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Previously discovered dwarf satellite galaxies (in blue) and the newly discovered candidates (in red)  (Yao-Yuan Mao, Ralf Kaehler, Risa Wechsler (KIPAC/SLAC))

Previously discovered dwarf satellite galaxies (in blue) and the newly discovered candidates (in red) (Yao-Yuan Mao, Ralf Kaehler, Risa Wechsler (KIPAC/SLAC))

We have some new galactic neighbors! Well, actually maybe “new” is not the right term: they have been there for a long time but we only just now noticed. Astronomers are reporting the discovery of nine dwarf satellite galaxies orbiting the Milky Way like remoras stuck to a cosmic shark. These nine miniature galaxies are additional to the well-known Large and Small Magellanic Clouds—two dwarf galaxies which are located right next to the Milky Way (being respectively 160,000 and 200,000 light years away).

The new dwarf galaxies were discovered by a team of astronomers poring over data recovered from the Dark Energy Survey (a super-high resolution digital array which is part of the Victor M Blanco telescope in the Andes). The closest is a mere 97,000 light years from the Milky Way whereas the farthest lies 1.2 million light years away from us. The dwarf galaxies are a billion times fainter than the Milky Way. They are made up of millions (or hundreds of millions or even billions) of stars but are insignificant in size compared to the hundreds of billions of stars which constitute a true galaxy. Scientists believe that there are hundreds of similar miniature galaxies and pseudo-galaxies near the Milky Way, but they are dark and difficult to find (comparitively speaking).

The Large and Small Magellanic Clouds, near which the satellites were found. (image from European Southern Observatory)

The Large and Small Magellanic Clouds, near which the satellites were found. (image from European Southern Observatory)

I have been saying “dwarf galaxies” because I like the way it sounds (like the new galaxies live together in the woods in a little hut and work in the mines!), but actually only three of the new companions are definitely dwarf galaxies. The remaining six structures may be dwarf galaxies or they may merely be globular clusters—a far less euphonic phrase which indicates a group of stars which orbits a galactic core as a satellite. Unlike globular clusters, dwarf galaxies are held together by the gravitational mass of large quantities of dark matter (um, assuming it actually exists). Indeed dwarf galaxies seem to contain far greater quantities of dark matter than actual galaxies. This makes the newly discovered galactic neighbors a potentially useful focus for studying the properties of dark matter and refining our model of the universe.

A Composite Image of M104--The Sombrero Galaxy--taken from the Hubble Space Teelscope in Summer of 2003

A Composite Image of M104–The Sombrero Galaxy–taken from the Hubble Space Teelscope in Summer of 2003 (click on the image for a full-sized version)

Today I am posting some pictures of what I think is the most beautiful deep space object.  The Sombrero Galaxy (M104) is a nearby galaxy which is visible edge-on in the constellation of Virgo.  Actually, calling it an object might be a bit misleading since M104 consists of more than 400 billion stars–not to mention numerous associated globular clusters, innumerable planets, immense clouds of gas & gas, and a supermassive black hole which lies in the center.  The black hole in the center of M104 isn’t a mild mannered & quiescent black hole like the one in the center of the Milky Way either.  Based on the speed of revolution of the stars near the middle of M104, astronomers calculate that the central black hole has a billion times the mass of the sun.

An Infrared false-color image of the Sombrero Galaxy

An Infrared false-color image of the Sombrero Galaxy

In cosmic terms, the Sombrero galaxy is nearby—which is to say it is merely 28-odd million light years away.  The galaxy was discovered in the late eighteenth century by Pierre Méchain . Other prominent 18th century astronomers subsequently observed and studied M104, including Charles Messier (which is the reason the galaxy is included in the “Messier” catalog and has a M-designation) and the redoubtable William Herschel who noted a “dark-stratum” bounding the luminous central bulge.  We now know that this ring around M104 is a toroid dust lane of vast proportions which halos the galaxy.   Astronomers initially thought that the Sombrero Galaxy was an unbarred spiral galaxy, but thanks to observations from NASA’s Spitzer space telescope (an infrared scope orbiting Earth), the scientific community has revised their estimation of its size upward.  It lies somewhere between a spiral galaxy and an elliptical galaxy.   In other words, when you look at the Sombrero Galaxy, you are looking at something vast beyond human comprehension—a galaxy bigger than our own filled with who knows what things we will never know.  And yet if you expand the Hubble photo at the top of this post, you will see that all of the little stars shining around M104 are other galaxies farther away.

Olé!

Olé!

 

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