Scientists generated the most precise three-dimensional image of star formation zones in the Milky Way galaxy using data from the European Space Agency’s Gaia space telescope. This map will reveal more about these far overcast regions and the blazing young stars that form them.
Gaia’s star-formation map (slider). Image Credit: European Space Agency
Mapping and analyzing star-forming regions in space is notoriously challenging, largely because they’re often hidden behind massive clouds of gas and dust, making it difficult to accurately determine their distances.
Gaia cannot view these clouds directly, but it can detect stellar locations and 'extinction' of stars. This implies that it can detect how much light from stars is blocked by dust. This allows scientists to generate 3D maps of where the dust is and use those images to calculate how much ionised hydrogen gas is there - a telltale indicator of star formation.
Extremely Bright, Young Stars
The new 3D image of star-forming areas in the Milky Way was created using Gaia measurements of 44 million 'ordinary' stars and 87 O-type stars. The map covers a distance of 4000 light-years from Earth, with the Sun in the center.
O stars are rare because they are young, huge, and exceedingly brilliant and hot. They sparkle brightly in ultraviolet light. These light beams are so powerful that they may remove electrons from hydrogen atoms when they strike them. In this fashion, they ‘ionize’ the hydrogen gas around the blazing stars, causing it to become a combination of charged particles. This is one method that astronomers use to pinpoint places in space where stars are born.
Many telescopes have viewed these areas, so astronomers have a solid concept of how they seem from a human perspective. But no one knew how they looked in three dimensions or from the outside.
While many telescopes have provided a good understanding of what these regions look like from the vantage point, their true three-dimensional structure and appearance from an outside perspective remained a mystery.
The Milky Way From Above
Imagine looking at the Milky Way from another galaxy. Since no spacecraft has ever traveled beyond our galaxy, capturing a photo from that vantage point isn’t currently possible. Fortunately, the Gaia mission is producing the most precise multi-dimensional image of the Milky Way, allowing scientists to predict what it might look like.
Gaia's sky maps, which include all three spatial coordinates (3D) and three velocities (moving towards, away from, and across the sky), have revealed the precise movements and locations of millions of nearby stars. The telescope has already deepened our understanding of the solar neighborhood, enabling scientists to study the stars and interstellar material surrounding the Sun in ways that weren’t possible before.
Gaia provides the first accurate view of what our section of the Milky Way would look like from above.
Lewis McCallum, Study First Author and Astronomer, University of St Andrews
“There has never been a model of the distribution of the ionized gas in the local Milky Way that matches other telescope’s observations of the sky so well. That’s why we are confident that our top-down view and fly-through movies are a good approximation of what these clouds would look like in 3D,” added McCallum.
Lewis's new map shows 3D views of the Gum Nebula, the North American Nebula, the California Nebula, and the Orion-Eridanus Superbubble. It enables one to travel around, through, and above locations with stellar nurseries.
Giant Cavity of Interstellar Matter
The map allows scientists to understand more about how massive O stars energize gas in the galaxy and how far their effect extends. Lewis and his colleagues have already detected that parts of the clouds in the star-forming areas appear to have broken open, allowing streams of gas and dust to discharge into a massive void.
This map nicely shows how radiation of massive stars ionizes the surrounding interstellar medium and how dust and gas interact with this radiation. The 3D model provides a detailed look at the processes that shape our local galactic environment and helps astronomers understand interactions between the warm and cold components of the local Universe.
Sasha Zeegers, Research Fellow, European Space Agency
In the future, this map will cover a wider portion of the Milky Way.
“It required huge computational power to generate the map out to ‘just’ 4000 light-years from the Sun in high resolution. We hope that the map can be expanded further out once Gaia has released its new set of data,” added Lewis.
“Gaia’s distance measurements of the nearby hot stars, and the 3D maps of dust – obtained from measuring the extinction and positions of millions of ordinary stars using Gaia data – are both crucial ingredients of this new map. Gaia’s fourth data release will contain data of even better quality and quantity, making it possible to further advance our knowledge of star-forming regions,” confirmed Johannes Sahlmann, Gaia Project Scientist, ESA.
The most accurate 3D map of stellar nurseries in the Milky Way. Video Credit: European Space Agency
Journal Reference:
McCallum, L., et al. (2025) The Hα sky in three dimensions. Monthly Notices of the Royal Astronomical Society. doi.org/10.1093/mnrasl/slaf023