Star formation revealed by ALMA in distant Milky Way region

Astronomers have made a groundbreaking discovery that sheds new light on star formation in some of the galaxy’s most remote regions.

Using the powerful Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, scientists captured the first spatially resolved images of protostellar outflows and jets in the Milky Way’s outer disk.

The observations focused on the protostellar source Sh 2-283-1a SMM1, located around 26,000 light-years from Earth and more than 51,000 light-years from the Galactic Centre.

This region contains only a third of the heavy elements found near the Sun, making it a rare natural laboratory for studying how stars are born in low-metallicity environments similar to those of the early Milky Way.

Jets that pulse like a heartbeat

ALMA’s high-resolution imaging revealed a striking bipolar structure: narrow, high-velocity jets streaming away from the protostar, surrounded by slower, broader outflows.

By mapping the movement of gas toward and away from Earth, researchers could track the dynamics of these jets with unprecedented clarity at such a large galactic distance.

One of the most significant findings was the discovery that these jets are episodic rather than continuous. Instead of a steady stream of ejected material, the protostar emits bursts every 900 to 4,000 years.

This stop-and-start rhythm regulates stellar growth – allowing the young star to keep accreting matter from its disk while shedding excess mass and angular momentum.

Although episodic outflows have been recorded in nearby stellar nurseries, this marks the first detection of such behaviour in a protostar over 15 kiloparsecs from the Galactic Centre.

The finding suggests that the physical processes driving star formation are consistent across environments, even when the surrounding chemistry differs dramatically.

Chemistry tells a different story

While the physics of jet formation remains universal, the chemistry of Sh 2-283-1a SMM1 shows unique signatures.

Protostellar outflows and jets discovered in the outer Galaxy. The left panel shows CO line emission images obtained with ALMA observations. The red and blue contours represent high-velocity jet gas moving away from and toward us, respectively. The grayscale background indicates the distribution of lower-velocity outflow gas. The green star indicates the positions of the protostar. The yellow and green squares indicate the regions observed with ALMA in this study. Credit: Ikeda et al. (Niigata univ.), background: R. Hurt/NASA/JPL-Caltech/ESO

Measurements of carbon monoxide (CO) and silicon monoxide (SiO) revealed unusually low SiO-to-CO ratios compared with inner-galaxy protostars.

This implies that the shock chemistry and dust properties in the outer galaxy differ from those near the Sun, reflecting the scarcity of heavy elements in this region.

The protostar was also classified as a ‘hot core’ – a compact, warm, chemically rich region often associated with complex organic molecules.

Only one other hot core has been confirmed so far out in the galaxy, highlighting the rarity of such chemically active environments in low-metallicity regions.

The luminosity of Sh 2-283-1a SMM1 is estimated to be about 6,700 times that of the Sun, placing it in the intermediate- to high-mass range.

Extending the frontier of star formation studies

Beyond this single protostar, ALMA detected molecular outflows from four additional sources in the outer galaxy, proving that star formation is both active and widespread in these distant environments.

Until now, detailed studies of protostellar jets were limited to regions only a few thousand light-years from Earth. Extending this research to the galaxy’s outskirts allows astronomers to test long-standing models of stellar birth under more primitive conditions.

These results also bridge modern star formation with cosmic history. Low-metallicity environments like that of Sh 2-283-1a SMM1 resemble the conditions of the early Universe, when heavy elements were scarce.

Studying how stars form in such settings provides insights into how the first generations of stars ignited and shaped the galaxies we see today.

Future research

The research team plans to expand its survey to more protostars in the Milky Way’s outer regions.

By comparing episodic jet cycles and molecular abundances across environments, scientists hope to determine whether metallicity directly influences the rhythm and chemistry of stellar birth.

The findings also open the door to investigating how planets might eventually emerge in chemically diverse environments.

If the underlying physics of star formation remains constant, planetary systems may also arise under conditions once thought inhospitable.

This landmark study shows that while chemistry varies with environment, the fundamental physics of star formation remains unchanged across the Milky Way.

By capturing the first resolved protostellar jets so far from the Galactic Centre, astronomers have confirmed that the processes shaping stars near the Sun are the same ones at work in the galaxy’s far reaches.

In other words, from our stellar neighbourhood to the ancient outskirts of the Milky Way, the blueprint of star birth is universal.