I have been reading recently on the quantitative easing programmes by the ECB and the BOJ, see http://www.cnbc.com/2016/04/07/what-the-bank-of-japan-boj-will-do-now-that-negative-rates-have-disappointed.html, and, http://www.bloomberg.com/news/articles/2016-04-21/ecb-to-start-buying-corporate-bonds-in-june-as-part-of-stimulus.
The ECB will be expanding its current programme to include corporate bonds and it is being suggested that the BOJ may give up on negative interest rates and possibly could buy japanese equities instead. It seems that these central banks are just working their way up the risk asset spectrum. My question is where do these asset buying programmes stop (penny stocks/distressed debt?)? Also what happens to these assets, surely if they sit on the central banks books it could go bankrupt like a commercial bank? Moreover, what could cause these asset buying programmes to be abandoned/fail?