Messier 96

Lore & Background

M96 was discovered by French astronomer Pierre Méchain on March 20, 1781. After communicating his finding, French astronomer Charles Messier confirmed the finding four days later and added it to his catalogue of nebulous objects. Finding this object is burdensome with large binoculars; ideal minimum resolution, in a good sky, is via a telescope of 25.4 cm (10.0 in) aperture, to reveal its three-by-five-arcminute halo with a brighter core region. This complex galaxy is inclined by an angle of about 53° to the line of sight from the Earth, which is oriented at a position angle of 172°.

Messier 96 is categorized as a double-barred spiral galaxy with a small inner bulge through the core along with an outer bulge. The nucleus displays a weak level of activity of the LINER2 type. Variations in ultraviolet emission from the core suggest the presence of a supermassive black hole, with mass estimates ranging from 1.5×10⁶ to 4.8×10⁷ solar masses. Messier 96 is about the same mass and size as the Milky Way. It is a very asymmetric galaxy; its dust and gas are unevenly spread throughout its weak spiral arms, and its core is just offset from the midpoint of its extremes. Its arms are also asymmetrical, thought to have been influenced by the gravitational pull of other galaxies within its group.

Messier 96 is being studied as part of a survey of 50 nearby galaxies known as the Legacy ExtraGalactic UV Survey (LEGUS), providing an unprecedented view of star formation within the local universe. One supernova has been observed in M96: SN 1998bu (Type Ia, mag. 13), discovered by Mirko Villi on May 9, 1998. It reached maximum brightness on May 21 at about magnitude 11.6, making it the brightest supernova of 1998, then steadily faded. Observations of the ejecta a year later showed creation of 0.4 solar masses of iron, and the spectrum confirmed radioactive ⁵⁶Co, which decays into ⁵⁶Fe.

Reader's Guide

Messier 96 holds significance as the brightest member of the M96 Group, the nearest group to the Local Group that combines bright spirals and a bright elliptical galaxy (M105). Its asymmetric structure—uneven dust and gas, offset core, and asymmetrical spiral arms—provides a natural laboratory for studying galactic interactions and the gravitational influence of neighboring galaxies. The detection of a supermassive black hole candidate in its core, with mass estimates spanning an order of magnitude, underscores ongoing uncertainties in black hole mass measurements. The observation of SN 1998bu, the brightest supernova of 1998, and the subsequent confirmation of iron production from radioactive cobalt decay, offers direct insight into nucleosynthesis in Type Ia supernovae. Additionally, M96's inclusion in the LEGUS survey contributes to high-resolution studies of star formation in the local universe, making it a key object for understanding galaxy evolution and stellar birth processes.

Did You Know?

• M96 was discovered by Pierre Méchain on March 20, 1781, and confirmed by Charles Messier four days later.
• The galaxy is asymmetric, with its core offset from the midpoint of its extremes and unevenly distributed dust and gas.
• SN 1998bu, the only supernova observed in M96, reached magnitude 11.6 and was the brightest supernova of 1998.
• M96 is the brightest galaxy in the M96 Group, which includes M95 and M105 and at least nine other galaxies.