While today's (repeat) APOD gives a fascinating 3D insight into the inner workings of the Sombrero galaxy, two other pictures may shed further enlightenment on this iconic "island universe".
The Sombrero Galaxy. R. Kennicut et al, NASA
The Sombrero Galaxy. JPL/NASA
In the picture at left, today's APOD, we mostly see the contrast between the stars and the dust of M104. In the picture at right, we can more easily see structures in the distribution of stars. At right, the relatively bright (light blue) flat inner disk entirely made up of stars is quite obvious. It is clearly set off from the fainter, spherical halo of stars.
It has been argued that the Sombrero galaxy is two galaxies in one!
And it is the red ring of dust and stars that is "the other galaxy".
(Or possibly it is the inner disk that is "the other galaxy". Don't ask me about the halo.)
Jason Major of Universe Today
Spitzer discerned that the flat disk within the galaxy is made up of two sections — an inner disk composed almost entirely of stars with no dust, and an outer ring containing both dust and stars.
“The Sombrero is more complex than previously thought,” said Dimitri Gadotti of the European Southern Observatory in Chile and lead author of the report. “The only way to understand all we know about this galaxy is to think of it as two galaxies, one inside the other
(I)t's thought that the Sombrero accumulated a lot of extra gas billions of years ago when the Universe was populated with large clouds of gas and dust. The extra gas fell into orbit around the galaxy, eventually spinning into a flattened disk and forming new stars
The vigorously starforming days of M104 are long over. There exists an ultraviolet GALEX image of M104, which shows that M104 is virtually "all yellow and no blue", meaning that there are extremely few young ultraviolet-bright stars in this galaxy.
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