paradox of youth
Fr.: paradoxe de jeunesse
The observed presence of young stars in the immediate vicinity of the → supermassive black hole (SMBH), → Sgr A*, residing in the center of our Galaxy. The stellar population within 1 pc of the SMBH contains a variety of young and → massive stars orbiting the SMBH. Some of them are only about 20 Myr old and get as close as a few light-days to the SMBH, while from 0.1 to 0.4 pc even younger stars are found with ages of 3-7 Myr. The presence of these stars so near to the SMBH is a paradox. Their → in situ formation should be almost impossible, since the environment is too hostile for these stars to form. Indeed the strong → tidal influence of the SMBH should hamper their formation. On the other hand, the scenario considering their → migration from other places does not seem to be adequate. The time required for the migration from > 1 pc by dynamical friction would exceed their inferred ages unless the migration rate were somehow accelerated. This apparent contradiction was termed "paradox of youth" by Ghez et al. (2003, ApJ 586, L127). See also Genzel et al. (2010, Rev.Mod.Phys. 82, 3121, also at astro-ph/1006.0064).