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→ MERGING GALAXIES A XMM-NEWTON & HUBBLE SPACE TELESCOPE ARCHIVE TUTORIAL SCIENCE ARCHIVES AND VO TEAM Tutorial Science Case Idea: Deborah Baines Tutorial Written By: Madeleine Finlay, as part of an ESAC Trainee Project 2013 (ESA Student Placement) Tutorial Design and Layout: Pedro Osuna & Madeleine Finlay Tutorial Science Support: Deborah Baines Acknowledgments would like to be given to the following, for their advice and verification of the scientific explanations in this tutorial. Ignacio de la Calle, Nora Loiseau, Jiri Svoboda. CONTACT [email protected] [email protected] ESAC Science Archives and Virtual Observatory Team European Space Agency European Space Astronomy Centre (ESAC) Tutorial → CONTENTS PART 1 .....................................................................................................3 BACKGROUND ...........................................................................................4-9 THE EXPERIMENT ....................................................................................10-16 CONCLUSIONS & ADDITIONAL ACTIVITIES ................................................17 PART 2 ..................................................................................................19 BACKGROUND ........................................................................................20-21 THE EXPERIMENT ...................................................................................22-28 CONCLUSIONS & ADDITIONAL ACTIVITIES .................................................29 NUMERICAL SOLUTIONS ...................................................................30-31 This is an image of a pair of merging galaxies: the Antennae galaxies. During the course of the collision, billions of stars will be formed. Image Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration PART 1 In Part 1, the tutorial will explain how to measure the distance between two supermassive black holes contained within an extragalactic object NGC 6240. NGC 6240 is made up from two spiral galaxies which are merging, pulled together by their cumulative gravitational forces. Next, the mass of one of the supermassive black holes will be calculated. Therefore, in the background a number of subjects will be covered to introduce the main topics used in the tutorial: → NGC 6240 → Black Holes → Merging Galaxies → Cosmological Concepts → Spacecraft (data from which are used in this tutorial). Then, the experiment will be explained step by step. The tools used will be the XMM-Newton Science Archive and Aladin. Some basic calculations will be made in order to determine the distance between the supermassive black holes and the mass of one of the black holes. Finally, conclusions will be made about the performed experiment and some ad- ditional activities will be provided. BACKGROUND → NGC 6240 NGC 6240 is the object that → BLACK HOLES Background will be studied in this tutorial. NGC 6240 contains two supermassive → black holes. But what exactly are they? NGC 6240 is a remnant of a galaxy colli- sion between two spiral galaxies. Both A black hole is an object that has sufficient were similar in size to the Milky Way. mass in a small enough volume so that noth- This merged body has two supermassive black ing can escape its huge gravitational pull be- holes at its centre, and around them a vast yond a certain point. This distance is known quantity of gas which is forming new stars at as the Schwarzschild Radius, and af- an immense rate. The two black holes are spi- ter this even light is swallowed: Which is ralling towards each other and ultimately may why they are known as black holes. We can- become one even larger black hole. not directly see them as no light is emit- ted from within the Schwarzschild Radius. The merging of the galaxies has also generated substantial infrared emission from dust heated Everything that enters the Schwarzschild Ra- by newly forming stars and by the Active Galac- dius of the black hole is squashed into its sin- tic Nuclei (AGN). As there is so much infrared gularity at the centre; which is believed to be emission the system is extremely luminous (1012 an infinitely small point with infinite density. solar luminosities), and therefore is known as a (Ultra)-Luminous Infrared Galaxy ((U)-LIRG). Although it is not possible to see a black hole directly, astronomers are aware of their exist- NGC 6240 is located in the Ophiuchus (which ence and some of their properties due to their means Serpent-Bearer) constellation, a mere influence on the material in their vicinity. For 98 Mpc or around 3.2 x 108 light-years from the example, the mass of a black hole can be cal- Milky Way. culated using the orbital velocity of the material travelling around it. So far, two types of black holes have been ob- servationally confirmed: Stellar-mass black holes, which are just a few times more massive than our Sun and supermassive black holes. Supermassive black holes can have masses ranging from millions to billions of times the mass of the Sun. ↑ This is an image of the galaxy merger NGC 6240. The shape of this combined-galaxy is clearly very irregular. NGC 6240 is the product of two Milky Way sized spiral galaxies and it is predicted to become an elliptical galaxy. Theories also state that the supermassive black holes from each of the galaxies will eventually collide. As, with respect to the size of the observable Universe, NGC 6240 is nearby to our own gal- axy, it provides an opportunity to easily witness ↑ This is a computer simulated image of a black hole a galaxy collision. Even so, collisions are sur- with mass ten times the mass of the Sun, as seen prisingly common, although it is difficult to get from a distance of 600km with the Milky Way in the an exact estimate; NASA’s Hubble Space Tele- background. The light from the Milky Way has been scope found results implying between 5% to 25 bent due to the relativistic gravitational effect of the % of galaxies were merging.It is expected that black hole. the Milky Way will eventually collide with the Andromeda galaxy - our closest spiral galaxy, Image: Ute Kraus, Institute of Physics, Universität in about 4 billions years. European Space Agency | ESAC Tutorial Background → ↑ An artist’s depiction of the accretion of a thick ring of dust into a supermassive black hole. The accretion produces jets of gamma rays and X-rays. Credit: ESA / V. Beckmann (NASA-GSFC) → AGN Supermassive black holes have masses which An Active Galactic Nucleus (AGN) is the can be as large as small galaxies. The Milky compact area at the innermost part of a Way has a supermassive black hole in the cen- galaxy which has a vast luminosity over tre, which approximately has the mass of 4 some or all of the electromagnetic spec- million Suns! trum in comparison with the rest of the gal- Some black holes have accretion discs sur- axy. They are actually the most luminous rounding them, which are made from material sources the Universe. in orbital motion as it falls into the black hole, As the matter gets closer to the black hole it is As the emission from the AGN is so bright (it compressed, its speed increases and it gains can outshine billions of stars) it can only be energy. The difference between the speeds, in caused by something that can generate enor- comparison to distance from the black hole, is mous amounts of energy. Accretion onto a large and this generates a substantial friction black hole is such a mechanism; it has an ef- in the disc. This heats the matter, causing it to ficiency of 10%, which seems small, but is in emit thermal radiation. The frequency of the fact a very powerful way to produce energy. radiation is dependent on the heat of the mat- There are many different types of AGN, which ter, which in turn is dependent on the distance are mainly categorised according to their bright- to the black hole. Consequently stellar mass ness and what type of electromagnetic radiation black holes emit mainly X-rays, whereas su- they emit. The main distinction is ‘Radio Loud’ permassive black holes emit more towards the and ‘Radio Quiet’ which represent 10% and 90% UV wavelength range. of AGN respectively. ‘Radio Loud’ describes ob- jects such as Radio Galaxies and Blazars, where- Another important feature of a black hole is as AGN galaxies such as Seyferts and Starbursts whether it rotates or not. Rotating black holes are ‘Radio Quiet’ objects. are formed from rotating stars through the conservation of angular momentum. They are Although the Milky Way contains a supermassive known as ‘Kerr’ black holes. The amount spin black hole, it does not contain an AGN as there of the black changes the size of the Schwar- is not enough matter currently accreting onto zschild Radius. the black hole. → MORE ON MERGING → COSMOLOGICAL CONCEPTS GALAXIES REDSHIFT Background It has been found that galaxies often merge As objects move away from us, the light → due to their small separation in comparison waves or sound waves appear to become with their size. There is a huge cumulative longer. This effect can be observed by lis- gravitational pull of each galaxy towards tening to the sound of an ambulance rush- the other which causes them to merge. ing past; the sound pitch gets lower as it travels away. This is the wave stretching However, whilst galaxies are merging, stars or and elongating in relation to you. This is star systems (like the Solar System) do not actu- known as the Doppler Effect. ally collide, as the distances between them are too great. Many stars or star systems may be thrown off into space or their orbits completely changed. This results in most of the stars having complex orbits and moving in random directions, which is one of the reasons merged galaxies be- come irregular or peculiar eventually becoming elliptical. In the merging process of two galaxies, large amounts of gas and dust are directed towards ↑ An illustration to show how the Doppler Effect changes the central region, and are compressed. This the appearance of wavelengths. induces active star formation. Galaxies with high rates of star formation are known as ‘star- The same thing happens with light.
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