Dark Matter, calculating missing mass

In summary: ENDMENT: In summary, the andromeda galaxy has a velocity of 250 km/s and an observed mass of 1 x 10^42 kg. With a diameter of 66,000 light years, the missing mass that cannot be accounted for visibly can be calculated by finding the difference between the calculated mass and the gravitational mass, and then dividing by the gravitational mass to determine the percentage of missing mass. However, the problem may be more complex if the galaxy is not assumed to have uniform density.
  • #1
cherioslover
4
0

Homework Statement


The andromeda galaxy has a velocity of 250 km/s as it rotates. The observed mass is 1 x 10^42 kg. If the galaxy is roughly a circle with a diameter of 66,00 light years how much mass is not accounted for visibly?


Homework Equations



Fc=mv^2/R Fg=Gm1m2/R^2

The Attempt at a Solution



I know you're supposed to calculate the mass of the galaxy as well as a calculated speed, then divide the differences in masses by gravitational mass to find the percentage of mass missing, but honestly i can't seem to get it and there was no answer given :(

someone pleas be my hero :')
 
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  • #2
cherioslover said:

Homework Statement


The andromeda galaxy has a velocity of 250 km/s as it rotates. The observed mass is 1 x 10^42 kg. If the galaxy is roughly a circle with a diameter of 66,00 light years how much mass is not accounted for visibly?


Homework Equations



Fc=mv^2/R Fg=Gm1m2/R^2

The Attempt at a Solution



I know you're supposed to calculate the mass of the galaxy as well as a calculated speed, then divide the differences in masses by gravitational mass to find the percentage of mass missing, but honestly i can't seem to get it and there was no answer given :(

someone pleas be my hero :')
Can you give us the exact wording of the problem?

If the question is stating that the mass on the outer edge of the galaxy is moving at a tangential speed of 250 km/sec, then you can work out the angular speed of the outer mass.

Does the problem state that you should assume that the galaxy is a disc of uniform density?

AM
 

What is dark matter?

Dark matter is a hypothetical form of matter that makes up about 85% of the total mass of the universe. It does not emit or absorb light, making it invisible and difficult to detect.

Why is dark matter important?

Dark matter plays a crucial role in the formation and evolution of galaxies and the large-scale structure of the universe. It helps explain the gravitational forces that hold galaxies together and the observed rotation curves of galaxies.

How do scientists calculate the missing mass in galaxies?

Scientists use various methods to calculate the missing mass in galaxies, such as measuring the rotation curves of galaxies, analyzing the gravitational lensing effects of dark matter, and studying the distribution of matter in galaxy clusters.

What are the current theories about the nature of dark matter?

There are several theories about the nature of dark matter, including the particle nature hypothesis, where dark matter is made up of yet-to-be-discovered particles, and the modified gravity hypothesis, which proposes that gravity behaves differently on large scales.

Can dark matter be observed directly?

No, dark matter cannot be observed directly because it does not interact with light. However, scientists continue to search for ways to indirectly detect dark matter, such as through collisions with other particles or through the effects of its gravity on visible matter.

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