Which stars contain elliptical galaxies

Elliptical galaxies

Elliptical galaxies are very different from spiral galaxies. They do not have spiral arms and show a circular or elliptical shape and are otherwise structureless. Elliptical galaxies come in giant and dwarf formats. Elliptical giant galaxies are real giants in the cosmos and can contain up to 1 billion (!) Stars and be surrounded by several thousand globular clusters!

Elliptical galaxies are identified with the letter E followed by a number that indicates the degree of flattening. A 0 means a circular galaxy, and 7 an extremely flattened galaxy. This classification, which goes back to the astronomer Edwin Hubble, only takes into account the appearance. Today there is a more precise classification of elliptical galaxies, which also takes the type into account.

Modern classification of elliptical galaxies

Giant elliptical galaxies (cD)
They are true giants in the universe and are up to 3 million light years in diameter (that's more than the distance between the Milky Way System and the Andromeda Galaxy!) And contain up to 1 billion stars! They are mostly found in the center of galaxy clusters and are likely the result of numerous mergers of galaxies. Example: NGC 4881 in the Coma cluster.

Normal elliptical galaxies
They are several hundred thousand light years across and contain several hundred billion stars. They have medium to high brightness. Example: M 86 in the Virgo cluster.

Dwarf elliptical galaxies (dE)
They are 3,000 to 30,000 light years in diameter. Their brightness is significantly weaker than that of normal elliptical galaxies. Example: M 32, companion of the Andromeda Galaxy M 31.

Spherical dwarf galaxies (dSph)
Very faint little galaxies with a spherical shape. Up to now they have only been observed in the vicinity of the Milky Way system due to their low brightness. Example: M 110, another companion of the Andromeda Galaxy M 31.

Blue dwarf galaxies (BCD)
In contrast to all other elliptical galaxies, they contain mostly blue and young stars and a lot of interstellar gas.

In contrast to spiral galaxies, elliptical galaxies seem to contain hardly any gas and dust masses. They mainly consist of red and therefore old stars. The formation of stars seems to have almost come to a standstill in them. At the time, Hubble suspected that elliptical galaxies would one day develop into spiral galaxies. Today, however, there is a different theory.


NGC 720 (left) and NGC 1395 (right)
Excerpts from the POSS (15 x 15 ′)
Source: Digitized Sky Survey

At first glance, elliptical galaxies seem unstructured and boring. They are also not so photogenic and mostly underrepresented in books. Nevertheless, they make up more than 20 percent of all galaxies.

In reality, some things are even more complicated with elliptical galaxies. The stars in an elliptical galaxy do not run in a plane around the center as in a spiral galaxy, but criss-cross on all possible planes.

M 86 (center)
a normal elliptical galaxy in the Virgo Cluster
Detail from the POSS (60 x 60 ′)
Source: Digitized Sky Survey

In recent years we have learned a lot about elliptical galaxies through improved observation techniques such as adaptive optics and space telescopes (Hubble). Thus, elliptical galaxies also show structures, e.g. B. in brightness analyzes. Inside, many elliptical galaxies have disks or nuclei that often have a different rotation than the rest of the stars in the galaxy. The existence of such disks or nuclei suggests that large elliptical galaxies were formed by the merging of several galaxies. Further collisions can result in the aforementioned giant elliptical galaxies of the cD type. Did at least the large elliptical galaxies originally arise from the collision of spiral galaxies?

Even the statement that elliptical galaxies contain no gas is history today. It is true that there is hardly any gas inside. Investigations with X-ray satellites have shown, however, that elliptical galaxies are surrounded by extensive clouds of very hot gas. The evaluation of this data is still ongoing, however. Exploring the elliptical galaxies is and will remain an exciting thing!

NGC 4881 (center)
is a giant elliptical galaxy of type cD in the Coma galaxy cluster!
Only because of its huge distance of 300 million light years does NGC 4881 appear so small!
Detail from the POSS (30 x 30 ′)
Source: Digitized Sky Survey

M 32
an elliptical dwarf galaxy of type dE - a companion of the Andromeda galaxy M 31
Section from the POSS (20 x 20 ′)
Source: Digitized Sky Survey

M 110 (NGC 205)
a spherical dwarf galaxy of the type dSph - also a companion of the Andromeda galaxy M 31
Section from the POSS (20 x 20 ′)
Source: Digitized Sky Survey