Exam 21: The Milky Waya Normal Spiral Galaxy

The energy of a cosmic ray is given by γmc²,where m is the mass of the particle,c is the speed of light,and γ is the Lorentz factor and .If a cosmic ray proton is traveling at a speed of ν = 0.999999c,what is its energy? How does that compare to the kinetic energy of a grape thrown up in the air and caught in your mouth? Assume the grape has a mass of about 5 grams and a speed of 0.5 m/s when you catch it.The mass of a proton is 1.7 × 10⁻²⁷ kg.

By comparing globular clusters,you find that Cluster A's RR Lyrae stars are 100 times fainter than Cluster B's RR Lyrae stars.You know that Cluster A's stars are 1.5 times more luminous than Cluster B's stars,because Cluster A is more metal-rich and somewhat younger.How do the clusters' distances compare?

The oldest disk stars are both __________ and __________ compared to halo stars.

If RR Lyrae stars in a globular cluster had an apparent magnitude of 11.5 and an absolute magnitude of 0.5,what would the globular cluster's distance be?

The Milky Way has lived out its life mainly in isolation and has not experienced many mergers with other galaxies.

The Milky Way is classified as an __________ galaxy.

A typical globular cluster is composed of 500,000 stars in a sphere whose radius is approximately 5 pc.The distance between stars in a globular cluster is given approximately by d ≈ r/N^1⁄3,where r is the radius and N is the number of stars in the cluster.Calculate this distance,and determine how many times smaller it is than the typical distance between stars in the solar neighborhood,which is 3 light-years.

The Milky Way is like most other galaxies in that its mass is dominated by dark matter.

Halo stars formed before the Milky Way developed a thin stellar disk.

Cosmic rays in our galaxy can produce synchrotron radiation at what wavelengths?

Globular clusters have much higher stellar densities than the local solar neighborhood.

Sagittarius A*,the radio source located at the center of our galaxy,is believed to be:

If the central black hole started accreting a lot of gas,it would appear as what kind of an object?