In a Universe populated with distinct, bright and often glamorous objects such as stars and planets, it can be easy to overlook the morphing and often indistinct clouds of gas that fill much of the space in between. But in fact interstellar gas, when it is heated up and accelerated, can form some incredibly beautiful and striking ‘bubble’ features that also provide valuable clues about the processes going on to create them. Let’s have a look at some of my favourites.
‘The Bubble Nebula’ lives up to its name as you can see here in this image from the Hubble Space Telescope at optical wavelengths. Also known by the more prosaic name of NGC 7635, it is 7 light years across. Towards the top left of the bubble you can see a bright star and it’s this that is responsible for puffing out this feature. This young, very hot star, about 45 times the size of our sun, is giving off a very fast and powerful stellar wind that pushes the surrounding cold gas outwards in all directions, causing it to pile up at the edges of the bubble. Interestingly, the bubble is asymmetric (the parent star is not in the centre), indicating that the bubble is encountering denser gas on the top left side, preventing it expanding equally in all directions.
Young, energetic stars often form together in clusters within a cloud of dusty matter that is collapsing due to gravity.
As a result, bubbles of piled up gas around such stars can occur in dramatic groups, as you can see here in this image of the ‘Cat’s Paw Nebula by the Spitzer Space Telescope at infra-red wavelengths.
The stars themselves are buried deep in clouds of dust, but the gas bubbles that are heated up and expanded by the stars glow clearly in infrared. The whole nebula is about 80 to 90 light years across.
Truly enormous bubbles can form on a galactic scale. In this image of galaxy NGC 3079, published just last month, you can see two glowing bubbles above and below the plane of the galaxy – the upper one is estimated to be 4900 light years in diameter!
This is a combination of images at X-ray and optical wavelengths (Chandra and Hubble Space Telescopes). The huge bubbles are thought to be the result of highly energetic accelerated particles colliding with the surrounding gas.
A similar pair of bubbles, known as ‘Fermi Bubbles’, has been detected above and below the plane of our own Milky Way galaxy, and astronomers believe the creation of such galactic bubbles could be linked to powerful forces created by the supermassive black hole at the centre of these galaxies.
The Bubble Nebula: http://heritage.stsci.edu/2016/13/caption.html
Cat’s Paw Nebula: https://www.nasa.gov/image-feature/jpl/newborn-stars-blow-bubbles-in-the-cats-paw-nebula
Galactic Superbubbles: https://phys.org/news/2019-02-ngc-galactic-cosmic-pinball-energetic.html
fermi.gsfc.nasa.gov/science/constellations/pages/bubbles.html
Image credits:
- NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
- NASA/JPL-Caltech
- X-ray: NASA/CXC/University of Michigan/J-T Li et al.; Optical: NASA/STScI