What does "Mass Discrepancy Problem" mean?

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The mass discrepancy problem is an issue in astronomy that deals with the difference between the amount of mass we can see and the mass we expect based on the motion of objects in space, particularly in galaxies.

When scientists look at galaxies, they can observe stars, gas, and dust, which all have mass. However, when they measure how these objects move, they find that there must be much more mass present to explain their speeds and orbits. This missing mass is often referred to as "dark matter," a type of matter that does not emit light or energy, making it hard to detect.

The problem becomes more complicated when we consider that even in smaller galaxies, the amount of mass we can directly observe is less than what we expect based on how fast things are moving. This has led to questions about our current understanding of gravity and the forces at play in the universe.

Some scientists propose that instead of relying on dark matter, we should look for new ways to explain these discrepancies, suggesting modifications to the laws of gravity to better fit the observations. These ideas aim to provide a clearer picture of the forces affecting galaxies without needing to add unseen matter.