# The Death of Stars - Nebulae It's 1054, and you're an astronomer in the Northern Hemisphere. You've got a nice cup of tea by your side, sitting in your reclining chair - everything's nice! All of a sudden, someone comes running towards you - someone's reported a new 'star' in As stars die, they turn from a big, hulking fusion engine to a small, slowly-cooling ball of matter. Depending on the starting mass of the star, this'll create either a [[White Dwarves (Astro)|white dwarf]] or a [[Basics of Neutron Stars (Astro)|neutron star]] - both consisting of degenerate matter. Sometimes, a death can even produce [[Black Holes (Astro)|black holes]] - the densest objects in our universe! However, there's a transition period between the 'stellar engine' and 'stellar remnant' that we've got to cover - the **planetary nebula.** They're very, very pretty. Take a look at them yourself! ![[Pasted image 20240203212653.png]] *The Crab Nebula. Credit: NASA, ESA, CSA, STScI, T. Temim (Princeton University)* # Emission Nebulae ## Planetary Stars less than 8 solar masses expel their outer layers once they reach the end of the [[Red Giants and the Pre-Death of Stars (Astro)#AGB Stars|asymptotic giant branch]]. As the star continues to expand down the red giant branch, the outer layers slowly but surely get further away from the core. This reaches a point where the outer layers aren't bound to the core anymore, and the outer layers start to unravel around the core, one 'layer' at a time. ![[Pasted image 20240204151349.png]] However, it's important to note that while all of this is happening, the core of the star's still burning hot and bright. With the now-stellar remnant reaching surface temperatures of over 100,000 Kelvins, it ionises the surrounding gas and dust that now surrounds it, creating the beautiful patterns you see in planetary nebula today! Most of the time, these nebulae are circular - the progenitor star ejects its shells uniformly. However, this world isn't perfect - and we've got intricate shapes for many >[!Abstract]- Planetary Nebula - Shapes and Sizes ## H II Regions A galaxy wouldn't be a galaxy without stars.[^1] Something, however, has got to fuel that formation - that's the # Reflection Nebulae Nebulae are different colours... because they have different lines! $H_{\alpha} = 656.3nm$ --> Those are responsible for **red colours** 658.4nm --> Green (singly ionized nitrogen (so only one lost electron N^+ ion) 500.7nm --> Blue (doubly ionized oxygen so spectra will be shifted) //planetary nebulae --> gas thrown off by AGB and post-AGB stars create ionised dust and gas around the remnant star --> this creates gaseous structures that shine in different colours depending on how you look at it (different spectra) --> white dwarf in the middle - ionises! ////crab nebula! visible and x-ray within this nebula is a pulsar, the crab pulsar! # Reflection Nebulae ## Pulsar Wind Nebulae Often times, there's going to be a bright, bright star surrounded by gas. This happens primarily in areas where there is significant star formation - H II regions, mostly. When light from this bright star hits the dust surrounding it, it reflects off the dust - forming patterns within the dust of the nebula. Amazing! ![[Pasted image 20230714092235.png]] *The Vela Pulsar in X-Rays. The bright star in the middle is the Vela Pulsar!* # What's Next? Navigate back to the astro-page here: [[Everything Astronomy]] Move on to Doppler shifts here: [[Redshift & the Doppler Effect (Astro)]]