Repeated Relativistic Ejections in GRS 1915+105

In 1994 February-August we observed with the VLA four ejection events of radio emitting clouds from the high energy source GRS 1915+105. These events are all consistent with anti-parallel ejections of twin pairs of clouds moving away from the compact source at $\sim$ 0.92 of the speed of light and angles of $\sim$ 70$^{\circ}$ with respect to the line of sight. The flux ratios and time evolution of the expelled clouds are consistent with actual motions of the radiating matter rather than with the simple propagation of pulses in a medium moving at slower velocities. The large kinetic power of the sudden, short, and rather discontinuous ejections exceeds by more than an order of magnitude the maximum steady photon luminosity of the source, suggesting that in GRS 1915+105 a radiation acceleration mechanism of the ejecta is unlikely. As in other galactic and extragalactic radio sources, the decrease in flux density as a function of angular separation from the central source shows a steepening with distance. Additional ejection events have been observed in 1995 and 1997 and we compare them with the 1994 events.Comment: 20 pages, 7 figures. To appear in The Astrophysical Journal, January 10, 1999 issu

Microquasars: disk-jet coupling in stellar-mass black holes

Microquasars provide new insights into: 1) the physics of relativistic jets from black holes, 2) the connection between accretion and ejection, and 3) the physical mechanisms in the formation of stellar-mass black holes. Furthermore, the studies of microquasars in our Galaxy can provide in the future new insights on: 1) a large fraction of the ultraluminous X-ray sources in nearby galaxies, 2) gamma-ray bursts (GRBs) of long duration in distant galaxies, and 3) the physics in the jets of blazars. If jets in GRBs, microquasars and Active Galactic Nuclei (AGN) are due to a unique universal magnetohydrodynamic mechanism, synergy of the research on these three different classes of cosmic objects will lead to further progress in black hole physics and astrophysics.Comment: 4 pages, 3 figures. To appear in Proceedings of IAU Symp. No 238 "Black Holes: from Stars to Galaxies - across the Range of Masses. Held in Prague, August 21-25, 2006. Eds. V. Karas & G. Mat

Jets from black hole binaries and Galactic Nuclei

Relativistic outflows are a common phenomenon in accreting black holes. Despite the enormous differences in scale, stellar-mass black holes in binaries and supermassive black holes in Galactic Nuclei produce jets with analogous properties. In both are observed two types of relativistic outflows: 1) steady compact jets with flat-spectrum, and 2) sporadic extended jets with steep-spectrum and apparent superluminal motions. Besides, the most common class of gamma-ray bursts are afterglows from ultra-relativistic jets associated to the formation of black holes at cosmological distances.Comment: 6 pages, 3 figures. To be published at the Proceedings of the ESO Workshop on Black holes in binaries and galactic nuclei. September 6-8, 1999, Garching, German

The Most Luminous Galaxies

Ultraluminous galaxies in the local universe (z$\leq$0.2) emit the bulk of their energy in the mid and far-infrared. The multiwavelength approach to these objects has shown that they are advanced mergers of gas-rich spiral galaxies. Galaxy-galaxy collisions took place on all cosmological time-scales, and nearby mergers serve as local analogs to gain insight into the physical processes that lead to the formation and trans-formation of galaxies in the more distant universe. Here I review multiwavelength observations --with particular emphasis on recent results obtained with ISO-- of mergers of massive galaxies driving the formation of: 1) luminous infrared galaxies, 2) elliptical galaxy cores, 3) luminous dust-enshrouded extranuclear starbursts, 4) symbiotic galaxies that host AGNs, and 5) tidal dwarf galaxies. The most important implication for studies on the formation of galaxies at early cosmological timescales is that the distant analogs to the local ultraluminous infrared galaxies are invisible in the ultraviolet and optical wavelength rest-frames and should be detected as sub-millimeter sources with no optical counterparts.Comment: 12 pages, 6 figures. Invited Review at the Conference Lighthouses of the universe. August 6-10, 2001 (Garching, Germany

Phenomenological Analogies in Black Hole Systems of all Masses

I review the progress made on the physics of relativistic jets from black hole systems in the context of the analogy between AGN and microquasars that was proposed one decade ago. If the emerging empirical correlations between the observational properties of stellar and supermassive black holes will become more robust, we will use them to determine the mass and spin of black holes, independently of theoretical models. Microquasars are fossils of sources of Gamma-ray bursts (GRBs) of long duration, and their kinematics provides observational clues on the physics of collapsars. If jets in GRBs, microquasars and AGN are due to a unique universal magnetohydrodynamic mechanism, synergy between the research on these three different classes of cosmic objects will lead to further progress in black hole physics and astrophysics.Comment: Invited review at the conference "Stellar-Mass, Intermediate-Mass, and Supermassive Black Holes." Kyoto, 25-31 October 2003. 11 pages, 5 figures (4 in color). To be published as Progress of Theoretical Physics, Supplemen