Sunyaev–Zeldovich effect
The Sunyaev-Zeldovich (SZ) effect is when light from the cosmic microwave background (CMB) passes through a hot, ionized gas in a cluster of galaxies. This gas is called the intracluster medium (ICM).
Think of it like this: Imagine you're driving in a fast car on a hot day and you stick your hand out of the window. You'll feel the wind rush past your hand and it might even feel cooler than the air around it. This is because of something called adiabatic cooling, which is a fancy way of saying that as the air rushes past your hand, it expands and cools down.
In a similar way, when CMB light passes through the hot ICM in a galaxy cluster, it interacts with the free electrons in the gas. The electrons are moving around at high speeds, which causes them to scatter CMB photons. As a result, the photons gain energy and become slightly hotter than they were before they interacted with the gas.
This process is called the thermal SZ effect. Scientists can detect this effect by measuring the temperature of the CMB in different parts of the sky. Areas where the CMB is slightly hotter than expected are likely to be regions where there are galaxy clusters and hot ICM gas.
There's also something called the kinematic SZ effect, which is a bit harder to explain. Basically, it happens when the gas in a cluster is moving towards or away from us at high speeds. This motion causes a slight shift in the wavelength of the CMB photons that pass through the gas. Scientists can use this shift to measure the speed of the gas.
So, in summary, the SZ effect is when CMB light passing through a hot gas in a galaxy cluster gets scattered by free electrons, causing the CMB to become slightly hotter. This effect can be used to detect the presence and motion of hot gas in galaxy clusters.
Think of it like this: Imagine you're driving in a fast car on a hot day and you stick your hand out of the window. You'll feel the wind rush past your hand and it might even feel cooler than the air around it. This is because of something called adiabatic cooling, which is a fancy way of saying that as the air rushes past your hand, it expands and cools down.
In a similar way, when CMB light passes through the hot ICM in a galaxy cluster, it interacts with the free electrons in the gas. The electrons are moving around at high speeds, which causes them to scatter CMB photons. As a result, the photons gain energy and become slightly hotter than they were before they interacted with the gas.
This process is called the thermal SZ effect. Scientists can detect this effect by measuring the temperature of the CMB in different parts of the sky. Areas where the CMB is slightly hotter than expected are likely to be regions where there are galaxy clusters and hot ICM gas.
There's also something called the kinematic SZ effect, which is a bit harder to explain. Basically, it happens when the gas in a cluster is moving towards or away from us at high speeds. This motion causes a slight shift in the wavelength of the CMB photons that pass through the gas. Scientists can use this shift to measure the speed of the gas.
So, in summary, the SZ effect is when CMB light passing through a hot gas in a galaxy cluster gets scattered by free electrons, causing the CMB to become slightly hotter. This effect can be used to detect the presence and motion of hot gas in galaxy clusters.