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


dwarf galaxyHappy, Sneezy, Dopey, … No, no … Balin, Bifur, Bofur, … No, not them either. This post is about one of the dwarf galaxies that is part of the M101 group. Ursa Major (The Great Bear) is home to Messier 101, the Pinwheel Galaxy. Messier 101 is one of the biggest and brightest spiral galaxies in the night sky. Like the Milky Way, Messier 101 is not alone with smaller dwarf galaxies in its neighborhood. NGC 5477, which is the main subject of the Hubble Space Telescope image above, is one of those companion galaxies. It’s a typical irregular dwarf galaxy with no obvious structure but plenty of signs of new star creation. The bright nebulae that extend across the galaxy are clouds of glowing hydrogen gas in which those new stars are forming. These glow pinkish red in real life, but appear white in this false color image which was taken through green and infrared filters using Hubble‘s Advanced Camera for Surveys. The field of view is about 3.3 arcminutes wide.

The picture includes numerous galaxies in the background; some are visible right through NGC 5477. This demonstrates that galaxies, far from being solid, opaque objects, are actually largely made up of the empty space between their stars.

Image Credit: NASA

A Dwarf Tadpole Galaxy

This Hubble Space Telescope image shows a firestorm of star birth is lighting up one end of the dwarf galaxy Kiso 5639. Kiso 5639 is really shaped like a pancake but, from our point of view, it seems to have brilliant blazing head and a long, starry tail. Its appearance earns it a place in the “tadpole” class of galaxies.

The bright pink head is glowing of hydrogen lit by radiation from new stars grouped into large clusters that less than a million years old.

Image Credit: ESA / NASA

NGC 1569

The NGC 1569 is a relatively nearby dwarf irregular galaxy in Camelopardalis. It’s characterized by a large starburst that has formed stars at a rate 100 times greater than that of the Milky Way during the last 100 million years.

The spectrum of NGC 1569 is blueshifted. This means that the galaxy is moving towards the Earth. In contrast, the spectra of most other galaxies are redshifted because of the expansion of the universe.

Image Credit: NASA

A Dwarf Galaxy

NGC 5949 is a dwarf galaxy around 44 million light-years from us. NGC 5949 is a relatively bulky example of a dwarf galaxy with a mass of about one percent of the Milk Way’s. It’s classified as a dwarf because of its relatively small number of constituent stars, but with loosely-bound spiral arms it is also classified as a barred spiral galaxy.

Image Credit: ESA / NASA

A Lonely Dwarf

Wolf – Lundmark – Melotte (WLM) is a lonely dwarf galaxy named for the three astronomers who discovered it. It’s about 3 million light-years from the Milky Way in the constellation Cetus, and it’s one of the most remote members of our local galaxy group. It’s so isolated that it may never have interacted with any other local group galaxy.

Image Credit: ESO