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Southern Stars the JOURNAL of the ROYAL ASTRONOMICAL SOCIETY of NEW ZEALAND P Southern Stars THE JOURNAL OF THE ROYAL ASTRONOMICAL SOCIETY OF NEW ZEALAND P VolumeVolume 55, No 2 2016 JuneJune ISSN Page0049-1640 1 Royal Astronomical Society Southern Stars of New Zealand (Inc.) Journal of the RASNZ Founded in 1920 as the New Zealand Astronomical Volume 55, Number 2 Society and assumed its present title on receiving the 2016 June Royal Charter in 1946. In 1967 it became a member body of the R oyal Society of New Zealand. CONTENTS P O Box 3181, Wellington 6140, New Zealand Quasars - The Brightest Objects in the Universe [email protected] http://www.rasnz.org.nz Anushka Kharbanda ................................................ 3 Subscriptions (NZ$) for 2016: Norman Dickie ........................................................... 5 Ordinary member: $40.00 Student member: $20.00 Astronomy and Me! Affi liated society: $3.75 per member. Joshua Daglish ........................................................ 6 Minimum $75.00, Maximum $375.00 Corporate member: $200.00 SN 2015lh: Printed copies of Southern Stars (NZ$): The Most Luminous Supernova Discovered $35.00 (NZ) Brent Nicholls .......................................................... 7 $45.00 (Australia & South Pacifi c) $50.00 (Rest of World) The 2015 June 29 Occultation by Pluto Brian Loader .......................................................... 10 Council & Offi cers 2016 to 2018 President: Murray Geddes Prize - Dave Cochrane ................. 17 John Drummond P O Box 113, Patutahi 4045. [email protected] Jennie McCormick - FRASNZ, MNZM .................... 18 Immediate Past President: John Hearnshaw Dep’t Physics & Astronomy, Book Review University of Canterbury, John Drummond ..................................................... 22 Private Bag 4800, Christchurch 8140. [email protected] Vice President: Nicholas Rattenbury The Department of Physics, FRONT COVER The University of Auckland, Brian Loader’s light curve of the Pluto occultation of a th th 38 Princes St, Auckland. 12 magnitude star on 2015 June 29 superimposed on [email protected] a New Horizon’s image of Pluto. Pluto is scaled to fi t that Secretary: part of the light curve that endured the total occultation. Nichola Van der Aa 32A Louvain St, Whakatane 3120. The fact that light was still getting through is explained in [email protected] Brian’s paper within. Treasurer: Simon Lowther 19 Cape Vista Crescent, Pukekohe 2120. Light curve courtesy of Brian Loader, [email protected] Members’ Councillors: Pluto image courtesy of Steve Butler 30 Hoffman Court, Invercargill 9810. NASA: National Aeronautics and Space Administration, [email protected] JHO-APL: John Hopkins University Applied Physics Bob Evans 15 Taiepa Rd, Otatara RD9, Invercargill 9879. Laboratory, [email protected] SWRI: Southwest Research Institute. Sergei Gulyaev 120 Mayoral Drive, Auckland, 1010. [email protected] Orlon Petterson Dep’t Physics & Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8140. [email protected] Glen Rowe 23 Stanhope Grove, Korokoro, Lower Hutt 5012. [email protected] Affi liated Societies’ Councillors: Peter Jaquiery 31 Wright St, Dunedin 9010 [email protected] Gary Sparks 67 Meeanee Road, Taradale, Napier 4112. [email protected] Fellows’ Councillor: Karen Pollard Dep’t Physics & Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8140. [email protected] Page 2 Southern Stars Quasars - The Brightest Objects in the Universe:- Anushka Kharbanda Quasars - The Brightest Objects in the Universe Anushka Kharbanda SWAPA This is one of the papers presented at the 2016 Conference in Napier by Students With A Passion for Astronomy - SWAPA. Introduction We constantly search the skies, in the hopes of fi nding more about our universe. And, most of the time what we fi nd, renders us speechless about the grand expanse of our universe and it’s majestic components. One of such components that astonished many astronomers due to their incomprehensible brightness are quasars. These are the topics we will look at: ● The backstory of quasars and how they were found ● What gives birth to them ● We will also look at their unique spectra ● Their different types ● And moreover, we will also look at some examples of quasars and will try to compare their brightness to other celestial objects so that we are able to truly appreciate their immense brightness Anushka Kharbanda Photo supplied. How were they found? However, what they actually saw was this : Back in 1936, when Grote Reber built the very fi rst radio telescope in his backyard, he had detected strong radio sources by just 1944. Those radio emissions seemed to originate from the constellation of Cassiopeia, Sagittarius and Cygnus. Two of those sources, Cassiopeia A and Sagittarius A, seemed to originate from our own galaxy, and were later found out to be just supernova remnants. However, the characteristics of Cygnus A seemed to be very puzzling. When further investigation was done on this object, it seemed to be embedded in a faint looking galaxy. But, when the source’s spectra was taken, the results that were produced were not at all expected. When we take an object’s spectra we analyse the electromagnetic radiation it emits. Each object interacts This showed emission lines which was the opposite of what differently with the electromagnetic spectrum. they expected. So, astronomers could deduce that whatever the source of brightness was, it wasn’t starlight from the galaxy. So, when the spectra of Cygnus A’s galaxy was taken, Moreover, these peaks or emission lines were redshifted. We astronomers expected absorption lines or dips in the radiation can actually calculate how far an object is from us from its intensity like this: Because that is the kind of spectra galaxies redshift, by using the Hubble Law. Cygnus A, was found to have. be 740 million light years away. This was a staggering fact, because objects hundreds of millions of light years away are not usually able to be picked up by simple backyard astronomy tools. And this signal wasn’t a faint fuzz, it was bold and it stood out. This implied that this object had to be the most luminous one ever observed. Later, there was a very heated debate about the topic, because this object was so incomprehensibly bright, astronomers thought that there must be a problem by which we calculated its distance from the Earth. But, that was not true and later, these objects came to be known as the part of the brightest objects in the Universe called Quasars. 55, 2, 2016 June Page 3 Quasars - The Brightest Objects in the Universe:- Anushka Kharbanda Their Progenitors inward motion of the matter stops abruptly. This abrupt stop To know what gives birth to the brightest objects in the causes the inner edge of the accretion to be very well defi ned Universe, we fi rst have to look at the darkest- Black Holes. as we can see in this diagram. The faster the spin, however, the closer to the black hole, that abrupt stop occurs. Quasars are powered by Active Galactic Nuclei or AGNs which are basically, Supermassive Black Holes at the centre So, only a small proportion of the matter in the accretion of galaxies, that have matter around them they can “eat” up. disc falls into the black hole. Because of that, a lot of matter When matter falls towards a supermassive black hole due to bulges and accumulates in the inner accretion disc and pressure its immense gravity, it doesn’t just fall straight in, but forms increases rapidly. This pressure is then relieved by expelling an accretion disc around it, due to a law called conservation of matter at high speeds away from the accretion disc in the form angular momentum. The particles are moving at relativistic or of Dipolar Jets. near light speeds in this accretion disc. Closer to the black hole, matter is swirling faster than at the edges of the accretion disc. This causes the particles to rub against each other and radiation is emitted due to friction, as we can see in this diagram. Moreover, the swirling hot and charged plasma in the accretion disc, creates an intense, twisted magnetic fi eld which is at right angles to the accretion disc. This also facilitates the expulsion of matter. The radiation expelled is called synchrotron radiation and has no emission or absorption lines. Different Types of Active Galactic Nuclei It is commonly believed that the different types of active Keeping in mind that these particles are moving at near light galactic nuclei observed are just due to the angular view we speeds, the amount of friction and hence the radiation emitted get of the AGN. is enormous. At fi rst, matter accelerates at near light speeds near the black hole. However, at a certain distance away from the black hole, the matter stops falling in. This phenomena occurs due to the conservation of angular momentum. We have all seen it’s effect in our lives. For example, when a ball of pizza dough is spinning the dough tends to expand outwards and become fl at. It turns out that not only pizza dough but all spinning objects, including the matter in accretion discs, has a tendency to spread out and fl atten. When this tendency to expand outwards balances the gravitational pull of the black hole, the When the jet of the quasar is pointing directly at us, we receive tons of synchrotron radiation, with no emission or absorption lines and we see a blazar. However, when we see a quasar at a more oblique angle, we observe both the synchrotron radiation and the intense thermal radiation from the accretion disc. In this case, we would report seeing a radio loud quasar. Slow spinning accretion disc Fast spinning accretion disc Page 4 Southern Stars Quasars - The Brightest Objects in the Universe:- Anushka Kharbanda However, when we are getting a nearly edge on view of the accretion disc, we cannot get much of the thermal radiation from the accretion disc but the synchrotron radiation is still visible.
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