What is gravitational lensing?

The brightening of a star when a planet passes in front of it The bending of light from a distant object by the gravity of a massive foreground object The change in color of light as it passes through a galaxy The way a telescope focuses light using curved mirrors

Which physical theory predicts that massive objects bend light?

Newton's law of universal gravitation The special theory of relativity Einstein's general theory of relativity Quantum electrodynamics

What is an Einstein ring?

A ring of stars orbiting a supermassive black hole A complete circular arc of light that forms when a background galaxy is perfectly aligned behind a massive foreground object The accretion disk around a black hole that glows in X-rays A ring-shaped galaxy formed by a collision

What is the difference between strong gravitational lensing and weak gravitational lensing?

Strong lensing requires a space telescope; weak lensing can be done from the ground Strong lensing only works for dark matter; weak lensing works for visible matter Strong lensing produces clearly visible arcs and multiple images; weak lensing causes tiny, subtle distortions detected only statistically across many galaxies Strong lensing makes objects look brighter; weak lensing makes them look dimmer

Why is gravitational lensing useful for detecting dark matter?

Dark matter emits a special type of light that lensing focuses Lensing responds to all mass — visible or invisible — so it maps the total mass including dark matter that emits no light Lensing only works for dark matter and cannot detect ordinary stars Dark matter bends light differently from ordinary matter, making it easy to identify

What is the Bullet Cluster?

A single galaxy with a bullet-shaped jet of material from its central black hole An asteroid cluster near Jupiter that poses a threat to Earth Two galaxy clusters that have collided; their hot gas was slowed and separated from their dark matter halos during the collision A star cluster shaped like a bullet, discovered by the Hubble Space Telescope

Why does the hot gas in the Bullet Cluster slow down during the collision while the dark matter does not?

The gas is heavier than dark matter and therefore harder to move Dark matter is attracted to the center of each cluster and stays there Hot gas particles interact electromagnetically with each other and create drag; dark matter interacts only via gravity and passes through nearly unimpeded The X-ray emission from the gas removes energy and slows it down

How do astronomers detect the dark matter in the Bullet Cluster?

By detecting the radio waves emitted by dark matter particles By measuring gravitational lensing — the distortion of background galaxy shapes by the cluster mass By seeing the dark matter directly using infrared telescopes By measuring the temperature of the cluster and calculating mass from that

What do lensing maps of galaxy clusters consistently show about their mass distribution?

Mass is distributed exactly as expected from counting visible stars and gas All the mass is concentrated in the central black holes of the cluster galaxies Far more total mass than visible matter accounts for, distributed in extended halos around the clusters Mass is evenly spread throughout space between clusters

Why is the Bullet Cluster considered the most direct observational evidence for dark matter?

It is the largest galaxy cluster ever discovered, so it has the most dark matter It spatially separates the ordinary matter (hot gas) from the dominant mass component (dark matter halos), directly showing that most mass is not in the gas It was the first galaxy cluster close enough to Earth to be photographed clearly It produced dark matter particles that were detected by underground detectors

Which space telescopes have been specifically designed to perform weak gravitational lensing surveys to study dark matter?

The Chandra X-ray Observatory and the Fermi Gamma-ray Space Telescope The Hubble Space Telescope and the Spitzer Space Telescope The Euclid Space Telescope and the Nancy Grace Roman Space Telescope The James Webb Space Telescope and the Kepler Space Telescope