude (GLON)
459- 468 F10.6 deg GLAT Galactic latitude (GLAT)
470- 479 F10.8 deg r50 Projected half-number angular radius
(r50)
481- 491 F11.8 deg rc Core angular radius (rc)
493- 503 F11.8 deg rt Tidal angular radius (rt)
505- 515 F11.8 deg rtot Total angular radius limit (rtot)
517- 527 F11.8 pc r50pc Projected half-number radius in parsecs
(r50pc)
529- 540 F12.8 pc rcpc Core radius in parsecs (rcpc)
542- 553 F12.8 pc rtpc Tidal radius in parsecs (rtpc)
555- 566 F12.8 pc rtotpc Total radius limit in parsecs (rtotpc)
568- 579 F12.8 mas/yr pmRA Proper motion in Right Ascension
direction (pmRA)
581- 591 F11.8 mas/yr s_pmRA Standard deviation of pmRA (s_pmRA)
593- 602 F10.8 mas/yr e_pmRA Uncertainty error on pmRA (e_pmRA)
604- 615 F12.8 mas/yr pmDE Proper motion in Declination direction
(pmDE)
617- 627 F11.8 mas/yr s_pmDE Standard deviation of pmDE (s_pmDE)
629- 638 F10.8 mas/yr e_pmDE Uncertainty error on pmDE (e_pmDE)
640- 650 F11.8 mas Plx Median cluster parallax from Gaia (Plx)
652- 661 F10.8 mas s_Plx Standard deviation of Plx (s_Plx)
663- 672 F10.8 mas e_Plx Uncertainty error on Plx (e_Plx)
674- 687 F14.8 pc Dist16 16th percentile distance (dist16)
689- 702 F14.8 pc Dist50 Median cluster distance (Adopted)
(dist50)
704- 717 F14.8 pc Dist84 84th percentile distance (dist84)
719- 722 I4 --- Ndist Number of stars used for distance
(Ndist)
724 I1 mas globalPlx Global parallax zero-point correction
(globalPlx)
726- 738 F13.6 pc X Heliocentric Galactic coordinate X (X)
740- 754 F15.8 pc Y Heliocentric Galactic coordinate Y (Y)
756- 769 F14.8 pc Z Heliocentric Galactic coordinate Z (Z)
771- 783 F13.8 km/s RV ? Radial velocity (if available) (RV)
785- 797 F13.8 km/s s_RV ? Standard deviation of RV (s_RV)
799- 810 F12.8 km/s e_RV ? Uncertainty error on RV (e_RV)
812- 814 I3 --- n_RV Number of stars used for RV (n_RV)
816- 824 F9.7 --- CMDCl2.5 2.5th percentile CMD classification
score (CMDCl2.5)
826- 834 F9.7 --- CMDCl16 16th percentile CMD classification score
(CMDCl16)
836- 845 F10.8 --- CMDCl50 Median CMD classification score
(CMDCl50)
847- 856 F10.8 --- CMDCl84 84th percentile CMD classification score
(CMDCl84)
858- 867 F10.8 --- CMDCl97.5 97.5th percentile CMD classification
score (CMDCl97.5)
869- 871 A3 --- CMDClHuman Human verification flag for CMD
(CMDClHuman)
873- 882 F10.8 [yr] logAge16 16th percentile of log(Age) (logAge16)
884- 893 F10.8 [yr] logAge50 Median cluster log(Age) (logAge50)
895- 905 F11.8 [yr] logAge84 84th percentile of log(Age) (logAge84)
907- 915 E9.7 mag AV16 16th percentile of V-band extinction
(AV16)
917- 926 F10.8 mag AV50 Median cluster V-band extinction (AV50)
928- 937 F10.8 mag AV84 84th percentile of V-band extinction
(AV84)
939- 947 E9.7 mag diffAV16 16th percentile differential extinction
(diffAV16)
949- 958 F10.8 mag diffAV50 Median differential extinction
(diffAV50)
960- 969 F10.8 mag diffAV84 84th percentile differential extinction
(diffAV84)
971- 981 F11.8 mag MOD16 16th percentile distance modulus (MOD16)
983- 993 F11.8 mag MOD50 Median cluster distance modulus (MOD50)
995-1005 F11.8 mag MOD84 84th percentile distance modulus (MOD84)
1007-1016 F10.8 --- r50J Projected half-number angular radius (J)
(r50J)
1018-1027 F10.8 --- rJ Total structural radius (J) (rJ)
1029-1039 F11.8 pc r50Jpc Projected half-number radius (J) in pc
(r50Jpc)
1041-1051 F11.8 pc rJpc Total structural radius (J) in pc (rJpc)
1053-1061 F9.4 --- probJ Probability threshold parameter (J)
(probJ)
1063-1066 I4 --- NJ Number of selected members (J) (NJ)
1068-1081 F14.8 Msun MassJ Calculated integrated cluster mass (J)
(MassJ)
1083-1096 F14.8 Msun e_MassJ Uncertainty on cluster mass (J)
(e_MassJ)
1098-1111 F14.8 Msun MassTot Total integrated cluster mass (MassTot)
1113-1126 F14.8 Msun e_MassTot Uncertainty on total cluster mass
(e_MassTot)
1128-1129 I2 --- minClSize Minimum cluster size threshold
(minClSize)
1131 I1 --- isMerged Cluster merger classification flag
(isMerged)
1133 I1 --- isGMMMemb GMM member classification flag
(isGMMMemb)
1135-1136 I2 --- NXmatches Number of catalog cross-matches
(NXmatches)
1138-1153 A16 --- XmatchType Cross-match classification type
descriptor (XmatchType)
1155-1168 F14.9 Myr trelax Half-mass relaxation time (this work)
(trelaxMyr)
1170-1182 F13.9 --- DynAge Dimensionless dynamical age tau
(this work) (Dynamical_Age)
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Acknowledgements:
From Su Zhang, youyouss(at)126.com
During the data analysis and preparation of this catalog table, we
acknowledge the use of data from the European Space Agency (ESA)
mission Gaia.
License: CC-BY-4.0
(End) Patricia Vannier [CDS] 03-Jun-2026