Interactive double star

Interacting binary star systems are binary stars that show a significant interaction between their components that goes beyond the influence of mutual gravitational forces . The influence can take place through mass exchange between the stars, through the action of electromagnetic or particle radiation or through tidal forces . Due to the interaction between the stars, the stars can take development paths that they cannot go through as individual stars. Interacting binary stars are somewhat imprecisely referred to as close binary stars.

Interaction through mass exchange

Artist's impression of a low mass X-ray binary star (LMXB)

Mass transfer between the components of a double star can occur through stellar winds or by crossing the Roche limit . With a wind accretion , a wind flows from a massive star and is directed onto it by the gravitational field of the companion. For reasons of angular momentum conservation, an accretion disk forms around the mass receiving star , from which the matter falls onto the star. Accretion rates are usually too low to affect the evolutionary paths of stars, but many variable star eruptions are caused by wind accretion. During the collisions of stellar winds in close binary stars, particles can be accelerated to extremely high energies and observed as gamma-ray double stars .

If the Roche limit is exceeded, one of the stars in the double star has reached an expansion at which parts of its atmosphere are no longer gravitationally bound to the star. These can leave the binary star system or mostly pass over to the companion via an accretion disk. The mass transfers lead to a change in the orbit axis , a change in the mass of the components and a change in the rotation times of the components. Through the transfer of matter, the chemical signature in the atmospheres of the stars can change, as in the case of the barium stars, or the stars can take development paths that they would not have been able to achieve as individual stars in an undisturbed development. Examples are the blue sub-dwarfs , blue stragglers and some of the thermonuclear supernovae of type Ia .

The interacting binary star systems with active mass transfer between the components include:

Interaction by tidal forces

Coronal mass ejection on the sun

The tidal forces deform the stars and influence the light curve of the binary star system, which shows signs of an ellipsoidal light change . In addition, the tidal forces also lead to a synchronization of the rotation period of the stars with the orbital period of the binary star system. Older stars in close binary star systems therefore rotate considerably faster than single stars with corresponding age and since the rotation is the cause of magnetic activity in the chromosphere of these stars, these stars in interacting binary star systems show pronounced signs of chromospheric activity in the form of star spots , coronal mass ejections , flares and Radio bursts.

Many types of variable stars with magnetic activity therefore preferentially occur in interacting binary stars such as the UV Ceti stars , the BY Draconis stars and the RS Canum Venaticorum stars .

The bound rotation in close binary star systems also influences the mixing in the interior of the stars and thus the composition of the matter available in the core for thermonuclear reactions . This leads to a changed development path of the stars independent of a mass transfer between the components.

Radiation interaction

Schematic representation of the Eclipsing Binary Millisecond Pulsar PSR B1957 + 20. The radiation of the millisecond pulsar evaporates the surface of the companion star, from which a stellar wind leaves the binary star system.

By heating the side facing the companion, in extreme cases even the companion can be vaporized. This is the case with the black widows , where particle and electromagnetic radiation completely dissolve the companion within a few million years. The interaction through radiation otherwise only has an influence on the light curve in double stars, which show an illumination effect, since the day side is brighter due to the additional energy that the star receives from its companion. The star reacts to this by expanding its radius, which in turn allows it to exceed its Roche limit volume.

Interaction in a common shell

All variants of the interaction come into play in double stars with a common shell. These include the W-Ursae Majoris stars , the components of which are hidden under a common shell with a uniform temperature. The common temperature assumes a not yet understood energy transport in the atmosphere of the binary star system. A common envelope is when a star enters the atmosphere of its companion. Depending on the mass ratio and the evolutionary status of the stars, this can lead to different end results. If the two stars merge, the result is a luminous red nova . Should a neutron star merge with a star, the hypothetical result is a Thorne-Żytkow object .

Individual evidence

↑ SNShore, M. Livio, EPJ van den Heuvel: Interacting Binaries . Springer-Verlag, Berlin 1992, ISBN 3-540-57014-4 .
^ John R. Percy: Understanding Variable Stars . Cambridge University Press, Cambridge 2007, ISBN 978-0-521-23253-1 .
↑ H. Scheffler, H. Elsässer: Physics of the sun and the stars . Bibliographisches Institut, Mannheim 1990, ISBN 3-411-14172-7 .
↑ Klaus G. Strassmeier: Active stars: laboratories of solar astrophysics . Springer Verlag, Vienna 1997, ISBN 978-3-211-83005-5 .
↑ R. Kippenhahn, A.Weigert: Stellar Structure and Evolution (Astronomy and Astrophysics Library) . Springer Verlag GmbH, Mannheim 1994, ISBN 978-3-540-50211-1 .
^ Mallory SE Roberts: New Black Widows and Redbacks in the Galactic Field . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1103.0819 .
^ Cuno Hoffmeister , G. Richter, W. Wenzel: Veränderliche Sterne . JA Barth Verlag, Leipzig 1990, ISBN 3-335-00224-5 .
↑ K. Stepien: Evolution of Cool Close Binaries - Approach to Contact . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1105.2645 .
↑ R. Tylenda, M. Hajduk, T. Kamiński, A. Udalski, I. Soszyński, M. K Szymański, M. Kubiak, G. Pietrzyński, R. Poleski, Ł Wyrzykowski, K. Ulaczyk: V1309 Scorpii: merger of a contact binary . In: Astrophysics. Solar and Stellar Astrophysics . 2010, arxiv : 1012.0163 .

[1] SNShore, M. Livio, EPJ van den Heuvel: Interacting Binaries . Springer-Verlag, Berlin 1992, ISBN 3-540-57014-4 .

[2] John R. Percy: Understanding Variable Stars . Cambridge University Press, Cambridge 2007, ISBN 978-0-521-23253-1 .

[3] H. Scheffler, H. Elsässer: Physics of the sun and the stars . Bibliographisches Institut, Mannheim 1990, ISBN 3-411-14172-7 .

[4] Klaus G. Strassmeier: Active stars: laboratories of solar astrophysics . Springer Verlag, Vienna 1997, ISBN 978-3-211-83005-5 .

[5] R. Kippenhahn, A.Weigert: Stellar Structure and Evolution (Astronomy and Astrophysics Library) . Springer Verlag GmbH, Mannheim 1994, ISBN 978-3-540-50211-1 .

[6] Mallory SE Roberts: New Black Widows and Redbacks in the Galactic Field . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1103.0819 .

[7] Cuno Hoffmeister , G. Richter, W. Wenzel: Veränderliche Sterne . JA Barth Verlag, Leipzig 1990, ISBN 3-335-00224-5 .

[8] K. Stepien: Evolution of Cool Close Binaries - Approach to Contact . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1105.2645 .

[9] R. Tylenda, M. Hajduk, T. Kamiński, A. Udalski, I. Soszyński, M. K Szymański, M. Kubiak, G. Pietrzyński, R. Poleski, Ł Wyrzykowski, K. Ulaczyk: V1309 Scorpii: merger of a contact binary . In: Astrophysics. Solar and Stellar Astrophysics . 2010, arxiv : 1012.0163 .