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Galactic Imaging
UMass Amherst’s Giant Telescope to Attempt Imaging Black Hole at Center of Our Galaxy
Picture Of Black Hole Engulfing Nearby Stars And Distorting The Space Around It

“This is an example of the kind of science we are going to be able to do,” says Schloerb. “I expect the LMT to attract astronomers from around the world."

Astronomers at the University of Massachusetts Amherst, as part of an international team, have successfully completed a key test of their new Large Millimeter Telescope (LMT) in Mexico, one of the largest in the world, designed to probe the history of star formation in the Universe. Their success paves the way for LMT to be part of the first team ever to image the black hole at the center of our galaxy.

For this summer’s experiment, the LMT joined Very Long Baseline Array stations in Hawaii and New Mexico to conduct Very Long Baseline Interferometry (VLBI). In addition to INAOE and UMass, observations were carried out by scientists from MIT-Haystack Observatory, the National Radio Astronomy Observatory, the Smithsonian Astrophysical Observatory and the Center for Radio Astronomy and Astrophysics in Morelia, Mexico.

UMass Amherst astronomer Peter Schloerb says, “This early science using the LMT is an exciting milestone for our telescope and an achievement as well for the VLBI group. We record signals at each antenna, yielding terabytes of data. We then play it back into a device that correlates the signals between the antennas. If done correctly, the light waves from the two telescopes will interfere with each other creating an interference pattern called fringes. You can use all the telescopes in such an array to make an image of the source. We were able to get confirmation that fringes were detected within one day of our experiment.”

The giant radiotelescope, on a volcanic peak next to Mexico’s highest mountain, represents a collaboration between UMass Amherst and Mexico’s Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE). The LMT is located on the summit of Volcan Sierra Negra, a 15,000-foot extinct volcano. Construction started in 2000 and the LMT captured its first light in 2011.

Astronomers at MIT’s Haystack Observatory correlated the signal data collected this summer. Schloerb says that in the future a larger group of research collaborators led by Shep Doeleman of Haystack hope to make a picture of the black hole at the center of the Milky Way galaxy, which is known as the Sagittarius A star, or SgrA*.

At the center of the galaxy, SgrA* has been observed with VLBI, Schloerb adds, “but you need the really big LMT to move beyond observation to imaging. LMT is located in a prime spot between the others that are used for this kind of work. So this new instrument gives us one of the best opportunities to achieve that goal. Nobody has been able to take a picture of a black hole before, so this would be an important achievement.”

When the LMT’s current 32-meter dish is built out to its full 50-meter (164-foot) diameter size and fully operational in the next couple of years, it will be the largest, most sensitive single-aperture instrument of its kind in the world. Schloerb says he and colleagues were elated to find this summer that without any special effort, the LMT was accurate to within 2 or 3 arcseconds, and with fine tuning this should improve.

An arcsecond is one sixtieth of an arcminute, a unit for measuring angles that is equal to one sixtieth of a degree. Arcseconds are used in astronomy to express extremely small angles for focusing instruments on very distant objects.

“It appears that we also aligned the surface to within 80 or 90 microns root mean square for the parabola, corresponding to less than 4/1000s of an inch precision. It’s a nice accomplishment to meet that goal,” he adds. “The LMT is a few times more sensitive than a comparable-sized telescope elsewhere. One of the things it can do well is make maps of broadband continuous radiation of dust in our galaxy and others. It can discover very distant galaxies, and it’s a few times better than others for that particular kind of experiment.”

“This is an example of the kind of science we are going to be able to do,” says Schloerb. “I expect the LMT to attract astronomers from around the world. Once we establish and report on the LMT’s level of precision, which is excellent, I think people are going beat a path to our door to get time on it for their own projects. This instrument makes UMass Amherst a big-time player internationally. It’s been gratifying to see it come on line and to find that it works very well.”

The LMT is supported by grants from the National Science Foundation and NASA.

Janet Lathrop