The central bank says it expects the eurozone economy will contract by 8.7% this year
The central bank is buying an extra $132 billion in bonds
The Dow Jones was down more than 900 points early Monday afternoon
Some economists doubt how much good more stimulus will do
The central bank announced new stimulus on Thursday
The central bank also indicated it's considering a new round of bond-buying stimulus
The bank's next policy meeting is on Thursday
ECB head Mario Draghi said the bank was ready "to adjust all of its instruments'' in case of unexpected trouble
With interest rates at record lows, a downturn could make it hard to stimulate the economy
The central bank left its key interest rates unchanged this week