Messier 96 – the NGC 3368 Spiral Galaxy

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the barred spiral galaxy known as Messier 95!

During the 18th century, famed French astronomer Charles Messier noticed the presence of several “nebulous objects” while surveying the night sky. Originally mistaking these objects for comets, he began to catalog them so that others would not make the same mistake. Today, the resulting list (known as the Messier Catalog) includes over 100 objects and is one of the most influential catalogs of Deep Space Objects.

One of these objects is Messier 96 (M96, NGC 3368), an intermediate double-sparred spiral galaxy located about 31 million light-years away in the constellation Leo. This galaxy is known for having a small inner bulge through the core, an outer bulge, and is comparable in size to the Milky Way. M96 is the brightest member of the Leo I group of galaxies (which includes M95, M105, and a number of fainter galaxies), hence why it’s also known as the M96 group.

What You Are Looking At:

The M96 galaxy measures an estimated 66,000 light-years in diameter and is about 31 million light-years from Earth, placing the center of the M96 group about 35 million light-years away. As a small group, it’s got some very interesting things going for it. As Kim Pederson (Danish Space Science Institute, University of Copenhagen) said in a 2000 study:

“The nearby (D = 11 Mpc) sparse group of galaxies, Leo-I, is in many respects unique. It is the nearest group containing both bright spirals (M96 and M95) and a bright elliptical (M105). A giant (diameter ca. 200 kpc) intergalactic Hi ring orbits the central M105/NGC3384 galaxy pair and appears to interact with M96. If M96 is really in the group core, the Leo-I group provides an unusually ‘clean’ route to determining the Hubble constant.

“In our 22 ksec ASCA SIS exposure of M96 we have detected diffuse X-ray emission extending more than 10 arcminutes North of M96, in the direction of the Hi ring. The morphology and spectral characteristics of the diffuse emission shows that M96 has recently interacted with the Hi ring, indicating that M96, the Hi ring and the central galaxy M105 are at the same distance within a few percent.”

The M96 Group of galaxies in the heart of the constellation LEO. Credit: Wikisky

History of Observation:

This classy galaxy was first discovered by Pierre Mechain in 1781 and cataloged by Charles Messier 4 days later on March 24, 1781. As Messier wrote in his notes: “Nebula without star, in the Lion [Leo], near the preceding [No. 95]: this one is less distinct, both are on the same parallel of Regulus: they resemble the two nebulae in the Virgin [Virgo], Nos. 84 and 86. M. Mechain saw them both on March 20, 1781.”

On March 11, 1784, Sir William Herschel would also make note of it: “A fine, bright nebula, much like the former [M95], but the brightest part in the middle is more joined to the nebulosity than in the former, and the bright part is rather longer, tho’ not quite so vivid as in the former. It may still be called cometic, tho’ it begins to depart a little from that kind.”

Locating Messier 96:

M96 is the southernmost galaxy in the M96 group of galaxies, which includes M95. With good sky conditions, both M95 and M96 are easy to locate in the belly of the constellation of Leo. Begin by identifying Alpha (Regulus), the brightest, southernmost star in the backward-question-mark asterism. Now, look about a fist-width west where you will see the shallow triangle asterism which marks Leo’s hips. The westernmost of these stars (Theta) is your next marker.

Look between the two markers for a faint star in an almost central position. If the skies are right to see this galactic pair, you will also see another star just south of your last marker. M95 and M96 are between these last two stars, and it is the northernmost and brighter of the two. The pair can just barely be seen in larger binoculars and although they are faint, perceivable in a small telescope. A larger aperture will bring out far more details.

Messier 95 and Messier 96 in visible light. Credit: Messier Objects/Scott Anttila

Because these are fainter galaxies, they require a dark sky location and cannot be seen when there’s a background glow, such as what happens on moonlit nights. Of course, having a supernova event occur is also a big drawing card! In 1999, Saurabh W. Jha (et al.) observed such an event and reported the following in their study:

“We present optical and near-infrared photometry and spectroscopy of the type Ia SN 1998bu in the Leo I Group galaxy M96 (NGC 3368). The data set consists of 356 photometric measurements and 29 spectra of SN 1998bu between UT 1998 May 11 and July 15. The well-sampled light curve indicates the supernova reached maximum light in B on UT 1998 May 19.3 (JD 2450952.8 +/- 0.8) with B = 12.22 +/- 0.03 and V = 11.88 +/- 0.02.

“Application of a revised version of the Multicolor Light Curve Shape (MLCS) method yields an extinction toward the supernova of A_V = 0.94 +/- 0.15 mag, and indicates the supernova was of average luminosity compared to other normal type Ia supernovae.” says S. Jha (et al). “Using the HST Cepheid distance modulus to M96 (Tanvir et al. 1995) and the MLCS fit parameters for the supernova, we derive an extinction-corrected absolute magnitude for SN 1998bu at maximum, M_V = -19.42 +/- 0.22.

“Our independent results for this supernova are consistent with those of Suntzeff et al. (1999). Combining SN 1998bu with three other well-observed local calibrators and 42 supernovae in the Hubble flow yields a Hubble constant, H_0 = 64^{+8}_{-6} km/s/Mpc, where the error estimate incorporates possible sources of systematic uncertainty including the calibration of the Cepheid period-luminosity relation, the metallicity dependence of the Cepheid distance scale, and the distance to the LMC.”

Messier 95 and 96 location. Credit: Messier Objects/Roberto Mura

Before we leave, let’s take a look at just one more aspect of what happens to galaxies that come in groups. That’s right… interaction! According to a 1989 study led by Stephen Schneider:

“The M96 group is examined at 21 cm to study the galaxies’ neutral hydrogen content and to search for evidence of interactions that might help explain the origin of the large intergalactic H I feature found there. M96, an Sab spiral, has 90 percent of its H I concentrated outside of the central bright optical disk – possibly captured intergalactic gas. The ringlike distribution of the intergalactic gas may be shaped by interactions with M96.

“An extremely faint dwarf irregular galaxy was also found. Questions about the distance and membership of the M96 group are addressed. It is shown that many previous group catalogs must be in error. A mass-to-light ratio of less than 30 is found for the M96 group. A number of previous estimates are inflated by inclusion of background galaxies.”

Enjoy your galaxy-gazing! And here are the quick facts to help you get started:

Object Name: Messier 96
Alternative Designations: M96, NGC 3368
Object Type: Type Sa Spiral Galaxy
Constellation: Leo
Right Ascension: 10 : 46.8 (h:m)
Declination: +11 : 49 (deg:m)
Distance: 31 million (Mly)
Visual Brightness: 9.2 (mag)
Apparent Dimension: 6×4 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database and NASA’s Hubble Messier Catalog.

Sources:

Tammy Plotner

Tammy was a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status. (Tammy passed away in early 2015... she will be missed)

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