Group detects exoplanet indirectly and then photographs it – 04/16/2023 – Sidereal Messenger

One of the most beautiful things in astronomy –perhaps the most– occurs when the existence of a celestial object is predicted from an indirect detection and then it is observed directly. One more of these beautiful confirmations has now happened, with an exoplanet orbiting a star 133 light years from Earth.

These extrasolar worlds, as is known, are rarely photographed, basically because their tenuous glow is overshadowed by the parent star, which is usually too close to it to be able to detect it or even separate one object from the other.

A few (about 20 so far) have already been clicked through the telescope, in general because they are very large (with more mass than Jupiter), young (with great heat from their formation process, which makes them brighter in infrared) and far away. from their star (more distant than Jupiter from the Sun).

Searching for them randomly out there is not easy, which motivated the team led by Thayne Currie, from the Subaru Telescope, in Japan, and from the University of Texas at San Antonio (USA), to look for stars that presented indirect astrometric indications of the presence of potential gas giant planets around.

Astrometry is the effort to accurately measure a star’s position relative to very distant objects and record their discrete movement over time. Using data from the Hipparcos and Gaia satellites (separated by 25 years), the researchers found that the nearby star HIP 99770, in the constellation Cygnus, had acceleration consistent with the presence of a gas giant planet orbiting it.

So, the group went to Subaru, with its respectable 8.2-meter mirror, and used the SCExAO coronagraph (a device that blocks the star’s light, in order to record its surroundings), coupled to a camera and spectrograph set called Charis ( capable of collecting images and the “light signature” of objects), to photograph the surroundings of such a star. Then the planet appeared, orbiting about 17 astronomical units from its sun, with an estimated mass between 13.9 and 16.1 times that of Jupiter.

Observations separated by 15 months revealed that the motion is consistent even with a planet orbiting HIP 99770, versus a background star. And the set seems to resemble a steroided version of the Solar System. The star itself is hotter and brighter, with 80% more mass than the Sun, and because of that, even though the planet is more than three times as far from its star as Jupiter is from ours, it receives about the same amount of radiation. An important difference is that here four gaseous giant planets were formed and there, it seems, only one, but much larger than ours.

The finding, published in the latest issue of the journal Science, validates the effort to seek targets for direct imaging of planets via astrometry, which in turn can help us understand how planets form and evolve (in particular the giants, unique in the world). within reach of our direct detection technologies).

This column is published on Mondays in the printed version, in Folha Corrida.

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