DI Herculis
Encyclopedia
DI Herculis is an Algol-type binary star in the constellation Hercules. The system has an ensemble magnitude of about +8.5 and consists of two young blue stars of spectral type B5 and B4 ; it is about two thousand light years from Earth.
The orbit of the stars around their mutual centre of gravity is very elliptical, with an eccentricity of 0.2 and a semi-major axis of 0.496 astronomical units; stellar masses of 4.52 and 5.15 solar masses lead to a theoretical precession of 4.27 degrees per century (1.93 degrees from classical effects and 2.34 degrees from general relativistic effects); but the observed precession is by 1.04 degrees per century.
This observation has led to extensive studies of the bright binary system in the last thirty years; solutions discussed included
After observations of the Rossiter-McLaughlin effect
in 2009, it emerged that the rotation axes of the two stars lay roughly in the orbital plane of the system. When this is taken account in calculating the rate of precession, the difference between expected and observed precession disappears; so DI Hercules is no longer a test case for a possible falsification of general relativity
.
The orbit of the stars around their mutual centre of gravity is very elliptical, with an eccentricity of 0.2 and a semi-major axis of 0.496 astronomical units; stellar masses of 4.52 and 5.15 solar masses lead to a theoretical precession of 4.27 degrees per century (1.93 degrees from classical effects and 2.34 degrees from general relativistic effects); but the observed precession is by 1.04 degrees per century.
This observation has led to extensive studies of the bright binary system in the last thirty years; solutions discussed included
- new theories of gravitation such as MONDMondMond may refer to:* MOND - Modified Newtonian Dynamics. A proposed adjustment to the classical inverse-square law of gravity.* Der Mond, an opera in one act* Mond Nickel Company, a defunct mining company...
- tidal forces (perhaps due to unusual internal structure in the stars) leading to a circularisation of the elliptical orbit
- a third body in the system
- presence of a circumstellar cloud between the two components
- unusual rotation axes of the stars
After observations of the Rossiter-McLaughlin effect
Rossiter-McLaughlin effect
The Rossiter–McLaughlin effect is a spectroscopic phenomenon observed when either an eclipsing binary's secondary star or an extrasolar planet is seen to transit across the face of the primary or parent star. As the main star rotates on its axis, one quadrant of its photosphere will be seen to be...
in 2009, it emerged that the rotation axes of the two stars lay roughly in the orbital plane of the system. When this is taken account in calculating the rate of precession, the difference between expected and observed precession disappears; so DI Hercules is no longer a test case for a possible falsification of general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
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