Pillars of creation 2014 HST WFC3-UVIS full-res denoised

Elephant trunks (more formally, cold molecular pillars) are a type of

interstellar matter In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstellar ...

formations found in

molecular cloud A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydroge ...

s. They are located in the neighborhood of massive O type and B type stars, which, through their intense radiation, can create expanding regions of ionized gas known as

H II region An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundre ...

s. Elephant trunks resemble massive pillars or columns of gas and dust, but they come in various shapes, lengths, and colors. Astronomers study elephant trunks because of their unique formation process and use 2-D and 3-D simulations to try to understand how this phenomenon occurs.

Formation

O type and B type stars are a classification of stars that strongly emit ultraviolet (UV) radiation. The UV radiation causes the surrounding cloud of hydrogen gas to ionize, forming

s. The gas does not ionize evenly throughout the cloud, therefore there are clumps of denser gas scattered throughout the cloud. These dense clumps are called

evaporating gaseous globule An evaporating gas globule or EGG is a region of hydrogen gas in outer space approximately 100 astronomical units in size, such that gases shaded by it are shielded from ionizing UV rays. Dense areas of gas shielded by an evaporating gas globule ...

s (EGGs), and they are the starting point for the formation of an elephant trunk. The pillar shape is formed when the EGGs act as shields for the gases that lie behind them from the stellar winds.

Stellar wind A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. ...

s are a continuous flow of gas that is ejected from the stars and causes the lighter and less dense gas to erode away. The EGGs and the column of gas "downwind" from them are the basic formations of an elephant trunk.

Structure

Elephant trunks form on the outer wall of the H II region cloud. At visible light wavelengths, astronomers can only study the structure of the surface of the trunks because the opaqueness of the gas obscures the internal core. The length of the columns are measured in light years, which is the distance that it takes light to travel in one year. Astronomers can calculate the densities and temperatures of the EGGs and the trunks by using infrared, millimeter, and radio observations. They have determined that elephant trunks have cold cores (20K) surrounded by warm gas (60K) with an outer hot shell (250-320K).

Examples

Pillars of Creation

The

Pillars of Creation ''Pillars of Creation'' is a photograph taken by the Hubble Space Telescope of elephant trunks of interstellar gas and dust in the Eagle Nebula, in the Serpens constellation, some from Earth. These elephant trunks had been discovered by J ...

are the most famous example of astronomic elephant trunks. NASA was able to produce a picture of this formation by compositing multiple images taken by the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most ver ...

. It is located 7,000 light years away, in the

Eagle Nebula The Eagle Nebula (catalogued as Messier 16 or M16, and as NGC 6611, and also known as the Star Queen Nebula) is a young open cluster of stars in the constellation Serpens, discovered by Jean-Philippe de Cheseaux in 1745–46. Both the "Eagle" ...

. There are multiple elephant trunks in the formation, one of which is approximately seven light years long. Astronomers have made observations suggesting that the Pillars were possibly destroyed by the shock waves of a supernova 6,000 years ago.

Rosette Nebula

The

Rosette Nebula The Rosette Nebula (also known as Caldwell 49) is an H II region located near one end of a giant molecular cloud in the Monoceros region of the Milky Way Galaxy. The open cluster NGC 2244 (Caldwell 50) is closely associated with the nebulosity, th ...

is an example of an unusual shape that an elephant trunk can assume. It has a double helix structure instead of the normal straight column. The double helix is caused by the presence of magnetic fields and electric currents lined up along the trunk axis of the trunks. This makes the filaments of the columns wavy instead of straight, as they are in normal trunks. These filaments wrap around each other rather than line up next to each other, which forms the twisted structure.

NGC 7822

The star forming complex NGC 7822 in the constellation of Cepheus has several elephant trunk formations.Gahm G. F., Carlqvist P., Johansson L. E. B., Nikolić S. (2008)
''Rotating elephant trunks''
Astronomy and Astrophysics, Volume 454, Issue 1, July IV 2006, pp.201-212

References

{{Reflist Interstellar media