Space

Four New Giant Planets Observed Around Massive Stars

March 17, 2016 | by Alfredo Carpineti

Photo credit: This is an artistic illustration of a gas giant planet. NASA, ESA, G. Bacon (STScI) and N. Madhusudhan (UC)

We have now become used to the discovery of new exoplanets, but there are still many unknowns that are yet to be understood.

An international team of astronomers set out to answer one of these unknowns: What are the more favorable characteristics that stars need to have for the formation of giant planets? In doing so, they have discovered four new exoplanets orbiting four different stars more massive than the Sun.

The team computed the radial velocity of 166 stars, and discovered four new planets around four of them: HIP95124b, HIP8541b, HIP74890b, and HIP84056b. The results were published in a paper accepted for publication in the journal Astronomy & Astrophysics.

HIP95124b has the shortest orbital period of the four planets (about 560 days) and has 2.9 Jupiter masses. It orbits a star that is almost twice as massive as the Sun and with five times its radius.

HIP8541b, on the other hand, is the one with the furthest orbit (about 1,560 days) and is the largest with a mass of 5.5 Jupiters. Its star is only slightly heavier than the Sun but almost eight times wider.

HIP74890b and HIP84056b are remarkably similar, orbiting stars about 1.7 times the mass of the Sun in about 820 days. Even their mass is pretty similar, 2.4 and 2.6 times the mass of Jupiter, respectively.

The scientists also found an interesting trend. They noticed that giant planets tend to be found more often around stars that are rich in elements like oxygen, carbon, and iron. As giant planets are not necessarily made by heavier elements, this might indicate the need for a rocky core for gas giants to form.

And they also discovered that intermediate mass stars, slightly bigger than the Sun, are more likely to host giant planets.

"We show that the fraction of giant planets increases with the stellar mass in the range between 1 to 2.1 solar masses, despite the fact that planets are more easily detected around less massive stars," the team wrote in the paper.

Although the study was conducted on a relatively small sample of stars, the findings might have a profound impact on our understanding of the Solar System. After all, our Sun has four giant planets.

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