Hyper-fast runner

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Hyper fast running ( Engl. Hyper velocity stars in short HVS ) are star , dealing with 300 to 1000 km / s (that is one to three thousand of the.. The speed of light ) move quickly enough to the gravitational field of the galaxy to leave; they are thus even faster than normal speed blanking whose kinetic energy to leave is not sufficient to home galaxy.

Hyper-fast runners are predominantly main sequence stars of the spectral type  B with surface temperatures around 12,000  K and masses between three and eight solar masses . There are various hypotheses as to where the necessary kinetic energies could come from.

properties

While there are a number of B-stars that are counted among the hyper-speed runners, there seem to be no hyper-runners with a later spectral type. Hyper speed runners are mostly found in the galactic halo . The origin of the galactic hyper-speed runners seems to be in the center of the Milky Way , since the direction of movement is always directed away from there. The speed of the HVS stars near the sun is in the range of 300 to 700 km / s, with the values ​​being evenly distributed as a first approximation . This corresponds to an original speed of 700 to 1000 km / s near the Galactic Center.

origin

The most common theory is that if a binary star system breaks up , hyper-speed runners will be accelerated when they encounter the central black hole inside the Milky Way.

However, this cannot apply to all hyper-speed runners, since the lifespan of some stars is too short to get from the galactic center to their current location even at these speeds. Furthermore, there are 100 times too many hyper-speed runners in the Milky Way if the only origin were the breakup of binary stars near the central black hole. Third, the potential gain in kinetic energy would be far too low to allow one of the stars to escape from a close orbit around the black hole in the center of the Milky Way. The binary star system would have to fall almost directly towards the central black hole from an extremely large distance and the stars in the binary star system would almost have to touch each other, for which the probability is extremely low.

Alternative hypotheses are:

  • Asymmetrical supernova explosions in binary star systems:
    These are also discussed for normal high-speed skiers. The fact that many hyper-speed runners seem to come from the direction of the galactic center could be explained by the fact that the star density and thus also the number of high-speed runners caused by supernova explosions is higher there than in the outer areas of the galactic disk .
  • A second black hole near the galactic center:
    This would make the original source understandable, but then even higher escape speeds should be observed.
  • Activity of the galactic core :
    This leads to jet formation also in the center of the Milky Way, which is currently in sleep mode. If the jet hits gas, this leads to a compression with subsequent star formation and an acceleration of the molecular cloud to escape speeds over the course of 10 million years. The highest final speeds are then again the result of a binary star system breaking apart through a supernova explosion. Since the stars are accelerated out of the center as soon as they are formed, even short-lived main sequence stars of the spectral class O could move so far away from the galactic center.
  • The interaction between a black hole with less than 20 solar masses and a binary star system
  • The B star, moving at high speed through the galaxy, could also be a blue subdwarf . In the simple degenerate scenario for thermonuclear supernovae, a main sequence star transfers mass to a white dwarf , which can then no longer prevent the gravitational collapse . In the supernova explosion , the white dwarf is completely destroyed, and the former companion develops into a blue subdwarf due to the impact of the explosion.
  • Some of the hyper-speed runners could produce the tidal effect on dwarf galaxies near the central black hole, which, as in the case of the Sagittarius dwarf galaxy, can lead to a dissolution of the dwarf galaxy.

Well-known hyper-speed runners

  • HVS 1: SDSS J090745.0 + 024507
  • HVS 2 : SDSS J093320.86 + 441705.4, also: US 708, supernova of a binary star partner
  • HVS 3 : HE 0437-5439, blue giant, V = 715 km / s, encounter with the Galactic Center about 100 mya ago
  • HVS 4 : SDSS J091301.00 + 305120.0, also: USNO-A2.0 1200-06254578, constellation Cancer, V = 603 km / s, encounter with the Galactic Center 130 mya
  • HVS 5: SDSS J091759.42 + 672238.7
  • HVS 6: SDSS J110557.45 + 093439.5
  • HVS 7: SDSS J113312.12 + 010824.9
  • HVS 8: SDSS J094214.04 + 200322.1
  • HVS 9: SDSS J102137.08-005234.8
  • HVS 10: SDSS J120337.85 + 180250.4

HD 271791

For HD 271791, by observing the trajectory , it was found that this star could never have come near the center of the Milky Way. It is likely that it gained this high speed from the collision of the Milky Way with another, smaller galaxy 150 million years ago. In addition, HD 271791 deviates from the normal chemical composition of stars; he has silicon , for example .

Web links

Spektrum .de: Stellar speedsters from the neighborhood - hyper-fast runners

Individual evidence

  1. ↑ Elena M. Rossi, Shiho Kobayashi, Re'em Sari: The Velocity Distribution of Hypervelocity Stars . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1307.1134v1 .
  2. ↑ Bo Wanga, Zhanwen Hana: Progenitors of type Ia supernovae . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1204.1155v1 .
  3. Jump up ↑ Joseph Silk, Vincenzo Antonuccio-Delogu, Yohan Dubois, Volker Gaibler, Marcel R. Haas, Sadegh Khochfar, Martin Krause: Jet interactions with a giant molecular cloud in the Galactic center and ejection of hypervelocity stars . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1209.1175v1 .
  4. ↑ Idan Ginsburg, Warren R. Brown and Gary. A. Wegner: VARIABILITY OF HYPERVELOCITY STARS . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1302.1899v1 .
  5. ↑ Kuo-Chuan Pan, Paul M. Ricker and Ronald E. Taam: EVOLUTION OF POST-IMPACT REMNANT HELIUM STARS IN TYPE Ia SUPERNOVA REMNANTS WITHIN THE SINGLE-DEGENERATE SCENARIO . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1303.1228v1 .
  6. ↑ Kastytis Zubovas, Graham A. Wynn and Alessia Gualandris: SUPERNOVAE IN THE CENTRAL PARSEC: A MECHANISM FOR PRODUCING SPATIALLY ANISOTROPIC HYPERVELOCITY STARS . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1305.3997v1 .
  7. ↑ Olaf Stampf : Catapult for Suns , Spiegel Online September 7, 2009
  8. ↑ Ulrich Heber: On the Schleuderbahn out of the galaxy , innovations report March 3, 2009
  9. ↑ Maria Fernanda Nieva, Ulrich Heber and Norbert Przybilla: New hyper-fast runner discovered: This time it wasn't the black hole in the center of the Milky Way , Max Planck Institute for Astrophysics January 7, 2009
  10. ↑ Olaf Stampf: ASTRONOMY: Catapult for suns . In: Der Spiegel . No. 37 , 2009 ( online - Sept. 7, 2009 ).