Classroom Aid - Discovering the 1st Quasar

in the 1950s radio telescopes were searching the sky for celestial objects that radiated radio waves from spots where no visible light could be detected the objects were referred to as radio Stars a method for accurately determining the positions of radio sources was developed using lunar occultations on March 16th 1963 three astronom C Hazard MB Mackey and AJ Simmons published a paper in nature describing what they found in 1962 using lunar occultations with the new parks radio telescope in Australia to study the intense radio Source 3c273 the moon would be occulting this Radio Star three times one on April 15th one on August 5th and one on October 26th they were able to locate its position to within one Arc second here's a short clip illustrating how it works with a visible star The Disappearance of a light source behind the Moon is called immersion and its subsequent reappearance on the other side is called immersion we can use the edge of the Moon as a diffracting straight line for both of vents the technique enables locating a source to within one Ark second here's an illustration that covers how it works we have a star shining on a telescope on the earth with the moon's Edge moving down between them on immersion the starting distance is zero at the point where the moon's Shadow blocks the Leading Edge of the star light and its ending distance is at the point where the moon's Shadow covers the entire star a defraction pattern develops on the radio telescope that provides additional information about the source the Optics are described by the French physicist Augustine fresnel's equation developed in the early 1800s exact knowledge of the location and velocity of the moon's Edge gives us the exact location of the star on the sky and it gives us the intensity of the light at any distance from the geometric Shadows starting point it also provides us with the size of the source on the sky it is easier to see the quantitative Behavior with a slice through the pattern radio astronomers take advantage of two main points one is that the light intensity of the maximum Peak is always around 40% of the light intensity from The Source when the telescope is viewing it without any blockage if we zoom in a bit to focus on the largest Peaks we can get a measure of the ratios of the distance between Peaks at different distances for different radiated frequencies this provides a good measure of how the radiation from the object is distributed across the plane of the source with the selected frequencies now let's take a look at what the astronomers found when they actually monitored their three occlusions in 1962 here's the immersion pattern on August 5th this bump at the end indicated that the source had some sort of structure it's not just one object here's the pattern on ersion the bump is gone this was interpreted to be caused by the alignment between Earth and the source changing with a small angle between the two on entry and aligned an hour and 19 minutes later on exit as the Earth observer's position changed during the occlusion with the angular data the astronomers were able to calculate accurate positions for the two components and here are two immersions at different frequencies collected on October 26th note the significant reduction in intensity for component a at the higher frequency the ratios along with the power law show component a producing the same radiation across its entire diameter and component B producing most of its radiation from its Center and fading at the edges in addition the radiation magnitudes show that component a is contributing 90% of all the radiation from the combined pair the astronomers concluded that component a looked like a jet but no one had ever seen anything like component B without redshift information it was assumed to be a strange kind of star in our galaxy it was called a quasi Stellar object shortened later to quazar an abbreviation of the phrase quasi Stellar radio Source in December 1962 the accurate position of 3c273 obtained by Hazard was passed on to Caltech astronomer Martin Schmidt using the 200 in Mount Palomar telescope Schmidt obtained an image and Spectra of the source using the Baseline Balmer series for hydrogen along with a strong line for oxygen he found a red shift of 0.158 he argued that either this was a relatively dim object inside our galaxy with enough Mass packed into a 10 km radius to create a gravitational red shift this large or it's a Galaxy 2.14 billion light years away with enough Luminosity to be seen here all known knowledge of stars ruled out the first possibility he concluded that it must be a distant Galaxy this discovery had immense consequences for our understanding of the universe for one it led to the discovery that the intergalactic medium had transformed from neutral to ionized hydrogen we'll cover this in the next segment