Fast runner (astronomy)

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As high-speed in the will Astronomy individual star with a large proper motion referred.

The speeds of stars near the sun can be divided into two groups:

  • one group has an average speed of 15 km / s
  • the second group with fewer members has an average speed of 40 km / s.

The distribution of the two groups is superimposed so that a star can only be clearly assigned to the fast runners at a speed of more than 50 km / s.

While most stars have approximate circular orbits around the galactic center (the sun needs around 250 million years for this), they run fast!

  • strongly elliptical (elongated) orbits,
  • which are strongly inclined towards the sun's path .
  • Their speed components in the direction of the galactic rotation (see Oort's formula ) are usually lower than those of the sun, so that they generally lag behind the sun.
  • They mostly belong to the star population  II.

root cause

Two causes are assumed to be the cause of the high relative speeds of the high-speed runners:

  • The fast runner was part of a binary star system , and the companion exploded in a supernova . The binary star system is destroyed.
  • During the dynamic interaction between stars and binary stars in the cores of star clusters , the lighter stars absorb gravitational energy and are ejected from the cluster.

Examples

Fast runner in the broader sense

Fast-moving stars in the broader sense are stars that move at a speed that is just below the escape speed of the gravitationally binding system. These high speeds are observed in dwarf galaxies and globular star clusters . The cause of the high speed is also assumed to be dynamic interactions between a binary star system and a single star or an interaction between a black hole and a binary star system.

Differentiation from hyper-fast runners

Hyper- high- speed runners reach speeds of 300 to 1000 km / s, which are sufficient to leave the gravitational field of the Milky Way . All hyper-speed runners seem to come from the center of the galaxy.

Field stars of the spectral type O

Field stars of the spectral type  O are stars with more than ten solar masses and a lifespan of only a few million years. They are outside of a star cluster or an OB star association and, as long as they are not fast-moving, have arisen as single stars because they cannot have moved far enough away from the place of their formation.

An investigation, however, shows that all O field stars either show a high intrinsic motion, a high radial velocity or a shock front of the interstellar medium in the direction of motion. This means that all early field stars are likely to be fast-moving if they are not observed at the place of their formation.

Individual evidence

  1. ↑ Paula Benaglia, Ian R. Stevens, Cintia S. Peri: Runaway stars: Their impact on the interstellar medium . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1307.2293v1 .
  2. ^ Helmut Zimmermann: Lexicon of Astronomy . Spektrum-Verlag, Heidelberg 1999, ISBN 3-8274-0575-0 , p. 313 ff., 359 .
  3. ^ Hagai B. Perets, Ladislav Subr: The properties of dynamically ejected runaway and hyper-runaway stars . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1202.2356v1 .
  4. ↑ Nora Lützgendorf, Alessia Gualandris, Markus Kissler-Patig, Karl Gebhardt, Holger Baumgardt, Eva Noyola, JM Diederik Kruijssen, Behrang Jalali, P. Tim de Zeeuw, Nadine Neumayer: High-velocity stars in the cores of globular clusters: The illustrative case of NGC 2808 . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1205.4022 .
  5. ↑ Elena M. Rossi, Shiho Kobayashi, Re'em Sari: The Velocity Distribution of Hypervelocity Stars . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1307.1134v1 .
  6. ↑ VV Gvaramadze, C. Weidner, P. Kroupa, J. Pflamm-Altenburg Field O stars: FORMED in situ or as runaways? In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1206.1596v1 .