|Designation|| NGC 7635|
|Right ascension||23h 20m 48.3s|
|Declination||+61° 12′ 06″|
|Type of object||Emission nebula|
|Magnitude|| Apparent Mag: +10|
Absoulte Mag: -2
|Distance from Earth||7,100-11,000 ly|
The Bubble nebula (NGC 7635, Cadwell 11, Sharpless 162) is an emission nebula in the constellation of Cassiopeia. Discovered by William Herschel, the nebula has a distinctive spherical shape, making it look like a bubble of gas and giving it the name, the "Bubble nebula." Best observed in late summer/early autumn, the Bubble nebula can just about be seen with small telescopes but is best observed with larger telescopes. To celebrate the 26th anniversary of the launch of the Hubble Space Telescope, the HST took a spectacular photo of the nebula in 2016.
Properties and Structure
The nebula's great distance means it has a physical size of around 10 light years. The nebula's distinctive shape comes from its central star which emits vast amounts of radiation. This produces a large stellar wind which "blows" gas and dust away from the star. The radiation the star emits is enough to ionize the gas surrounding the star and make it glow as an emission nebula. The stellar wind is nearly uniform across the star resulting in an almost spherical shell of gas enclosing the star. A cold region of gas on one side of the star means the nebula is not completely symmetric. This along with the stars motion means it is not at the centre of the nebula, but slightly off centre.
The central star, with designations SAO 20575 and BD+60 2522, belongs to a class of stars known as Wolf-Rayet stars and has a spectral type of O6.5. It has an apparent magnitude of +8.71 and a mass around 45 times that of the Sun. This corresponds to an absolute magnitude of -5.5 making the star around 398,000 times more luminous than the Sun. The star itself is approaching us at around 26 km/s and has a parallax of 0.41 milliarcseconds. The star has a radius or some 15 solar radii and is extremely hot with a surface temperature of 37,500 K.
- Bubble Nebula – NGC 7635 from constellation-guide.com
- From definition of absolute magnitude, using apparent magnitude given here and a midpoint distance of (7,000+11,000)/2=9,000 light years.
- NGC 7635 from freestarcharts.com
- Hubble sees a star inflating a giant bubble from nasa.gov
- The star BD+60 2522 from simbad.u-strasbg.fr