William Atkins
Wednesday, 13 January 2010 22:15
Science -
Space
Page 1 of 3
The evolution of galaxies has taken a diverse road over 13.7 billion years or so. Their shapes were classified by U.S. astronomer Edwin Hubble in the 1930s. Now, in the 2010s, two U.S. physicists have finally, for the first time, explained in detail how and why those shapes came to be.
The Hubble Sequence, as it came to be known, is a classification of galaxies that was developed by Edwin Hubble in the 1930s.
Read more about the Hubble Sequence at the Department of Physics and Astronomy’s (University of Alabama) website “
Galaxy Classification.”
Galaxies are collections of stars, planets, gas, dust, and other galactic components that make up most of the visible part of the Universe.
The smallest galaxies only have a few million stars, while the largest ones have as many as one trillion stars (that’s one million million stars).
Hubble classified galaxies, in what is also called the
Tuning Fork diagram, in three primary shapes: spirals, barred spirals, and ellipticals.
Spiral galaxies consist of material from stars, gas, and dust in arms that spread out in a flat, rotating disk (of mostly young stars and interstellar matter) from a central concentration of stars (mostly older stars) known as the bulge.
The
Whirlpool Galaxy is one example of a spiral galaxy.
The second type of galaxy is the barred spiral.
Barred spiral galaxies has material that does the same thing as spiral galaxies (spread out in arms in a disk) but their central bulge is much larger (than those in spiral galaxies) and it is shaped like a bar (and hence its name).
Barred spirals (SB) are further sub-classified as SBa (tightly bound arms), SBb (in-between tightly and loosely bound arms), SBc (loosely bound arms), and SBm (irregularly shaped barred spirals).
Our home galaxy, the
Milky Way Galaxy, is an example of a barred spiral galaxy.
Page two continues with the last type of galaxy, along with information on the discovery by these two U.S. scientists.
