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

Lonely Dwarfs

Luhman 16AB is a double star system composed of two brown dwarfs. It’s only about six light-years away, and is the third closest stellar system to Earth—after the triple star system Alpha Centauri and Barnard’s Star. Because the brown dwarfs are so dim, Luhman 16AB was only discovered in 2013.

This series of dots with varying spacings between them in the image above shows the slow waltz of the two brown dwarfs. It’s a composite of 12 images made over the course of three years by the Hubble Space Telescope. Using high-precision astrometry, a team of astronomers tracked the two components of the system as they moved both across the sky and around each other.

The brown dwarfs, Luhman 16A and Luhman 16B, orbit each other at a distance of only about 500,000,000 km, roughly three times the distance between the Earth and the Sun. Observations of the system require high resolution. The astronomers using Hubble to study Luhman 16AB were not only interested in the waltz of the two stars as they orbited each other but also were also searching for a third, invisible partner. Earlier ground-based observation suggested the presence of an exoplanet in the system, but the Hubble data showed that the two dwarfs are indeed dancing alone, unperturbed by a massive planetary companion.

Image Credit: NASA / ESA

NGC 3447

Some galaxies are hard to classify. The more diffuse and patchy blue glow covering the right side of the image above is known as NGC 3447B. The smaller clump to the upper left is known as NGC 3447A. The pair are know collectively as NGC 3447.

The two are so close that they are strongly influenced and distorted by the gravitational forces between them, causing the galaxies to twist themselves into unusual  shapes seen here. Astronomers are unsure what the originals shapes of the two galaxies were before they encountered each other. NGC 3447A appears to display the remnants of a central bar structure and some disrupted spiral arms, both properties characteristic of certain spiral galaxies. NGC 3447B may also have been spiral galaxy, or it may have been an irregular galaxy.

Image Credit: NASA / ESA

NGC 5364

Despite being classified ias a grand spiral galaxy, NGC 5364 is far from perfect. Its arms are asymmetrical compared to other grand design spirals. This is probably caused by interactions with a neighboring galaxy. This neighbor and NGC 5364 are pulling on one another, moving their stars and gas around. Thus, NGC 5364’s misshapen appearance.

Image Credit: NASA / ESA