|Red spider nebula|
|Designation|| NGC 6537|
|Right ascension||18h 05m 13.1s|
|Declination||-19° 50′ 34.9″|
|Type of object||Planetary nebula|
|Magnitude|| Apparent Mag: +13|
Absolute Mag: +3
|Distance from Earth||3,000 ly|
|Radial velocity||-17.3±2 km/s|
|Proper motion|| RA: 17.5 mas/yr|
Dec.: -1.4 mas/yr
The Red spider nebula (NGC 6537, PN G010.1+00.7) is a planetary nebula in the constellation of Sagittarius. The nebula has a bipolar shape meaning it consists of two lobes. These lobes possesses a "S" shaped symmetry meaning that the lobes opposite each other have a similar appearance. It is thought that there may be another star, in addition to the central white dwarf star, though it has not as yet been observed. These "S" shaped appear somewhat similar to legs giving the nebula its name. It is located not far from well known nebulae such as the Eagle nebula and the Lagoon nebula.
Properties and Structure
The precise distance to the nebula is not known with estimates ranging from 3,000 to 8,000 light years so it is likely its apparent size of 150 arcminutes corresponds to somewhere between 130 and 150 light years. The Red spider nebula is in fact approaching the Earth at around 17.3 km/s. The nebula is observed near the centre of the Milky Way and as a result, interstellar dust obscures the nebula meaning it appears around 40 times dimmer than it would without the obscuring dust. As a result, the nebula has an apparent magnitude of +13.
The Red spider nebula is home to one of the hottest stars known. The star, a white dwarf, is enclosed by a thick layer of dust making observation difficult. Its surface temperature is thought to be 150,000-250,000 K but some estimates put it as high as 340,000 K. This great temperature means it produces an incredibly strong stellar wind of charged particles, with a temperature of 10,000 K at a speed of 300 km/s. These winds create supersonic shocks where gas is compressed and heated in the lobes. These shock produce waves 100 billion km high They are also the cause of the nebula's spider like appearance. The shock is responsible for the nebula's glow, caused by ionized hydrogen and nitrogen.
Unlike other bipolar planetary nebulae, like the Butterfly nebula, the lobes appear rippled rather than smooth. This may be due to the gravitational effects of an unseen companion star to the white dwarf. An unseen companion star could also explain nebula's "S" shaped lobes. The nebula is also aligned with other bipolar nebulae in the night sky. This appears to be true for over 100 such nebulae in the central bulge of the Milky Way. It has been suggested that this may be caused by the strong magnetic field at the centre of the galaxy. The nebulae are aligned along the axis between the two lobes in the plane of the galaxy.
- Red spider nebula from constellation-guide.com
- From definition of absolute magnitude, using apparent magnitude (+13) and distance (3,000 ly) given here.
- NGC 6537 from simbad.u-strasbg.fr
- Physical size based direct calculation using an apparent size of 150 arcminutes and distance of 3,000-8,000 light years.
- Hubble Spins a Web Into a Giant Red Spider Nebula from nasa.gov
- Bizarre Alignment of Planetary Nebulae from eso.org
- Rees, B.; Zijlstra, A. A., 2013. Alignment of the Angular Momentum Vectors of Planetary Nebulae in the Galactic Bulge. Monthly Notices of the Royal Astronomical Society, (Online). 435, 975-991. Available on ArXiv (Accessed 25 January 2018).