Dusty Globules and Globulettes PDF
Preview Dusty Globules and Globulettes
DOCTORA L T H E S IS Department of Engineering Sciences and Mathematics Division of Material Science T Dusty Globules and Globulettes i i ISSN 1402-1544 a G ISBN 978-91-7790-092-4 (print) r e ISBN 978-91-7790-093-1 (pdf) n m a Luleå University of Technology 2018 n D u s t y G lo b u le s a n d G lo b u le t t e s Tiia Grenman Applied Physics Doctoral Thesis Dusty Globules and Globulettes Tiia Grenman Division of Applied Physics Lule˚a University of Technology SE-971 87 Lule˚a Sweden E-mail: [email protected] Lule˚a, May 2018 © 2018 Tiia Grenman Division of Applied Physics Department of Engineering Sciences and Mathematics Luleå University of Technology SE-971 87 Luleå Sweden The cover image shows the northern part of the Rosette Nebula. In the lower right part of the image the Wrench, an elephant trunk is shown. This trunk is mainly made up of thin threads that are twisted and connected to two jaws at the lower massive head. In the upper part of this Wrench a string of dark dots, globulettes, are seen in silhouette against the bright background. This false-color image shows emission from lines of Sulfur, Hydrogen and Oxygen (shaded red, green and blue). Credit: Astronomy Picture of the Day, March 2014. Printed by Luleå University of Technology, Graphic Production 2018 ISSN 1402-1544 ISBN 978-91-7790-092-4 (print) ISBN 978-91-7790-093-1 (pdf) Luleå 2018 www.ltu.se i We are just an advanced breed of monkeys on a minor planet of a very average star. But we can understand the Universe. That makes us something very special. Stephen Hawking To my family ABSTRACT Interstellargasanddustcancondenseintocloudsofverydifferentsize,ranging from giant molecular cloud complexes to massive, isolated, dark cloudlets, called globules with a few solar masses. This thesis focuses on a new category of small globules, named globulettes. These have been found in the bright surroundings of H II regions of young, massive stellar clusters. The globulettes are much smaller and less massive than normal globules. The analysis is based on H-alpha images of e.g., the Rosette Nebula and the Carina Nebula collected with the Nordic Optical Tele- scope and the Hubble Space Telescope. Most globulettes found in different H II regions have distinct contours and are well isolated from the surrounding molecular shell structures. Masses and densities were derived from the extinction of light through the globulettes and the measured shape of the objects. A majority of the globulettes have planetary masses, <13M (Jupiter masses). Very few objects have masses J above 100M ≈ 0.1M (Solar masses). Hence, there is no smooth overlap J (cid:12) between globulettes and globules, which makes us conclude that globulettes represent a distinct, new class of objects. Globulettes might have been formed either by the fragmentation of larger filaments, or by the disintegration of large molecular clouds originally hosting compact and small cores. At a later stage, globulettes expand, disrupt or evaporate. However, preliminary calculations of their lifetimes show that some might survive for a relatively long time, in several cases even longer than their estimated contraction time. The tiny high density globulettes in the Carina Nebula indicate that they are in a more evolved state than those in the Rosette Nebula, and hence they may have survived for a longer time. It is possible that the globulettes could host low mass brown dwarfs or planets. Using the virial theorem on the Rosette Nebula globulettes and including only the thermal and gravitational potential energy indicated that the 133 iii iv found globulettes are all either expanding or disrupting. When the ram and the radiation pressure were included, we found that about half of our objects aregravitationallyboundorunstabletocontractionandcouldcollapsetoform brown dwarfs or free floating planets. Wealsoestimatedtheamountofglobulettesandthenumberoffreefloating planetary mass objects, originating from globulettes, during the history of the Milky Way. We found that a conservative value of the number of globulettes formedis5.7×1010. Alessconservativeestimategave2×1011 globulettesand if10%oftheseformsfreefloatingplanetsthentheglobuletteshavecontributed about 0.2 free floating planets per star. In the Crab Nebula, which is a supernova remnant from the explosion of a massive old star, one can find dusty globules appearing as dark spots against the background nebulosity. These globules are very similar to the globulettes wehavefoundinHIIregions. Thetotalmassofdustinglobuleswasestimated to be 4.5×10−4M , which corresponds to (cid:46) 2% of the total dust content of (cid:12) the nebula. These globules move outward from the center with transversal velocities of 60–1600kms−1. Using the extinction law for globules, we found thatthedustgrainsaresimilartotheinterstellardustgrains. Thismeansthat they contribute to the ISM dust population. We concluded that the majority of the globules are not located in bright filaments and we proposed that these globulesmaybeproductsofcell-likeblobsorgranulesintheatmosphereofthe progenitor star. Theses blobs collapse and form globules during the passage of the blast wave during the explosion. Preface The research behind this doctoral thesis has been carried out at the Division of Applied Physics, Lule˚a University of Technology. It had not been possible withoutthehelpandsupportofmanyindividuals, who, inonewayoranother, have helped me to complete my work. First of all, I would like to express my gratitude to my supervisors, Hans Weber and Erik Elfgren for invaluable advice, guidance, comments, and for theirencouragement. Ialsowantexpressmythankstomysupervisor,professor Go¨sta Gahm at the AlbaNova Centre of Stockholm University. He suggested my research topic, provided the observational data, and has been advising me through the research work. His expertise in astronomy has been necessary for my daily work and he is also a great inspiration. I also wish to express my gratitude to my late supervisor, Sverker Fredriksson for his support during the first part of this work. Special thanks to my friends, Britt-Mari, Armi and Rose-Marie who kept me smiling through even the hardest of times. I am grateful also for support from the National Graduate School of Space Technology. Finally, andmostofall, IwouldliketothankmypartnerLeifand my children Liina, Jane, and Lucia for their moral support and unconditional love over the years. I also thank my grandchildren Athena, Leah, Nathalie and Ameliah for they always make me smile. Astronomers are one of those lucky people who can make a living out of their pure interest. I feel lucky. Tiia Grenman v
Description:The list of books you might like
