What is a pantograph and why does the MBTA Green Line use them?

A pantograph is the flexible, angled arm on the top of the trolley that connects the train to overhead power lines.

Green Line (MBTA) - Wikipedia

They didn't tell us anything': Sudden B Branch closure leaves riders fuming on the curb - The Boston Globe

Car collides with MBTA Green Line trolley in Brookline; shuttle buses replace trains - The Boston Globe

Disabled Green Line train brings in more MBTA shuttle buses – NBC Boston

MBTA Green Line

Green Line trolley taken out of service following small fire - The Boston Globe

MBTA Green Line

Boston: Subways, Wonderland, Trams and Mattapan

Service resumes after electrical issue strikes Green Line for second day - The Boston Globe

Boston: Subways, Wonderland, Trams and Mattapan

Lego model I designed of the Green Line trains! : r/boston

Lego model I designed of the Green Line trains! : r/boston