Charlottesville Astronomical Society

May Meeting Minutes

June 7, 2006

McCormick Observatory

Guest Speaker: Don Wells NRAO

Don Wells NRAO took the floor at 7:10PM

I'm a retired radio astronomer who worked at the NRAO on the VLA. There used to be a dichotomy between the radio and optical astronomers, but multi-wavelength studies across both fields of study are now common. Neutrinos and even gravity waves are now open for study.

Only a small part of the electromagnetic spectrum is visible light that we can see. Optical astronomy is about half of the astronomical field these days. The new fields are exciting science.

Visible light is but a tiny portion of the total spectrum. We can use frequency, wavelength or energy to describe the "color" of the waves or photons. When light is a photon it's appropriate to speak about the energy of the photons. The atmosphere's absorption of wavelengths is crucial to both optical and radio astronomies and the percentage of transmission is diminished, especially in the x-ray and gamma ray and UV area. There is a huge section of the radio where there is transparency to incoming waves.

The high energy, IR and low frequency radio do not make it through to the ground and must be studied from space. The discovery that invisible energy was radiating in from outer space goes back to Edison's IR experiments. Karl Jansky of Bell Labs in NJ was asked to find out what was causing noise on long distance (transatlantic) phone lines. He built a low frequency radio antenna on wheels and discovered that the bulk of the noise on the phone lines was coming from the galaxy. The Milky Way's hot plasma gas, particularly in the galactic center, is emitting radio waves.

The full consequences of Jansky's discovery was hard for astronomers & physicists to grasp. Grote Reber, a young radio engineer from Wheaton Ill. proceeded to build a parabolic radio antenna, in 1938. He tried out multiple radio frequencies and replicated and improved on Jansky's discoveries.

WWII's impetus on radar was a big boon to radio astronomy. The BIG breakthrough in radio astronomy (in my opinion) is the VLA in Socorro NM. There are 27 antennas on 3 arms that are combined in pairs interferometrically giving you a superb image. On 15 month cycles the dishes are swapped from short baseline to long baseline configurations to do wide field/low res or narrow field/high res (respectively) images.

Quasars are a fascinating area of study, 3C175's image is shown, illustrating 2 jets emanating from a black hole. AGNs (active galactic nuclei) are active because of supermassive black holes. Our Milky Way has a black hole, but (thankfully) not a supermassive one.

The IR spectrum is a fertile area as well. The 2 micron all sky survey (2mass) penetrated dust clouds and imaged the galaxy nicely.

Protoplanetary disks where planets are forming are disks of dust and gas swirling around a star. The HST near infrared studies were critical in understanding planetary formation.

Dark nebulae occult starlight in the galactic plane of the Milky Way and IR penetrates them handily. NICMOS also studies M31 and shows areas of older stars, and dust thermal emission where star formation is happening.

The Hubble Ultra Deep Field is shown to us and a small section of that has a red object that is visible in NICMOS' IR that is invisible in optical. The Spitzer IR satellite is able to go deeper into the IR than NICMOS and finds a stronger source still. The Spitzer works at lower resolution but even so it shows from the object's strength that it is a very, very distant galaxy from quite early in the universe's history.

UV light can be studied by HST, but it doesn't get much publicity, partly because the UV detectors on Hubble aren't very efficient. NASA built the EUVE, the Extreme UltraViolet Explorer spacecraft and found a surprising number of UV sources in places where there are no Radio sources or X-ray sources either. It's a mystery for further study.

Chandra X-ray observatory has been hugely successful. 3C75 (object #75 in the 3rd Cambridge catalog of quasars) is also NGC 1128 and Abell 400, so there are multiple designations for the same object to keep track of. It has 2 pairs of jets, trailing off and bent. The 2 merging galaxies are both AGNs and x-ray bright. Jets from radio data, nuclei from x-ray data, it's a fascinating object. The jets are from black holes, of course.

GRO J1655-40, the APOD from May 28th 2006, artist's representation of an accretion disk around a black hole. Quasi-periodic oscilations (QPO) a fast flickering of 450 Hz in x-rays coming from the event horizon.

Gamma Ray astronomy is the next area we cover, CGRO Compton Gamma Ray Observatory, deorbited in 2000, was the heaviest spacecraft ever launched. There are no optics, Gamma Rays don't reflect! There are detection chambers, and you look at hits on multiple detectors to determine the direction of incoming gamma rays. One of the instruments on board was EGRET and detected high energy GRs. BATSE detected GRBs or Gamma Ray Bursts. The equal area elliptical plot of GRBs shows that they aren't coming from the Milky Way and are uniformly distributed in the Universe and thus are coming from a very long distance away and thus are very old phenomenon.

Cosmic rays are particles, not waves, where you have protons, nothing more than a bare, electronless hydrogen nucleus, smashing into the Earth's atmosphere. Build a bunch of detectors on the ground and you can detect these cascades of particles.

Neutrinos are essentially massless particles that pass through us continuously. To detect a neutrino, you look for Cherenkov light flashes in a large tank of water deep in the earth. In 1987 the Kamiokande II and the IMB in Ohio detected about 15 neutrinos in a span of about 10 seconds, showing that something big had happened. That night Cerro Tololo's night operator noticed that the LMC had a supernova. The Neutrinos had escaped the SN quickly and only later did the light get out of the chaos of the supernova.

Gravity waves, "ripples in spacetime", they've been called. Not radiation or particles, but changes in the very shape of spacetime. LIGO a laser interferometer is set up to try to detect them. Hasn't been successful just yet. This will be a new view on the universe, some of the most interesting and least understood things in the universe.

What makes G-waves?

- Compact binary inspirals

- Supernovae/GRBs

- Pulsars in our galaxy

- Cosmological signals, Stochastic or noisy backgrounds.

Livingston Louisiana and Hanford Washington are the 2 LIGO sites. Each has 2 arms at 90 degrees from each other. You have to see the same signal with both of them or you're just seeing noise.

All of these signals, across the spectrum, are important to our understanding of the universe we live in. If we only had the visible light to work with we'd be in the dark.

At 8:47 the floor was turned over to Vice President Richard Drumm, who conducted club business. The door prize, a moon observing packet, was won by Gary Cornick. The meeting adjourned at about 9PM.