A team of astronomers have recently discovered eighteen new planets, the largest collection of planets around stars that are more massive than the sun.The research crew, hailing from California Institute of Technology call this the largest announcement of planets that are in orbit around stars that are more massive than the sun. The paper, published in the December issue of The Astrophysical Journal Supplement Series, outlines how the team did it.

The researchers looked at about three hundred stars using the Keck Observatory in Hawaii, with follow-up completed at the Fairborn Observatory in Arizona and the McDonald Observatory in Texas. They focused their research on what are called “retired” stars. These A-type stars are more than one and a half times more massive than the sun, and are just past the prime in their life, which is why they are retired. Now, they are puffing into what is called a subgiant star.

When they were looking for planets around the stars, they searched for these A-type stars that would wobble. This indicated that there was a possible gravitational tug of a planet orbiting around them.  They would search the stars’ spectra for lengthening and contracting of wavelengths due to motion going away from and toward the observer, also called Doppler shifts. With this criteria, the research team found eighteen planets with masses that are similar to Jupiter’s.

These new planets is a fifty percent increase in the number of planets that are already known to orbit around massive stars. And this also helps provide more information on how planets form, as well as solar systems. This backs up the theory that tiny paricles clump together and eventually form into a planet. In other words, the planets grow from seed particles that gather gas and dust surrounding a new star. In turn, this means that the resultant planet and its characteristics, such as number, size, and shape, depends on the mass of the star. The larger the star, the greater number of giant planets. This also coincides with previous research.

Another interesting note about these discovered is that not only are they finding that these A-type planets are most frequently around massive stars, but that they are also in wider orbits. The new planets are all farther away than most planets, which orbit close to their stars.

Usually there are close orbits, but gas giants could only form far from their stars because it is a colder area. That means, in order for these giants to orbit near their stars, there has to be something else to pull them in. According to the research, the new subgiants don’t expand enough, so they must have a unique characteristic.

In addition, the new planets have a mainly circular orbit, whereas other planets generally follow an elliptical path.

These findings are significant in further planet research.

Published in the December issue of The Astrophysical Journal Supplement Series, “Retired A stars and their companions VII. Eighteen new Jovian planets,” was authored by  John Johnson, assistant professor of astronomy at Caltech, Christian Clanton, Justin Crepp; and scholars from the Institute for Astronomy at the University of Hawaii; the University of California, Berkeley; the Center of Excellence in Information Systems at Tennessee State University; the McDonald Observatory at the University of Texas, Austin; and the Pennsylvania State University. The research was supported by the National Science Foundation and NASA.

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