Some space groups look like a bar.
They have a long line of stars. This line is in the middle. Our home is in one too! It is a very big place. Can you see the stars?
Some space groups have a bar in the middle.
This bar is a long line of stars. It can help make new stars. The bar pulls gas toward the center. This gas helps new stars grow.
Most spiral groups have this bar. Our own home is one too! These bars do not last forever. They can change or go away over time. They are a very cool part of space.
Some large groups of stars have a special shape.
These are called barred spiral galaxies. They have a long bar of stars in the middle. This bar can change how stars and gas move. It also changes the shape of the spiral arms. Our own home, the Milky Way, is one of these.
Scientists use the letters SB to name them. SB stands for spiral barred. Some have tight arms. We call these SBa types. Others have loose arms. We call these SBc types. Some are even a bit messy. These are SBm types.
How does a bar form? A wave of density moves from the center. This wave changes how stars orbit. This builds a bar over time. The bar acts like a nursery for stars. It pulls gas toward the center to make new stars.
These bars do not last forever. They can buckle or collapse. This makes them shorter and thicker. A bar might go away after two billion years. Then, a new bar might form again.
A barred spiral galaxy is a huge group of stars with a special shape.
Most spiral galaxies in our local universe have a central bar made of stars. These bars are found in about two thirds of all spiral galaxies. The bar is important because it changes how stars and gas move. It can even change the shape of the galaxy's spiral arms. Our own home, the Milky Way Galaxy, is a barred spiral galaxy.
How does this bar shape form in a galaxy? It starts with a density wave radiating from the center. This wave changes the paths of the inner stars. Over time, this effect reaches stars that orbit farther out. This creates a structure that keeps itself going. The bar acts like a stellar nursery, which is a place where stars are born.
It does this by channeling gas from the spiral arms toward the center. This extra gas can fuel the birth of many new stars.
Edwin Hubble was the scientist who classified these types of galaxies. He used the label "SB" to stand for spiral barred. He put them into different groups based on their arms. SBa types have arms that are tightly bound. SBc types have arms that are loosely bound. SBb types are right in the middle of those two.
There is also a type called SBm for irregular barred spirals. This includes the Magellanic Clouds, which were once called irregular galaxies.
There are many different examples of these galaxies in space. The galaxy IC 5201 was discovered by Joseph Lunt. It is located more than 40 million light-years from Earth.
Other examples include NGC 1300 and the Southern Pinwheel Galaxy. Some galaxies, like NGC 2787, are called SB0 or barred lenticular galaxies. Scientists found that only 20 percent of galaxies in the distant past had bars. Today, about 65 percent of local spiral galaxies have them.
Bars do not stay in a galaxy forever. They are thought to be temporary parts of a galaxy's life. As a bar grows, it can become too heavy and unstable. This can cause a buckling event where the bar collapses inward. This makes the bar look shorter and thicker.
A supermassive black hole in the center can help delay this. The whole cycle of forming and losing a bar might take two billion years. Because of this, bars likely keep appearing and disappearing over time.
A barred spiral galaxy is a massive system of stars with a distinct central structure. This structure is a bar-shaped formation made of stars.
These bars are quite common in our local universe. Surveys show that about two-thirds of all spiral galaxies possess them. The bar is not just a decoration. It actively influences the motion of stars and interstellar gas. It can even change the shape of the spiral arms. Our own home, the Milky Way Galaxy, is classified as a barred spiral galaxy.
The formation of a bar is a complex physical process. It is generally thought to begin with a density wave. This wave radiates outward from the center of the galaxy. As it moves, it reshapes the orbits of the inner stars. This effect gradually moves to stars orbiting farther out. This process eventually creates a self-perpetuating bar structure.
The bar acts as a type of stellar nursery. It uses orbital resonance to channel gas from the spiral arms toward the center. This influx of gas can fuel intense star birth near the galactic center. This mechanism may also explain why many barred spirals have active galactic nuclei. The Southern Pinwheel Galaxy is one such example.
Astronomers use specific categories to organize these galaxies. Edwin Hubble created the Hubble sequence to classify them. He labeled barred spiral galaxies as "SB," which stands for spiral barred. He then divided them into sub-categories based on their arm structure. SBa types have tightly bound arms. SBc types are at the opposite extreme with loosely bound arms. SBb types represent the middle ground between these two.
There is also a category called SBm. This describes somewhat irregular barred spirals. The Magellanic Clouds were once called irregular galaxies, but they are now known to have barred spiral structures.
There are several other specialized types within this classification system. An SB0 galaxy is known as a barred lenticular galaxy. An example of this is NGC 2787.
There are also more irregular versions like the SBdm type. The galaxy NGC 5398 is an example of this type. Some galaxies, like NGC 55, are classified as SBm, which is a type of Magellanic spiral. These various categories help scientists understand the different shapes and stages of galactic life.
Research shows that bars are a sign of galactic maturity. In the distant past, bars were much less common. A 2008 investigation found that only 20 percent of spiral galaxies in the early universe had bars. In contrast, about 65 percent of local spiral galaxies possess them today.
This suggests that galaxies develop bars as they grow older. However, bars are also thought to be temporary phenomena. They do not last forever in a single continuous state. The bar structure eventually decays over time. This transforms the galaxy back into a more regular spiral pattern.
As a bar accumulates mass, it can lose its stability. Once the bar reaches a certain size, the mass can compromise the entire structure. This can lead to what scientists call a "buckling" event. During buckling, a disturbance in the orbital resonances of stars causes an inward collapse. This makes the bar become both thicker and shorter.
Galaxies with high mass accumulated in their centers often have short, stubby bars. A supermassive black hole at the galactic center can suppress or delay this buckling. Despite this, the instability usually occurs eventually.
Because bars can form and then decay, they are likely recurring phenomena. A galaxy may move through an oscillating evolutionary cycle. This cycle from a regular spiral to a barred spiral takes about two billion years on average.
This means a single galaxy might develop bars multiple times throughout its history. This cycle connects the study of individual galaxy shapes to the broader evolution of the universe. It shows that even the largest structures in space are constantly changing and reshaping themselves over billions of years.
Where will your curiosity go next?
🖼️ Images & Media (24)
+ 12 more
More to explore
✨ What else?
Related topics you might enjoy
🔬 Go deeper
More advanced topics to explore
🪜 Step back
Simpler topics to build understanding
What is Nepedia?
A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.