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SETI
- Allen Telescope Array
- Optical SETI
- Interstellar Message Construction
- Project Phoenix 1995-2004
- Background Science
- History of SETI
- Center for SETI Research Team
- Other people doing SETI
- Hollywood's View of SETI
A Different Look at M31, the Andromeda Galaxy
by Jill Tarter, Director of SETI Research
The first 3 images below are examples of images of M31, the Andromeda Galaxy, made with the first few elements (antennas) of the Allen Telescope Array (ATA). These maps (or radio images), extending over three degrees on the sky, were made with a single pointing of the ATA array. These images demonstrate the extraordinary ability of the ATA to explore quickly large areas on the sky with good spatial resolution. Comparison of figures 1 and 2 shows how the spatial resolution of the maps improves as more antennas are added to the array, progressing from 4 to 7. The resolution will continue to improve as the array is expanded to 42 elements in the next few months, and eventually to the full 350 element array.
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| Figure 1 - ATA-4 Map made in June 2005 using 4 antennas and FX4 correlator prototype. Includes continuum data. |
Figure 2 - ATA-7 Map made in Sept. 2006 using 7 antennas and two FX4 correlator prototypes. Includes continuum data. |
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Figure 3 - ATA-20 |
Figure 4 - Familiar optical of M31, Andromeda Galaxy. |
The first two maps include continuum data that are sensitive to the thermal emission from the hot, ionized (mostly hydrogen) gas that surrounds regions of massive star formation. Those same regions can also be seen as blue-white clusters of stars and gas in the optical image of M31 in figure 4. The improved spatial resolution of the ATA-7 compared with the ATA-4 can be seen in the decreased size of the red symbol representing the synthesized beam of the array in figure 2 compared to figure 1.
In figure 2, little or no thermal emission is detected at the center of the galaxy because there the ionized gas is heated to much higher temperatures and the emission is peaked in the UV and X-ray regions of the spectrum.
Figure 3 contains only data recorded from spectral chan¬nels near 1420 MHz, so it maps out the neutral hydrogen gas in the galaxy. There’s no neutral gas near the galaxy center and the difference in brightness in the HI ring in the galactic disk shows where there are massive clumps of neutral gas surrounding the giant molecular clouds in which the stars are forming. Scientists use HI to symbolize neutral hydrogen, and HII for ionized hydrogen.