The TESS space telescope helped detect a planet located nearly 40,000 light-years away. This result is based on the principle of gravitational microlensing, a phenomenon related to Albert Einstein's general relativity.
The planet, named Gaia23bra b, has an estimated mass of about 1.6 times that of Jupiter. It orbits an orange star with a mass of about 80% of the Sun's mass. Its orbit is at a distance comparable to Jupiter's around the Sun. This type of configuration is difficult to detect with the transit method, mainly used by TESS.
This illustration shows Gaia23bra b, the first gravitational microlensing planet orbiting a distant star discovered by NASA's TESS (Transiting Exoplanet Survey Satellite). This super-Jupiter orbits an orange dwarf at a distance comparable to Jupiter's from the Sun.
NASA's Goddard Space Flight Center
When a planet passes in front of its star, it can block a small part of its light. The phenomenon then produces a periodic drop in brightness, searched for by space instruments including TESS.
Microlensing relies on a very different physical principle: a foreground star warps spacetime and temporarily amplifies the light of a more distant star behind it.
The presence of a planet around this foreground lens star adds brief variations to the light amplification. It is this signature that allowed identifying Gaia23bra b in available observations. So we are here with a planet detected around a star that amplifies the light of another star.
This animation illustrates the concept of gravitational microlensing. When a star (center of animation) appears to pass nearly in front of another (in the dashed circle on the right) from our viewpoint, the light rays from the background star are bent by the curvature of spacetime around the foreground star. The latter acts as a virtual magnifying glass, amplifying the brightness of the background star and slightly shifting its apparent position.
If the closer star has a planetary system, these planets can also act as lenses, each inducing a slight deviation in the source's brightness. By discovering planets this way, astronomers can measure their mass and orbital distance relative to their star.
Credit: NASA's Goddard Space Flight Center/CI
The first signal was detected in 2023 by the European Space Agency's Gaia satellite. The researchers then found the event in TESS archives.
This discovery shows that TESS can contribute to the search for planets by microlensing, despite its original design for transits. Other exoplanets may still be hidden in its archived data.