  The high-velocity, neutral hydrogen feature known as MI may be the result of
a supernova that took place about 100,000 years ago at a distance of 163 pc.
Low-velocity HI data show a clear cavity, a structure indicative of regions
evacuated by old exploding stars, centered on the spatial coordinates of MI,
(l,b) = (165o, 65.o5). The invisible companion of the yellow giant star, 56
Ursae Majoris, may be the remains of the supernova that evacuated the cavity
and blasted MI itself outward at 120 km/s. The mass and energy of MI are easily
in line with what is expected from a supernova. The X-rays seen by ROSAT are
consistent with an origin in the resulting bow shock. Ironically, this scenario
for MI only came together because we were exploring low-velocity gas in the
direction of high-velocity clouds.
