For the first time astronomers “weigh” a young exoplanet

Collected over more than two decades of data with the help of two stellar cartographic satellites of the European space Agency has for the first time allowed astronomers to calculate the mass of very young exoplanets. About the study reported in the journal Nature Astronomy.

Study planet Beta Painter b is a gas giant, the weight of which, according to scientists from 9 to 13 times the mass of Jupiter. Discovered in 2008, the exoplanet revolves around the star Beta Painter, which is about 63 light years from Earth in the constellation pictor and is the second brightest in the constellation.

Since the very star of this constellation is very young (she is 8 to 20 million years), a planet in the system represents an excellent target for studying the processes of formation and development of exoplanets. However, this task is complicated by the fact that the process of formation of stars is not yet complete — she was still very active pulses that creates a problem for measurement of its radial velocity (the speed with which the star moves toward us and away from us as the orbit of its planet). This method is often used to measure the mass of exoplanets.

To measure the mass of Beta Painter b scientists did not use a method of measuring radial velocity, and instead make calculations based evolution of the movement of the stars in the night sky for a long period of time. That is why the process took more than 20 years, reports the website of the European space Agency.

“The stars are moving for different reasons. First, they, like the Sun, rotate around the center of the milky way. From the Ground it looks like linear motion projected on the sky. We call it their own movement. In addition, there is a parallax effect, which is caused by the rotation of the Earth around the sun. Thanks to him, within a year we see one star at a different angle,” says astronomer Ignas Snellen of Leiden University.

The researchers conducted calculations of the path of motion of the star Beta Painter in the sky, as well as small oscillations in the trajectories of stars moving across the celestial sphere — the minimum deviation from the expected course, caused by the gravitational influence of a rotating planet side by side.

White dotted spiral shows the trajectory of the stars visible from Earth. The brown stripe shows the range of deviation in the movement of the stars caused by the gravitational influence of the young planets revolving around it

“We looked for deviations from the expected rate, due to this we were able to calculate the mass of the planet. The more massive a planet is, the more significant deviations from the expected forecasts we are seeing,” says study co — author Anthony brown from the same University of Leiden.

However, in order to register deviations, and to calculate on the basis of this information the mass of the planet, scientists need to observe the object for a long time. To solve this problem was helped by the combination of data from the space telescope Hipparcos, which saw a Beta of the Painter 111 times between 1990 and 1993, and data from 32 observations of the star with a telescope Gaia in 2014-2016.

“By combining observational data with Hipparco and Gaia, we received a difference in her movement about 25 years. Alone the same Hipparcos could not cope with the task. To see ekzoplanetu, had to observe the star for much longer,” notes brown.

Data analysis showed that the mass of the planet Beta Painter b at 13 times the mass of Jupiter. Its period of rotation around its own axis presumably equal to 22.2 years.

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