Question

Which of the following methods have astronomers used to detect extrasolar planets?

a) Direct imaging
b) Gravitational microlensing
c) Radial velocity measurements
d) All of the above

Answer 1

Astronomers detect extrasolar planets using various methods including direct imaging, gravitational microlensing, and radial velocity measurements, with the latter being instrumental in detecting many such planets. 'All of the above' is the correct answer to the question.

Step-by-step explanation:

The methods astronomers have used to detect extrasolar planets include direct imaging, gravitational microlensing, and radial velocity measurements. Therefore, the correct answer to the question 'Which of the following methods have astronomers used to detect extrasolar planets?' is d) All of the above.

Radial velocity measurements involve high-resolution spectroscopy to detect the Doppler effect due to the wobble of a star caused by the gravitational pull of an orbiting planet. This technique is sensitive to large planets close to their star and has been used to detect hundreds of extrasolar planets.

Direct imaging is challenging due to the faintness of planets in comparison to their host stars, yet it is effective for young gas giants emitting infrared light at large distances from their star. Techniques have to be adjusted to subtract starlight and reveal the planetary signal, as demonstrated by the discovery of planets orbiting the star HR 8799.

Gravitational microlensing, though not detailed here, relies on the gravitational lens effect when a planet passes in front of a distant star, temporarily magnifying the star's light to indicate the presence of the planet.