Question

24. How is dark matter believed to be similar to luminous matter, and how does it differ? How do we know this?

25. Where in the Milky Way is our Solar System located?

26. What are the so-called peculiar motions of disk stars?

27. Describe the differences in age, color, metallicity, and location of Population I and Population II stars. Can you explain why we would expect the age, color, and metallicity of stars to be interrelated?

Answer 1

Dark matter interacts with the ordinary matter only weakly and gravitationally. We must have detected dark matter particles already otherwise. Dark matter does not emit light or absorb light, which means that dark matter does not interact via the electro-magnetic force. Dark matter does not have any charges.

The Solar System is located at a radius of about 27,000 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge.

peculiar velocity refers to the velocity of an object relative to a rest frame usually a frame in which the average velocity of some objects is zero.

Population I stars include the sun and tend to be luminous, hot and young, concentrated in the disks of spiral galaxies. Population II stars tend to be found in globular clusters and the nucleus of a galaxy. They tend to be older, less luminous and cooler than Population I stars.

Because color of a star defines the temperature by wein's law

Also luminosity depend upon the temperature of a body. Age is also influenced by that fuel and which also further depend upon the temperature of star