Galaxies are formations that have fascinated astronomers for years. What has modern science let us learn about them? In this article, we will summarize what galaxies are, what types of galaxies exist and the most interesting examples.
What are galaxies?
The galaxy is a large object composed of gravitationally bound stars, clouds of dust and interstellar gas, as well as planets and dark matter. They all orbit around one common center of mass, known as the galaxy’s nucleus, most often taking the form of a black hole. Galaxies were formed by the merging of stars and other objects into larger and larger clusters over the years. A typical formation of this type ranges in diameter from tens to about 200,000 light years.
Galaxy observations were already carried out by ancient astronomers, but modern technology has greatly improved the process of finding answers to questions troubling humanity, and we are slowly starting to discover such properties of objects located many light-years from Earth, which until recently were purely speculative. We do not know the exact number of galaxies in space, but some researchers estimate it to be around 200 billion.
Not only spiral galaxies. What types of galaxies have been observed in the universe?
Close your eyes and imagine a galaxy. What do you see? Probably this object takes the form of a spiral galaxy in your thoughts, that is, one with curved arms arranged in the shape of a spiral converging to the center. While such a picture is perfectly valid and we can discover many such formations in the night sky, it is not the only form that these unusual structures can take. The morphological classification of these objects developed by astronomer Edwin Hubble in 1936 is used to determine what type of galaxy it is.
Barred spiral galaxies (labeled Sb)
Their structure differentiates them from typical spiral galaxies (labeled S) in that their arms appear to extend from a horizontal bar through the galactic center. These elements of the structure, however, follow a visible direction and can be distinguished from other parts of the formation. The most famous objects of this type include the Milky Way. The galaxy’s core is made up of the oldest stars, while much younger objects can be found in the arms of the system. 50% of the observed galaxies are of the spiral type, most often consisting of two or three arms.
Elliptical galaxies (marked E)
Real dinosaurs in the world of galaxies – elliptical formations are made of stars that have existed in the universe for a very long time. They have regular shapes, most often spheres or ellipses, do not have any unusual structures, and the even distribution of stars on the edges makes it difficult for observers to determine a rigid boundary of an elliptical galaxy.
Lenticular galaxies (marked s0)
The intermediate link between a spiral and an elliptical galaxy, resembles a lens in shape. The core of such a galaxy appears to resemble a flattened version of the core at the center of an elliptical system. Unlike these structures, however, lenticular galaxies lack interstellar material.
Irregular galaxies (designation Irr)
Among the structures of irregular galaxies, it is often in vain to look for symmetry or clear clustering around the nucleus. The stars in this formation appear to be distributed freely and randomly, and the structures themselves are most often relatively small and very bright. Irregular galaxies often consist only of young objects, and thanks to their abundance in gas and dust clouds, they are often the source of star-forming processes.
The mysterious hearts of stellar aggregates – is the black hole the center of the galaxy?
What do stars clustered within galaxies orbit around? Scientists have long wondered what could have such a mass as to attract so many distant objects to it. Eventually, the suspicion fell on the presence in the core of a supermassive black hole – a difficult-to-observe object with a mass of millions or even billions of solar masses, which irretrievably absorbs light, waves and matter. It is now suspected that such a supermassive black hole may lie at the heart of the vast majority or even of every galaxy. An object of this type can be a source of cyclic jets of matter that are capable of traversing the system at great speed and traveling beyond the limits of the disk.
Superclusters of galaxies – what are they?
Clusters of many distinct groups and clusters of galaxies are called supergalaxies or superclusters of galaxies. These structures can be enormous, sometimes exceeding hundreds of millions of light years. Although the galaxies in such a cluster are often located very far apart, astronomers observe that the elements of the formation influence each other. And not only at each other – massive superclusters can attract objects located outside their boundaries at high speed. The Milky Way and the nearby Andromeda galaxy are also located in the supercluster, a huge cluster called Laniakea, which has about 100,000 galaxies at its center.
The Milky Way – our place in the universe
The Milky Way is our galaxy – ours, because the Solar System is among the elements of this cluster. Its stars can be easily seen in the night sky, and in conditions of low light pollution, it can even be seen as a clear and bright belt in the sky. It is worth remembering that observing the Milky Way from Earth is an observation from the inside of the disk, so we will not see the arms or other structures of the galaxy in its full glory. It belongs to the barred spiral galaxy type, and its mass is approximately10-12 of the Sun. As static as it might seem, the Milky Way is in constant motion – it is racing through space at a speed of over 2 million kilometers per hour.
Why is this happening? In this case, it is primarily a cluster of galaxies located 250 light-years from Earth, known as the Great Attractor. It is a specific area of gravitational disturbance in the Universe. Its gravitational impact is so great that it constantly attracts even the most distant fragments of the Local Supercluster. The Andromeda galaxy is also rushing towards the Milky Way, and in the distant future, both of these formations are to merge with each other as a result of a collision. The beginnings of the collisions of objects have already been observed on the basis of the interpenetration of the Andromeda halo and our galaxy. The Milky Way is also facing a collision with the dwarf SagDEG formation – but it won’t happen until 10 million years from now.
The most interesting galaxies apart from the Milky Way
The stars visible in the night sky with the naked eye are usually part of the Milky Way. However, this is only a fraction of what astronomers can see when looking beyond our home galaxy using specialized equipment. Many thousands of galaxies are behind other huge objects or are difficult to observe because of the great distance from our cluster. See fun facts about the most interesting galaxies.
W2246-0526 – What do we know about the brightest galaxy observed?
The galaxy W2246-0526 is more than 12 billion light years from the Sun. At its heart there is a huge black hole with a mass of 4 billion times that of the sun. It absorbs successive masses of stars at great speed, while emitting powerful beams of energy. This galaxy is also the most distant formation known to mankind, whose strongly active black hole also draws other elements of the cluster in its direction. As reported by NASA, W2246-0526 is being eaten by this object along with three other galaxies.
GN-z11 – double record holder
This galaxy is considered both the most distant (13.4 billion light years from Earth) and the oldest object in the observable part of the universe. It is credited with emerging no later than 400 million years after the Big Bang, which means that the galaxy was formed at a time when the universe was less than 3% of its present age. The discovery of this formation caused quite a stir among astronomers – they did not think that an object formed so early could contain so many stars.
IC 1011 – what is known about the giant galaxy?
IC 1011 is currently the largest galaxy known to mankind. It is elliptical in type, about 6 million light-years in diameter, and located 349.5 light-years from Earth. According to NASA estimates, the visible star formation in IC 1011 is very faint. This means that if it does not merge with other, younger galaxies as a result of the collision, it will gradually decrease in diameter as the age-old stars present there die.
NASA and other space agencies meticulously study galaxies and the processes behind their formation. Thanks to the knowledge they provide, we can not only be aware of what lies beyond the Milky Way, but also answer questions about the origins of the universe with even greater precision.