Messier Objects in Leo

Leo contains five Messier objects. All five are galaxies that lie in the region between the constellation’s brightest stars, Regulus and Denebola. They are:

Messier 65
Messier 66
Messier 95
Messier 96
Messier 105

Four of these objects – M65, M66, M95, and M96 – are spiral galaxies, while M105 is an elliptical galaxy. The five galaxies are divided between two groups: the Leo Triplet (the M66 Group) and the Leo I Group (the M96 Group). The two groups may be parts of a larger galaxy group. It has also been suggested that the M66 Group is part of the larger M96 Group.

As the name suggests, the Leo Triplet is a small group consisting of three interacting galaxies: Messier 65, Messier 66 and NGC 3628. The galaxies appear in the same field of view. With apparent magnitudes of 10.25, 8.9, and 10.2, they can be seen in small telescopes, but only appear as patches of light. The galaxies’ spiral arms are visible in 10-inch and larger telescopes.

The Leo Triplet and the Leo I Group, image: Wikisky

Messier 65 and Messier 66 are intermediate spirals with apparent sizes of 8.709 by 2.454 arcminutes and 9.1 by 4.2 arcminutes. NGC 3628, also known as Sarah’s Galaxy or the Hamburger Galaxy, is the longest of the three, appearing edge-on, with an apparent size of 15 by 3.6 arcminutes. It is classified as an unbarred spiral galaxy, but it has been suggested that it may be a barred spiral with the bar appearing end-on. Messier 65 and NGC 3628 lie approximately 35 million light years away, while Messier 66 is a little closer to us, at 31 million light years.

Leo Triplet, image: Wikimedia Commons/Marekmazuch (CC BY-SA 4.0)

The Leo Triplet is easy to find because it lies at the intersection of the imaginary lines connecting Denebola and Regulus and Chertan (Theta Leonis) and Iota Leonis. Theta and Iota Leonis have apparent magnitudes of 3.324 and 4.00, which makes them visible to the naked eye, but challenging to see from light-polluted areas.

The Leo I Group contains Messier 95, Messier 96, Messier 105 and at least five other members, including NGC 3377, NGC 3384, and NGC 3489. The group lies at a distance of about 37 million light years. It can be found about a third of the way from Regulus to Denebola.

Messier 95 is a barred spiral galaxy with an apparent magnitude of 11.4 and an apparent size of 3.1 by 2.9 arcminutes. It lies 32.6 million light years away.

Messier 95, image: Adam Block/Mount Lemmon SkyCenter/University of Arizona (CC BY-SA 4.0)

Messier 96 appears brighter and larger, with an apparent magnitude of 10.1 and an apparent size of 7.6 by 5.2 arcminutes. It is also closer to us than M95, at a distance of 31 million light years. It is classified as an intermediate spiral galaxy.

This NASA/ESA Hubble Space Telescope image shows Messier 96, a spiral galaxy just over 35 million light-years away in the constellation of Leo (The Lion). It is of about the same mass and size as the Milky Way. It was first discovered by astronomer Pierre Méchain in 1781, and added to Charles Messier’s famous catalogue of astronomical objects just four days later. The galaxy resembles a giant maelstrom of glowing gas, rippled with dark dust that swirls inwards towards the nucleus. Messier 96 is a very asymmetric galaxy; its dust and gas are unevenly spread throughout its weak spiral arms, and its core is not exactly at the galactic center. Its arms are also asymmetrical, thought to have been influenced by the gravitational pull of other galaxies within the same group as Messier 96. This group, named the M96 Group, also includes the bright galaxies Messier 105 and Messier 95, as well as a number of smaller and fainter galaxies. It is the nearest group containing both bright spirals and a bright elliptical galaxy (Messier 105). Image credit: ESA/Hubble & NASA and the LEGUS Team, Acknowledgement: R. Gendler

Messier 105 is an elliptical galaxy with an apparent magnitude of 10.2 and an apparent size of 5.4 by 4.8 arcminutes. It lies 36.6 million light years away. Like all elliptical galaxies, M105 appears as a featureless ball of light, even in the largest of telescopes. It is interacting with its elliptical neighbour NGC 3384 and the spiral galaxy NGC 3389. NGC 3384 has an apparent magnitude of 10.9 and NGC 3389 is fainter at magnitude 11.80. The three galaxies can be seen in the same field of view of a 10-inch telescope.

It might appear featureless and unexciting at first glance, but NASA/ESA Hubble Space Telescope observations of this elliptical galaxy — known as Messier 105 — show that the stars near the galaxy’s centre are moving very rapidly. Astronomers have concluded that these stars are zooming around a supermassive black hole with an estimated mass of 200 million Suns! This black hole releases huge amounts of energy as it consumes matter falling into it and causing the centre to shine far brighter than its surroundings. This system is known as an active galactic nucleus. Hubble also surprised astronomers by revealing a few young stars and clusters in Messer 105, which was thought to be a “dead” galaxy incapable of star formation. Messier 105 is now thought to form roughly one Sun-like star every 10 000 years. Star-forming activity has also been spotted in a vast ring of hydrogen gas encircling both Messier 105 and its closest neighbour, the lenticular galaxy NGC 3384. Image: ESA/Hubble & NASA, C. Sarazin et al.

The best time of year to observe the deep sky objects in Leo is during the month of April, when the constellation rises high in the evening sky.