Herschel: SMA unveils how small cosmic seeds in Snake nebula grow into big stars

These two panels show the Snake nebula as photographed by the Spitzer and Herschel space telescopes. 

At mid-infrared wavelengths (the upper panel taken by Spitzer), the thick nebular material blocks light from more distant stars. 

At far-infrared wavelengths, however (the lower panel taken by Herschel), the nebula glows due to emission from cold dust. 

The two boxed regions, P1 and P6, were examined in more detail by the Submillimeter Array. 

Credit: Spitzer /GLIMPSE /MIPS, Herschel /HiGal, Ke Wang, European Southern Observatory

New images from the Smithsonian's Submillimeter Array (SMA) telescope provide the most detailed view yet of stellar nurseries within the Snake nebula.

These images offer new insights into how cosmic seeds can grow into massive stars.

Stretching across almost 100 light-years of space, the Snake nebula is located about 11,700 light-years from Earth in the direction of the constellation Ophiuchus.

In images from NASA's Spitzer Space Telescope it appears as a sinuous, dark tendril against the starry background. It was targeted because it shows the potential to form many massive stars (stars heavier than 8 times our Sun).

"To learn how stars form, we have to catch them in their earliest phases, while they're still deeply embedded in clouds of gas and dust, and the SMA is an excellent telescope to do so," explained lead author Ke Wang of the European Southern Observatory (ESO), who started the research as a predoctoral fellow at the Harvard-Smithsonian Center for Astrophysics (CfA).

The team studied two specific spots within the Snake nebula, designated P1 and P6. Within those two regions they detected a total of 23 cosmic "seeds" - faintly glowing spots that will eventually birth one or a few stars.

The seeds generally weigh between 5 and 25 times the mass of the Sun, and each spans only a few thousand astronomical units (the average Earth-Sun distance).

The sensitive, high-resolution SMA images not only unveil the small seeds, but also differentiate them in age.

Previous theories proposed that high-mass stars form within very massive, isolated "cores" weighing at least 100 times the mass of the Sun.

These new results show that that is not the case. The data also demonstrate that massive stars aren't born alone but in groups.

"High-mass stars form in villages," said co-author Qizhou Zhang of the CfA. "It's a family affair."

The team also was surprised to find that these two nebular patches had fragmented into individual star seeds so early in the star formation process.

They detected bipolar outflows and other signs of active, ongoing star formation. Eventually, the Snake nebula will dissolve and shine as a chain of several star clusters.

SMA reveals giant star cluster in the making

This image from the Smithsonian's Submillimeter Array maps the projected density of molecular gas in the central 30 light years of W49A. 

Brighter colours mark denser regions. 

The brightest region at the image center is less than three light-years across, yet it contains about 50,000 suns' worth of molecular gas. 

Credit: Roberto Galván-Madrid (ESO), Hauyu Baobab Liu (ASIAA, Taiwan), Tzu-Cheng Peng (ESO)

W49A might be one of the best-kept secrets in our galaxy.

This star-forming region shines 100 times brighter than the Orion nebula, but is so obscured by dust that very little visible or infrared light escapes.

The Smithsonian's Submillimeter Array (SMA) has peered through the dusty fog to provide the first clear view of this stellar nursery. The SMA revealed an active site of star formation being fed by streamers of infalling gas.

"We were amazed by all the features we saw in the SMA 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).

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 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 SMA also revealed an intricate network of filaments feeding gas into the center, much like tributaries feed water into mighty rivers on Earth.

Being denser than average will help the W49A star cluster to survive. Most star clusters in the galactic disk dissolve rapidly, 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 Submillimeter Array 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.