In astronomy, the common envelope of a system ( English common envelope, CE ) is the gas envelope containing a double star [1] . The gas rotates at a speed different from that of a double star immersed in it. A similar system is called being at the stage of having a common shell.
During the stage of the common envelope, the immersed binary system is exposed to from the envelope, due to which the distance between the stars decreases. Ultimately, the shell will be ejected from the system, the stars in which will be at a significantly shorter distance, or two stars will be so close to each other that they merge and form one star. The stage of the presence of a common shell is relatively short compared with the lifetime of stellar components.
Evolution at the stage of the general shell, culminating in the discharge of the shell, can lead to the formation of a binary system consisting of a compact object and a second component located close to it. Examples of systems of this kind are cataclysmic variables , x-ray binary stars, and systems of two closely spaced white dwarfs or neutron stars. In all such systems, there is a compact remnant (a white dwarf , a neutron star, or a black hole ), which is, apparently, the core of a star whose size exceeded the current distance between the components of the binary system. If similar objects were formed during evolution in a joint shell, then their modern close arrangement can be explained. Short-period systems containing compact objects are sources of gravitational waves and the forerunners of the first type of supernovae .
Predictions of the results of evolution in a system with a common shell are not entirely unambiguous [2] [3] [4] .
A common shell system is often confused with a close binary system . The general shell usually does not rotate at the same speed as the immersed binary system; therefore, it is not limited to the equipotential surface passing through the Lagrange point L2 [1] . In a close binary system, the common shell rotates with the binary star and fills the inner region of the equipotential surface [5] .
Content
Formation
A common shell forms around a binary star when the distance between the components decreases rapidly or one of the components expands rapidly [2] . A donor star, when filling the Roche lobe, begins to transfer matter to the second star, while the mutual orbit of the stars decreases, as a result, the mass transfer process accelerates, the orbit decreases more. This leads to dynamically unstable mass flow. In some cases, the second component cannot accrete all incoming material onto itself, while a shell begins to form around the second component [7] .
Evolution
The nucleus of a donor star does not participate in the expansion of the stellar envelope and the formation of a common envelope, which will subsequently contain two objects: the nucleus of a donor star and a companion star. Initially, these objects continue to move in orbit inside a common shell. It is believed that due to the impact from the side of the gas shell, objects lose energy, as a result of which they transfer to a closer orbit, and the speeds of movement increase. The loss of orbital energy is supposed to heat and expand the shell; in general, the stage of the presence of a common shell ends either when the shell is dropped into the surrounding space, or when objects within the shell merge [7] . With a gradual spatial decrease in the length of the orbit, objects move closer together, moving in a certain spiral.
Observed manifestations
Objects with a common shell are quite difficult to observe. Their presence was indicated implicitly: by the existence of binary stars whose parameters are not explained by any other mechanism of formation. The processes at the completion of the stage of the presence of a common shell are usually brighter than ordinary new ones , but weaker than supernovae . The photosphere of the common shell should be relatively cold (about 5,000 K), radiating mainly in the red part of the spectrum. Moreover, due to the large size of the shell, its luminosity is high, approximately like that of a red supergiant . Phenomena associated with evolution in the common envelope begin with a sharp increase in luminosity, followed by a period of constant luminosity lasting about several months (almost like type II supernovae), accompanied by recombination of hydrogen in the envelope. After the end of this period, the luminosity rapidly decreases [7] .
Several phenomena resembling the process described above were observed. Such phenomena were called bright red new. The expansion rates are 200–1000 km / s, the amount of radiated energy is from 10 38 J to 10 40 J [7] .
Among the observed phenomena can be mentioned
- M85 OT2006-1 , possibly dropping the entire shell.
- V1309 Sco , probable merger of stars.
- M31 RV
- V838 Unicorn [7] [8]
Notes
- ↑ 1 2 Paczyński, B. (1976). "Common Envelope Binaries" in IAU Symposium No. 73 . Structure and Evolution of Close Binary Systems : 75–80, Dordrecht: D. Reidel .
- ↑ 1 2 Iben, Livio, 1993 .
- ↑ Taam, Sandquist, 2000 .
- ↑ Ivanova, Justham, Chen et al., 2013 .
- ↑ Eggleton, 2006 .
- ↑ Izzard, Hall, Tauris et al., 2011 .
- ↑ 1 2 3 4 5 Ivanova, Justham, Nandez et al., 2013 .
- ↑ Mystery of Strange Star Outbursts May Be Solved . Date of treatment August 30, 2015.
Literature
- Icko, Jr. Iben, Livio M. Common envelopes in binary star evolution // Publications of the Astronomical Society of the Pacific - University of Chicago Press , 1993. - Vol. 105. - P. 1373. - ISSN 0004-6280 ; 1538-3873 - doi: 10.1086 / 133321
- Taam R. E., Sandquist E. L. Common Envelope Evolution of Massive Binary Stars // Annu. Rev. Astron. Astrophys. / S. Faber - Annual Reviews , 2000. - Vol. 38, Iss. 1. - P. 113–141. - ISSN 0066-4146 ; 1545-4282 - doi: 10.1146 / ANNUREV.ASTRO.38.1.113
- Eggleton P. P. Evolutionary processes in binary and multiple stars - Cambridge : Cambridge University Press , 2006 .-- 322 p. - ISBN 978-1-10-740342-0
- Izzard R. G., Hall P. D., Tauris T. M. et al. Common envelope evolution // Proceedings of the International Astronomical Union - Cambridge University Press , 2011 .-- Vol. 7, Iss. S283. - P. 95-102. - ISSN 1743-9221 - doi: 10.1017 / S1743921312010769
- N Ivanova, S Justham, JL Avendano Nandez et al. Identification of the long-sought common-envelope events. // Science / M. McNutt - AAAS , 2013 .-- Vol. 339, Iss. 6118. - P. 433-435. - ISSN 0036-8075 ; 1095-9203 - doi: 10.1126 / SCIENCE.1225540 - PMID: 23349287 - arXiv: 1301.5897
- N. Ivanova, S. Justham, X. Chen et al. Common envelope evolution: where we stand and how we can move forward // Astron. Astrophys. Rev. - Springer Science + Business Media , 2013 .-- Vol. 21, Iss. 1.- ISSN 0935-4956 ; 1432-0754 - doi: 10.1007 / S00159-013-0059-2 - arXiv: 1209.4302