Caldwell 90


Caldwell 90 is a planetary nebula formed in the late stages of the life of a Sun-like star. Initially, the star’s energy was derived by fusing hydrogen into helium. When the supply of hydrogen ran low, it produced less energy, so the force of gravity caused it to contract. Eventually, that contraction increased the pressure in the star’s core and triggered fusion of the heavier element carbon. That process caused the star to expand into a red giant. Finally, the red giant’s outer layers were eject to form the nebula and the star collapsed again into a small, dense star whose intense radiation continues to push the nebula boundaries outward.

The Sun will probably go through a similar process in 4 or 5 billion years.

Image Credit: NASA / ESA

NGC 4689


NGC 4689 is a spiral galaxy located about 54 million light-years away in the constellation of Coma Berenices and a member of the Virgo Cluster of galaxies.

The galaxy’s star forming disk has been truncated which has caused the amount of star formation to be significantly reduced. The truncation may have been the result of interaction with other galaxies in the Virgo Cluster which caused the galaxy to lose much of its interstellar gas and dust, the fuel for new star formation. NGC 4689 has been classified as an Anemic galaxy because its lack of material for making new stars.

Image Credit: NASA / ESA