Irregular galaxy facts for kids
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An irregular galaxy is a galaxy that doesn't have a clear, regular shape. Unlike spiral galaxies with their swirling arms or elliptical galaxies that look like stretched-out balls, irregular galaxies are often messy and undefined.
These galaxies don't fit into the usual categories of the Hubble sequence, which is a way scientists classify galaxies. They don't have a central "bulge" (a bright, round area in the middle) or any sign of spiral arms. Even though they look a bit chaotic, irregular galaxies are very common. They might make up about a quarter of all galaxies in the universe! Many of them were once spiral or elliptical galaxies but got pulled out of shape by the strong gravity of other nearby galaxies. Irregular galaxies are also full of gas and dust, which are the building blocks for new stars.
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Types of Irregular Galaxies
Scientists group irregular galaxies into a few different types based on how much structure they show.
Irr-I Galaxies
An Irr-I galaxy is an irregular galaxy that has some signs of organization, but not enough to be called a regular spiral or elliptical galaxy. Sometimes, these are actually small spiral galaxies that are being stretched and pulled apart by the gravity of a much larger galaxy nearby. Imagine a small puddle being disturbed by a big wave!
Irr-II Galaxies
An Irr-II galaxy is an irregular galaxy that looks completely disorganized. It doesn't seem to have any clear structure at all, making it impossible to place it anywhere on the Hubble sequence. These are truly "irregular" in every sense.
Dwarf Irregular Galaxies
Dwarf irregular galaxies are smaller irregular galaxies. They are quite special because they often have very low levels of "metals" (which astronomers call any element heavier than hydrogen and helium) and lots of gas. This is similar to the very first galaxies that formed in the early universe. So, studying dwarf irregulars can help us understand what the universe was like billions of years ago! They might be like a modern version of the "faint blue galaxies" that scientists see in very deep space images.
Magellanic Clouds
The Magellanic Clouds are two well-known galaxies that orbit our own Milky Way galaxy. For a long time, they were thought to be irregular galaxies. However, scientists have since discovered that they actually have a "barred spiral" structure, meaning they have a bar-shaped group of stars in their center, similar to some spiral galaxies. This shows how our understanding of galaxies can change as we get better at observing them!
Images for kids
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Blue compact dwarf galaxy ESO 338-4.
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IC 4710 lies roughly 25 million light-years away in the southern constellation of Pavo.
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ESO 486-21 is a spiral galaxy with a somewhat irregular and ill-defined structure.
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Irregular galaxy IC 3583 has been found to have a bar of stars running through its center.
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NGC 2337 is an irregular galaxy that resides 25 million light-years away in the constellation of Lynx.
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UGC 4459 is an irregular dwarf galaxy located approximately 11 million light-years away in the constellation of Ursa Major.
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Dwarf irregular galaxy known as PGC 18431.
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IC 559 is classified as a type Sm galaxy.
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Irregular dwarf galaxy PGC 16389 covers its neighboring galaxy APMBGC 252+125-117.
See also
In Spanish: Galaxia irregular para niños
