|Designation|| NGC 2070|
|Right ascension||05h 38m 38s|
|Declination||-69° 05′ 05.7″|
|Type of object||Emission nebula|
|Dimensions||40' x 25'|
|Magnitude|| Apparent Mag: +8.0|
Absolute Mag: -11.7
|Distance from Earth||160,000 ly|
|Radial velocity||251.0 km/s|
The Tarantula nebula (NGC 2070, 30 Doradus) is an emission nebula in the constellation of Dorado. Situated in the Large Magellanic Cloud, the nebula is the largest known nebula in the Local Group of galaxies. The nebula is one of the best known nebulae not in the Messier catalogue, probably due to the fact it is mainly visible from southern latitudes. First thought to be a star, the nebular nature of the Tarantula nebula was first observed by Nicolas Louis de Lacaille in 1751. More recently, a supernova (designated SN 1987A) was observed in the nebula in February 1987. The nebula's name derives from the long filaments of dust that resemble the legs of a spider.
Properties and Structure
The nebula's great distance of 160,000 light years means that its apparent size of some 40 x 25 arcminutes corresponds to a size of 550 to 1,000 light years across. This makes it the largest nebula in the Local Group, the collection of galaxies surrounding the Milky Way including the Andromeda galaxy. The nebula is an emission nebula, meaning that is a gigantic cloud of ionized hydrogen gas. The ultraviolet radiation emitted by the stars ionizes the enveloping hydrogen gas causing it to glow. The mass of the nebula is thought to be on the order of 1,000,000 times that of the Sun.
Other objects of interest within the nebula include the supernova remnant NGC 2060, which was discovered by John Herschel in 1836. More recently in 1998, a pulsar was observed. Catalogued as PSR J0537-6910, the pulsar has a period of 18 ms (milliseconds).
Stars Within the Nebula
The nebula contains two clusters of stars, one designated Hodge 301 and the other a compact cluster designated R136. The compact cluster R136 contains massive stars (blue supergiants), some 100 times as heavy as the Sun, and counts for around 45% of the nebula's mass. R136 is around 35 light years in diameter and the radiation it emits illuminates the nebula. One of the stars in this cluster, R136a1, is the largest star ever seen based on its mass. The star belongs to a class of stars known as Wolf-Rayet stars which are known for being extremely heavy and luminous. R136a1 is no exception, possessing a mass of 265 solar masses and 8.7 million times brighter. It is thought to have a radius of 35.4 solar radii and a surface temperature of some 53,000 K. The star produces a strong stellar wind which blasts dust and other material that surrounds away. VFTS 682 is another Wolf-Rayet star in the nebula, though less massive at 150 solar masses.
The other cluster, Hodge 301, also contains some large bright stars, but not as many. The nebula contains 800,000 stars, making it a super cluster of stars. it is the nearest such object to Earth, making it an object of interest for astronomers. Many of the stars are obscured by the dust in the nebula, so infrared observation is required to observed them. There are thousands of massive stars in the central region of the nebula, producing extraordinarily strong stellar winds of charged particles. Supernova explosions add to this and cause the surrounding gas to heat up to millions of degrees.
In late February 1987, a supernova (SN 1987A) occurred in the nebula. The close proximity of the Large Magellanic Clouds means that SN 1987A was the closest observed supernova since the invention of the telescope in the early 1600s. At a distance of 168,000 light years, the nebula reached a peak apparent magnitude of +3 or an absolute magnitude of -16.
-  from constellation-guide.com
- NGC 2070 from simbad.u-strasbg.fr
- Tarantula Nebula from britannica.com
- The Tarantula Nebula from apod.nasa.gov
- How big are the biggest monster stars? from earthsky.org
- From definition of absolute magnitude, using apparent magnitude (+3) and distance (168,000 ly) given here.