David Dunlap Observatory
...that the first direct observational evidence that Cygnus X-1 was a black hole was discovered at the David Dunlap Observatory outside Toronto?
...that the first direct observational evidence that <a href="./Cygnus_X-1" id="mwDi4" rel="mw:WikiLink" title="Cygnus X-1">Cygnus X-1</a> was a <a href="./Black_hole" id="mwDi8" rel="mw:WikiLink" title="Black hole">black hole</a> was discovered at the <b id="mwDjA"><a href="./David_Dunlap_Observatory" id="mwDjE" rel="mw:WikiLink" title="David Dunlap Observatory">David Dunlap Observatory</a></b> <i id="mwDjI">(pictured)</i> outside <a href="./Toronto" id="mwDjM" rel="mw:WikiLink" title="Toronto">Toronto</a>?