Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard

Science - Galaxies

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Magellanic Clouds
NGC4449
Irr-I galaxy has some structure but not enough to identify it as a disk or elliptical. 
Irr-II galaxy does not have any identifiable structure.  A typical example is the galaxy NGC4449.  Credit NASA, ESA and HST. 
dI or dIrrs galaxy
dwarf irregular galaxies.   They tend to have a low level of heavier elements, and relatively high levels of gas, and are thought to be similar to the galaxies that formed early in the life of the Universe.  They may be similar to the faint blue galaxies that have been found in deep field galaxy surveys.    The nearby Large and Small Magellanic clouds are typical dwarf irregular galaxies. 
Irregular galaxies have no discernable structure, like a spiral or an elliptical galaxy has; just a fuzzy agglomeration of stars.  They do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a central bulge nor any trace of spiral arm structure. Good examples are the two dwarf galaxies comprising the Magellanic clouds around 179,000 light-years away that orbit the Milky Way.  While there are some very large irregular galaxies, they tend to be smaller usually less than 25% the size of the Milky Way.  They tend to contain many new stars, with a lot of current new star formation.  Collectively they are thought to make up about a quarter of all galaxies. Most irregular galaxies were once spiral or elliptical galaxies but were deformed by gravitational action from nearby large galaxies. Irregular galaxies may also contain abundant amounts of gas and dust.  These are the broad categories of irregular galaxy:

Irregular Galaxies