One Ring to Rule Them All

Zw II 28 is a ring galaxy. Ring galaxies are thought to form when one galaxy passes through the disc of another, larger one. Because galaxies are mostly empty space, such “collisions” are not as destructive as one might suppose. The probability of two stars physically colliding is nearly zero. It’s the gravitational effects of the two galaxies that causes disruption, upsetting the balance both galaxies and causing the pair to redistribute to form a dense central core surrounded by bright stars. In the process, clouds of gas and dust collapse, triggering intense star formation in the outer ring and filling it with hot, young, blue stars.

Zw II 28’s sparkling pink and purple loop is not typical of a ring galaxy. It lacks a visible central companion, but recent observations using Hubble have shown that there may be a possible companion lurking just inside the ring, where the loop seems to double back on itself.

Image Credit: ESA / NASA

HH 901

Herbig Haro 901 is a multiple light-years tall pillar of gas and dust inside the star-forming region know as the Carina Nebula. It contains several massive young stars which emit powerful jets that emerge from the cloud. Some of the jets create bow-shock patterns similar to the bow waves of a ship plowing through the ocean. Very few of these stars can be seen  because the gas and dust block starlight, but in an infrared view, more stars become visible. The visible-light colors result from the glow of different gases: oxygen (blue), hydrogen/nitrogen (green), and sulfur (red). The Carina Nebula is approximately 7,500 light years from Earth.

Video Credit: NASA / ESA / STScI

I Zwicky 18

I_Zwicky_18I Zwicky 18 is a dwarf irregular galaxy located about 59 million light years away. Spectroscopic observations with ground-based telescopes showed that I Zwicky 18 to be almost completely made up of hydrogen and helium, the main ingredients created in the Big Bang, and galaxies with I Zwicky 18’s youthful appearance are typically found only in the early universe. Initial observations with the Hubble Space Telescope suggested an age of 500 million years, but later Hubble observations found faint, older stars in the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as ten billion years ago. It’s possible that the galaxy may have formed around the same time as most other galaxies.

Image Credit: NASA / ESA


Icarus, officially know as MACS J1149+2223 Lensed Star 1, is the farthest individual star ever seen. It is only visible because it is being magnified by the gravity lensing of a massive galaxy cluster, located about 5 billion light-years from Earth. That cluster, MACS J1149+2223, shown at left, sits between Earth and the galaxy that contains the distant star. Icarus and its galaxy are 9 billion light-years away. The panels at the right show a view taken in 2011 without Icarus visible and after the star was lensed in 2016.

Image Credit: NASA / ESA