New recipe for dwarf galaxies: Start with leftover gas

February 19, 2009

There is more than one way to make a dwarf galaxy, and NASA's Galaxy Evolution Explorer has found a new recipe. It has, for the first time, identified dwarf galaxies forming out of nothing more than pristine gas likely leftover from the early universe. Dwarf galaxies are relatively small collections of stars that often orbit around larger galaxies like our Milky Way.

The findings surprised astronomers because most galaxies form in association with a mysterious substance called dark matter or out of gas containing metals. The infant galaxies spotted by the Galaxy Evolution Explorer are springing up out of gas that lacks both dark matter and metals. Though never seen before, this new type of dwarf galaxy may be common throughout the more distant and early universe, when pristine gas was more pervasive.

Led by David Thilker of the Henry A. Rowland Department of Physics and Astronomy at The Johns Hopkins University, a team of astronomers spotted the unexpected new galaxies forming inside the Leo Ring, a huge cloud of hydrogen and helium that traces a ragged path around two massive galaxies in the constellation Leo. The cloud is thought likely to be a primordial object, an ancient remnant of material that has remained relatively unchanged since the very earliest days of the universe. Identified about 25 years ago by radio waves, the ring cannot be seen in visible light.

"This intriguing object has been studied for decades with world-class telescopes operating at radio and optical wavelengths," said Thilker, a research scientist. "Despite such effort, nothing except the gas was detected. No stars at all, young or old, were found. But when we looked at the ring with the Galaxy Evolution Explorer, which is remarkably sensitive to ultraviolet light, we saw telltale evidence of recent massive star formation. It was really unexpected. We are witnessing galaxies forming out of a cloud of primordial gas."

In a recent study, Thilker and his team found the ultraviolet signature of young stars emanating from several clumps of gas within the Leo Ring. "We speculate that these young stellar complexes are dwarf galaxies, although, as previously shown by radio astronomers, the gaseous clumps forming these galaxies lack dark matter," he said. "Almost all other galaxies we know are dominated by dark matter, which acted as a seed for the collection of their luminous components -- stars, gas, and dust. What we see occurring in the Leo Ring is a new mode for the formation of dwarf galaxies in material remaining from the much earlier assembly of this galaxy group."

Our local universe contains two large galaxies, the Milky Way and the Andromeda galaxy, each with hundreds of billions of stars, and the Triangulum galaxy, with several tens of billions of stars. It also holds more than 40 much smaller dwarf galaxies, which have only a few billion stars. Invisible dark matter, detected by its gravitational influence, is a major component of both giant and dwarf galaxies with one exception -- tidal dwarf galaxies.

Tidal dwarf galaxies condense out of gas recycled from other galaxies and have been separated from most of the dark matter with which they were originally associated. They are produced when galaxies collide and their gravitational masses interact. In the violence of the encounter, streamers of galactic material are pulled out away from the parent galaxies and the halos of dark matter that surround them.

Because they lack dark matter, the new galaxies observed in the Leo Ring resemble tidal dwarf galaxies, but they differ in a fundamental way. The gaseous material making up tidal dwarfs has already been cycled through a galaxy. It has been enriched with metals--elements heavier than helium--produced as stars evolve. "Leo Ring dwarfs are made of much more pristine material without metals," said Thilker. "This discovery allows us to study the star formation process in gas that has not yet been enriched."

Large, pristine clouds similar to the Leo Ring may have been more common throughout the early universe, Thilker said, and consequently may have produced many dark-matter-lacking, dwarf galaxies yet to be discovered.

The results of the new study reporting star formation in the Leo Ring appear in the Feb. 19, 2009, issue of the journal Nature.

Johns Hopkins University

Dwarf Galaxies: Keys to Galaxy Formation and Evolution: Proceedings of Symposium 3 of JENAM 2010 (Astrophysics and Space Science Proceedings)
by Polychronis Papaderos (Editor), Simone Recchi (Editor), Gerhard Hensler (Editor)

Dwarf galaxy research constitutes an extremely vibrant field of astrophysical research, with many long-standing questions still unsettled and new ones constantly arising. The intriguing diversity of the dwarf galaxy population, observed with advanced ground-based and space-borne observatories over a wide spectral window providing an unprecedented level of detail, poses new challenges for both observers and theoreticians. The aim of this symposium was to bring together these two groups to exchange ideas and new results on the many evolutionary aspects of and open issues concerning dwarf galaxies. The main topics addressed include: the birth of dwarf galaxies: theoretical concepts and observable relics across wavelengths and time, the morphological, structural and chemical evolution of...

Pluto: A Dwarf Planet (Pebble Plus: Exploring the Galaxy)
by Adamson (Author), Thomas K. (Author)

Pluto is now a dwarf planet. Learn more about the fascinating, cold world of Pluto.

Low-metallicity Star Formation (IAU S255): From the First Stars to Dwarf Galaxies (Proceedings of the International Astronomical Union Symposia and Colloquia)
by Leslie K. Hunt (Editor), Suzanne C. Madden (Editor), Raffaella Schneider (Editor)

Although low-mass metal-poor galaxies in the local universe have often been proposed as the 'primordial building blocks' in the hierarchical scenario of structure formation, several lines of evidence suggest that this may not be true. Moreover, it is not clear to what extent dwarf galaxies, because they are metal poor and because of their kinematics and structure, can tell us about how star formation proceeded in the early universe. This volume provides an overview and the most recent advances in this debate. IAU Symposium 255 presents the most up-to-date developments in six key areas, including: Population III and metal-free star formation; metal-enrichment, chemical evolution and feedback; explosive events in low-metallicity environments; dust and gas as seeds for metal-poor star...

New Light on Dark Stars: Red Dwarfs, Low-Mass Stars, Brown Stars (Springer Praxis Books / Astronomy and Planetary Sciences)
by Neil Reid (Author), Suzanne Hawley (Author)

There has been very considerable progress in research into low-mass stars, brown dwarfs and extrasolar planets during the past few years, particularly since the fist edtion of this book was published in 2000. In this new edtion the authors present a comprehensive review of both the astrophysical nature of individual red dwarf and brown dwarf stars and their collective statistical properties as an important Galactic stellar population. Chapters dealing with the observational properies of low-mass dwarfs, the stellar mass function and extrasolar planets have been completely revised. Other chapters have been significantly revised and updated as appropriate, including important new material on observational techniques, stellar acivity, the Galactic halo and field star surveys. The authors...

Mysteries of Galaxy Formation (Springer Praxis Books / Popular Astronomy)
by Francoise Combes (Author)

The mystery of how the galaxies formed is a complex and intriguing subject, involving several different theories and an understanding of many different phenomena. Françoise Combes outlines the context in which the Big Bang and the expansion of the universe occurred and the first ‘inhomogeneities’ from which arose the early structures of the universe. The author describes how, contrary to our everyday experience, space and time appear to be intimately connected. In astronomy, a telescope is a time machine. We can look today at distant galaxies and, although we describe them in the present tense, we are really seeing them in their youthful stages, now long over. Having outlined the evolution and structure of galaxies, black holes are introduced. What do we know about their origins and...

Galaxies in the Local Volume (Astrophysics and Space Science Proceedings)
by Bärbel Silvia Koribalski (Editor), H. Jerjen (Editor)

This timely book presents an overview of the galaxies within the Local Volume, including the Local Group and our closest neighbours, the Andromeda Galaxy and the Magellanic Clouds. Presented here are the latest results from radio, infrared and optical surveys as well as detailed multi-wavelength studies of individual galaxies. The book aims to provide a vibrant forum for presentations and discussions across a broad range of astrophysical topics.

Near-Field Cosmology with Dwarf Elliptical Galaxies (IAU C198) (Proceedings of the International Astronomical Union Symposia and Colloquia)
by Helmut Jerjen (Editor), Bruno Binggeli (Editor)

Dwarf galaxies offer a valuable insight into the physical processes that govern galaxy formation and evolution at high redshift. These elusive stellar systems are helping astronomers to find answers to some of the most burning questions in extragalactic astronomy. Present-day dwarf galaxies, the easily studied survivors of the primordial galaxy population, are important targets for research in the quest to provide local benchmarks for cosmological studies, in particular theories of structure formation. The proceedings of IAUC198 offer an exciting multidisciplinary collection of research results. The interpretation of the faint blue galaxy excess; the mismatch of the observed dwarf galaxy numbers with popular cosmological model predictions; and the puzzling diversity of star-formation...

Star-forming dwarf galaxies and related objects
by Frontieres (Publisher)

Ultracool Dwarfs: New Spectral Types L and T
by Hugh R.A. Jones (Editor), Iain A. Steele (Editor)

This book records our current understanding of the observational and theoretical properties of objects known as ultracool dwarfs. It covers the state of the art in this new field. It is split into theoretical, observational and spectral classification sections. Each subject area begins with an introduction by an eminent scientist. It covers a wide range of issues, such as the transition from L to T dwarfs, dust and alkali metal modelling, companions, activity, the deuterium test, and brown dwarf variability, and contains considerable discussion about spectral classification schemes. The articles arose from an IAU meeting and they address researchers as well as graduate students.

Galaxies: A Very Short Introduction
by John Gribbin (Author)

In this fascinating Very Short Introduction, popular science writer John Gribben tells the story of our growing understanding of galaxies, from the days before Galileo to our present-day observations of our many hundreds of millions of galactic neighbors. Not only are galaxies fascinating astronomical structures in themselves, but their study has revealed much of what we know today about the cosmos, providing a window on the Big Bang and the origins of the Universe. Gribben looks at our own "Milky Way" Galaxy in detail, from the different kinds of stars that are born within it, to the origins of its magnificent spiral structure. Perhaps most interesting, Gribben describes the many exciting discoveries have been made about our own galaxy and about those beyond: how a supermassive black...