Dwarf Galaxy Leo A Shows an Unusual Star Formation Timescale

At first glance this NASA/ESA Hubble Space Telescope image seems to show an array of different cosmic objects, but the speckling of stars shown here actually forms a single body — a nearby dwarf galaxy known as Leo A. Its few million stars are so sparsely distributed that some distant background galaxies are visible through it. Leo A itself is at a distance of about 2.5 million light-years from Earth and a member of the Local Group of galaxies; a group that includes the Milky Way and the well-known Andromeda galaxy. Astronomers study dwarf galaxies because they are very numerous and are  simpler in structure than their giant cousins. However, their small size makes them difficult to study at great distances. As a result, the dwarf galaxies of the Local Group are of particular interest, as they are close enough to study in detail. As it turns out, Leo A is a rather unusual galaxy. It is one of the most isolated galaxies in the Local Group, has no obvious structural features beyond being a roughly spherical mass of stars, and shows no evidence for recent interactions with any of its few neighbours. However, the galaxy’s contents are overwhelmingly dominated by relatively young stars, something that would normally be the result of a recent interaction with another galaxy. Around 90% of the stars in Leo A are less than eight billion years old — young in cosmic terms! This raises a number of intriguing questions about why star formation in Leo A did not take place on the “usual” timescale, but instead waited until it was good and ready.
It’s hard to pick out a single, cohesive body of stars in this image taken by the Hubble Space Telescope, but the array of cosmos objects seen make up the dwarf galaxy Leo A (Leo III). The millions of stars in this smaller galaxy are sparsely distributed enough for distant background galaxies to be visible.  

Nearly 90 percent of its stars were formed only 8 billion years ago, which is young in comparison to the majority of stars surveyed in the cosmos, so far

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Irregular dwarf galaxies like Leo A are thought to be the building blocks of larger galaxies like our own Milky Way. 

Space news (new star formation in dwarf galaxy Leo A, 2.54 million light-years from Earth) – It appears star formation in this smaller galaxy didn’t start until it was good and ready, which for astronomers poses a few puzzling questions –

Astronomers studying planetary formation in smaller dwarf galaxies sprinkled around the nearby cosmos have found something different about the process of star formation in a member of the Local Group of galaxies. This nearby group contains two large spiral galaxies, the Milky Way and Andromeda galaxy (M31), and about 30 galaxies in total. 

Dwarf galaxies are both more numerous in the cosmos and simpler in structure than larger spiral galaxies, but harder to study in most cases due to the extreme distances involved. In the case of closer dwarf galaxies, like Leo A, they’re easier to study in detail, but still hard to study due to their smaller size of around 10,000 light-years.

Astronomers studying dwarf galaxy Leo A also called UGC 5364 and LEDA 28868, have found no evidence of recent mergers with any of its neighbours. They have discovered, however, that nearly 90 percent of the stars in this smaller galaxy are younger than 8 billion years. This goes against the current theory that such a result would normally be due to a recent merger with another galaxy. A finding that has astronomers asking a puzzling question concerning star formation timescales in dwarf galaxies viewed during the human journey to the beginning of space and time. 

Why is Leo A dominated by young stars, despite showing no signs of a recent merger with another galaxy?

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Other astronomers studying Leo A recently reported the discovery of an old stellar halo and sharp edge, along with a distribution of stars extending just beyond its gaseous envelope. This implies smaller galaxies with less mass and stars also develop complex structures like larger spiral galaxies. This challenges current galaxy evolution theory and our understanding of smaller island universes.

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