Comets
https://en.wikipedia.org/wiki/Comet
https://www.space.com/53-comets-formation-discovery-and-exploration.html

Asteroids
https://en.wikipedia.org/wiki/Asteroid
https://www.space.com/51-asteroids-formation-discovery-and-exploration.html

Coronal Ejections
https://en.wikipedia.org/wiki/Coronal_mass_ejection#Physical_properties
https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections

Interstellar Planets
https://en.wikipedia.org/wiki/Rogue_planet#Retention_of_heat_in_interstellar_space
https://www.scientificamerican.com/article/wandering-in-the-void-billions-of-rogue-planets-without-a-home/

Hypervelocity Stars
https://en.wikipedia.org/wiki/Stellar_kinematics#High-velocity_stars
http://www.bbc.co.uk/earth/story/20150907-the-fastest-stars-in-the-universe
Supernova
https://en.wikipedia.org/wiki/Supernova
https://www.space.com/6638-supernova.html

Rogue Black Holes
http://uk.businessinsider.com/stray-black-hole-hiding-milky-way-2017-2
https://www.space.com/34360-rogue-black-hole-wanders-galaxy-edge.html
https://www.space.com/25048-rogue-black-holes-radio-telescopes.html

Gamma Ray Burst
https://quarkmag.com/what-would-happen-if-a-grb-hit-the-earth-again-b636f2e5ed54
https://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_extinction_events#Gamma_ray_burst_hypothesis
https://en.wikipedia.org/wiki/Gamma-ray_burst#Effects_on_Earth

Galactic Cannibalism
https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision
https://gohighbrow.com/galactic-cannibalism/

The Big Rip
https://en.wikipedia.org/wiki/Big_Rip
http://www.wired.co.uk/article/big-rip-end-of-the-universe