The Great Barred Spiral Galaxy in the constellation Fornax is, at 200,000 light-years across, one of the largest galaxies known to astronomers. Credit: ESO, IDA, Danish 1.5 m, R. Gendler, J-E. Ovaldsen, C. Thöne, and C. Feron
FORTIS will give clues to how galaxies grow with birth and growth cessation of new stars. Rocketeers led by Johns Hopkins astrophysicist Stephan R. McCandliss fired a 58-ft unmanned rocket from the White Sands Missile Range in New Mexico more than 170 miles up for a brief but clear look at the Great Barred Spiral Galaxy. Using an onboard spectrographic telescope McCandliss team recorded UV observations of H2, the main fuel of star formation, that surrounds the galaxy.
The parabolic flight lasted about 15 min from liftoff to the time the rocket parachuted back to Earth. That gave the telescope containing an intricate array of tiny light-admitting shutters about 6 min above the Earth’s atmosphere – where light from the far UV end of the spectrum is not filtered out – for a clear view of the target galaxy 56 million light years away.
The rocket flight was part of NASA’s Sounding Rocket Program, which supports about 20 missions a year, exploring space at relatively low cost.
FORTIS (Far ultraviolet Off-Rowland circle Telescope) for Imaging and Spectroscopy.”is the most sensitive instrument the group has ever used for a couple of reasons. The instrument’s array of light-reflecting mirrors “bounces” the light only twice, meaning less light is lost before it reaches the telescope’s detector. FORTIS also can simultaneously target and record many spectra from several targets automatically.
This was the third FORTIS mission, and promised to return the most useful information. In two previous attempts in 2013 – one aimed at observing a different galaxy, another targeting the Comet Ison – technical problems affected the quality of the information returned. Each mission, however, achieved enough to be considered a substantial success. This time, it all appeared to have worked as planned.
FORTIS sent down a stream of information about the light from bright spots in the spiral arms of the galaxy being fed by gas flowing in from the surrounding circumgalactic medium. That’s the region showing significant gas ebb and flow – the activity that feeds star formation. It will take months to analyze the information, potentially adding to scientists’ understanding of how galaxies sustain themselves and what causes them to stop producing new stars. The team’s hypothesis is that ultraviolet radiation from new stars temporarily stifles star formation, regulating the rate at which stars form.
The FORTIS spectrographic element splits the light captured by the telescope into segments of varying wavelength intensity, which help scientists discern hydrogen emission and absorption. McCandliss hopes that the success of the microshutter array in a far ultraviolet application will qualify its use on larger orbital missions, such as a newly conceived ultraviolet/optical High Definition Space Telescope (HDST). Planned as larger and offering images many times sharper than the Hubble Space Telescope, the HDST could be used to study relatively near Earthlike planets for signs of life. http://hub.jhu.edu/2015/12/18/sounding-rocket-launch-observes-galaxy-far-far-away
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