Instead, the observations appear to be the first direct proof of dark matter. Compared to stars, galaxies are relatively close to one another. They interact and even collide. However, gravitational interactions between colliding galaxies could create new waves of star formation, supernovas and even black holes. Four billion years from now, our own Milky Way galaxy is destined for a collision with the neighboring spiral Andromeda galaxy. The Sun will likely be flung into a new region of our galaxy, but our Earth and solar system are in no danger of being destroyed.
Andromeda, also known as M31, is now 2. Computer simulations derived from Hubble data show that it will take an additional two billion years or more after the encounter for the interacting galaxies to completely merge under the tug of gravity. They will reshape into a single elliptical galaxy similar to the kind commonly seen in the local universe.
Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today. There is a small chance that M33 will hit the Milky Way first. The appearance and make-up of galaxies are shaped over billions of years by interactions with groups of stars and other galaxies. While we don't know for certain how galaxies formed and took the many shapes that we presently see, we have some ideas about their origins and evolution.
Using supercomputers, scientists can look back in time and simulate how a galaxy may have formed in the early universe and grown into what we see today. Scientists estimate the age of the universe at Because the deeper you look into space, the further you see back in time, we can conclude that galaxies several billions of light-years away formed fairly soon after the big bang.
While most galaxies formed early, data indicates that some galaxies have formed within the past few billion years — relatively recently in cosmic terms. The early universe was filled mainly with hydrogen and helium, with some areas slightly denser than others. Gravity caused the gas in these clouds to collapse and form the first generation of stars.
These first stars rapidly burned out. Gravity continued to collapse the clouds. As other clouds came close to each other, gravity sent them careening into one another and knitted the clouds into larger, spinning packs. As the clouds further collapsed, they became rotating disks, which amassed more gas and dust.
New stars formed, creating extensive spiral arms filled with colonies of stars. Sprinkled along the periphery were globular clusters, along with a halo of gas, dust and dark matter.
History And Achievements. As we have already learned about spiral galaxies, we will now enlist a few characteristics of the concept to understand the concept in a better way. They have a flat, circular disc surrounded by spiral arms with a lighter concentration of stars and dark matter. A spiral nebula surrounds the flat disc in a spiral galaxy. The movement of dark matter in spiral galaxies is dominated by a structured rotation path - orbital movement, unlike other galaxies that do not have such structured movement rotations.
The disc of stars and space matter revolving around the bulge form separate spiral arms that form the spiral galaxy. A spiral galaxy consists of millions of globular clusters spherical arrangement of stars apart from a disc of stars that revolve in the center of the entire galaxy. The most common types of galaxies found in the universe are spiral galaxies that have a thick concentration of stars in between and a thin concentration of stars in the region of spiral arms. Top read: The big bang theory.
Based on the bond of stars and dark matter in a spiral nebula, spiral galaxies can be classified as follows -. With a large spiral nebula, tightly wound spiral arms around the nucleus, SA spiral galaxies are defined as having the closest set-up among all classes of the category. In addition, the SA galaxies represent a smooth center with a dense concentration of stars.
Sa Spiral Galaxies. This class is defined by its structure of a medium-sized nucleus with more widely spread arms around the nebula. The appearance of this spiral galaxy is less smooth and also has a reduced concentration of stars, as compared to the SA spiral galaxy. Sc Spiral Galaxies- The third class of all, the SC Spiral Galaxy is represented by its much smaller nucleus size and far more widely spread arms around the nucleus.
These galaxies have lumpy arms that have an increased number of stars and dark matter as compared to that of the SA and SB spiral galaxies. The galaxies that appear to have a spiral disc but no visible arms are called S0.
Broadly, there are two types of spiral galaxies that have been observed by space scientists to date. Here is a brief introduction of the two types of spiral galaxies -. Normal Spiral Galaxy is a spiral galaxy that has its spiral arms protruding from the nucleus all over.
With a flat and circular disc in the center, normal spiral galaxies have a spiral nebula that surrounds the nucleus from all ends. Encounters between galaxies may cause such waves as the mass of the smaller galaxy could affect the structure of the larger galaxy as they unite. Their size usually varies greatly, from 5 up to kiloparsecs across. The same can be said regarding their mass which typically is between 10 9 and 10 12 solar masses, and luminosities ranging from 10 8 to 10 11 time that of the Sun.
The vast majority of spiral galaxies rotate in the sense that the arms trail the direction of the spin.
Measurements of the rotation curves revealed that the orbital speed of the material in the disk does not fall off as expected if most of the mass is concentrated near the center. Because of this, the visible portion of spiral galaxies is regarded as having only a small fraction of the total mass of the galaxy. Thus it is concluded that spiral galaxies are surrounded by an extensive halo consisting mostly of dark matter.
Spiral galaxies can be classified according to the tightness of their spiral, the lumpiness of their arms, and the overall size of their central bulge.
The relative amounts of gas and dust contained within these galaxies can portray these differences. There are currently 3 classifications of classical spiral galaxies and another 3 for barred spiral galaxies:. Spiral galaxy type A — abbreviation Sa — they have a big central bulge and smooth, broad spiral arms.
This means that a relatively small proportion of Sa galaxies are involved in star formation. Spiral galaxy type B — abbreviation Sb — have a moderately-sized central bulge and moderately-well-defined spiral arms.
Spiral Galaxy type C — abbreviation Sc — small central bulge as well as narrow and well-defined central arms. Barred spiral galaxy type A — abbreviation SBa — they feature tightly bound arms. Barred spiral galaxy type B — abbreviation SBb — they feature both tightly and loosely bond arms. Barred spiral galaxy type C — abbreviation Sbc — they have loosely bound arms. Usually, spiral galaxies are believed to evolve into elliptical galaxies as they get older.
Elliptical galaxies show various degrees of flattening, ranging from systems that are approximately spherical to those that approach the flatness of spirals. The mass in a giant elliptical can be as large as 10 13 M Sun. The diameters of these large galaxies extend over several hundred thousand light-years and are considerably larger than the largest spirals.
Although individual stars orbit the center of an elliptical galaxy, the orbits are not all in the same direction, as occurs in spirals. We find that elliptical galaxies range all the way from the giants, just described, to dwarfs, which may be the most common kind of galaxy.
Dwarf ellipticals sometimes called dwarf spheroidals escaped our notice for a long time because they are very faint and difficult to see. The luminosity of this typical dwarf is about equal to that of the brightest globular clusters.
Intermediate between the giant and dwarf elliptical galaxies are systems such as M32 and M, the two companions of the Andromeda galaxy. While they are often referred to as dwarf ellipticals, these galaxies are significantly larger than galaxies such as Leo I. Figure 5: Dwarf Elliptical Galaxy. M32, a dwarf elliptical galaxy and one of the companions to the giant Andromeda galaxy M M32 is a dwarf by galactic standards, as it is only light-years across.
Hubble classified galaxies that do not have the regular shapes associated with the categories we just described into the catchall bin of an irregular galaxy , and we continue to use his term. Typically, irregular galaxies have lower masses and luminosities than spiral galaxies. Irregular galaxies often appear disorganized, and many are undergoing relatively intense star formation activity. They contain both young population I stars and old population II stars. The two best-known irregular galaxies are the Large Magellanic Cloud and Small Magellanic Cloud Figure 6 , which are at a distance of a little more than , light-years away and are among our nearest extragalactic neighbors.
Their names reflect the fact that Ferdinand Magellan and his crew, making their round-the-world journey, were the first European travelers to notice them.
Although not visible from the United States and Europe, these two systems are prominent from the Southern Hemisphere, where they look like wispy clouds in the night sky.
Since they are only about one-tenth as distant as the Andromeda galaxy, they present an excellent opportunity for astronomers to study nebulae, star clusters, variable stars, and other key objects in the setting of another galaxy.
For example, the Large Magellanic Cloud contains the 30 Doradus complex also known as the Tarantula Nebula , one of the largest and most luminous groups of supergiant stars known in any galaxy. The Small Magellanic Cloud is considerably less massive than the Large Magellanic Cloud, and it is six times longer than it is wide. This narrow wisp of material points directly toward our Galaxy like an arrow. The Small Magellanic Cloud was most likely contorted into its current shape through gravitational interactions with the Milky Way.
A large trail of debris from this interaction between the Milky Way and the Small Magellanic Cloud has been strewn across the sky and is seen as a series of gas clouds moving at abnormally high velocity, known as the Magellanic Stream.
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