Milky Way: Black hole was a duo

Gravity giant with junior partner: The central black hole of our Milky Way was not always alone – it had a smaller partner for about 200 million years, as astronomers have found. This only 15,000 solar masses heavy intermediate black hole formed an unequal pair with the larger Sagittarius A*, as astronomers have determined. Only about ten million years ago the two unequal black holes merged. At the center of our Milky Way lies the four million s…