The Violent Universe1 by Professor Thierry Courvoisier, University of Geneva and INTEGRAL Science Data Centre, Versoix, Switzerland
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INTERNATIONAL SPACE SCIENCE INSTITUTE SPATIUM Published by the Association Pro ISSI No. 37, May 2016 162004_Spatium_37_2016_(001_020).indd 1 19.04.16 07:32 Editorial A quiet glance at the starry night rushes right through the entire sky may give you the impression Universe. Impressum that nothing is happening out there: the stars are still at the very Curious to learn more? Okay, let same spot you saw them in your us enter the store of astrophysics to early youth. Their light is flicker- rummage around in what they ISSN 2297-5888 (Print) ing a bit, yes, but you know, it is have on offer! Follow Professor ISSN 2297-590X (Online) the turbulent atmosphere that Thierry Courvoisier from the Uni- causes the illusion. So, business as versity of Geneva and Head of the usual in the heavens! INTEGRAL Science Data Centre SPATIUM in Versoix: he will present you a Published by the Beware! Your conclusion might be rich assortment of quasars, gamma Association Pro ISSI a bit over-hasty. Rather read first ray bursts and the like, and when this Spatium to learn why. You are you feel familiar with all that vio- blessed with living in an amazingly lent stuff, you will gladly lean back, clement corner of the Universe, happy to live in your quiet corner where things remain more or less of the Universe! Association Pro ISSI stable over periods that exceed by Hallerstrasse 6, CH-3012 Bern far an ephemeral human’s life span. We are thankful to Professor Cour- Phone +41 (0)31 631 48 96 The Universe has other measures voisier for the kind support he see of time. Our Sun, for instance, granted in publishing the current www.issibern.ch/pro-issi.html started shining 4.6 billion years issue of Spatium, which summa- for the whole Spatium series ago, and it will do so for a further rizes his lecture for the Pro ISSI as- appeasing 5 billion years. But sud- sociation in March 2014. President denly then, your calm corner will Prof. Adrian Jäggi, turn into an apocalyptic scene: our Hansjörg Schlaepfer University of Bern merciful daytime star will explode, Brissago, May 2016 shed parts of its matter out to space Layout and Publisher to form a beautiful planetary neb- Dr. Hansjörg Schlaepfer ula similar to those you may know CH-6614 Brissago from the skyrockets on Swiss Na- tional Holiday. That is what phys- Printing ics requires stars to do at the end Stämpf li AG of their lives. CH-3001 Bern Yet, physics has much more in stock. Take for example a black hole. It is a kind of a handy star, perhaps a mere 20 km across. Yet, it is so densely packed and hence possesses such a tremendous grav- ity that nothing can escape, not even a flimsy beam of light. The Front Cover hole is there, but you cannot see it. This is an artist’s rendering of Cygnus X-1, a black hole 10,000 light years And every now and then, two such away from Earth. Its tremendous gravitational field pulls matter away monsters collide and produce a rip- from its companion star. As the gas spirals towards the black hole, it heats ple in the fabric of space-time that up and gives off x-rays and gamma rays. (Based on an ESA image) SPATIUM 37 2 162004_Spatium_37_2016_(001_020).indd 2 19.04.16 07:32 The Violent Universe1 by Professor Thierry Courvoisier, University of Geneva and INTEGRAL Science Data Centre, Versoix, Switzerland. Traditional Earth-bound telescopes country, the INTEGRAL Science Prologue portray the sky in the waveband of Data Centre (ISDC) at Versoix visible light, for which the atmos- plays a pivotal role when it comes phere is transparent. This radiation to exploiting the science data col- The space age was just dawning comes mainly from objects in the lected by INTEGRAL. The sig- when a few scientists at the AS&E2 temperature range of a few thou- nals gathered by the spacecraft ar- conducted an experiment that was sand K showing galaxies, stars and rive at Versoix a mere six seconds going to change our view of the planets in their eternal quietness. later, where they are then pro- Universe radically. On 12 June In contrast, x-rays and the even cessed, archived and distributed for 1962, they launched an experimen- more energetic gamma rays4 stem the benefit of the international sci- tal sensor on a sounding rocket to from objects heated up to several ence community. probe the Moon’s x-ray radiation. million K and therefore reveal Even though no lunar signal was them in a phase of fervid turmoil. Altogether, high-energy astro- observed, incidental findings This is why high energy astrophys- physics has evolved to become a turned out so revolutionary that ics is so important for understand- staggering and prolific research they earned the programme man- ing the most powerful processes oc- field to which the current issue of ager Riccardo Giacconi3 (Fig. 1) the curring in the Universe and other Spatium intends to guide our Nobel Prize in Physics forty years events that are at the origin of in- readers. later. tense non-thermal phenomena. Unfortunately for astrophysicists, Unsurprisingly, astrophysicists Fig. 1: Riccardo Giacconi won the fortunately, however, for all other grasped the potential of this new Nobel Prize in Physics in 2002 for pio- neering contributions to astrophysics, beings, the Earth’s atmosphere ab- window quickly by commission- which have led to the discovery of cos- sorbs x-rays. Therefore, to probe ing an entire flotilla of spacecraft mic x-ray sources. the x-ray sky, sensors must be placed of ever-increasing sophistication. high enough beyond the atmos- Among the most successful mis- phere. This was known to Giac- sions stands the European Space coni. Yet, he could not know that Agency’s International Gamma- his instrument’s sensitivity was in- Ray Astrophysics Laboratory (IN- sufficient for registering the Moon’s TEGRAL). Launched in 2002, it weak x-ray radiation he was head- continues to gather the most ener- ing for. It was, however, sensitive getic radiation from deep space in enough to stumble across a bright 2016 telling us stories far beyond x-ray source in the constellation of any imagination. It offers scientists Scorpius and mysterious diffuse insights in spectacular cosmic background radiation. These dis- events from within our Milky Way coveries opened an entirely new out to the very edge of the observ- window to the Universe to able Universe. On the other hand, astronomy. inside the borders of our small 1 This text is based on a lecture by Prof. Thierry Courvoisier for the Pro ISSI audience in March 2014 as well as on sev- eral of his publications. It was prepared by Dr. Hansjörg Schlaepfer and reviewed by Prof. Courvoisier. 2 American Science and Engineering, Inc., Billerica, Massachusetts, USA, a US manufacturer of x-ray equipment and related technologies. 3 Riccardo Giacconi, 1931, Genova, Italy, Italian astrophysicist, Nobel Prize laureate in physics in 2002. 4 Gamma rays represent the most energetic part of the electromagnetic spectrum. SPATIUM 37 3 162004_Spatium_37_2016_(001_020).indd 3 19.04.16 07:32 Introduction The protostar attracts matter from the current orbits of Mercury, Ve- its environment thereby gaining nus, and possibly Earth as well. further mass. Its core gets increas- ingly hotter and denser, due to the What happens next depends on the Virtually all types of mass-rich growing strength of its gravity. At mass of the star. compact cosmic objects are signif- some point, it is hot enough and icant sources of high-energy emis- dense enough for hydrogen to start sion because of the enormous fusing into helium. This nuclear Small Stars strength of their gravitational reaction releases huge amounts of fields. Here, gravity can accelerate energy heating the core further up A small star in the range of 0.05 … particles to extreme velocities, to several million K. This makes 1 solar mass equivalents reaches the which then emit x-rays and gamma the protostar become a veritable density and temperature required rays. In order to familiarize our- shining star. to fuse hydrogen to helium. Mod- selves with those compact objects, els suggest that such a dwarf star’s we are now going to sketch the Of the various chapters of a star’s hydrogen stock may last for some processes that make them come biography, hydrogen fusion is by 1012 years, which is considerably into being. far the longest. Its duration de- longer than the actual age of the pends on the star’s size: the larger Universe. This is why the evolu- the mass, the faster it consumes the tion of such small stars is beyond Stellar Evolution hydrogen supplies. Our Sun for ex- any observational reach. ample is a relatively small star; its Stars are born; stars live, stars die, initial hydrogen stock grants it a much like everything else in lifetime of 10 billion years (of Medium-sized Stars nature. which 4.6 billion are gone). In contrast, a more massive star with A medium-size star holds between Stars are born during the collapse several times the mass of the Sun one to seven solar mass equivalents. of giant nebulae that are large in- has a life expectancy in the order Similar to a small star, its core starts terstellar clouds of dust, hydrogen, of some hundred million years with hydrogen fusing; yet, in con- helium and other ionized gases, only. Anyway, when the hydrogen trast, when the hydrogen stock is (Fig.) 2 .