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I love imaging galaxies, especially the galactic ones like spirals and quasars. Last year, when I started astrophotography, I discovered that it was possible to photograph galaxies that were millions of light-years away! On this page, though, I want to focus on one kind of galaxy, the lenticular type of galaxy from the Hubble sequence, and help you understand why it is so important to astronomers.
A lenticular galaxy, also known as a galactic bulge, is a type of galaxy found in the Milky Way. It has a bulge in its centre and a flat disc surrounding it, lacking the spiral arms typically seen in other galaxies, such as spirals. The formation of lenticular galaxies is believed to occur when two spiral galaxies collide, according to astronomers.
As we shall see, lenticular galaxies are important to our understanding of the universe, and personally, I have always found them to be quite appealing deep-sky astrophotography targets. I have managed to image a few of these, and one example I have photographed is the Needle Galaxy.
Before we go further, in case you’re wondering, check out my guide on how you can get into astrophotography cheaply.
Let’s now look more closely at the form and importance of irregular galaxies, galactic galaxies, elliptical galaxies, and spiral galaxies.
Why are lenticular galaxies important?
Astronomers study galaxies in general to better understand the organisation and formation of matter in the universe. Galaxies represent physics working on a huge scale, whereas quantum physics is the exact opposite. If we understand how galaxies formed and organised themselves into what we see today, together with what we learn about subatomic-level physics, we can better understand how the universe works. See this article, published by Nasa, for more information about how the James Webb Telescope will try to help us understand the nature and formation of galaxies better and solve other related questions we have about the universe.
Now let’s consider lenticular galaxies specifically, which are a type of galactic structure, and what scientists can learn from them. Lenticular galaxies have a unique spiral shape and emit a distinct light that can provide valuable insights.
Lenticular galaxies are important for several reasons:
- They are the first quasi-stellar objects (QSOs) that Edwin Hubble discovered and observed in 1923. This discovery helped Hubble make the statement that we live in an expanding universe.
- Lenticular galaxies provide a unique observational perspective on how dark matter is distributed in space. There appears to be dark matter in the outer area of this type of galaxy in the form of a halo.
- The study of lenticular galaxies can help astronomers understand the process of star formation. See this article published by Phys.org for more about this.
What is a lenticular galaxy?
A lenticular galaxy is a type of galaxy that is between an elliptical and a spiral, as described in the Hubble sequence. These galaxies have a lens-like shape, hence the name ‘lenticular’, which comes from the Latin word ‘lenticula’, meaning ‘lens’.
Lenticular galaxies are unique because they share the properties of both spiral and elliptical galaxies. They have a central bulge like elliptical galaxies, and this is surrounded by a thin disc of stars and interstellar matter like spiral galaxies.
However, unlike spiral galaxies, a lenticular galaxy doesn’t have spiral arms and instead has a smooth appearance without distinctive features.
Lenticular galaxies are composed of older stars because the theory is that they are the result of a collision between two spiral galaxies.
This means that the galaxy must at least be as old as the oldest of the pair of original galaxies. More than that, we also need to add the time that was needed for the final galaxy to form after the collision. Check out my images of Markarian’s Chain, where you can see several lenticular galaxies.
Despite the above theory of how these types of galaxies are formed, there is much doubt and confusion about this question. This article by Sidney Van Den Bergh (1999) touches upon a few of these ideas.
When we observe a lenticular galaxy, we are looking at a long period of the history of star and galaxy formation. This is what makes them so important to astronomers studying them.
Lenticular galaxies are not very common, but they are more frequently found in clusters, especially in the Virgo Cluster.
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Features of Lenticular Galaxies
Lenticular galaxies are oval or elliptical, resembling a lentil.
The lenticular galaxy has an outer disc that surrounds the nucleus and an inner disc that contains young stars, dust, and a bulge. Since they are the result of two spiral galaxies colliding, lenticular galaxies have more gas and dust than other types of galaxies.
While they may appear static and unchanging, lenticular galaxies are often filled with intense stellar activity. They are known to host starburst events, which are periods of rapid star formation. These events can drastically alter the galaxy’s appearance and composition over relatively short astronomical timescales.
Another intriguing aspect of lenticular galaxies is their colour. Unlike the blue hues of spiral galaxies, which are indicative of young, hot stars, lenticular galaxies are often reddish or yellowish. This is due to the presence of older, cooler stars, suggesting that star formation in these galaxies has significantly slowed down or stopped.
The lack of star formation in a lenticular galaxy is thought to be due to the absence of cool gas within these galaxies, which is a necessary ingredient for star birth. They are a fascinating subject for astronomers studying stellar evolution and the late stages of galaxy growth.
Lenticular galaxies, like spiral galaxies, have a bright central bulge made up of stars. However, the bulges in lenticular galaxies are often more prominent and can make up a significant portion of the galaxy’s total light. These bulges are thought to be the result of the merging of two or more galaxies in the past or the gravitational influence of nearby galaxies.
Finally, lenticular galaxies are often found in dense galaxy clusters. Their location in these clusters suggests that they may have once been spiral galaxies that lost their gas and dust due to interactions with other galaxies or the hot gas present in the cluster. This process, known as ‘ram-pressure stripping’, can remove the gas from a galaxy, halting star formation and leading to the creation of a lenticular galaxy. This also makes lenticular galaxies important in understanding how galaxies develop and evolve.
Lenticular vs spiral galaxies
Lenticular galaxies and spiral galaxies are different in many ways. One of the most noticeable differences is their structure.
Spiral galaxies, as their name implies, are spiral in shape, with arms extending from a central bulge. These arms are active areas of star formation. As a result, we see blue stars, gas, and dust clouds.
Lenticular galaxies lack these spiral arms. Instead, they have a shape resembling a lens or a disc.
Lenticular galaxies contain older stars than those we see in spiral galaxies. The stars in lenticular galaxies are generally cooler and redder, indicating a lack of recent star formation.
On the other hand, spiral galaxies are known for their ongoing star formation, especially in their spiral arms, which gives them a bluer colour. This difference in star formation is often attributed to the amount of gas and dust available within the galaxy. Spiral galaxies have a lot of gas and dust, the raw materials for star formation, while lenticular galaxies have used up most of their gas and dust.
Another big difference between these two types of galaxies is the presence of a central bar structure. While both spiral and lenticular galaxies can have a bar structure, it is more common in spiral galaxies.
These central bars extend from the central bulge, around which the spiral arms wrap. In lenticular galaxies, the bar, if present, is often less obvious.
Lastly, the motion of stars within these galaxies also differs. In spiral galaxies, the stars in the arms follow neat, circular orbits around the centre. In lenticular galaxies, however, the stars follow more random, elliptical paths. This is due to the lack of a distinct spiral structure to guide the stars’ orbits.
These differences in structure, star formation, and stellar motion clearly distinguish the characteristics and visual appearance of lenticular and spiral galaxies.
Examples of Lenticular Galaxies
Lenticular galaxies, also known as spiral galaxies, are galaxies that have a disc, a bulge, and an extended halo.
Lenticular galaxies, also known as disc galaxies, may resemble elliptical galaxies at first glance. However, they possess a spiral-like bulge and disc structure, containing more stars and dust than their elliptical counterparts. While lenticular galaxies typically lack active star formation, those in close proximity to the Milky Way may exhibit star-forming activity.
The Spindle Galaxy
The Spindle Galaxy, located within the constellation of Coma Berenices, is a small bulge of stars near its centre. Discovered in 1845 by James Dunlop, this galaxy is an example of a spiral galaxy.
The Spindle Galaxy, with its disc, has been classified as a lenticular galaxy, but some astronomers argue it is a dwarf spiral galaxy with a bulge.
However, dwarf galaxies are usually smaller than the Spindle Galaxy and have a more chaotic appearance with spiral arms. The Spindle galaxy has neither of these, so it seems wrong to label it as a dwarf galaxy.
There are two main arguments for why the Spindle Galaxy may not be a lenticular galaxy: first, the disc of the galaxy lacks enough gas to form new stars, and second, it lacks an outer ring of old red stars typically found in elliptical galaxies. These factors suggest that the spiral Galaxy does not exhibit a spiral or bulge structure.
The Sombrero Galaxy
The Sombrero Galaxy, or M104 (see my photo at the beginning of this article), is classified as an elliptical galaxy, although some prefer to classify it as a spiral disc.
Many consider the Sombrero Galaxy to be a lenticular galaxy because of its structure and its appearance. It does have a lens-like appearance as we view it from the side. In truth, the Sombrero Galaxy could be considered to be either an elliptical or spiral galaxy.
The large bulge at the centre of this galaxy suggests that the stars are quite old. In conclusion, the Spindle Galaxy’s distinct lens-like appearance, bright central bulge, and lack of spiral arms all contribute to its classification as a lenticular galaxy rather than a dwarf spiral galaxy. and it also has a disc shape. These two features are typical of lenticular galaxies.
NGC 6861
Copyright: NASA/ESA Hubble Space Telescope
How to find lenticular galaxies
We can find lenticular galaxies by using a telescope to look for them. A good-quality telescope is needed because they cannot be seen with the naked eye.
Below is an example of a good telescope that is great for galaxies and has a large aperture:
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You’ll have to point your telescope towards areas in the sky where there are large clusters of galaxies. How do you find these? Try using a star map or an astronomy app.
Another way to find lenticular galaxies is to look up the coordinates of the lenticular galaxy you are looking for and then use either a manual method or plate solving to point your telescope at the correct place in the night sky.
If you are trying to observe a lenticular galaxy in a telescope, this can be difficult because they are usually very faint due to their apparent size and distance from us.
Try to go to a dark site away from light pollution. You will also need to allow your eyes to adjust to low light levels before you can see them in your telescope eyepiece. This is challenging, and the bigger the telescope you have, the easier it will be to spot them.
Finding lenticular galaxies will become easier with practice as you improve your skills at observation and your skills with the equipment you have.
Lenticular Galaxies and How They Are Shaping the Future of the Universe
Lenticular galaxies are unique for their disk-like shape, distinct from spiral or elliptical shapes. They host two supermassive black holes, which, as they orbit each other, can cause gravitational waves and produce bright bursts of light. These galaxies have a bulge.
Lenticular galaxies, with their spiral and disc shapes, are shaping the future of the universe as we know it.
How Did Lenticular Galaxies Come to Be?
Lenticular galaxies, with their striking spiral or disc shapes, are a rare celestial spectacle in the universe. So how did these galaxies come about?
The prevalent theory is that collisions between two or more galaxies are what create lenticular galaxies. The collision causes the gas and stars to accumulate in one area, producing a disc shape. These discs are usually seen when looking at them from one side, but if you view them from the other side, it looks like a spiral galaxy.
Conclusion
Lenticular galaxies, including spiral ones, are crucial for comprehending the universe as they provide insights into its history.
Firstly, they appear to be relatively rare; there are only about 25 known lenticular galaxies in the entire universe. Secondly, these galaxies contain some of the oldest stars in the universe. Thirdly, they can provide insight into how gas is distributed in the galaxy. Personally, one of the favourites that I’ve been able to photograph is the Sombrero Galaxy, which looks like a giant UFO! If you want to photograph galaxies, you will need to buy a good-quality telescope, but how much should you pay? Find out how much different telescopes cost here.
