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Stars Born in Galactic Wind

Astronomers have found newborn stars in gas pouring out of a galactic nucleus.

stars forming in galactic outflow

ESO / M. Kornmesser

This artist’s illustration depicts stars forming in gas streaming out of the center of a galaxy. Outflows are a natural part of galaxy development, powered by bursts of starbirth or maniacally accreting black holes (or both) in galactic cores. Astronomers expect such outflows to ignite star formation. Although they’ve seen outflow-triggered star formation before, for example in cold gas condensing around bubbles inflated by black hole outbursts, it’s been difficult to conclusively spot stars forming in the winds themselves.

Reporting March 27th in Nature, Roberto Maiolino (University of Cambridge, UK) and colleagues say they’ve finally managed to find such stars. The team studied the system IRAS F23128−5919, a mishmash of (what was once two) merging galaxies in the far southern constellation Tucana, the Toucan. The system’s southern nucleus has a big stream of gas coming out of it.

The astronomers detected emission in this outflow that matches what’s seen in star-forming regions. They also found a population of young stars — just a few million years old — that’s moving with the gas at speeds up to 100 km/s (2 million mph). This rate is actually less than half the gas’s speed, but that’s expected: when the stars form, they feel the galaxy’s gravitational attraction and slow down; the gas, on the other hand, is driven onward by outward-shoving pressures. The team even sees a hint of stars losing the fight with gravity and beginning to fall back toward the disk.

The team estimates that about 15 Suns’ worth of stars form each year in the part of the outflow they can see. (The flow has a receding component that’s obscured by dust.) That’s more than 10% of the total estimated starbirth for this system.

Read more about the discovery in the European Southern Observatory’s press release.

Reference: R. Maiolino et al. “Star formation inside a galactic outflow.” Nature. March 27, 2017.

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