2023-06-13 13:44:16
TOI-1338b, one of the few planets known to orbit two stars, is not alone. A team of astronomers from the University of Ohio announces the discovery of a new, much larger world in this same Tatooine system. Why is this discovery interesting? Details of the study are published in the journal Nature Astronomy.
What are Tatooine systems?
It is possible that binary systems, consisting of two stars orbiting each other, harbor planets. By the way, binary systems are relatively common in our galaxy. In these environments, the two stars orbit each other around a common center of mass, while a planet usually orbits around one of the two stars. If the second is far enough away, then its orbit can be relatively stable.
The so-called systems circumbinaires, named “Tatooine” following Luke Skywalker’s home planet, are far more interesting, however. Here the planets orbit around the two stars. These systems were once considered unlikely. It was indeed imagined that the interactions between the two stars would end up, whatever happens, by expelling these said planets. However, astronomers have discovered a few in recent years, but most are lonely worlds, which brings us back to this new discovery.
The BEBOP-1 system
Since 2018, the TESS space telescope has been searching for planets around nearby stars in systems called TOI (Tess Objects of Interest). A subset of TOI is binary systems.
In 2020, a planet named TOI-1338b was discovered in one of these systems, named BEBOP-1, by a teenager on an internship at NASA. Unfortunately, while TESS data can identify the presence of a planet and the length of its orbit, it does not determine the mass of these planets. However, this is one of the most fundamental parameters. As part of a new study, astronomers have therefore sought to determine the mass of this planet using another method called radial velocity.
What is the radial velocity method?
In detail, when a planet orbits around its star, it exerts a gravitational force on her. This gravitational interaction then causes a movement of the star, causing variations in speed at which it approaches or moves away from us. The method therefore consists in measuring these speed variations.
To do this, we use the doppler effect, which is the change in frequency of a wave as the source of the wave moves towards or away from the observer. When the star approaches us, the spectral lines it emits are blue shiftedwhile when the star moves away, they are red shifted. By measuring these shifts in the star’s spectrum, astronomers can determine variations in the star’s velocity caused by the planet’s orbit. These variations are periodic and make it possible to deduce the orbital period of the planet, i.e. the time it takes to make a complete orbit.
From the orbital period and the amplitude of the speed variations, astronomers can finally calculate the minimum mass of the planet using Kepler’s laws and the laws of gravity.
Two stars, two planets
Unfortunately, the researchers were unable to determine the mass of TOI-1338b using this method. The complications of having two stars affect each other make such detections particularly difficult. On the other hand, it allowed them to isolate another planet in the same system, further away than the first. Appointed BEBOP-1cthis world would have an orbital period of 215 days and a mass 65 times greater than the Earth, or regarding five times less than the mass of Jupiter.
Of the twelve Tatooine systems known to date, only the second is home to more than one planet. It is also the first time that a circumbinary planet has been discovered using this method.
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