2003A&A...409..809D

Holz & Wheeler (2002ApJ...578..330H) have recently proposed that a Schwarzschild black hole may act as a retro-lens which, if illuminated by a powerful light source, deflects light ray paths to large bending angles and a series of luminous arcs (or rings in the case of aligned objects) centered on the black hole may form. Obviously, the most convenient geometry to get retro-lensing images would be that of a very bright star close to a massive black hole, say the putative ∼4x10⁶M_☉ black hole at the galactic center. Recent observations of the galactic center region in the K-band have revealed the presence of a very bright main sequence star (labelled S2) with mass ∼15M_☉ orbiting at close distance (130-1900AU) from Sgr A^*. The relatively vicinity of S2 to the central massive black hole may offer a unique laboratory to test the formation of retro-lensing images. The next generation of space-based telescopes in the K-band (like NGST) may have high enough limiting magnitude necessary to observe such retro-lensing images.