Professor Paul Wiita on “Measuring and Modeling Variability in Quasars and Blazars”

On Friday, November 10th, College of New Jersey Professor of Physics and Astronomy Paul Wiita, fascinated an audience at the American Museum of Natural History, explaining what Quasars and Blazars are, how they were discovered, what the difference between them is and how he and his research team models them in two and three dimensional simulations.

First, Professor Wiita explained that Quasars and Blazars are some of the most powerful objects in the Universe, excepting Gamma Ray bursts, which can be a little more powerful, but only for a very short period. In contrast, Quasars and Blazars last tens of millions and sometimes hundreds of millions of years at tremendous powers. The Professor noted that one of the most remarkable things about these objects is the great speeds at which these objects change in brightness. He explained that while Quasars were first discovered as being very bright in the radio part of the electromagnetic spectrum in the early 1960’s, “they were weird because they looked like a star but no stars give off a lot of radio waves.” Another early difference astronomers noted was that Quasars gave up much more light in the ultraviolet part of the spectrum than stars. Further, Quasars have broad emission lines all across the spectrum, rather than emission lines, stars have absorption lines all across the spectrum. “The Quasars had big broad lines of various elements, hydrogen, helium, nitrogen, oxygen and carbon.”

Wiita explained that in 1963, Martin Schmidt observed a Quasar with an incredibly high red shift which suggested it was very far away. Seven years ago, we found a Quasar with a red shift so high, the Quasar seems to have been formed around 750 million years after the big bang. Wiita said it is incredible that an object massive enough to make light still visible over 12 billion years later was able to form within the first billion years after the big bang. Wiita said that some Quasars we found “put out up to 1040 watts…which is about ten trillion times the luminosity of the Sun and that’s about a hundred times the luminosity of the (Milky Way) Galaxy.” He added that a Quasar can sometimes outshine “hundreds of trillions of stars in its Galaxy.” Wiita said that since Quasars so far outshine their host Galaxies, they at first appeared to be lone points of light and therefore were thought to be individual stars.

Wiita said that the fast variability of the brightness of Quasars was a central focus of his talk, adding that their brightness can change by a few percent in the course of a week or 50% in the course of a year. Wiita explained that the speed at which an entire luminous object changes brightness tells you its size because if an entire object can appear to us to change brightness in one month, it has be equal to or smaller than the distance light can travel in a month. Wiita added that if you take Special Relativity of light into account Quasars could be somewhat larger. “So we are talking about things pumping out the luminosity of a very big galaxy, or hundreds of times the luminosity of an average galaxy in the size just of our Solar System.” As telescopic resolution improved, we were able to see the red shifted rings or lobes of gas and dust which surround Quasars. Thus, we came to understand that Quasars are the most extreme and powerful of active galactic nuclei.

Later, with the great optical imaging from the Spitzer Telescope and in other wavelengths with other telescopes, we saw a massive jet of plasma streaming out of the center of the accretion disk at the center of Quasar 3C 273. From this, we learned that when jets of plasma are being ejected from the centers of a galaxies, those galaxies have the most active galactic nuclei. Wiita stated that the biggest of these radio galaxy quasars have jets that extend over ten million light years, which makes them, “the largest connected objects in the Universe.” Also as incredible, Wiita said that the plasma in these enormous jets is sometimes moving these vast distances at .98 to .995 the speed of light. So, he said, “something is launching them from the center of the galaxy and somehow they are surviving as they propagate…hundred million years…going out tremendous distances.”

Wiita then discussed his favorite Quasar, M87, which earned this status by being close by and thus yielding images in optical and infrared ranges of jets coming out of the center of both sides of the galaxy. Wiita said that when the first Blazar was discovered, it was called BL Lacertae, and BL meant that it was a variable star and Lacertae referred to the constellation it was found in. At first, because light from the original BL Lacertae and other Blazars looked like a point source, people thought they were stars. But, the Blazars’ spectral data from the entire electromagnetic spectrum, including radio, infra-red, optical, ultraviolet, X-rays and gamma rays suggested Blazars weren’t stars. Further, Blazar radiation is almost always strongly polarized, whereas stellar optical emission is polarized only in a tiny fraction of the emissions. Wiita said that no observational data of Blazars matched the profile of any star or galaxy. Ultimately, there was a scientific consensus that Blazars are Quasars whose enormously long, fast, hot and bright plasma jet emissions point directly at Earth. These jets are so erratic, their brightness can vary 10 to 20% in a night. Wiita said that the jets coming out of Blazar poles are from electrons “moving at 99.9999% the speed of light spiraling around magnetic fields and giving off the radio photons we see.”

Summarizing his explanation of Quasars and Blazars, Professor Wiita stated that the size should be “the speed of light times their variation time and that the typical time is about a year.” Wiita said that means that Quasars are about equal in size to the outermost edges of our Solar System’s Oort Cloud, i.e. nearly a quarter of the way to the nearest star…and yet Quasars this size spend millions of years making more light than entire Galaxies. Wiita said complete annihilation of matter and antimatter could make this much energy in an area that size, but that we doubt there is enough antimatter anywhere for that to happen. Instead, the prevailing theory is that in Galaxies with a mass of a million to ten billion times the mass of the Sun, there will be supermassive black holes.

Early in the life of such Galaxies, accretion disks will have mass quantities of gas spiraling towards the black hole, emitting radiation in most known forms and then, outside the accretion disk, millions to tens of millions of miles away, there will be “a clump torus of clouds and a lot of dust.” Accretion disks heat the ring like clouds and the clouds give off infrared radiation so the clouds obscure the center of the Quasar, unless we are looking down on the accretion disk. The force of gravity pulling the rapidly spiraling accretion disk leaves no room to expel all of their mass energy back into the accretion disk. With nowhere else to go, the excess mass-energy from accretion disks shoots up and down from the center of the disks into the incredibly hot and fast millions of miles long plasma jets.

Having explained what Quasars and Blazars are, Wiita showed the audience photos of Blazar emissions and then showed the audience photos of Quasars and Blazars, as well as 2d and 3d computer simulations of the Jets coming out of Quasars. Describing those visuals as Professor Wiita did defies the space limitations of this publication (and the skills of this writer); that’s part of why one should go to these presentations.

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