On the Detectability of Very Massive Compact Objects with Gravitational Microlensing

Original · EN

If the dark halo of our galaxy is made of compact objects as massive as M = 10⁶ solar masses, their detection by means of ordinary microlensing searches would take a very long time as the characteristic time scale of such a lensing event, t₀, is approximately 200 years. Fortunately, the very high magnification events of the numerous faint stars, which are normally well below the detection threshold, have short duration peaks with a characteristic time scale of only t₀ / Amax, where Amax >> 1 is the peak magnification factor. The two almost equally bright images are separated by approximately 2'' (M/10⁶ solar masses)¹/², and they rotate very rapidly around the lens with the relative proper motion enhanced by a factor 2 Amax. The same events will offer an opportunity to study spectroscopically stars which are normally far too faint to be reached.