An Isolated, Irregular Dwarf

NGC 1156 is located around 25 million light-years from Earth in the constellation Aries. It’s a dwarf irregular galaxy and isolated, meaning no other galaxies are close enough to influence its odd shape or star formation. The extreme energy of young stars ionizes hydrogen gas which glows red, while its centre is filled with older stars.

Video Credits: ESA / NASA / R. B. Tully / R. Jansen / R. Windhorst

An Isolated Dwarf

Some galaxies are comparatively isolated. One such galaxy is the dwarf galaxy known as DDO 190 (DDO stands for the David Dunlap Observatory where the DDO catalog was created). DDO 190 is classified as a dwarf irregular galaxy because of its relatively small size and amorphous structure with a mix of old and new stars. The older red stars are generally found in DDO 190’s outskirts, and the younger, blue ones are mostly in the interior.

DDO 190 is about 9 million light years away. It’s a member of the loosely associated Messier 94 group of galaxies. Although within the Messier 94 group, DDO 190 is fairly isolated. The galaxy’s nearest dwarf galaxy neighbor is thought to be at least 3 million light years away from DDO 190. Many of the Milky Way’s companion galaxies, including the Large and Small Magellanic Clouds, are within 20 percent of that distance. The Andromeda Galaxy is closer to the Milky Way than DDO 190 is to its nearest neighbor.

Image Credit: NASA

An Odd Dwarf : The Sky Rocket Galaxy

Kiso 5639A firestorm of star birth is lighting up one end of the diminutive galaxy Kiso 5639. The dwarf galaxy is shaped like a flattened pancake, but because we see it edge-on, it resembles a skyrocket with a blazing head and a long tail.

Kiso 5639 is rare among nearby galaxies. It’s an example of a sort of elongated galaxies that occur in abundance at larger distances, where we observe the universe during earlier epochs. The bright gas in the galaxy’s head contains fewer heavier elements (referred to as “metals” by astronomers) such as carbon and oxygen than the rest of the galaxy. Stars consist mainly of hydrogen and helium, but cook up other “heavier” elements. When the stars die, they release their heavy elements and enrich the surrounding gas.

The galaxy, located 82 million light-years away, has taken billions of years to develop because it has been drifting through an isolated “desert” in the universe, devoid of much gas. Several dozen clusters of stars have been observed in the galaxy’s star-forming head, which spans 2,700 light-years across. These clusters have an average age of less than a million years. Other star formation is taking place throughout the galaxy but on a much smaller scale. Star clusters in the rest of the galaxy are between several million to a few billion years old. Observations suggest that less than a million years ago, Kiso 5639’s leading edge encountered a filament of gas in intergalactic space. The filament could have lost a large amount of matter the galaxy, stoking the vigorous star birth.

Image Credit: NASA

An Irregular Dwarf

content/uploads/2015/04/i_zwicky_18.jpg”>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

A Neighborhood Dwarf

A case of suspended animation?The speckling of stares in this image taken by the Hubble Space Telescope image seems to show an array of different cosmic objects, actually forms a single body—the nearby dwarf galaxy known as Leo A. Its few million stars are so sparsely distributed that distant galaxies in the background can be seen behind it. Leo A is about 2.5 million light-years from Earth and is a member of the Local Group of galaxies, a group that includes the Milky Way.

Image Credit: NASA / ESA

A Chaotic Dwarf

The mysteries of UGC 8201The galaxy UGC 8201 is classified as a dwarf irregular galaxy because of its small size and chaotic structure. It’s a bit less than15 million light-years away in the constellation of Draco (the Dragon). As with most dwarf galaxies, it is a member of a larger group of galaxies, in this case, the M81 galaxy group. This group is one of the nearby neighbors to the Local Group of galaxies which contains our galaxy, the Milky Way.

Image Credit: ESA / NASA

A Disorganized Dwarf

A distinctly disorganised dwarfUGC 4459’s diffused and disorganized appearance is characteristic of an irregular dwarf galaxy. Because they lack distinctive structure or shape, irregular dwarf galaxies are typically chaotic in appearance, with neither a nuclear bulge (a tightly-packed central group of stars) nor any trace of spiral arms extending from the center of the galaxy.

Image Credit: NASA

An Irregular Dwarf Galaxy

ngc-4214This is dwarf galaxy NGC 4214 which is forming clusters of new stars from its interstellar gas and dust. The young clusters of new stars are within glowing gas clouds. The gas glows because it is excited by the strong ultraviolet light emitted from the young stars forming in the gravitational collapse of the gas. These hot stars eject stellar winds moving at thousands of km/s which blow bubbles in the gas. Near the center of the galaxy, there is a cluster of hundreds of massive blue stars, each more than 10,000 X brighter than our Sun, and a huge bubble inflated by stellar winds and radiation pressure surrounds the cluster.

Image Credit: NASA / ESA

A Nearby Dwarf

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 with a Supermassive Black Hole

A dwarf starburst galaxy about 30 million light years from Earth.Henize 2-10 is a dwarf galaxy, and it is the first dwarf galaxy ever discovered to contain a supermassive black hole at its center. This was surprising because the black hole is about one quarter of the size of the one at the center of the Milky Way Galaxy. However, Henize 2-10 is only about1/1,000th the size of the Milky Way..

This image combines x-ray (Chandra), visible light (Hubble), and radio telescope (Very Large Array) views.

Image Credit: NASA / NRAO

A Dwarf Flock

dwarf galaxyThis Hubble image looks a bit like a flock of birds. It’s really a picture of a dwarf galaxy called ESO 540-31 a bit more than 11 million light-years from Earth in the constellation of Cetus (The Whale). All those galaxies in the background are much further away.

Dwarf galaxies are some of the smaller and dimmer members of the galactic family with only a few hundred million stars or so. Although that may seem like a large number, it is tiny compared to spiral galaxies like our Milky Way, which are made up of hundreds of billions of stars.

Image Credit: NASA / ESA

A Doomed Dwarf

This is the dwarf galaxy known as NGC 1140. It lies 60 million light-years away in the constellation of Eridanus. It has an irregular form, much like the Large Magellanic Cloud, a small galaxy that orbits the Milky Way. This small galaxy is undergoing a starburst. Despite being only about one-tenth the size of the Milky Way, it is creating stars at about the same rate—the equivalent of one star the size of our sun being created per year. The galaxy is full of bright, blue-white, young stars.

Galaxies like NGC 1140 are of particular interest to astronomers because their composition makes them similar to the intensely star-forming galaxies in the early Universe, and those early Universe galaxies were the building blocks of present-day large galaxies like our Milky Way. Because they are so far away, the early Universe galaxies are harder to study, so these closer starbursting galaxies are a good substitute for studyingt galaxy evolution.

Its vigorous star formation eventually will have a very destructive effect on this small dwarf galaxy. When the larger stars in the galaxy die and explode as supernovae, the gas blown into space may escape the gravitational pull of the galaxy. The ejection of gas from the galaxy will starve future star formation. Thus, NGC 1140’s starburst cannot last for long.

Image Credit: ESA

A Lonely Dwarf

The Local Void is a vast, empty region of space adjacent to the Local Group, the group of galaxies that included our Milky Way. It’s composed of three separate sectors which are separated by bridges of “wispy filaments” of gas and dust. The exact size of the Local Void is unknown, but it is at least 150 million light-years across—and possibly 3 to 6 times larger still. It’s called a void because it has significantly fewer galaxies than expected from standard cosmology.

The irregular dwarf galaxy in the foreground of the picture is cataloged as KK 246, and it’s one of the few galaxies in the Local Void.

Image Credit: NASA / ESA

The Fornax Dwarf Spheroidal

Fornax_dwarf_galaxy
The Fornax Dwarf Spheroidal is an elliptical dwarf galaxy found in the constellation Fornax. The galaxy is a satellite of the Milky Way and contains six globular clusters. NGC 1049, the largest of its clusters, was discovered before the galaxy itself. The galaxy is receding from the Milky Way at 53 km/s.

Image Credit: ESO

Henize 2-10

A dwarf starburst galaxy about 30 million light years from Earth.Henize 2-10 is a dwarf galaxy, and it is the first dwarf galaxy ever discovered to contain a supermassive black hole at its center. This was surprising because the black hole is about one quarter of the size of the one at the center of the Milky Way Galaxy. However, Henize 2-10 is only about1/1,000th the size of the Milky Way..

This image combines x-ray (Chandra), visible light (Hubble), and radio telescope (Very Large Array) views.

Image Credit: NASA / NRAO

A Starbursting Galaxy

This is the dwarf galaxy known as NGC 1140. It lies 60 million light-years away in the constellation of Eridanus. It has an irregular form, much like the Large Magellanic Cloud, a small galaxy that orbits the Milky Way. This small galaxy is undergoing a starburst. Despite being only about one-tenth the size of the Milky Way, it is creating stars at about the same rate—the equivalent of one star the size of our sun being created per year. The galaxy is full of bright, blue-white, young stars.

Galaxies like NGC 1140 are of particular interest to astronomers because their composition makes them similar to the intensely star-forming galaxies in the early Universe, and those early Universe galaxies were the building blocks of present-day large galaxies like our Milky Way. Because they are so far away, the early Universe galaxies are harder to study, so these closer starbursting galaxies are a good substitute for studyingt galaxy evolution.

Its vigorous star formation eventually will have a very destructive effect on this small dwarf galaxy. When the larger stars in the galaxy die and explode as supernovae, the gas blown into space may escape the gravitational pull of the galaxy. The ejection of gas from the galaxy throws away one of the building blocks for future star formation. Thus, NGC 1140’s starburst cannot last for long.

Image Credit: ESA

Henize 2-10

A dwarf starburst galaxy about 30 million light years from Earth.Henize 2-10 is a dwarf galaxy, and it is the first dwarf galaxy ever discovered to contain a supermassive black hole at its center. This was surprising because the black hole is about one quarter of the size of the one at the center of the Milky Way Galaxy. However, Henize 2-10 is only about1/1,000th the size of the Milky Way..

This image combines x-ray (Chandra), visible light (Hubble), and radio telescope (Very Large Array) views.

Image Credit: NASA / NRAO

A Recently Discovered Dwarf Galaxy

When the Hubble Space Telescope photographed the globular star cluster NGC 6752 (located 13,000 light-years away in our Milky Way’s halo), the image revealed a never-before-seen dwarf galaxy cataloged as Bedin 1 located far behind the cluster’s crowded stellar population. The galaxy is only 30 million light-years away but had not been noticed before. It’s classified as a dwarf spheroidal galaxy because it measures only around 3,000 light-years at its greatest extent. Because it’s so small, it’s roughly a thousand times dimmer than the Milky Way.

Because it’s very old, 13 billion years, and relatively isolated, it’s seen hardly any interaction with other galaxies It’s the astronomical equivalent of a living fossil from the early universe.

This composite image above  shows the location of Bedin 1 behind the globular cluster NGC 6752. The lower image of the complete cluster is a ground-based observation from the Digitized Sky Survey 2. The upper right image shows the full field of view of the Hubble Space Telescope. The upper left image highlights the region containing the galaxy Bedin 1.

Image Credits: NASA / ESA / DSS / STScI