Journey Inside M104

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Almost every amateur astronomer is familiar with the Sombrero Galaxy (also known as M104 or NGC 4594) – an unbarred spiral galaxy in the constellation Virgo. We’ve seen it in both small and large telescopes, picked up its ghostly signature in binoculars and dreamed over its structure in photographs. Now, for the first time ever, Jukka Metsavainio is giving us the opportunity to visualize what it might be like to approach this amazing galaxy from space and see it in dimension. Step inside and let’s learn.

Like all our our “stereo” image produced for UT by Jukka Metsavainio, two versions are presented here. The one above is parallel vision – where you relax your eyes and when you are a certain distance from the monitor screen the two images will merge into one to produce a 3D version. The second – which appears below – is crossed vision. This is for those who have better success crossing their eyes to form a third, central image where the dimensional effect occurs. Jukka’s visualizations of what M104 would look like if we were able to see it in dimension comes from studying the object, photographing it, knowing the field star distances and the different wavelengths of light. Are you ready to “cross” the boundary? Then let’s rock…

Discovered by Pierre Mechain in 1781 and added by Charles Messier’s own hand to his personal notes on May 11, 1781, Messier Object 104 wasn’t officially added to the official catalog of Messier objects until 1921 by Camille Flammarion. Although Messier had already ended his studies, he hadn’t quite ended his fascination with the sky and when Pierre discovered this amazing galaxy, he confirmed his observation by adding his description of a “very faint nebula” to the records. On May 9, 1784 – almost three years later to the date – Sir William Herschel independently recovered the galaxy and whose notes state: “Extended [elongated]. Very bright toward the middle. 5 or 6′ long.”

By 1828, John Herschel was seeing things much differently: “There is a faint diffused oval light all about it, and I am almost positive that there is a dark interval or stratum separating the nucleus and general mass of the nebula from the light above (s of) it. Surely no illusion.” Then Emil Dreyer in 1877: “Remarkable, very bright, very large, extremely extended toward position angle 92 deg, very suddenly much brighter toward the middle where there is a nucleus.” And the results of Curtis from the same year “A remarkable, slightly curved, clear-cut dark lane runs along the entire length to the south of the nucleus; probably the finest known example of this phenomenon. There are very slight traces of spiral whorls.” But it was 1912 and Vesto M. Slipher at Lowell Observatory who was about to make the most amazing discovery of all…

During 1910, Slipher (and later Carl Wirtz) was the first to use a spectroscope to observe the radial velocities of galaxies. What Vesto noticed was that M104 appeared to be cruising away from Earth at 700 miles per second. Such an tremendous speed was an important clue that the Sombrero was really another galaxy, and that the universe was expanding in all directions – but they didn’t know that at the time. At home (within our Milky Way galaxy) noted redshifts almost always correspond to the line of sight velocities associated with the objects being observed. These observations of redshifts and blueshifts have allowed science to measure velocities by a method first designed in 1868 by British astronomer William Huggins. Redshift is also an important tool to measure the velocity of gas of interstellar clouds, the rotation of galaxies, and the actions of accretion around neutron stars and black holes.

What we know now is there’s a supermassive black hole at the center of the Sombrero… one of the most massive black holes measured in any nearby galaxies. According the the findings by a research group led by John Kormendy and using spectroscopy data from both the CFHT and the Hubble Space Telescope, the group showed that the speed of rotation of the stars within the center of the galaxy could not be maintained unless a mass 1 billion times the mass of the Sun was present at the core. No wonder the eye is drawn there! The nucleus is also a strong source of synchrotron emission – produced when high velocity electrons oscillate as they pass through regions with strong magnetic fields. Although we can’t see radio waves, the low ionization nuclear emission region (LINER) at M104’s heart may be the energy source that weakly ionizes the gas in the Sombrero Galaxy.

And what of the dark dust ring? It’s cold atomic hydrogen gas. According to infrared spectroscopic studies, it’s the primary site for star formation and not the amazing nucleus. “The brightest infrared sources in the galaxy are the nucleus and the dust ring. The spectral energy distribution of the AGN demonstrates that, while the environment around the AGN is a prominent source of mid-infrared emission, it is a relatively weak source of far-infrared emission, as had been inferred for AGNs in previous research.” Says George Bendo, “The weak nuclear 160 um emission and the negligible polycyclic aromatic hydrocarbon emission from the nucleus also implies that the nucleus is a site of only weak star formation activity and the nucleus contains relatively little cool interstellar gas needed to fuel such activity. We propose that this galaxy may be representative of a subset of low-ionization nuclear emission region galaxies that are in a quiescent AGN phase because of the lack of gas needed to fuel circumnuclear star formation and Seyfert-like AGN activity.”

Take the time to check out this beautiful galaxy yourself. You’ll find it eleven degrees west of Spica….