Astro Practice 2 – Flashcards

globular clusters

Open clusters, O stars, B stars, old K stars, old M stars, Gas, and dust

In elliptical orbits when an object is close to the focal point it moves faster than when it is in the part of the orbit that is farther away. For example, a planet orbiting the Sun will speed up along its orbital path when it is closest to the Sun and it will slow down when it is farthest away from the Sun. For this reason, our estimates of the period of the stars around the center of the Milky Way are not precise. Also, We did not take into account the inclination of the orbit, so our measurement of the semimajor axis is not accurate

from the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun.

There are no blue halo stars.

Halo stars formed in an environment where there were few heavy elements to create rocky planets.

It should have a higher fraction of elements heavier than hydrogen and helium.

through observations of the 21 cm line of atomic hydrogen

We observe clouds of atomic hydrogen far from the galactic center orbiting the galaxy at unexpectedly high speeds, higher speeds than they would have if they felt only the gravitational attraction from objects that we can see.

Since they do not interact with the electromagnetic force, they do not feel friction or drag and hence do not contract with the rest of the protogalactic cloud.

They respond to the weak force but not to the electromagnetic force, which means they cannot emit light.

Yes, they tell us that dark matter is spread throughout the galaxy, with most located at large distances from the galactic center.

Galaxy B is four times as far as Galaxy A.

Observations at different distances show galaxies of different ages and therefore different stages of evolution.

The universe began with the forces unified. During the first fraction of a second, the forces separated and there was a brief but important episode of inflation. Subatomic particles of both matter and antimatter then began to appear from the energy present in the universe. Most of the particles annihilated to make photons, but some became protons, neutrons, electrons, and neutrinos. The protons and neutrons underwent some fusion during the first three minutes, thereby determining the basic chemical composition of the universe.

Take a spectrum of the galaxy, and measure the difference in wavelength of spectral lines from the wavelengths of those same lines as measured in the laboratory.

The inside of the balloon does not represent any part of our universe.

the shock waves from the exploding supernovae of the earliest stars

the end of the era of nuclei

The cosmic background radiation is expected to contain spectral lines of hydrogen and helium, and it does.

Infrared observations show that many stars are forming near the centers of active galaxies.

observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy, observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies, the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies, and observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies.

Active galactic nuclei tend to become less active as they age.

the discovery of powerful jets coming from a compact core, rapid changes in the luminosity of the galaxy nucleus, very high speed orbital motions around galactic nuclei, and quasars emit approximately equal power at all wavelengths from infrared to gamma rays