W49A is located about 36,000 light-years from Earth, on the opposite side of the Milky Way. It represents a nearby example of the sort of vigorous star formation seen in so-called "starburst" galaxies, where stars form 100 times faster than in our galaxy.
The purple mountain observatory (PMO) 13.7m telescope has peered through the dusty fog to provide the first clear view of this stellar nursery. The study revealed an active site of star formation being fed by streamers of infalling gas, with combined observations with PMO 13.7m, Submillimeter Array (SMA) and IRAM 30m telescopes.
"We were amazed by all the features we saw in these images," says lead author Roberto Galván-Madrid, who conducted this research at the Harvard-Smithsonian Center for Astrophysics (CfA) and the European Southern Observatory (ESO).
The heart of W49A holds a giant yet surprisingly compact star cluster. About 100,000 stars already exist within a space only 10 light-years on a side. In contrast, fewer than 10 stars lie within 10 light-years of our Sun. In a few million years, the giant star cluster in
W49A will be almost as crowded as a globular cluster.
The PMO 13.7m also revealed an intricate network of filaments feeding gas into the center, much like tributaries feed water into mighty rivers on Earth. The gaseous filaments in W49A form three big streamers, which funnel star-building material inward at speeds of about 4,500 miles per hour (2 km/sec).
"Move over, Mississippi!" quips co-author Qizhou Zhang of the CfA.
Being denser than average will help the W49A star cluster to survive. Most star clusters in the galactic disk dissolve rapidly, their stars migrating away from each other under the influence of gravitational tides. This is why none of the Sun's sibling stars remain nearby. Since it is so compact, the cluster in W49A might remain intact for billions of years.
The PMO 13.7m mapped the molecular gas within W49A in exquisite detail. It showed that central 30 light-years of W49A is several hundred times denser than the average molecular cloud in the Milky Way. In total, the nebula contains about 1 million suns' worth of gas, mostly molecular hydrogen.
The column density of molecular gas in the central 30 light years in W49A. The brighter color shows higher column density regions. This figure is from the combined data of PMO 13.7m, SMA, and IRAM 30m telescopes.
The column density of molecular gas in the 3 light year central region of W49A. The brightest region has a size less than 3 light years, but contains molecular gas of more than 105 solar mass.
Their research was published in the December 2013 Astrophysical Journal.
（http://iopscience.iop.org/0004-637X/779/2/121/pdf/0004-637X_779_2_121.pdf）
