A star is born at the center when a dense clump of interstellar gas and dust collapses under its gravitational pull. The leftover material forms a swirling disk around it, feeding stellar growth and often giving rise to planets. Newborn stars with these circumstellar disks had been observed by astronomers only in our Milky Way galaxy – until now. Scientists said on Wednesday they have spotted such a disk encircling a giant, luminous, and potentially planet-forming star that’s more than 20 times as massive as the Sun and about 10,000 times more luminous.
The discovery of the newborn star and its massive disk in the outer regions of our Milky Way confirms decades of theory, speculation, and conjecture about how these systems form. It also may explain why some of these newborns are more likely than others to eventually become supermassive, or even super-hot, stars such as our own Sun.
Our Sun and other stars are born in mammoth clouds of cool, molten hydrogen that stretch miles across the sky. Once they’re formed, the gravity of these newborns causes the hydrogen molecules in those clouds to fall together and clump into a dense mass that is then engulfed by a rapidly spinning disc of dust and other materials, which astronomers call a protostar. That spinning disk, in turn, cradles the infant star as it gathers its growing mass and emits jets of radiation that span the galaxy.
At this early stage, a protostar feeds on its dusty natal disk with a Jabba the Hut-like appetite. Then, as its nuclear furnace rages on, the star shoots superheated material into space in twin jets like a celestial double-bladed lightsaber.
While this process can be challenging to observe with ground-based telescopes, the heat-sensitive infrared eyes of NASA’s Spitzer Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA) allow astronomers to spy on the inner workings of these celestial systems. They can measure the temperature and composition of the disk material and spot telltale signs that the disk has begun to spin, indicating that a planet is likely forming there.
Researchers surveyed the skies of our Milky Way and other galaxies for silhouettes of these nascent star-forming disks. They searched for the telltale marks of a disk’s structure and composition and the gases that make up its dusty surface. The FLAMINGOS survey was particularly effective because it targeted areas in space where many forming stars are clustered together, a setting that makes them easier to detect.
The team used the ALMA observatory in Chile to study a region of the Orion Molecular Cloud Complex, one of the most prolific sites for star formation in our Milky Way. They spotted the silhouette of a disk surrounding the star HL Tau, about 160,000 light-years from Earth, or 5.9 trillion miles. The newly spotted disk was about 12,000 times larger than the size of the disk that surrounded our solar system as it formed 4.5 billion years ago, and it is drawing in and absorbing the material that will eventually agglomerate into our planets.