More star births than astronomers have calculated

October 02, 2008

Bonn study in Nature' explains the discrepancy

The "birth rate" for stars is certainly not easy to determine. Distances in the universe are far too great for astronomers to be able to count all the newly formed celestial bodies with the aid of a telescope. So it is fortunate that the emerging stars give themselves away by a characteristic signal known as "H-alpha" emissions. The larger the number of stars being formed in a particular region of the firmament, the more H-alpha rays are emitted from that region.

"H-alpha emissions only occur in the vicinity of very heavy stars," explains Jan Pflamm-Altenburg of the Argelander Institute of Astronomy at Bonn University. It has long been accepted that heavy and light stars are always born in a certain ratio to each other. One "H-alpha baby" is thought to be accompanied by 230 lighter stars with a mass too low for them to emit H-alpha rays.

However, new observations make this theory untenable. On the edges of "disc galaxies" (like the Milky Way) the H-alpha radiation ceases abruptly. For a long time astronomers concluded from this finding that no stars are being born in this region. "The explanation offered is simply that too little gaseous matter exists for it to collapse into balls and form stars," says Jan Pflamm-Altenburg. "These theories largely inform our understanding of how galaxies developed from the Big Bang to the present."

Satellite mission baffles astronomers

A satellite mission has recently revealed that stars are in fact being formed beyond the H-alpha perimeter. These stars are, without exception, so light that no H-alpha radiation is emitted. Consequently, the numerical ratio of 230 light stars to one heavy star does not apply to the edges of galaxies. "This observation presented the astronomy community with quite a conundrum," says Professor Dr. Pavel Kroupa of the Argelander Institute.

Kroupa and Pflamm-Altenburg have come up with a solution which, they say, is basically very simple. They note that star births are not evenly distributed across galaxies but are focused on the star clusters - well known examples being the Seven Sisters and the Orion Nebula. And only large, high-mass clusters produce heavy stars, i.e. the newborn stars that can create the H-alpha emission. "But these heavy star clusters primarily occur in the core regions of disc galaxies," says Jan Pflamm-Altenburg. "Towards the edges they become increasingly rare. The outer regions tend to contain smaller clusters in which the formation of lighter stars is more frequent."

The conclusion is that a numerical ratio of 230 to 1 is only valid for the centres of galaxies. On the edges of galaxies each "H-alpha baby" might be accompanied by a thousand or more light stars. Those astronomers who always use the same factor when calculating total star formations from their H-alpha readings therefore underestimate the number of newborn stars.

The theoretical work of the two Bonn-based astrophysicists supports affirms that the mass of new stars depends linearly on the mass of the gas in their vicinity. Their conclusions open up completely new perspectives for research into the development of galaxies.

University of Bonn

---

---

	Concise Catalog of Deep-sky Objects: Astrophysical Information for 500 Galaxies, Clusters and Nebulae by W.H. Finlay (Author)   Here is a unique and fascinating reference book for every serious deep-sky observer! Entries for each of more than 500 deep-sky objects provide far more than the usual astronomical data – they also detail, in every case, the most interesting facts. Physical factors, astrophysical information, evolution, unusual features, the list is endless. The objects are all listed in NGC order.  Astronomers can now get an insight into exactly what they are looking at, to add a new level of insight and enjoyment to deep-sky observing.
	Galaxies by Seymour Simon (Author) This close-up look at our own Milky Way and other enormous clusters of stars describes the many different types of galaxies, how they were formed, and how they got their different shapes. "A dazzling photo-essay."--School Library Journal.
	Galaxy Formation (Astronomy and Astrophysics Library) by Malcolm S. Longair (Author) Delineating the huge strides taken in cosmology in the past ten years, this much-anticipated second edition of Malcolm Longair's highly appreciated textbook has been extensively and thoroughly updated. It tells the story of modern astrophysical cosmology from the perspective of one of its most important and fundamental problems – how did the galaxies come about? Longair uses this approach to introduce the whole of what may be called "classical cosmology". What’s more, he describes how the study of the origin of galaxies and larger-scale structures in the Universe has provided us with direct information about the physics of the very early Universe.
	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...
	The Complete Guide to the Herschel Objects: Sir William Herschel's Star Clusters, Nebulae and Galaxies by Mark Bratton (Author) Sir William Herschel's contributions to astronomy during the late eighteenth century are unrivaled. His lasting legacy is his dedicated all-sky survey of star clusters and nebulae, and these objects continue to be among the most studied in the night sky. This unique book provides a complete re-examination of Herschel's entire catalog of non-stellar discoveries, making it the most accurate and up-to-date reference of its kind. Retrace the footsteps of one of history's greatest astronomers and explore every one of Herschel's landmark discoveries, including those considered to be lost or non-existent. Read detailed notes about each object's appearance and physical characteristics, and view hundreds of photos of the most intriguing Herschel objects, along with dozens of sketches of what is...
	Galaxies and How to Observe Them (Astronomers' Observing Guides) by Wolfgang Steinicke (Author), Richard Jakiel (Author) This book is a unique work satisfying the need for a modern, comprehensive review of all major aspects of galaxy observation. The book combines the physical background on the nature and data of galaxies, the relevant instrumentation and viewing techniques, and finally the targets and their individual appearance in telescopes of various apertures. A comprehensive sample of galaxies, including quasars, groups and clusters of galaxies is presented. This combination of theoretical knowledge and practical information guarantees successful observing sessions. Furthermore, the book is clearly structured with outstanding images and graphics.
	Clusters of Galaxies (Space Telescope Science Institute Symposium Series) by W. Oegerle (Editor), M. Fitchett (Editor), L. Danly (Editor) Collected in this volume are the review papers from the Space Telescope Science Institute symposium on Clusters of Galaxies held in May 1989. Fifteen experts in the field have presented summaries of our current understanding of the formation and evolution of clusters and their constituent galaxies. Subjects covered include the existence and importance of subclustering, models of the evolution of clusters and the intracluster medium, the effect of the cluster environment on galaxies, observations of high redshift clusters, and the use of clusters as tracers of large scale structure. This book provides a timely focus for future observational and theoretical work on clusters of galaxies.
	A Pan-Chromatic View of Clusters of Galaxies and the Large-Scale Structure (Lecture Notes in Physics) by Manolis Plionis (Editor), O. López-Cruz (Editor), D. Hughes (Editor) The reviews presented in this volume cover a huge range of cluster of galaxies topics. Readers will find the book essential reading on subjects such as the physics of the ICM gas, the internal cluster dynamics, and the detection of clusters using different observational techniques. The expert chapter authors also cover the huge advances being made in analytical or numerical modeling of clusters, weak and strong lensing effects, and the large scale structure as traced by clusters.
	X-Ray Emission from Clusters of Galaxies (Cambridge Astrophysics) by Craig L. Sarazin (Author) First published in 1988, this book is a comprehensive survey of the astrophysical characteristics of the hot gas which pervades clusters of galaxies. In our universe, clusters of galaxies are the largest organised structures. Typically they comprise hundreds of galaxies moving through a region of space ten million light years in diameter. The volume between the galaxies is filled with gas having a temperature of 100 million degrees. This material is a strong source of cosmic X-rays. Dr Sarazin describes the theoretical description of the origin, dynamics, and physical state of the cluster gas. Observations by radio and optical telescopes are also summarised. This account is addressed to professional astronomers and to graduate students. It is an exhaustive summary of a rapidly expanding...
	Globular Clusters - Guides to Galaxies: Proceedings of the Joint ESO-FONDAP Workshop on Globular Clusters held in Concepción, Chile, 6-10 March 2006 (ESO Astrophysics Symposia) by Tom Richtler (Editor), Søren Larsen (Editor) The principal question of whether and how globular clusters can contribute to a better understanding of galaxy formation and evolution is perhaps the main driving force behind the overall endeavour of studying globular cluster systems. Naturally, this splits up into many individual problems. The objective of the Joint ESO-FONDAP Workshop on Globular Clusters - Guides to Galaxies was to bring together researchers, both observational and theoretical, to present and discuss the most recent results. Topics covered in these proceedings are: internal dynamics of globular clusters and interaction with host galaxies (tidal tails, evolution of cluster masses), accretion of globular clusters, detailed descriptions of nearby cluster systems, ultracompact dwarfs, formations of massive clusters in...