Astronomical Sources of Radio Frequency Emissions GAVRT Chapter 6

Source Classification Discrete Source: flux has a direction Point Sources like stars and far away galaxies Extended Source like our solar system’s Sun and planets, also some nebula Background Radiation=source behind what observing Foreground Radiation=source in front of what observing Non-discrete source: flux same in all directions like CMBR

Interference Sources Natural Signals Human made signals Lightning Sun Earth’s Ionosphere Human made signals Power facilities Tracking transmitters (GPS, Radar) =>DOY 41 Commercial Transmitters (Cell phones, radio and television) Radio Telescopes located in remote valleys to shield from the human made signals.

Stellar Radio Sources

Cepheid Variables

Pulsars

Stellar Radio Sources Stars produce black body radiation due to their temperatures. Wein’s Law and Planck’s Law can be used to determine temperature of star. Temperature determines color of star w/ red stars being cooler than yellow and blue stars Variable Stars More stars are variable in radio compared to visible light Cepheid Variable’s luminousity vs. period relationship allows them to be used as ”standard candles” for distance Pulsars form when large stars implode leavin a quickly spinning nucleus of neutrons. Strong magnetic field results in beams of radio waves formed by the synchrotron process being directed at Earth many times/second. Used to confirm relativity. Picture of neutron star Other variables include irregular variables, flare stars, binary stars

The Sun Black Body Radiation Sporadic Radio Emissions (Solar Flares) Fusion reactions emit energy in the form of radiation at all EM frequencies resulting in plasma continuous emission Emission lines of mostly hydrogen and helium are found indicating spectral line emission in photosphere. Absorption lines found when looking at corona where gases engaged in spectral line absorption Sporadic Radio Emissions (Solar Flares) Sunspots are cooler areas due to energy stored in twisted magnetic fields. When fields untwists then energy released as EM radiation at numerous frequencies Circular polarization due to untwisting of field 1-60 m in wavelength Picture of Sun structure page 54

Jupiter System

Radio Jove X band signal flux increases with frequency and stays pretty much steady =>Black Body radiation from cloud tops of planet S band signal flux decreases with frequency and changes with longitude of magnetic field and location of Io => Synchrotron radiation from volcanic ions spiraling around Jupiter’s strong magnetic field lines.

Jupiter’s Radio Signal Patterns S band has greatest radio brightness when Io is on opposite side of Jupiter as Earth S band has several peaks when certain longitudes of the planet’s magnetic field are facing Earth S band signal varies w/ passing of solar wind storms (solar flares). Comet crash result in changing of X but not S band radiation

Quasar Radio Signals

Quasars Extremely distant and thus old objects at edge of observable universe Visible light absorption lines have been red shifted to the radio part of spectrum => moving away at speeds near the speed of light. Radio emission brightness decreases with frequency=> non-thermal source Producing synchrotron radiation as charged matter orbits black hole Believed to be first galaxies after big bang

The Blinking Quasar Problem Quasar seems to have variable flux at radio frequencies. Could be quasar actually brightening and dimming. Could be intergalactic clouds moving between quasar and Earth Could be result of Earth’s motion around Sun Period for brightening and dimming have been 4 months, 8 months and 6 months.

The Jupiter System Strong and large magnetic field Thermal, blackbody radiation in S band Temperature just below cloud tops Constant Non-thermal Synchrotron radiation in X band Io’s volcanoes pumps 10 tons/sec of plasma into torus around Jupiter Varies with time Study of this signature can tell us something about Jupiter’s core and magnetic field Relating it back to Earth Picture of Jupiter magnetic field and plasma torus

Galactic Sources Non-thermal radiation from point or extended source due to synchrotron radiation. Types of Radio Galaxies Radio Galaxies Quasars (fast moving far away galaxies) Blasars (Quasars that vary) Seyfert Galaxies (Quasars that exhibit emission lines) Most galaxies not strong radio emitters