Fast runner (astronomy)
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
- 61 Cygni , a star 6. size in the constellation Swan . His annual position shift of about 5 " made Friedrich Wilhelm Bessel assume that he was relatively close to us. He succeeded in the first parallax measurement that numerous astronomers had tried for over 100 years. The measured parallax of around 0.3" found that 61 Cygni is 11 light years from Earth and is one of the 20 closest stars .
- Barnard's arrow star in the constellation Serpent Bearer is the star with the highest known proper motion of 10.34 ″ per year.
- Groombridge 1830
- Kapteyn's star
- Teegarden's star
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
- ↑ 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 .
- ^ Helmut Zimmermann: Lexicon of Astronomy . Spektrum-Verlag, Heidelberg 1999, ISBN 3-8274-0575-0 , p. 313 ff., 359 .
- ^ 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 .
- ↑ 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 .
- ↑ Elena M. Rossi, Shiho Kobayashi, Re'em Sari: The Velocity Distribution of Hypervelocity Stars . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1307.1134v1 .
- ↑ 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 .