Astronomers Confirm Exoplanet Discovery With Direct Image For The First Time

Artist's impression of a planet orbiting the young star Beta Pictoris. ESO L. Calçada/N. Risinger (skysurvey.org)

Hunting for exoplanets is not an easy task. Astronomers typically use several different techniques to gain indirect evidence of their existence. When a candidate is spotted, researchers then resort to a different method to confirm its existence. For the first time, astronomers have now confirmed an exoplanet by imaging it directly.

Yes, it is a speck of light in the image but it required incredible technological advancements to remove the source star's light and track the planet. Such observations were possible with the GRAVITY instrument on the Very Large Telescope.

Reported in Astronomy & Astrophysics in two papers (here & here), the newly confirmed planet orbits the star Beta Pictoris and is dubbed Beta Pictoris c. The system is 63 light-years from Earth and formed about 18 million years ago.

The image on the left shows both the star and the two planets embedded in the dusty disk as seen from the Solar System, constructed from the actual observations. The middle panel contains an artist's impression of the disk/planet system. The image on the right shows the dimensions of the system when viewed from above and previous observations included. Axel Quetz / MPIA Graphics Department

"This means, we can now obtain both the brightness and the mass of this exoplanet," lead author Mathias Nowak, from the Institute of Astronomy, said in a statement. "As a general rule, the more massive the planet, the more luminous it is."

But some of the findings challenge what we know about planetary formation and their properties. Beta Pictoris c appears to have been formed from an instability in the disk that surrounds the star, but it is too close to the star for that to be the case. The team suggest that a dramatic hot shock in the disk led to its formation.

The system also brings into question the mass-luminosity relation. Based on previous data, Beta Pictoris b is about 13 times the mass of Jupiter, while the newly confirmed planet is about eight times. And yet Beta Pictoris b is six times more luminous, suggesting it should be a lot more massive than it is unless something else is going on.  

"We used GRAVITY before to obtain spectra of other directly imaged exoplanets, which themselves already contained hints on their formation process," adds co-author Paul Molliere, from the Max Planck Institute for Astronomy. "This brightness measurement of b Pictoris c, combined with its mass, is a particularly important step to constraining our planet formation models."

An upgraded version of the GRAVITY instrument, known as GRAVITY+, is currently under construction.

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