A lecture on “Active Galaxies and Extragalactic Radio Jets” was given by Dan Homan of Denison University. (Department of Physics and Astronomy.)
       The topic of radio astronomy discussed in the lecture described radio emission as well as non-thermal emission, of which it was mentioned that during World War, the scientists grew in higher interest over such field that was later further elaborated in more depth after the War; to determine accurate positions for the identity of radio stars. A slide of Cygnus A, a type of radiogalaxy was shown in which two lobes were connected by jets. At the center of the jets there existed a core, which he mentioned was the galaxy. The end sides of the lobes as well as the core showed bright light and high temperature. It was mentioned that the “extragalactic radio sources contain vast amount of energy in magnetic fields and relativistic charged particles.” Such suspected energy was said to come from super massive black hole, the first gas motion that seemed to have required, which was three billion solar mass concentrated in the center. The magnetic field was twisted and created a funnel for the jet.
       Such two radio lobes mentioned were said to be in balance, which was first proposed in 1959 and determined correct with much more recent works. It was also said that the lobes were not emitting rays merely because they were hot, but also due to the intense brightness that matched the frequency same as that of the heat known as “bright temperature.”
       One of the instruments, the very long baseline array, appeared very amusing as he mentioned that with this, the resolution is so clear and high powered that for instance, one could spot a person holding a penny in Los Angels from Boston using VLA to VLBI scales.
The other interesting point to me was the fact of “apparent light,” the time from our point of view which creates optical illusion that makes us assume that the jet flow is about four times more that the speed of light, known as the “superluminal motion.” It was interesting to know that our perception is affected by “apparent light” in that although jet flows at close to the speed of light, it makes us think it is much shorter than it really is.
       Among the many slides that were shown, some lobes had only one jet coming out of one of the lobes unlike the other few that showed two jets. This was due to the “Doppler factor,” a beaming in which one is aiming towards us while the other is going away, which once again makes it seem like there is only one jet when there really are two of them. Beaming also enhances the observed light temperature and since the Doppler factor is a difficult one to measure, the brightness temperature is assumed by looking at the population of radio jets and selecting only the bright jets that are able to be seen. This was called the “flux limited sample” in which the data are kept in track by the MOJAVE program that he is also involved in. It was concluded that the jets near the origin have “distinct high and low brightness stated and these states are similar for different jets.”
       It was especially interesting to find out that although I had assumed the galaxy to hold extreme amount of energy, actually hearing that it is three billion times more than the sun and so much more than the energy held by the Milky Way was very striking. Also, as mentioned above, the instrument used as well as the optical illusions created in the jets appeared very interesting. It was amazing to find out how such factors lied behind the many pretty sparkles shown in the images of various slides.
       For future, he mentioned that he hopes to “finish the ‘complete’ MOJAVE sample and repeat the study [as well as] to incorporate fitting to the distribution of points in the plane rather than simply their locus.”