Hydrogen phases on the surface of a strongly magnetized neutron star

被引:99
作者
Lai, D [1 ]
Salpeter, EE [1 ]
机构
[1] CALTECH, PASADENA, CA 91125 USA
关键词
equation of state; radiation mechanisms; thermal; stars; magnetic fields; neutron;
D O I
10.1086/304937
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
The outermost layers of some neutron stars are likely to be dominated by hydrogen, as a result of fast gravitational settling of heavier elements. These layers directly mediate thermal radiation from the stars and determine the characteristics of X-ray/EUV spectra. For a neutron star with surface temperature T less than or similar to 10(6) K and magnetic field B greater than or similar to 10(12) G, various forms of hydrogen can be present in the envelope, including atoms, polyatomic molecules, and condensed metal. We study the physical properties of different hydrogen phases on the surface of a strongly magnetized neutron star for a wide range of field strengths B and surface temperatures T. Depending on the values of B and T, the outer envelope can be either in a nondegenerate gaseous phase or in a degenerate metallic phase. For T greater than or similar to 10(5) K and moderately strong magnetic field, B less than or similar to 10(13) G, the envelope is nondegenerate and the surface material gradually transforms into a degenerate Coulomb plasma as density increases. For higher field strength, B much greater than 10(13) G, there exists a first-order phase transition from the non-degenerate gaseous phase to the condensed metallic phase. The column density of saturated vapor above the metallic hydrogen decreases rapidly as the magnetic field increases or/and temperature decreases. Thus the thermal radiation can directly emerge from the degenerate metallic hydrogen surface. The characteristics of surface X-ray/EUV emission for different phases are discussed. We also study the possibility of magnetic field-induced nuclear fusion on the neutron star surface. Because of the strong compression of molecules and condensed droplets by the magnetic field, the fusion rate can be significantly enhanced even at a low temperature and external pressure. This implies that for nonaccreting neutron stars, there is a limit to the field strength, similar to 10(14) G, above which the surface hydrogen layer is absent.
引用
收藏
页码:270 / 285
页数:16
相关论文
共 61 条
[41]   STRUCTURE AND RADIATIVE TRANSITIONS OF THE HYDROGEN-ATOM MOVING IN A STRONG MAGNETIC-FIELD [J].
POTEKHIN, AY .
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 1994, 27 (06) :1073-1090
[42]   PHOTOIONIZATION OF THE HYDROGEN-ATOM IN STRONG MAGNETIC-FIELDS [J].
POTEKHIN, AY ;
PAVLOV, GG .
ASTROPHYSICAL JOURNAL, 1993, 407 (01) :330-341
[43]   Model atmospheres for low-field neutron stars [J].
Rajagopal, M ;
Romani, RW .
ASTROPHYSICAL JOURNAL, 1996, 461 (01) :327-333
[44]   DEVIATIONS FROM CHEMICAL-EQUILIBRIUM DUE TO SPIN-DOWN AS AN INTERNAL HEAT-SOURCE IN NEUTRON-STARS [J].
REISENEGGER, A .
ASTROPHYSICAL JOURNAL, 1995, 442 (02) :749-757
[45]   MODEL ATMOSPHERES FOR COOLING NEUTRON-STARS [J].
ROMANI, RW .
ASTROPHYSICAL JOURNAL, 1987, 313 (02) :718-726
[46]  
RUDER H, 1994, ATOMS STORNG MAGNETI
[47]  
Ruderman M., 1974, International Astronomical Union Symposium No. 53 Physics of Dense Matter, P117
[48]   MATTER IN SUPERSTRONG MAGNETIC FIELDS - SURFACE OF A NEUTRON STAR [J].
RUDERMAN, M .
PHYSICAL REVIEW LETTERS, 1971, 27 (19) :1306-&
[49]   NUCLEAR REACTION RATES AT HIGH DENSITIES [J].
SALPETER, EE ;
VANHORN, HM .
ASTROPHYSICAL JOURNAL, 1969, 155 (1P1) :183-&
[50]   PYCNONUCLEAR FUSION RATES [J].
SCHRAMM, S ;
KOONIN, SE .
ASTROPHYSICAL JOURNAL, 1990, 365 (01) :296-300