There is a milli-Jansky radio source in the core of the nearby dwarf spheroidal galaxy in Ursa Minor, UGC 9749,
which may well be an intermediate-mass black hole. The radio source is within 20 ## of the center of UGC 9749 ---
the likelihood of an unrelated background source being this close to the center is only <1%. Our 1.7 GHz VLBI
observations showed that the radio source has a core of size <2 mas. If the radio source is in fact associated with
UGC 9749, and thus at a distance of only 66 kpc, it is quite unusual, and likely to be an intermediate-mass black
hole, of which only a very few examples are known or suspected. The most convincing way to rule out the possibility
of an unrelated background quasar is to determine if its proper motion is equal to that of UGC 9749, which is
0.55 ñ 0.17 mas year -1 . Phase-referenced VLBI astrometry on the compact core should allow us to determine a
su#ciently accurate proper motion within 2 years. We propose two epochs of VLBI observations, spaced >1.5 years
apart, to measure this proper motion and determine whether the Ursa Minor dwarf spheroidal has an active galactic
nucleus with an intermediate-mass black hole in its center. |