DI Herculis

DI Herculis is a binary star system of Algol - type in the constellation Hercules. The system has an apparent magnitude of about 8.5 likes consists of two young blue stars of spectral types B5 and B4, and is about 2,000 light years away.

The orbit of the stars around the common center of gravity is strongly elliptic with orbital eccentricity of 0.2. Together with a semi-major axis a of 0.496 astronomical units and stellar masses of 4.52 and 5.15 solar masses, a theoretical Apsidendrehung of 4.27 ° per 100 years is expected. This value consists of a relativistic share of 2.34 ° per 100 years, and a classic proportion of 1.93 ° per 100 years. In contrast, the observed value is only 1.04 ° per 100 years.

This deviation has in the bright double star has triggered intensive studies in the last 30 years. The following solutions were discussed:

  • New theories of gravitation ( see also Modified Newtonian dynamics)
  • Rapid circularization of the elliptical orbit
  • Change in the Apsidendrehung by a third body in the railway system
  • Presence of a circumstellar cloud between the components of the binary system with a gravitational influence
  • Position of the rotational axes of the stars

Based on the Rossiter - McLaughlin effect, in 2009 the evidence is given that the rotation axes of the two B stars are nearly in the orbital plane of the binary system. Is this included in the calculations of Apsidendrehung as the deviation between the expected and measured value within the measurement uncertainty disappears. This DI Herculis can no longer be considered an indication of a possible falsification of the general theory of relativity.

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