Which celestial objects did Hubble precisely measure to support the accelerating expansion attributed to dark energy?

Distant Type Ia supernovae

The existence of dark energy, the mysterious force driving the accelerated expansion of the universe, was significantly strengthened by Hubble's precise photometric measurements. These measurements focused on Type Ia supernovae, which are utilized as 'standard candles' because they explode with a remarkably consistent peak luminosity. By observing how dim these supernovae appeared over vast cosmological distances, Hubble's data confirmed that the expansion of space was not decelerating under gravity as expected, but rather speeding up. This confirmation provided the observational backbone necessary to establish dark energy as a primary component of the universe's overall composition and fate.