The Eagle Nebula
(M16 and Star Queen Nebula)
Facts Nebula: |  | |
| Right Ascension: | 18:18.8 (h:m) | |
| Declination: | -13:47 (deg:m) | |
| Distance | 7000 lightyears | |
| (there are different sources, the distance lies between 4200 and 11000 lightyears) | ||
| Visuel Brightness: | 6,4 mag | |
| Apparent Dimension | 35 arc minutes | |
| Extension: | 70x55 lightyears | |
| Mass | 12500 sunmasses | |
Facts Star Cluster: | ||
| Age: | 5,5 million years | |
| Brightness: | Up to 100000 times sun brightness | |
| Brightest Star: | 8,24 mag | |
| Temperature (Surface): | Up to 50000° Celsius | |
| Diameter: | 8 arc minutes | |
| Extension: | 20 lightyears | |
What is a Nebula?
All things considered the universe is quiet empty. One atom comes on 100000 cubic metres in space. You could think that they are constant distributed, but there are also areas where much more matter is. At a certain thickness you call it nebula. In nebulas are parts of dust, ions, molecules and free atoms in a much higher concentration. More than 60 different sorts of molecules are already proved, of which the most common one is the molecul hydrogen. The dust particles of a nebula are about one billion times thicker than the rest of the space.
Luminous clouds of hydrogen have already been watched by astronomers for a long time. Until the beginning of the 20 th century all objects, which were definitely no stars and looked like diffuse spots, have been titled nebulas. Finally scientists recognised that many of the so named nebulas are clusters of stars or galaxies.
Today only clouds of gas and / or dust are indicated as nebulas or more correctly diffuse nebulas. Other objects, consisting of gas and dust particles, which have other origins, are planetary nebulas or remainders of super novae.
Diffuse nebulas are divided into three groups, because of their behaviour in conjunction with light :
- emission nebulas
- reflection nebulas
- dark clouds
Like it is already mentioned, diffuse nebulas consist of dust and gas. Astronomers proceeded from the assumption that the dust is generated in the colder, exterior layers of Red Giants, which are already in the last phase of their existence. During this process, smallest parts of matter develop by condensation. Finally the exterior layers are repelled by radiation pressure. Today, we already don't know, how the dust particles are composed, but astronomers assume that the chief ingredients are graphite and different sorts of silicates. As a result of estimate one percent (1%) of the interstellar matter consists of dust.
The Emission Nebulas consist of self- illuminating gases and the stimulating energy is provided by the other stars nearby. Reflexion Nebulas reflect the light.
Dark Clouds can be observed as not - or weak - shining clouds, which darken parts of the milkyway. The distance from other stars is too large to reflect the light or to get stimulated to shine.
The Nebula M16, which we will describe, is a Emission Nebula.
History:
The cluster was discoverd by the swiss Philippe Loys de Cheseaux. The first, who also realized the round about Nebula, was Charles Messier in 1764. He als catalogized the Nebula, therefore it is called today M16.
The astronomer Robert Burnham thought of the name Eagle Nebula to prosaical,(and there are just two other objects, which are also called Eagle) and called it Star Queen.
E. Bernard and Isaac Roberts (Bernard in 1895 and in 1897 Roberts were the first who made photos of it.
1965 Y. Terzian found out, that the total mass of M16 has a weight about 12500 sun masses.
1995 there were spectacular outtakes of the Hubble- Space- Telescop, that the high dynamic of the gas masses in this areas where stars develop shows. There were observations and describes of the Eagle Nebula of Messier, de Cheseaux, Bode, Herrschel and Smyth.
Present and Future:
All stars run through a cycle of birth, development, death and revival. They develope of gas of the interstellar space and left at death a nebula of Energie and matter.
The Eagle Nebula is in the Serpens; on the south border of Sagittarius. The Eagle Nebula or the Messier object you call also nebula Eagle (IC 4703) or the open cluster (NGC 6611).
The Nebula is rounded by a thick cloud of interstellar gas. The biggest part is thick and cool, so that hydrogen atomes go together to molecules; these molecules are the base for new stars. Therefore there are in the cloud among others silicate and carbonate particles, which absorb the visible light, so that the real procedures can not be seen.
The cluster has - with a high probability - been developed by the gas of the Nebula, of which the process of Stardevelopment is not be finished yet.
Round about the Nebula there are 100 of very young, hot stars, there surface temperature is about 50000° Kelvin and the brightest star is about 100000 brighter than the sun.They have an age of circa 5,5 Million years old, what is like a blinker in astronomical views.
There is an high ultraviolet radiant of the stars of the O and B types, which warm the gas of the nebula and brings to glow.
In the interior fingers of the Nebula the gas has a very high thickness. These Pillars play an enourmous role at the development of stars.
In some cases there is such a high thickness, that the gas collapses because of gravity.
The development of stars is a protracted process that can be observed in the Eagle Nebula. The development stars, if areas in the interior of enormous clouds of gas collapse, because of their own weight. The cloud of M16 has got enough matter for the genesis of many stars, but not all of them develop at the same time. One cloud needs a period of some million years, to produce stars with its matter. During this time generations of stars develop and die within the surrounding of this cloud and influence the process of genesis of the following stars. The reason is that stars dispatch radiation and particles, which are smaller than atoms, during their existence.
Those emissions make the matter of the clouds moving and cause that the pressure and the volumetric weight gets much higher in some areas. In the most compact regions of that areas so called "lumps" are formed. In their centre a proto-star is developing. A proto-star is the central concentration of mass, which forms a star, when it has got enough mass. The difference between a star and a proto-star is the fact, that stars are shining. A star shines itself, because of nuclear reaction. But there must be an enormous pressure in the central region of a proto-star to get this nuclear reaction going. More and more molecules of gas assemble on the proto-star during its development, because of gravity and the pressure in the interior rises.
Equivalent to the pressure, also the temperature in the centre becomes higher, until it causes a nuclear reaction. This reaction make stars sending out energy, until they die. If the star, before this nuclear reaction starts, is cut off from more gas by Photoevaporation, he could not increase any more and stay still in this way. These objects, of which about 50 are visible in the pillars of M16, are called EGGs (evaporating gaseous globules). Photoevaporation is a process where UV radiation from nearby hot stars evaporates off gas of the nebula. The EGG protects a column of gas behind it. Many of these fingerlike structures are perceptible on the HST images of M16.
The Eagle Nebula, like all emission nebulas, is exceptionally bright and mainly consisting of hydrogen. They distinguish by their self-luminosity. In most times the emission nebulas seem to be reddish, because the main part, that is emitted by the hydrogen , processes a reddish colour. If the high-energetic ultraviolet radiation of a young star impinges an atom of hydrogen, the photons detach electrons of atoms, a process, which is called ionisation. During the following recombination of a proton and an electron, the earlier absorbed energy is released as visible light, the tone of the colour depends on the quantity of energy : the nebula starts to shine.
Comparison:
We'd like to compare the Eagle Nebula with the Orion Nebula (M43). Both have much in common. They are both Emission Nebulas, what means that there is interstellar mass (gas and dust) between Stars, which starts to illuminate through the light of young and hots stars and also straws this light.Within the Orion Nebula there is a group of stars which is called Trapez (Theta Orionis). These are six stars which belong to the oldest stars in the Nebula, but in contrast with other stars, existing outside of Orion Nebula, they are very young. These stars are, like most visible stars of the Eagle Nebula, stars of O and B type, what means that they are very hot and have a big discharge of UV radiation. Also the Orion Nebula has so called elephant trunks. These are not illuminating regions within the area of ionized hydrogen. These areas have a very big thickness and in their interior new stars arise. Around the H 2 area in both nebulas there is a cloud of neutral oxygen. In contrast to the Eagle Nebula in the Orion Nebula there is a sphere where not only stars but also planets develop. These Protoplanets that also exist within a non-shining sphere of very compact materia are discoid objects in which materia has conglobate as small hunk.But the radiation of the stars will possibly prevent that ??planets??(stars?) will ever develop planets from that. The Orion Nebula is located 1400 lightyears away from earth, the eagle nebula approximately 7000 lightyears, that means that M43 is about 7 times closer to the earth. But the quantity of the orion nebula is with about 700 sunmasses about 17 times less then the quantity of the eagle nebula.
Exercises:
- Calculate the average tightness of H 2 molecules assuming the complete nebula consisting of H 2 molecules and compare with the average tightness of materia in the universe.
- Try to illustrate the process of an EGG being uncovered by Photoevaporation with sand (the nebula), one half of a tennis-ball (the EGG) and water (UV radiation).
Closing Words
We were very fascinated of the Eagle Nebula because it is a very interesting object and there are fantastic photos, especially the ones from the Hubble Space Telescope and the picture from Volker Wendel and Bernd Flach-Wilken. We had much fun while we were dealing with this object and we have learnt much about astronomy especially about nebulas and the development of new stars.
We'd like to thank the following persons:
Dr. Bernd Epperlein, Andre Nikolai, Volker Wendel, Bernd Flach-Wilken, Dr. Christoph Oehm, Harald Kümpflein, Friederike Reinhardt
Sources: