A Lonely, Wandering Hermit of a Galaxy

Tells astronomers a thing or two about star birth throughout the cosmos 

A mysterious hermit

Space news (astrophysics: irregular dwarf galaxies; the formation of new stars) – a lonely, undefined looking galaxy an estimated 4.2 million light-years from Earth, approximately 2.3 million light-years from Leo A –  

The Sagittarius Dwarf Irregular Galaxy (SagDIG) is a metal-poor galaxy from the dawn of the cosmos. Almost as old as the universe, SagDIG is showing us things about the evolution of everything we see during our journey to the beginning of space and time. Spanning about 1,500 light-years, this ancient star wanderer is about 3.5 million light-years distant toward the constellation Sagittarius.

Astronomers think the chaotic, unusual looking smaller island universe seen in the Hubble Space Telescope image here hasn’t merged with any other galaxies lately. Classified as an irregular dwarf galaxy, UGC 4879 has no obvious form and lacks the magnificent whirl of a spiral galaxy or the coherence of an elliptical. Approximately 1.36 million parsecs from Earth this lonely, wandering hermit of a galaxy is showing astronomers new, interesting things about star birth in the universe

Irregular dwarf galaxy Leo A seen here has a much more complicated formation history than astronomers first thought. The simple structure astrophysicists were expecting isn’t what we see here. Instead, Leo A shows hints of an evolution just as chaotic and unpredictable as larger island universes. 

Spectral data of UGC 4879 indicates radial velocities for different sections of the galaxy, which could indicate the presence of a stellar disk. This lonely, isolated wanderer is studied closely and intensely by astronomers because of its history of few interactions with other galaxies. This isolation makes it less complicated to piece together its history of star birth and an ideal laboratory for study. 

Dwarf irregular galaxy NGC 1569 seen here underwent a brief starburst period about 25 million years ago. Hidden within the chaos are monstrous, gigantic supermassive stars and envelopes of gas expelled by huge stars that recently went supernova. Only 11 million light-years away in the long-necked constellation Camelopardalis and spanning 8,000 light-years, the blue, white hot young stars within are perfect for study. Credit: NASA/ESA/STScI/Hubble Heritage

Study of UGC 4879 indicates during the first 4 billion years after the beginning of the universe new stars were being born at a pretty fast rate. The next nine billion years of relative inactivity followed by a recent starburst about 1 billion years ago is a puzzle for astronomers. They continue to study this hermit of a galaxy hoping to find out more about both its history and the complex riddles of sun birth across the cosmos.  

Irregular dwarf galaxy NGC 4449 seen here is undergoing an intense period of starburst, with young, blue-white stars being created at an amazing rate and pinkish star forming regions in this deep colour image. Only 12.5 million light-years away in Canes Venatici, the constellation of the Hunting Dogs, NGC 4449’s the first such galaxy to have an identified star stream in the lower right composed mainly of supermassive red giant stars. These types of galaxies are thought to have a significant dark matter halo, which is a chance for astronomers to study the dark side’s role in the evolution and formation of galaxies. Credit: NASA/ESA/STScI 

Read about one of the most massive black holes ever discovered residing in a backwater part of the cosmos.

For the first time in space history the first moments of a supernova caught in visible light.

Read about Chandra observing the supermassive black hole in galaxy Pictor A having a little meal.

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Learn more about irregular dwarf galaxies

Read a paper on the star formation history of irregular dwarf galaxy UGC 4879 here.


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?

Breaking News

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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Learn more about Leo A.

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Read about the weird light signal emitted by two black holes that are destined to merge.

Learn more about the first moments of supernovas.