The elliptical galaxies they are astronomical objects of ellipsoidal shape. Inside, these galaxies are home to millions of stars, planets, some gas, dust and abundant dark matter, all linked thanks to the force of gravity..
They lack an obvious structure and their luminosity is quite uniform, since the stars are evenly distributed towards the edges, where the light diffuses smoothly in the form of a very faint halo..
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Astrophysicists at first thought that a large collapse was what gave rise to an elliptical galaxy, which gave rise to intense star formation that eventually ceased. This hypothesis is supported by the fact that the stellar population of these galaxies is older than that of the other types..
On the other hand, in elliptical galaxies there is very little gas and dust, which is known as interstellar matter, which is precisely the necessary raw material in the formation of new stars.
But current observations corroborate that despite their apparent stability, galaxies are not static. The force of gravity causes them to actively interact with each other whenever there is opportunity.
For this reason, the hypothesis currently prevails that elliptical galaxies have diverse origins and that galaxies of other shapes are likely to become elliptical over time..
The gravitational attraction can cause collisions that produce an eventual merger. Events of such magnitude are not uncommon, since gravity opens the doors to this possibility. Furthermore, elliptical galaxies are often found in the middle of galactic clusters, where there is an opportunity to trap material and merge with other galaxies..
This is confirmed by the fact that blue and young stars have been detected inside some elliptical galaxies - blue dwarf galaxies - showing that they are not completely devoid of interstellar matter..
It has also been suggested that when spiral galaxies use up their raw material, they evolve into a lenticular shape, that is, a disk shape without spiral arms. Successive collisions with other galaxies would lead to the loss of the disk and the transformation into an ellipsoid.
To get an approach to the dimensions in the universe, the units of distance commonly used on Earth are not appropriate. In astronomy, the light-year, the parsec (pc) and the kiloparsec (kpc) are in common use:
1 kpc = 1000 pc = 3300 light-years
In the measurement of the mass of objects as huge as galaxies, the unit called solar mass, which is denoted as M☉ equivalent to 2 x 10 ^ 30 kg.
Regarding the general characteristics of elliptical galaxies, it is clear that the most distinctive is their shape, there are from almost spherical to very flattened ellipsoids..
As explained at the beginning, elliptical galaxies are very unstructured. They have a fairly regular ellipsoidal distribution and are surrounded by a faint luminous halo, of greater or lesser extent. They lack a disc or other structure that stands out remarkably.
They can have satellite galaxies, much smaller galaxies that are under their gravitational domain, although this is not exclusive to elliptical galaxies, because our Milky Way, a barred spiral galaxy, has the Magellanic Clouds as satellites..
Some also have globular star clusters, which can be mistaken for elliptical dwarf galaxies. In terms of kinematics, the stars that make up an elliptical galaxy tend to follow complicated trajectories and the angular momentum of the galaxy is believed to be of low magnitude..
There is a lot of variability in terms of size. Because they have little interstellar gas and dust, the mass of an elliptical galaxy is stellar mass. The number of stars can vary from a few million stars to a million million stars..
Estimates to date give diameters of 1-200 kpc and in exceptional cases 1 Megaparsec - about 3 million light years-.
Normally the mass is in the range of 10 ^ 6-10 ^ 13 M☉. In the vicinity of our Milky Way galaxy there are many elliptical galaxies of small size, also called dwarf galaxies.
At the other extreme are the giant elliptical galaxies, of extraordinary luminosity. In fact, this class has the largest known galaxies, which are generally at the center of galaxy clusters, so they very possibly owe their immense size to fusion with neighboring galaxies..
Astronomer Edwin Hubble classified galaxies according to their shape and established five basic patterns. Its classification includes: elliptical, lenticular, spiral, barred and irregular spirals. Most galaxies, about 90% are elliptical or spiral.
Hubble placed elliptical galaxies at the beginning of his classification scheme, referring to them as "early-type galaxies" because he believed that later they evolved into other forms..
If a is the semi-major axis and b the semi-minor axis of the ellipse, the ellipticity e is given by:
E = 1 - b / a
E is an indicative measure of how flattened the ellipse is, for example if a and b are very close values, the quotient b / a is approximately 1 and the ellipticity is zero, resulting in a spherical galaxy.
The highest accepted value for E is 3 and in the Hubble classification, the first place on the left is occupied by spherical galaxies, which are denoted as E0, followed by the intermediate types E1, E2, ... until reaching EN, where N = 10 (1- b / a).
The flattest ones that are known reach up to E7, since above this value the structure of the galaxy is lost..
Hubble himself modified his original classification as more information arrived. So did other astrophysicists to include new features aside from the mere ellipsoidal shape. For this, other letters were used, as well as lowercase letters.
Outside of the Hubble sequence, Ralf Bender and his collaborators proposed in 1988 two new terms to classify elliptical galaxies, which not only take into account the shape, but also other very important characteristics..
In this way they were grouped into "boxy" and "disky", which are translated respectively into square and discoidal. This classification was made according to the isophotic lines, that join points with identical luminosity on the galactic surface.
Interestingly, these lines do not follow elliptical shape. In some galaxies they tend to be rather rectangular and in others they take the shape of a disk, hence the name.
The square ones have a greater luminosity, are larger and more active, in the sense that they have radio sources, as well as X-rays. The discoidal ones are calmer in this aspect and their luminosity is lower..
So even having the same classification in the Hubble sequence, two elliptical galaxies can have different characteristics if one of them is boxy or square and the other is disky or discoidal. These would tend to have higher rotation, while the boxy could be the result of many mergers and galactic interactions.
These are elliptical galaxies so colossal that it is impossible to miss them when it comes to the subject. They can be 1 Mega-parsec wide and are found in the middle of galactic clusters.
Their size is probably due to the fact that they are the result of the merger of several galaxies: between 1013 and 10 14 M☉. They have a very bright central nucleus and are home to hundreds of thousands of globular clusters. In addition, it is presumed that they contain a large amount of dark matter, necessary to explain that it remains cohesive.
The largest of all so far is IC 1101 in the Abell 2029 cluster, in the constellation Virgo. It was discovered by William Herschel in 1790 and has a maximum diameter of 6 million light-years..
Since its core is extremely active, it does not seem likely that it hosts life forms, or at least not as we know it on Earth..
Elliptical galaxies are usually found in the middle of galaxy clusters, which are associations of more or less large galaxies. In the constellation Virgo and Coma Berenice there are notable clusters.
Since most galaxies are so far away, it is quite difficult for the eye to identify them, but using telescopes or even good quality binoculars, it is possible to distinguish galaxies of all types.
On the net there are many maps, as well as applications to discover astronomical objects. Galaxies do not usually have proper names, with few exceptions such as the Milky Way, Andromeda, the Whirlpool or Whirlpool galaxy and the Sombrero galaxy..
Most are denoted by a catalog code: the catalog Messier (M), the NGC catalog or New General Catalog and the Catalog Index IC.
The stellar object known as M87 (or NGC 4486) belongs to the galaxy cluster of the constellation Virgo. It is among the closest elliptical galaxies to Earth, about 53 million light-years away and is of the type boxy described in the previous section. It has a very active nucleus in terms of radio frequency and plasma emission.
It is about twice the mass of our Milky Way, not including dark matter. If this could be detected, M87 would turn out to be about 200 times more massive than the Milky Way. Some 12,000 globular clusters have been identified in M87.
M87 emits a jet of matter about 5,000 light-years long, believed to come from a colossal black hole surrounded by hot material that is not exactly in the center..
This is a dwarf elliptical galaxy that accompanies Andromeda, in the constellation of the same name. Because it is very compact and rotates around a very massive object, some experts suggest that it is the core of an ancient galaxy dismembered by some gravitational collapse..
It is possible that in ancient times it collided with Andromeda itself and in the images you can see how the outer stars of M32 are inexorably drawn towards its larger neighbor.
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