Stars: Beginnings

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)

Which of the following stars is not a main sequence star?

Antares

Who was the astronomer who is the "H" in H-R diagram?

Hertzprung

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

In giant molecular clouds

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

A team of astronomers discovers one of the most massive stars ever found. If this star is just settling down in that stage of its life where it will be peacefully converting hydrogen to helium in its core, where will we find it on the H-R diagram?

Near the very top of the main sequence in the upper left

Which properties best describe the star Antares?

Red and bright

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

Which of the following stars is a class K star with an absolute magnitude of about 5? Hint: Use the search box on the right top side of the main window to locate each of these stars.

V4200 Sagittarii (HIP 97944)

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 form, their ultraviolet radiation and later their final explosions compress the gas in the cloud 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

Which of the following stars is a red giant (usually class K or M)?

Yed Prior

The Orion Nebula is

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

A star that is quite hot and has a very small radius compared to most stars is called

a white dwarf

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

all of these - a 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

. In an H-R diagram, where can you see the spectral type of a star (whether it is an O type star or a G type star, for example)?

along the bottom (the horizontal axis)

Some stars give off more than 50,000 times the energy of the Sun. Why are there no such stars among the stars that are close to the Sun?

because such very luminous stars are extremely rare, and thus any small neighborhood in the Galaxy is unlikely to contain one of them

Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life?

fusing hydrogen into helium in their cores

Imagine that powerful telescopes in the future give us a truly representative sampling of all the stars in the Sun's cosmic neighborhood. Where on the H-R diagram would most of the stars in our immediate vicinity lie?

in the lower right, among the least luminous main sequence stars

Measurements show a certain star has a very high luminosity (100,000 x the Sun's) while its temperature is quite cool (3500o K). How can this be?

it must be quite large in size

The most common kinds of stars in the Galaxy have

low luminosity compared to the sun

Stars that lie in different places on the main sequence of the H-R diagram differ from each other mainly by having different:

masses

Most of the stars we can see with the unaided eye from Earth are

more luminous (intrinsically brighter) than the Sun

Where on the H-R Diagram would we find stars that look red when seen through a telescope?

only on the right side of the diagram and never on the left

A white dwarf, compared to a main sequence star with the same mass, would always be:

smaller in diameter

An H-R Diagram plots the luminosity of stars against their:

surface temperature

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

Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call:

the main sequence

Most of the really bright stars in our sky are NOT among the stars that are very close to us. Why then do they look so bright to us?

these stars are intrinsically so luminous, that they can easily be seen even across great distances