Microlensing & Exoplanets

A planet does not have to shine to be detected. It does not even have to orbit a star. Free-floating planets, sometimes called rogue planets, travel through the Milky Way without being gravitationally bound to a host star. That makes them extraordinarily difficult to find. There is no parent star for the planet to transit, … Read more

In gravitational microlensing, astronomers often begin with a convenient simplification: they treat the distant source star as a single point of light. Usually, that approximation works remarkably well. But when the lens passes extremely close to the source, the star’s actual angular size can no longer be ignored. The resulting change in the observed light … Read more

Binary-lens microlensing events produce caustic crossings when a background star’s apparent path intersects a caustic created by two foreground masses. At an ordinary fold crossing, a pair of lensed images appears or disappears, producing a rapid change in the star’s observed brightness. The star does not physically pass through either lens. The crossing describes changing … Read more

Chromatic microlensing is a gravitational microlensing event in which the observed amount of magnification changes with wavelength, so the source appears to change color during the event. The important twist is that gravity itself is not acting like a prism. In ordinary gravitational lensing, the deflection of light is essentially independent of wavelength. The chromatic … Read more

When an exoplanet passes in front of its star, astronomers can measure a tiny decrease in the star’s brightness. This seemingly simple dip in light is one of the most powerful tools in modern astronomy. From it, researchers can estimate a planet’s size, orbital period, and sometimes even study gases in its atmosphere. But there … Read more

An exoplanet transit looks deceptively simple. A planet passes in front of its host star, blocks a small fraction of the starlight, and produces a dip in the observed light curve. If the same planet crosses the same star again, it might seem reasonable to expect exactly the same dip every time. Yet astronomers sometimes … Read more

When an exoplanet passes in front of its star, the resulting dip in starlight often looks reassuringly neat. Brightness falls as the planet begins to cross the stellar disk, remains lower for a while, and then rises again as the planet leaves. In an idealized diagram, the first half of the transit almost mirrors the … Read more

A planet passing in front of its star may seem almost like a celestial clock. Every orbit, the planet crosses the stellar disk. The star becomes slightly dimmer, the planet continues along its orbit, and the light returns to normal. If the orbit were perfectly isolated and unchanging, these transits would repeat with remarkable consistency. … Read more

When astronomers discover an exoplanet passing in front of its star, they usually expect the event to behave like a reliable clock. If a planet takes exactly 10 days to orbit its star, for example, its transits should occur roughly every 10 days. After observing several transits, astronomers can predict when the next one should … Read more