Boomer12k wrote:Eewww....It's all Clumpy....
Is that because of mergers?
Is that because of various times of in-falling gas clumps??
Good questions. I wish I knew the answers.
I can say this, however. My gut feeling tells me that most dwarf galaxies are dwarf spheroidals, which contain no star formation whatsoever, and all their constituent stars are old. A good example of such a dwarf spheroidal is Leo 1
, which can be seen in the direction of bright star Regulus. Galaxies such as Leo 1 stopped forming stars billions of years ago.
IC 10. Photo: Bill Snyder
However, while I believe it is true that most small (and smallish) galaxies are spheroidals, it is also true that some dwarf and smallish galaxies are extremely rich in star formation. An interesting example is IC 10, a starburst galaxy which is a little-known member of the Local Group.
The apparent distance between IC 10 and the Andromeda Galaxy is about the same as the apparent distance between the Andromeda Galaxy and the Triangulum Galaxy, which suggests that IC 10 may belong to the M31 subgroup.
So in a way, IC 10 can be thought of as the other Triangulum Galaxy (although IC 10 is in Cassiopeia). Fascinatingly, IC 10 can also be regarded as the other Small Magellanic Cloud:
IC 10 is the only known starburst galaxy in the Local Group of galaxies. It has many more Wolf-Rayet stars per square kiloparsec (5.1 stars/kpc²) than the Large Magellanic Cloud (2.0 stars/kpc²) or the Small Magellanic Cloud (0.9 stars/kpc²). Although the galaxy has a luminosity similar to the SMC, it is considerably smaller. Its higher metallicity compared to the SMC suggests that star formation activity has continued for a longer time period. The evolutionary status of the Wolf-Rayet stars suggests that they all formed in a relatively short timespan.
There is nothing in the Wikipedia article to suggest that IC 10 has merged with another galaxy. My complete amateur guess is that it might have picked up a lot of gas for one reason or another, or - and this is another interesting possibility - that IC 10 may have been born with a good supply of gas, and that, for one reason or another, much of this gas remained "untouched", so that it never collapsed into the kind of molecular clouds that give birth to stars. Much of its gas may have remained "unused", until something stirred it up and made it form new stars.
http://iopscience.iop.org/1538-4357/590 ... .text.html
It has become known that dwarf irregular galaxies generally have H I gas envelopes more extended than the stellar body that is observed in the optical wavelength (e.g., Huchtmeier, Sieradakis, & Materne 1981; Hunter & Gallagher 1985). Recently, the interplay of galactic and intergalactic material around dwarf irregular galaxies has been thought to be important in their evolution (e.g., Hunter et al. 1998; Wilcots & Miller 1998).
Sometimes small galaxies that exist in apparent isolation suddenly start forming stars at a furious rate for no obvious reason. A good example is the irregular galaxy NGC 1313
. NGC 4395, at left, is a small spiral galaxy whose brightest parts are its largest emission nebulae.