Team Spots Excess of Hot Jupiters in Dense Stellar Cluster

Planet HAT-P-7b and parent star

Artist’s rendition of hot Jupiter

Astronomers recently detected at least three hot Jupiters populating an open cluster of stars dubbed Messier 67 (M67). Scientists noted that until now they had no idea that hot jupiters could be present within an open cluster.

The newly found planets were discovered with help from the European Southern Observatory’s La Silla ground telescopes. The research team explained that denser stellar clusters may trigger an excess of interactions between host stars and planets which may provide an explanation to the unusual number of hot Jupiters in M67.

But the team has been keeping an eye on M67 for several years now. Astronomers have so far detected 88 stars within the cluster, which is estimated to be as old as the Sun. They also used the HARPS spectrograph at La Silla Observatory to look for “wobbles” in star’s orbits which may signal the presence of a dense planet such as a hot Jupiter.

Recently the team detected three stars which may host at least one hot Jupiter each. But researchers believe that there may be more planets out there in the cluster.

Hot Jupiters are exoplanets, or planets located outside the Solar System, which is orbiting its host star dangerously close. A hot Jupiter completes its orbital period in less then 10 days. By contrast, Jupiter needs 12 years to go once around the Sun and thus is much colder than our home planet.

Roberto Saglia, leader of the research team and astrophysicist at the Max-Planck-Institut für Extraterrestrische Physik in Germany, explained that such dense stellar clusters can help scientists better understand how these massive planets emerged. Saglia added that the dense environment within M67 spurred planetary formation like in no other places.

The analysis also revealed that hot Jupiters usually occur around stars located inside clusters than around the solitary ones. Anna Brucalassi, another researcher involved in the study, estimates that 5 percent of star within M67 may host hot Jupiters. By contrast, just 1 percent of isolated stars are closely orbited by a hot Jupiter.

“This is really a striking result,”

said Brucalassi.

The team estimates that the newly-found gas giants did not form in the proximity of their parent stars as the conditions there would not permit the formation of a Jupiterian planet. The team speculates that the planets might have formed further from their stellar companions just like our Jupiter did and slowly moved closer to the stars.

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