Messier 105 — Galaxy in Leo

M105 is an elliptical galaxy in the constellation Leo, located approximately 32.0 million light-years from Earth. Classified as type E1, it appears almost perfectly round with only a very slight elongation. M105 is the brightest elliptical galaxy in the Leo I group (M96 group) and lies close to M95 and M96 in the sky. Like most giant elliptical galaxies, M105 is composed primarily of old, yellow-red stars with little ongoing star formation. However, Hubble Space Telescope observations have revealed a small disk of young blue stars and gas near its center, as well as evidence for a central supermassive black hole of approximately 200 million solar masses. The galaxy spans about 55,000 light-years in diameter.

Located in Leo, just 48 arcminutes north-northeast of M96 and about 8 arcminutes from the fainter galaxy NGC 3384. At magnitude 9.3, M105 appears as a round, bright, concentrated glow in a 4-inch telescope — almost star-like at low power. An 8-inch telescope at moderate magnification shows the diffuse outer halo falling off gradually from the bright core. The companion galaxy NGC 3384 is visible in the same eyepiece field, forming a visual pair. All three Leo I galaxies — M95, M96, and M105 — can be seen within a 1-degree field. Best observed from February through May when Leo is high in the evening sky.

Discovered by Pierre Mechain on March 24, 1781, but not included in Messier's original 1781 catalog. It was added as M105 by Helen Sawyer Hogg in 1947, based on Mechain's description in a letter to Bernoulli. For many years, some astronomers identified M105 with NGC 3379. Hubble Space Telescope observations in the 1990s confirmed the presence of a 200-million-solar-mass black hole at its center by measuring the rapid orbital velocities of stars near the nucleus.