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Way out in the direction of the constellation Virgo, some 31 million light-years from Earth, astronomers have found a most unlikely looking galaxy that is hiding a supermassive black hole at its heart. Its technical name is M104, but most people refer to it by its nickname: the "Sombrero Galaxy". Through a small telescope, this distant stellar city does look a bit like a big Mexican hat. The Sombrero is incredibly massive, containing the equivalent of 800 million times the mass of the Sun, plus a collection of globular clusters, and a broad ring of gas and dust. Not only is this galaxy huge, but it's also speeding away from us at a rate of a thousand kilometers per second (about 621 miles per second). That's very fast!
What is That Galaxy?
At first, astronomers thought the Sombrero might be an elliptical-type galaxy with another flat galaxy embedded within it. This is because it did look more elliptical than flat. However, a closer look revealed that the puffy shape is caused by a spherical halo of stars around the central area. It also has that huge dust lane that contains star birth regions. So, it's most likely a very tightly wound spiral galaxy, the same type of galaxy as the Milky Way. How did it get that way? There's a good chance that multiple collisions with other galaxies (and a merger or two), have changed what may have been a spiral galaxy into a more complex galactic beast. Observations with the Hubble Space Telescope and the Spitzer Space Telescope have revealed a lot of detail in this object, and there's a lot more to learn!
Checking Out the Dust Ring
The dust ring that sits out in the "brim" of the Sombrero is very intriguing. It glows in infrared light and contains most of the star-forming material of the galaxy - such materials as hydrogen gas and dust. It completely encircles the central core of the galaxy and appears pretty wide. When astronomers looked at the ring with the Spitzer Space Telescope, it appeared very bright in infrared light. That's a good indication that the ring is the central star birth region of the galaxy.
What's Hiding in the Nucleus of the Sombrero?
Many galaxies have supermassive black holes at their hearts, and the Sombrero is no exception. Its black hole has more than a billion times the mass of the Sun, all packed away into a tiny region. It appears to be an active black hole, eating up material that happens to cross its path. The region around the black hole emits a tremendous amount of x-ray and radio waves. The region extending out from the core does emit some weak infrared radiation, which could be traced back to heating activity fostered by the presence of the black hole. Interestingly, the core of the galaxy does appear to have a number of globular clusters swarming around in tight orbits. There may be as many as 2,000 of these very old groupings of stars orbiting the core and may be related in some way to the very large size of the galactic bulge that houses the black hole.
Where is the Sombrero?
While astronomers know the general location of the Sombrero Galaxy, its exact distance was only recently determined. It seems to be about around 31 million light-years away. It does not travel the universe by itself but does appear to have a dwarf galaxy companion. Astronomers are not quite sure if the Sombrero is actually part of a grouping of galaxies called the Virgo Cluster or maybe a member of a smaller associated group of galaxies.
Want to Observe the Sombrero?
The Sombrero Galaxy is a favorite target for amateur stargazers. It takes a little doing to find it, and it does require a good backyard-type scope to view this galaxy. A good star chart shows where the galaxy is (in the constellation Virgo), halfway between Virgo's star Spica and the tiny constellation of Corvus the Crow. Practice star-hopping to the galaxy and then settle in for a good long look! And, you'll be following in a long line of amateurs who have checked out the Sombrero. It was discovered by an amateur in the 1700s, a guy by the name of Charles Messier, who compiled a list of "faint, fuzzy objects" that we now know are clusters, nebulae, and galaxies.