Question 1

Because of the severe interstellar dust interference blocking visual wavelengths,most of our information about the galactic center comes form infrared and radio observations.

Accepted Answer

Interstellar dust can block visual wavelengths of light, but infrared and radio wavelengths can penetrate or pass through the dust, allowing us to gather information about the galactic center using these observations.

Question 2

Stars are evenly distributed across the spherical region enclosing our Galaxy.

Accepted Answer

Stars are not evenly distributed across the spherical region enclosing our Galaxy. Instead, they are concentrated in the Galactic plane and in dense clusters and spiral arms.

Question 3

Only about 10% of the mass of the Galaxy is in the form of visible stars,gas,and dust.

Accepted Answer

The remaining 90% of the mass is believed to be in the form of dark matter and dark energy, which cannot be directly observed.

Question 4

X-ray flares coming from Sagittarius A* dramatically brighten in just 10 minutes,which shows that the source can be no larger than 10 light minutes across.

Accepted Answer

If the X-ray flares brighten in just 10 minutes, then the source that is emitting them cannot be larger than that distance. Therefore, the statement is true.

Question 5

Approximately 10% of the mass of the Galaxy is made up of dark matter.

Accepted Answer

The majority of the mass of the Galaxy (and other galaxies) is actually made up of dark matter, estimated to be about 85%, not 10%.

Question 6

All of the stars that have been observed near the supermassive black hole are being ripped apart and pulled into the event horizon to fall into the singularity.

Accepted Answer

Many stars observed near supermassive black holes can have stable orbits and are not necessarily being ripped apart or pulled into the event horizon. Some may experience tidal forces, but not all are destined to fall into the singularity.

Question 7

The Milky Way is an irregular galaxy.

Accepted Answer

The Milky Way is actually a barred spiral galaxy.

Question 8

Halo stars and globular clusters move in orbits that are oriented at random angles to the plane of the disk of a galaxy.

Accepted Answer

This is true as halo stars and globular clusters are part of the halo of a galaxy, which extends above and below the disk and has a more spherical shape. Their orbits are therefore oriented at random angles to the plane of the disk.

Question 9

One proposal for the mysterious dark matter in the Galaxy is that it is made of massive compact halo objects (MACHOs).

Accepted Answer

MACHOs are one proposed solution to the mystery of dark matter in the galaxy. They are hypothetical objects that are believed to be compact and massive, such as black holes, neutron stars, or brown dwarfs. Although they have not been directly observed, their existence would explain the gravitational effects observed in the galaxy.

Question 10

Dark streaks across the Milky Way from the viewpoint of Earth are caused by interstellar dust in the plane of our Galaxy.

Accepted Answer

Interstellar dust can be found in the plane of the Milky Way, and it absorbs and scatters visible light. This can create dark streaks or bands when observed from Earth.

Question 11

In a spin-flip transition of an electron,a photon is emitted.

Accepted Answer

When an electron undergoes a spin-flip transition, it changes its spin state and emits a photon with a specific energy and wavelength. This process is known as spin-photon interaction or spin-dependent radiative recombination. Therefore, a photon is indeed emitted in a spin-flip transition of an electron.

Question 12

The halo of the Galaxy is a spherical distribution that is traced by globular clusters.

Accepted Answer

The halo of the Galaxy is indeed a spherical distribution that is traced by globular clusters.

Question 13

The Galaxy rotates like a solid disk,like a CD or DVD.

Accepted Answer

The galaxy rotates differentially, meaning that different parts of the galaxy rotate at different speeds. The center rotates faster than the outer edges. This is similar to how a record player rotates, with the inner grooves moving faster than the outer grooves.

Question 14

Flocculent spiral galaxies have spiral arms that are broad,fuzzy,chaotic,and poorly defined and grand-design spiral galaxies have thin,graceful,well-defined spiral arms.

Accepted Answer

Flocculent spiral galaxies have broad and poorly defined spiral arms, while grand-design spiral galaxies have thin and well-defined spiral arms.

Question 15

Stars in the disk of the Galaxy are mostly old,metal-poor,Population II stars.

Accepted Answer

Stars in the disk of the Galaxy are actually young and metal-rich, and are classified as Population I stars. It is in the galactic bulge and halo where we see more old, metal-poor Population II stars.

Question 16

The 21-cm emission is used mainly to map out globular clusters around the Galaxy.

Accepted Answer

The 21-cm emission is mainly used to study the distribution of neutral hydrogen gas in the Galaxy and in other galaxies, as well as to investigate the large-scale structure of the Universe. It can also be used to investigate the properties of interstellar medium and to detect the presence of magnetic fields. Globular clusters are usually studied through optical and infrared observations.

Question 17

When protons and electrons in neutral hydrogen spin,they act like tiny magnets.

Accepted Answer

When protons and electrons in neutral hydrogen spin, they produce a magnetic moment and act like tiny magnets.

Question 18

Visible light passes more easily though dust and gas than infrared light in our Galaxy,revealing structures.

Accepted Answer

This statement is false. Infrared light can penetrate dust and gas better than visible light, allowing astronomers to study structures and phenomena that are otherwise obscured in visible light.

Question 19

The Sun takes about 220 million years to complete one trip around the Galaxy.

Accepted Answer

This is true. The Sun, along with the rest of the Solar System, takes approximately 220 million years to orbit around the center of the Milky Way Galaxy, which is about 26,000 light years away from Earth. This is known as a galactic year or cosmic year.

Question 20

RR Lyrae variable stars are bigger,brighter and have longer periods of pulsation than Cepheid variables.

Accepted Answer

Cepheid variables are generally larger, brighter, and have longer periods of pulsation compared to RR Lyrae stars, which are typically used as standard candles for closer distances.

Quiz 13: Exploring Our Galaxy