What was the primary instrumentation Hubble used, often employed in long exposures, to push the limits of detection for faint galaxies?

Wide Field Camera 3

Pushing the detection limits for ultra-distant objects required utilizing Hubble's most sensitive instruments in conjunction with extremely long observation periods. The text highlights that Hubble systematically tested these limits by relying on very long exposures and the sensitivity of specific hardware. Among the key instruments mentioned as enabling these frontier discoveries, especially those involving the stacking of redshifted light into visible wavelengths, was the Wide Field Camera 3. This instrument allowed astronomers to accumulate sufficient photons over many hours to pull the faint signals characteristic of these deep-field objects out of the pervasive background noise.