Astronomers have finally solved a long-standing mystery about how massive stars form, thanks to groundbreaking observations made with the National Radio Astronomy Observatory’s Very Large Array (VLA).
By studying a young star named HW2 in the star-forming region of Cepheus A, located 2,300 light years from Earth, scientists have, for the first time, mapped the massive flow of gas that fuels its rapid growth.
These findings help answer a major question in astrophysics: how do massive stars—those that often end their lives in spectacular supernova explosions—gather so much mass?
The study, soon to be published in Astronomy & Astrophysics, reveals the intricate structure and movement of gas around HW2.
The research team used ammonia, a molecule commonly found in interstellar clouds, as a tracer to observe how gas moves around the forming star.
They discovered a dense ring of hot ammonia gas, stretching from 200 to 700 times the distance between Earth and the Sun, forming what is known as an accretion disk. This structure plays a crucial role in star formation theories by feeding gas to the growing star.
What makes this discovery so special is the sheer amount of material falling onto HW2.
The researchers found that gas is streaming inward at a rate of two thousandths of a solar mass per year—an incredibly fast pace for a forming star.
Even more surprising, the gas is both collapsing inward and rotating around the star, confirming that massive stars can indeed grow through accretion disks, just like their smaller counterparts.
According to Dr. Alberto Sanna, the study’s lead author, these findings show that disk-mediated accretion can sustain massive stars up to tens of times the size of our Sun.
To make these observations, the team used the VLA’s powerful radio sensitivity to capture details as small as 100 times the distance between Earth and the Sun.
The results were compared with the latest computer simulations of massive star formation, and the two matched closely.
The ammonia gas around HW2 was found to be collapsing almost at the speed it would if gravity alone were pulling it in, while also rotating just slightly slower than expected—a delicate balance shaped by both gravity and centrifugal forces.
One unexpected finding was the discovery of turbulence and asymmetry in the disk’s structure, hinting at the presence of “streamers”—narrow streams of gas feeding fresh material to one side of the disk. These streamers have been spotted in other star-forming regions and may be vital for keeping accretion disks full of material.
The research not only settles debates about how massive stars like HW2 can sustain their rapid growth, but it also strengthens the idea that stars of all sizes form through similar processes.
According to Dr. Todd Hunter of the NRAO, the results show how radio interferometry allows scientists to uncover the hidden mechanisms behind the formation of the universe’s most influential stars.
In the next decade, an upgraded version of the VLA is expected to provide even clearer views of these cosmic nurseries, pushing our understanding of star formation to new levels.
Massive stars like HW2 are key players in the universe, driving powerful winds and explosive events that spread heavy elements across galaxies, shaping the evolution of entire star systems.
This new understanding marks a major step forward in unraveling the secrets of how these cosmic giants come to life.
Source: National Radio Astronomy Observatory.
