The largest study on runaway stars in the milky way reveals surprises about their origins

The positions and trajectories of 20 hypervelocity stars as reconstructed from data acquired by the Gaia satellite, overlaid on top of an artistic view of the Milky Way. Credit: ESA/Marchetti et al 2018/NASA/ESA/Hubble

doi.org/10.1051/0004-6361/202556646
Credibility: 989
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Runaway stars are celestial bodies that travel through the galaxy at extremely high speeds, sometimes so fast that they manage to escape the Milky Way’s gravity forever

They were discovered in the 1960s by the Dutch astronomer Adriaan Blaauw, who suggested that many originate in binary systems: when one of the stars explodes in a supernova, the other is launched away like a slingshot stone.

Later, in 2005, even faster stars, called hypervelocity stars, were identified.

These “runaway” stars play an important role: they spread energy and heavy elements through the interstellar medium, influencing where new stars and planets can be born.

Now, a team of Spanish researchers, linked to institutions such as the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), the Institute of Space Studies of Catalonia (IEEC), and the Institute of Astrophysics of the Canary Islands (IAC), has conducted the largest observational study ever done on massive runaway stars in our galaxy.

They analyzed 214 O-type stars-the brightest, hottest, and most massive stars in existence-combining precise data from the European Space Agency’s Gaia mission, which since 2013 has been mapping billions of stars with impressive detail about their movement, distance, and composition, with high-quality spectra from the IACOB project, which specializes in massive stars.

The goal was to better understand how these stars are ejected and where they come from.

To do this, the scientists measured not only their speed but also their rotation (how quickly they spin around their own axis) and whether they travel alone or in pairs (binaries).

Runaway stars were defined as those with speeds above about 700 km/s, sufficient to escape the galaxy.

The results brought unexpected revelations.

Most runaway stars rotate slowly, but the fastest-spinning ones are usually linked to supernova explosions in binary systems.

Those with the most extreme speeds tend to be solitary, suggesting they were ejected by intense gravitational interactions within young, dense star clusters.

Only a minority came from binary systems, contradicting the long-accepted idea that this was the primary mechanism.

The team found 12 runaway binary systems, including three X-ray binaries with neutron stars or black holes, and three that likely harbor black holes.

Very few stars combine high speed with rapid rotation, indicating that there are several different pathways for ejection: supernovae in binary systems for some, and dynamical interactions in clusters for others.

As lead author Mar Carretero-Castrillo stated: “This is the most comprehensive observational study of its kind in the Milky Way.

By combining information on rotation and binarity, we offer the scientific community unprecedented constraints on how these runaway stars form.”

These findings help refine models of stellar evolution, cluster formation, and the role of supernovae in galactic dynamics.

Massive runaway stars scatter elements essential for life throughout space and can even transport planetary systems to distant regions of the galaxy.

With future Gaia data and more in-depth spectroscopy, astronomers aim to pinpoint the exact birthplaces of these stars and discover even more exotic systems.

Gradually, we are gaining a better understanding of how the chaos in star birth shapes the structure of our own galaxy.

Published in 02/09/2026 08h09

Portuguese version

Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.

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