This spectacular view of the Bubble Nebula was created from four separate images from the Hubble Space Telescope to mark the observatory’s 26th birthday in April 2016. The Bubble Nebula is 10 light-years wide and sculpted by the bright star seen to the left of center. Credit: NASA, ESA, Hubble Heritage Team – See more at: http://www.space.com/32648-hubble-telescope-spectacular-birthday-bubble-image.html#sthash.rDIUMEqz.dpuf
This new Hubble image, released to celebrate Hubble’s 26th year in orbit, captures in stunning clarity what looks like a gigantic cosmic soap bubble. Bubble Nebula, is in fact a cloud of gas and dust illuminated by the brilliant star within it. The vivid new portrait wins the Bubble Nebula a place in the exclusive Hubble hall of fame, following an impressive lineage of Hubble anniversary images.
26 years ago, on 24 April 1990, the Hubble Space Telescope was launched into orbit aboard the space shuttle Discovery as the first space telescope of its kind. Every year, to commemorate this momentous day in space history, Hubble spends a modest portion of its observing time capturing a spectacular view of a specially chosen astronomical object.
This year’s anniversary object is the Bubble Nebula, also known as NGC 7635, which lies 8 000 light-years away in the constellation Cassiopeia. This object was first discovered by William Herschel in 1787. Due to its very large size on the sky, previous Hubble images have only shown small sections of the nebula, providing a much less spectacular overall effect. Now, a mosaic of 4 images from Hubble’s Wide Field Camera 3 (WFC3) allows us to see the whole object in one picture for the first time.
This complete view of the Bubble Nebula allows us to fully appreciate the almost perfectly symmetrical shell. This shell is the result of a stellar wind from the bright star visible just to the left of centre in this image. The star, SAO 20575, is between 10 and 20 times the mass of the Sun and the pressure created by its stellar wind forces the surrounding interstellar material outwards into this bubble-like form.
The Bubble Nebula is 8,000 light-years from Earth in the direction of the constellation Cassiopeia. This image shows the nebula (center) and its surrounding region as seen by the Hubble Space Telescope and the Digitized Sky Survey 2. Credit: NASA, ESA, Digitized Sky Survey; Acknowledgement: Davide De Martin – See more at: http://www.space.com/32648-hubble-telescope-spectacular-birthday-bubble-image.html#sthash.rDIUMEqz.dpuf
The giant molecular cloud that surrounds the star—glowing in the star’s intense UV—tries to stop the expansion of the bubble. However, although the sphere already measures ~10 light-years in diameter, it is still growing, owing to the constant pressure of the stellar wind—currently at >100 000 km/h. Aside from the symmetry of the bubble itself, one of the more striking features is that the star is not located at the centre. Astronomers are still discussing why this is the case and how the perfectly round bubble is created nonetheless.
The star is surrounded by a complex system of cometary knots, seen most clearly in this image just to the right of the star. The individual knots, generally larger in size than the Solar System and have masses comparable to Earth’s, consist of crescent shaped globules of dust with large trailing tails illuminated and ionised by the star. Observations of these knots, and of the nebula as a whole, help astronomers to better understand the geometry and dynamics of these very complicated systems.
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