Which 2009-launched ESA telescope studies black holes at far-infrared wavelengths?

The ESA telescope launched in 2009 that studied black holes and other objects at far-infrared wavelengths was the Herschel Space Observatory.

Herschel launched aboard an Ariane 5 rocket on 14 May 2009 and operated until 2013. Its 3.5-metre mirror and instruments covered wavelengths from about 55 to 672 micrometres, spanning the far-infrared and submillimetre regions of the spectrum.

Rather than observing black holes mainly through visible light, Herschel examined the cold dust and gas surrounding active galactic nuclei, star-forming regions and other energetic systems. Dust absorbs shorter-wavelength light and re-emits that energy in the infrared, making this range especially useful for studying obscured environments.

The observatory was originally called FIRST, short for Far Infrared and Sub-millimetre Telescope, before being renamed Herschel after astronomers William and Caroline Herschel. Planck launched with Herschel but primarily mapped the cosmic microwave background, while Gaia specializes in stellar positions and motions.