Hostname: page-component-78c5997874-xbtfd Total loading time: 0 Render date: 2024-11-03T05:20:31.317Z Has data issue: false hasContentIssue false
  • English
  • Français

The Galactic Nucleus

Published online by Cambridge University Press:  04 August 2017

J. H. Oort
J. H. Oort*
Affiliation:
Sterrewacht, Leiden, The Netherlands

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The ionized gas within 2 parsec from the centre region is distributed in spiral-like features which appear to emanate from a nucleus. This nucleus is close to the ultra-compact radio source and the infrared source IRS 16, but does not exactly coincide with either. The spiral is strongly inclined to the galactic plane. The arms are clumpy. The spiral appears to rotate, but there appear to be also large radial motions.

The phenomena show some resemblance to what is observed on a very much larger scale in the nuclei of radio galaxies and quasars.

An exceptionally powerful, variable source of hard X- and gamma-rays, GCX, has been found in the direction of the centre. This may be the true galactic nucleus. Strong, variable emission of the 511-keV electron-positron annihilation line has also been observed to come from the central region.

The evidence for a central black hole is discussed. It is not compelling. The energy required for the strong infrared radiation emitted by the central few parsecs is probably coming from a large number of luminous stars, and due to a recent burst of star formation. The observed state of ionization indicates the burst to have occurred about one million years ago.

The distribution of the dense molecular clouds within 300 pc from the centre is very asymmetric: practically all lie at positive longitudes. Their motions differ radically from circular motions. The layer of clouds is tilted relative to the galactic plane. The so-called “+40-km/s cloud” lies in front of the nuclear spiral, and is therefore moving towards the centre. Different interpretations of the systematic motions are considered. The outspoken asymmetry excludes a static condition. If the “molecular ring” at R ~ 150 parsec is actually an expanding feature, its origin might be sought in the same burst of star formation proposed to explain the state of ionization and the infrared radiation of the nuclear region.

Type
PART II: COMPOSITION, STRUCTURE AND KINEMATICS
Information
Symposium - International Astronomical Union , Volume 106: The Milky Way Galaxy , 1985 , pp. 349 - 366
Copyright
Copyright © Reidel 1985 

References

Bailey, M.E., 1980, MNRAS 190, 217 CrossRefGoogle Scholar
Bania, T.M., 1977, Ap. J. 216, 381 CrossRefGoogle Scholar
Becklin, E.E., Neugebauer, G., 1969, Ap. J. Lett. 157, L 31 CrossRefGoogle Scholar
Blandford, R.D., 1982, in The Galactic Center , eds. Riegler, G.R. & Blandford, R.D., p. 177 Google Scholar
Bolton, J.G., Gardner, F.F., McGee, R.X., Robinson, B.J., 1964, Nature 204, 30 CrossRefGoogle Scholar
Brown, R.L., Johnston, K.J., Lo, K.Y., 1981, Ap. J. 250, 155 CrossRefGoogle Scholar
Brown, R.L., Lo, K.Y., 1982, Ap. J. 253, 108 CrossRefGoogle Scholar
Brown, R.L., 1982, Ap. J. 262, 110 CrossRefGoogle Scholar
Cohen, R.J., Davies, R.D., 1976, MNRAS 175, 1 CrossRefGoogle Scholar
Ekers, R.D., van Gorkom, J.H., Schwarz, U.J., Goss, W.M., 1983, Astron. Astrophys. 122, 143 Google Scholar
Fukui, et al, 1977, Publ. Astron. Soc. Japan 29, 643 Google Scholar
Fukui, Y., Kaifu, N., Morimoto, M. Miyaji, T., 1980, Ap. J. 241, 147 CrossRefGoogle Scholar
Hall, D.N.B., Kleinmann, S.G., Scoville, N.Z., 1982, Ap. J. Lett. 260, L53 CrossRefGoogle Scholar
Isaacman, R., 1981, Astron. Astrophys. 95, 46 Google Scholar
Kellermann, K.I., Shaffer, D.B., Clark, B.G., Geldzahler, B.J., 1977, Ap. J. Lett. 214, L61 CrossRefGoogle Scholar
Lacy, J.H., Townes, C.H., Geballe, T.R., Hollenbach, D.J., 1980, Ap. J. 241, 132 CrossRefGoogle Scholar
Levine, A. et al, 1979, B.A.A.S. 11, 429 Google Scholar
Lingenfelter, R.E., Ramaty, R., 1982, in The Galactic Center , eds. Riegler, G.R. & Blandford, R.D., p. 148 Google Scholar
Liszt, H.S., Burton, W.B., Sanders, R.H., Scoville, N.Z., 1977, Ap. J. 213, 38 CrossRefGoogle Scholar
Liszt, H.S., Burton, W.B., 1980, Ap. J. 236, 779 CrossRefGoogle Scholar
Liszt, H.S., van der Hulst, J.M., Burton, W.B., Ondrechen, M.P., 1983. Submitted to Astron. Astrophys. Google Scholar
Matsumoto, T. et al, 1982, in The Galactic Center , eds. Riegler, G.R. & Blandford, R.D., p. 48 Google Scholar
Matteson, J.L., 1982, in The Galactic Center , eds. Riegler, G.R. & Blandford, R.D., p. 109 Google Scholar
Oort, J.H., 1977, Ann. Rev. Astron. Astrophys. 15, 295 CrossRefGoogle Scholar
Pauls, T., Downes, D., Mezger, P.G., Churchwell, E., 1976, Astron. Astrophys. 46, 407 Google Scholar
Rieke, G.H., Lebofsky, M.J., 1982, in The Galactic Center , eds. Riegler, G.R. & Blandford, R.D., p. 194 Google Scholar
Sanders, R.H., Lowinger, T., 1972, AJ , 77, 292 CrossRefGoogle Scholar
Sandqvist, Aa, 1982, in The Galactic Center , eds. Riegler, G.R. & Blandford, R.D., p. 12 Google Scholar
Van der Kruit, P.C., 1970, Astron. Astrophys. 4, 462 Google Scholar
van Gorkom, J.H., Schwarz, U.J., Bregman, J.D., 1985. In preparation and these Proceedings, p. 371 CrossRefGoogle Scholar
Watson, M.G., Willingale, J.E., Grindlay, J.E., Hertz, P., 1981, Ap. J. 250, 142 CrossRefGoogle Scholar
Whiteoak, J.B., Gardner, F.F., Pankonin, V., 1983, MNRAS 202, 11PCrossRefGoogle Scholar
Wollman, E.R., Smith, H.A., Larson, H.P., 1982, Ap. J. 258, 506 CrossRefGoogle Scholar