Chptr 21 The Birth of Stars and the Discovery of Planets outside the Solar System

The Orion Nebula is

a large cloud of gas and dust illuminated by the light of newly formed stars within it

The first ordinary star (other than our own Sun) around which planets were definitely discovered was:

51 Pegasi

An astronomy class is so excited by the discovery of planets around other stars that they decide to do a library exhibit on the subject so that everyone in the school can learn about it. In this exhibit they want to pay tribute to both the astronomers of today who have done the work AND some of the scientists of the past whose work was essential to making the discoveries possible (and directly related to the techniques involved). Which of the following scientists of the past should definitely be included in the exhibit?

Christian Doppler

Which of the following is a reason that astronomers have not found giant planets with the orbit of Neptune around other stars?

Neptune takes 165 years to go around the Sun; getting information about just one cycle of such a planet's orbit around another star would take astronomers 165 years

Astronomers call a ball of matter that is contracting to become a star

a protostar

If an astronomer wants to find and identify as many stars as possible in a star cluster that has recently formed near the surface of a giant molecular cloud (such as the Trapezium cluster in the Orion Nebula), what instrument would be best for her to use?

an infra-red telescope (and camera)

The star now called Kepler-444 is 11 billion years old (much older than the Sun) and has five planets orbiting close to it. What has this system taught astronomers about the history of star formation?

if such an old star has planets close to it, where it's really warm, those planets must be made of heavier elements. So heavier elements must have formed before the time this star formed

If you want to find stars that are just being born, where are the best places to search?

in giant molecular clouds

The closest star to the Sun, Proxima Centauri, was recently found to have a planet in its habitable zone. Proxima Centauri is a main sequence star with spectral type M. How would its habitable zone differ from the habitable zone of our Sun?

it would be significantly closer to Proxima Centauri than our is to the Sun

Astronomers believe that disks of material will form around protostars that are spinning. Which of the following observed phenomena is a good indication of the presence of a disk around a protostar?

jets and Herbig-Haro objects

What technique did astronomers use to make the first confirmed discovery of a planet around another star like the Sun?

measure the Doppler shift of the lines in the star's spectrum and look for periodic changes in this shift due to the pull of te planet as it orbits the star

Astronomers were surprised to find so many Jupiter-mass planets so close to their stars. According to their best theories and models, such "hot Jupiters"

must have formed further out from the star and must have "migrated inward" early on

The big surprise about the first planet discovered around another regular star was that it

orbited so close to its star it took only 4 days to go around

The telescope that allowed astronomers to discover most of the planets found with the transit method was called

the Kepler mission

With our current techniques, astronomers can typically only measure the minimum mass of a planet orbiting another star. To know the precise mass of the planet, they must also be able to determine

the angle at which the planet's orbit is tilted relative to us

You are an astronomy graduate student and you are observing the big Orion Nebula from an airplane that has a good-sized infrared telescope built into it (there really is such a plane.) On an infrared image of the Nebula, what would particularly stand out?

the clouds of the nebula that have a lot of dust in them

Which of the following are the small regions that are the embryos of stars (where individual stars are most likely to be born)?

the cores within the clumps of molecular clouds

To measure how dense a planet is (to know whether it is made of rock or gas and liquid) they must be able to measure the planet's mass from the Doppler shift and

the planet's radius using the transit method

Astronomers studying regions like the Orion Giant Molecular Cloud have observed that a wave of star formation can move through them over many millions of years. What sustains such a wave of star formation in a giant molecular cloud?

when massive stars from, their ultraviolet radiation and later their final explosions compress the gas int he clouds and cause a new group of stars to form

A Herbig-Haro (HH) object is

where a jet from a star in the process of being born collides with (and lights up) a nearby cloud of interstellar matter

Why is it so difficult for astronomers to see new stars in the process of birth?

~birth happens very quickly, so it is hard to "catch" stars "in the act" ~most stars are born inside dusty clouds, which block any light that may be coming from the stars ~the size of a newly forming star is typically quite small and thus hard to make out ~protostars which are not yet doing fusion do not give off a lot of visible light ~ALL OF THE ABOVE

How did astronomers determine that the planet orbiting the star HD 209458 is a gas giant like Jupiter and not made mostly of rocks or metals?

~they looked for light from the planet reflected into the spectrum of the star ~they measured the mass of the planet, which immediately told them whether it was gas or rock ~they watched the planet eclipse (cover) the light of the star, and thus were able to get the planet's size ~they knew that any planet as close to its star as this one was could not be made of rock or metal ~it took more than one of the above measurements to figure out this problem