Lenticular galaxies are intermediate galaxies in the Hubble classification scheme between elliptical and spiral galaxies. In this article, we will explore some interesting facts about these island universes, including how they are thought to be formed.
Facts About These Evolving Galaxies
Lenticular galaxies are considered early galaxies that are still evolving in our present universe. Let us take a look at some facts abut lenticular galaxies:
- When viewed edge on, lenticulars appear shaped like a lens, hence the name.
- These galaxies do not have spiral arms and are sometimes also known as "armless spiral galaxies"
- These galaxies are disk-like galaxies similar to spiral galaxies.
- Similar to spiral galaxies, some lenticular galaxies have a bar and are known as barred lenticular galaxies. They are denoted SB0.
- These galaxies have probably used up most of their interstellar material and there is very little going on in terms of star formation.
- They may contain significant amounts of dust in their disks and the population of stars in such galaxies is generally old or aging stars, similar to elliptical galaxies.
- Elliptical galaxies and Lenticular galaxies share similar features such as spectral properties and others.
- Lenticular galaxies have a disk component as well as a bulge component. The central bulge of these galaxies helps in identifying them. If the central bulge is not very bright, it can be hard to tell the difference between a lenticular galaxy and an elliptical one.
- Lenticular galaxies were initially proposed by the famous astronomer Edwin Hubble.
- It is now known that nearly 15-20 percent of all nearby galaxies are lenticular. This makes them even more common than ellipticals.
- Some lenticulars are peculiar and can be likened to irregular galaxies. Some of the well known peculiar lenticulars of this type include NGC 4753, which has dust lanes that are irregular and NGC 128 which has an almost rectangular bulge around its center. NGC 2685 is another peculiar lenticular in the constellation Ursa Major, which is also known as a polar ring galaxy.
- Lenticulars seem to contain prominent bulges as a common feature along with nuclear bars, rings and lenses which are also frequently found in them.
- The stars within lenticulars are generally Population II stars and it is because of this that sometimes lenticulars are misclassified as ellipticals.
- Lenticular galaxies have a much brighter surface brightness when compared to other spirals.
- IC1101 is a lenticular galaxy which is considered the largest galaxy known. Another popular lenticular galaxy is the Cartwheel galaxy, located some 500 million light years away.
- The most popular theory on the origins of lenticulars is that they formed from spiral galaxies by stopping global star formation and consuming the remaining gas.
- Another theory on the formation of lenticulars is that they were formed from the merger of other spiral galaxies.
- Lenticulars are subdivided as S01, S02 and S03 when the classification is based upon dust absorption in the disk and as SB01, SB02 AND SB03 when it is based upon a central bar.
- SB01 refers to the prominence of the central bar and galaxies of this type have the least defined bar whereas SBO3 galaxies have the most prominent central bars.
- Lenticulars contain redder or older stars that are thought to be more than a billion years old.
- In lenticulars, globular clusters are more common than in comparison to similar sized ellipticals.
- Lenticulars contain little to no molecular gas which means that their is very little star formation taking place in these galaxies.
IC1101 and the Cartwheel Galaxy
IC1101 is a spectacular supergiant lenticular galaxy. It is located in the center of the Abell 2029 galaxy cluster at a distance of some 1.07 billion light years from Earth in the constellation of Serpens. IC1101 has a diameter of 5.5. million light years making it the largest galaxy known. The galaxy contains a mass of nearly 100 trillion Suns. The galaxy is 50 times the size of our own Milky Way galaxy and nearly 2000 times as massive.
Another interesting lenticular galaxy is the Cartwheel galaxy which is located 500 million light years from Earth in the constellation of Sculptor. The galaxy is not as big or massive as IC1101, but it is still slightly larger than our Milky Way galaxy (100,000 light years across) being nearly 150,000 light years across. There are plenty such fascinating lenticular galaxies. So the next time you go star gazing you will have a better idea at what these galaxies are all about. Make sure to keep your eye out for one of them!
Image Credits:WikimediaCommons/NGC 2787 by NASA and The Hubble Heritage Team (STScI/AURA)/Cartwheel Galaxy makes waves by NASA/JPL-Caltech/P. N. Appleton (SSC/Caltech)