Nuclear Star Cluster

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A Nuclear Star Cluster (English literally for "nuclear cluster") or a compact stellar nucleus (sometimes also young stellar nucleus ) is a star cluster with a high density and great luminosity near the center of mass of most galaxies .

properties

Nuclear Star Clusters are found in most galaxies that can be sufficiently resolved :

  • at least 50% of all early spiral galaxies ( types  Sa-Sb)
  • at least 75% of all late spiral galaxies (types Sc-Sd)
  • at least 70% of all spheroid galaxies (types S0 and E).

Furthermore, with brightnesses between −14 and −10 mag in the infrared, they are on average 40 times more luminous than globular clusters , although their effective radius of 2 to 5  parsecs is no larger. With a dynamic mass of 10 6 to 10 8 solar masses , they are at the upper end of the values ​​achieved by globular clusters.

The Nuclear Star Clusters contain several populations , with mostly one generation of stars more than 1 billion years old and a younger generation with active star formation during the last 100 million years.

Possible mechanisms of origin

The formation can be explained by four principal mechanisms:

  • Nuclear Star Clusters arise elsewhere and are captured by the central black hole
  • or they arise due to an incidence of gas a few parsecs from the center of the galaxy.
  • The third possibility is a combination whereby the gravitational potential of a trapped object, such as the core of a dwarf galaxy , triggers new star formation from incident gas near the galactic center .
  • Nuclear Star Clusters are formed by the merging of star clusters with a subsequent migration to the galactic center due to dynamic friction with background stars .

Nuclear Star Clusters and Globular Clusters

Since Nuclear Star Clusters occur in most types of galaxies, they should still be present in the halo of the resulting galaxy after the galaxies have merged . This is assumed to be a hypothesis for the formation of globular clusters. Accordingly, globular clusters are the remains of nuclear star clusters that are excluded from gas incidence and in which no new star formation takes place.

According to other hypotheses, however, the Nuclear Star Clusters are the result of a merger of globular clusters that were captured by a supermassive black hole in the center of the galaxy and dynamically destroyed.

Individual evidence

  1. ^ R. Schoedel, D. Merritt, A. Eckart: The nuclear star cluster of the Milky Way: proper motions and mass . In: Astrophysics. Solar and Stellar Astrophysics . 2009, arxiv : 0902.3892v1 .
  2. ↑ Torsten Boeker: Nuclear Star Clusters . In: Astrophysics. Solar and Stellar Astrophysics . 2009, arxiv : 0910.4863v1 .
  3. ↑ Shogo Nishiyama, Rainer Schödel: Young, Massive Star Candidates Detected throughout the Nuclear Star Cluster of the Milky Way . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1210.6125 .
  4. ^ Fabio Antonini: Origin and growth of nuclear star clusters around massive black holes . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1207.6589v1 .
  5. ↑ ANN-MARIE MADIGAN: ON THE ORIGIN OF THE B-STARS IN THE GALACTIC CENTER . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1305.1625v1 .
  6. ^ Nicholas Scott, Alister W. Graham, Shifting Fundamentals: Scaling Relations involving Nuclear Star Clusters and Supermassive Black Holes . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1205.5338v1 .
  7. ↑ R. Capuzzo-Dolcetta: Galactic Nuclear Cluster Formation Via Globular cluster mergers . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1301.2899 .