Wobbling stars reveal giant companions

Two remarkable objects orbiting low-mass stars have been detected in our cosmic vicinity. This fascinating discovery was confirmed through observations from ESA’s Gaia spacecraft.

Gaia’s primary mission is mapping stars, so its ability to detect these unusual star companions highlights its unexpected contributions to exoplanet research.

The newly confirmed objects, Gaia-4b and Gaia-5b, challenge existing models of planet formation around low-mass stars.

Stars with hefty companions

Gaia-4b, classified as a “Super-Jupiter,” orbits the star Gaia-4 roughly 244 light-years away. Gaia-5b – considered a brown dwarf – travels around Gaia-5, located about 134 light-years from Earth.

“Gaia-4b is about twelve times more massive than Jupiter. With an orbital period of 570 days, it is a relatively cold gas giant planet,” explained Guðmundur Stefánsson, an astronomer at the University of Amsterdam.

“With a mass of around 21 Jupiters, Gaia-5b is a brown dwarf, more massive than a planet but too light to sustain nuclear fusion to be a star.”

Typically, such hefty objects are rarely found around low-mass stars, prompting astronomers to question traditional theories of planet formation.

Mapping the wobbling stars

Since its 2013 launch, ESA’s Gaia spacecraft has been constructing the largest and most detailed three-dimensional map of our Milky Way, charting the positions and movements of over two billion celestial objects.

Central to these recent findings is Gaia’s specialty: astrometry, the precise tracking of stellar motion. By repeatedly scanning the sky with dual optical telescopes, Gaia detects the minute “wobble” a star exhibits if it’s influenced by an orbiting companion.

In contrast to the transit method – which spots planets crossing in front of a star – astrometry is best suited to identifying massive objects in wide orbits, including Super-Jupiters and brown dwarfs that might otherwise be missed.

Power of multiple detection methods

“Gaia was repeatedly scanning these stars, building up an increasingly detailed picture over time,” Stefánsson said. 

“In 2022, Gaia Data Release 3 included a list of stars that appear to be moving as though pulled by an exoplanet. Using ground-based spectroscopic data and the radial velocity technique to investigate these stars, we confirmed our first planet and our first brown dwarf.”

The research highlights how multiple detection methods can together reveal new celestial bodies and clarify their nature.

Intriguing companions to modest stars

In the Milky Way, 75% of stars fall into the low-mass category, ranging from about 10% to 65% of the Sun’s mass. It’s been considered unlikely for huge gas giants or brown dwarfs to form around such stars, as smaller stars possess less material in their protoplanetary disks – material from which planets coalesce.

“About 75% of the stars in the Milky Way are low-mass stars, and when massive planets do occur around them, they cause a larger wobble and therefore a stronger astrometric signature that is easier to detect,” noted Stefánsson.

Finding Gaia-4b and Gaia-5b orbiting stars of modest mass challenges this assumption, illustrating that even limited-mass stellar environments can produce exceptionally large companions. 

This discovery encourages astronomers to refine or reconsider current models of how planets and brown dwarfs take shape, potentially exploring alternate scenarios – like disk instability or other yet-unknown processes.

A milestone in exoplanet studies

Gaia-4b’s detection marks a milestone in exoplanet studies, as it was confirmed using Gaia data exclusively. 

Historically, exoplanet candidates emerged from a combination of Gaia findings and data from its predecessor, Hipparcos. Gaia’s increasing precision, however, allows researchers to spot these signal “wobbles” without additional satellite missions.

“Gaia has seen the telltale signs of known exoplanets before, but this time Gaia revealed an entirely new extrasolar world,” said Johannes Sahlmann, Gaia Project Scientist at ESA.

This accomplishment foreshadows the impact of future Gaia data releases, particularly in 2026, when a more extensive set of observations (spanning 5.5 years) is expected. 

Astronomers anticipate hundreds or even thousands of discoveries, including not only gas giants and brown dwarfs but also smaller, rocky planets that challenge the limits of observational methods.

“This discovery is an exciting tip-of-the-iceberg for the exoplanet discoveries we can expect from Gaia in the future,” said ESA research fellow Matthew Standing.

A new era in exoplanetary science

As the Gaia spacecraft continues its sky-mapping mission, astronomers stand on the cusp of a golden age in exoplanet research. 

Upcoming data releases promise to unveil a broader spectrum of planetary systems, shedding light on how giant bodies form in environments once assumed too resource-poor to support them.

By providing continuous, highly accurate measurements of stars across the galaxy, Gaia is enabling scientists to piece together the puzzle of planetary system architectures – from small, dim red dwarfs to stars much larger than our Sun. 

The mission is bound to disrupt long-standing theories, opening the door to new questions about how diverse exoplanetary systems can be and how nature assembles them.

Ultimately, these findings serve as a reminder that our universe remains brimming with surprises. 

Image/ Video Credit: ESA/Gaia/DPAC/M. Marcussen

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–