The MIRI, or Mid InfraRed Instrument, was handed over to the European Space Agency at a ceremony in London Wednesday, the ESA reported from its Paris headquarters.
The James Webb telescope will be an infrared space observatory with a collecting area more than two and a half times larger than ESA's Herschel Space Observatory, the largest infrared scientific telescope so far flown to space.
MIRI will be able to penetrate thick layers of dust obscuring regions of intense star birth, will see galaxies formed near the beginning of the universe, and will study sites of new planet formation, officials said.
"The whole team is delighted that our hard work and dedication has resulted in a MIRI instrument that will meet all our scientific expectations," Gillian Wright, European Principal Investigator for MIRI, said in London. "It is wonderful to be the first to achieve this major milestone for the JWST project. We can now look forward to significant scientific discoveries when it is launched."