chapter 7 lecture

Question 1

Radial Velocity Method

Answer 1

• uses the Doppler shift
• we need the concept of the center of mass
• planet and star orbit center of mass

Question 2

History

Answer 2

Newton also mused over the possibility in his Principia (1687). The first confirmed discovery of an exoplanet was made in 1992

Question 3

How many

Answer 3

yyyyy

Question 4

How is it detected

Answer 4

yyyy

Question 5

What if a star with an unseen companion has a proper motion ?

Answer 5

As it moves across the sky, it would appear to wobble back and forth – pulled first in one direction and then the other by its unseen companion.

Question 6

What is an example of the star wobbeling back and forth

Answer 6

the bright star Sirius (Image #40). This motion was first observed by Bessel in 1844, but its faint companion (called Sirius B) was not actually observed until 1862. Sirius B is a white dwarf, a faint star which is very small and dense. Large exoplanets can be detected by this method as well.

Question 7

Gravitational lensing

Answer 7

-u

Question 8

What is the limit of detection for the dimming of the star?

Answer 8

Our limit of detection for the dimming of a star is about 1/10,000 of the star’s brightness. When Earth passes in front of the Sun, the dimming (viewed from beyond Earth’s orbit) is about 1/10,000 – so this method could just barely be used to detect Earth from some distant system with our present technology.

Question 9

Direct imaging and examples

Answer 9

• As mentioned above, direct imaging of exoplanets is particularly difficult, but it has been done.
• Images #45 & #46 show the first such direct image, the planet 2M1207b in orbit around the brown dwarf star 2M1207. This planet is four times the size of Jupiter and farther from its star than Pluto is from the Sun. Large planets far from their stars are the easiest to image directly
• Fomalhaut b, shows the first giant planet to be imaged with visible light since Neptune in 1846. This is particularly important because it is in the visible portion of the spectrum where astronomers hope to see evidence of life-supporting atmospheres in exoplanets.

Question 10

Gravitational lensing

Answer 10

-uses the interaction of light and mass predicted by the General Theory of Relativity.

Question 11

What is the general theory of Relativity

Answer 11

• mass warps the fabric of space-time so that a beam of light follows a curved path near a large mass. If a mass, like a star, interrupts a beam of light from some distant source, the light will be bent and focused around the mass.
• The image of the star will brighten momentarily, as if its light were being focused by a lens. If the star is accompanied by a planet, the image will again brighten when the light is focused by

Question 12

Problems of the structure in the Universe

Answer 12

The formation of structure is a major problem in cosmology. The Big Bang was assumed to be smooth and uniform. But the universe at present is clumpy.

Question 13

formation of the solar system

Answer 13

we know that the central plane of our galaxy has gas and dust enriched with heavy elements from earlier generations of stars. e.g the Sombrero Galaxy (M104), I, particularly M16 and the Eagle Nebula. Bernard 68,. All of these gas and dust clouds are part of the Interstellar Medium (ISM). It is in these regions new stars, and the associated solar systems, form.

Question 14

the collapse

Answer 14

In a uniform distribution of particles, each particle will be pulled equally in all directions by the gravitational attraction of the other particles. Since no particle feels a net force, the distribution is stable against collapse. This is why Newton believed the universe must be infinite.

The distributions in these images, however, and not uniform – with regions of higher density and regions of lower density. In this case, particles will be pulled harder toward regions of higher density, and the system will collapse. We will see in the next section that the result of such a collapse for a group of particles with an initial rotation is a rotating nebula or disk. The formation of the Solar System from such a nebula was proposed in the late Eighteenth Century by the German philosopher Immanuel Kant and the French mathematician Pierre-Simon Laplace.

Question 15

solar system began with a disk

Answer 15

So, we have a region (assume spherical for simplicity) which is dense enough (compared to its surroundings) that it collapses by its own mutual gravitational attraction.\
So, we have a region (assume spherical for simplicity) which is dense enough (compared to its surroundings) that it collapses by its own mutual gravitational attraction.