It is interesting to compare the new Webb image of M104 with an old Spitzer infrared image of the same galaxy:
Even though the JWST image is so much more detailed than the picture by Spitzer, both images reveal much the same inner structure of the Sombrero galaxy. There is a bright disk, and inside it there is a "gap" of some sort and inside that, close to the core, is another disk.
The text accompanying the Spitzer image contained this fascinating piece of into (or guesswork?):
Universe Today wrote:
“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.”
Although it might seem that the Sombrero is the result of a collision between two separate galaxies, that’s actually not thought to be the case. Such an event would have destroyed the disk structure that’s seen today; instead,
it’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.
This is one of the first galaxies to be seen with such a dual structure — even though M104 has been known about since the mid-1700s.
I find this so fascinating. Perhaps the inner disk that we can see in both the JWST and the Spitzer images is the original disk, and the dust ring surrounding it is the extra gas that fell into orbit around the galaxy, eventually forming new stars?
Speaking about forming new stars, M104 appears to be almost devoid of new stars, the way I understand it. Let me show you two (small) ultraviolet images from GALEX, one showing M104, one showing NGC 1512. Note that M104 looks "all yellow", whereas NGC 1512 contains a lot of blue stuff:
M104 in ultraviolet light.
Credit: NASA/JPL-Caltech.
This is my point. NGC 1512 is not a very blue galaxy. Its B-V index is 0.810, which is kind of red, and its U-B index is 0.170, which is "okay ultraviolet". The U-B index shows that there is indeed star formation going on in NGC 1512, and hot ultraviolet stars are present. These hot stars are detected by GALEX, and they are shown as blue in the GALEX image.
So what about M104? Well, its B-V index is 0.980, which definitely makes the Sombrero Galaxy redder than NGC 1512. More interesting, however, is the U-B index of M104. It is 0.530. This means that so few hot stars are present in M104 that star formation in this galaxy is negligible. And because there are so extremely few hot stars in M104, GALEX makes M104 look all yellow.
And finally, I can't help myself. Don't you think that M104 looks quite a bit like Saturn?
I guess that the ice particles of Saturn's rings have fallen into orbit around Saturn in much the same way that those extra gas clouds fell into orbit around what was the original version of M104. Well, that's my amateur guess, anyway!
Ann
The Sombrero Galaxy from Webb and Hubble
