Open Stax Astronomy - CH20
Describe how the 21-cm line of hydrogen is formed. Why is this line such an important tool for understanding the interstellar medium?
21CM line of hydrogen gas is the electromagnetic radiation that has a wavelength equal to 21cm and that is emitted during the change in energy levels of electrons of neutral hydrogen atoms. This helped astronomers detect and understand the interstellar medium.
Describe the properties of the dust grains found in the space between stars.
99% Gas w/ an abundance of Hydrogen and Helium 1% Dust grain, solid frozen particle containing several atoms and molecules.
Why can't we use visible light telescopes to study molecular clouds where stars and planets form? Why do infrared or radio telescopes work better?
Molecular clouds radiate a longer wavelength of light. The cooler stars emit more Infrared R than Visible R and the hotter stars emit more UV R than Visible R. Each type of telescope can only detect one type of light in the electromagnetic spectrum.
The mass of the interstellar medium is determined by a balance between sources (which add mass) and sinks (which remove it). Make a table listing the major sources and sinks,
Clouds of gases sink mostly by supernovae explosion driven out of the galaxy added to the interstellar medium. Dust grains, formed by condensed dust, mainly sink by supernovae explosion and heavy blow of the hot mass the dust particles are thrown out adding to interstellar material and forming new material.
Why is it difficult to determine where cosmic rays come from?
Cosmic particles are made up of magnetically charged matter so they change direction depending on the magnetic field. The magnetic field makes a cosmic ray spiral around earth before entering it's atmosphere making it difficult to determine its source.
What causes reddening of starlight? Explain how the reddish color of the Sun's disk at sunset is caused by the same process.
Dust grains interacting with starlight causes reddening by either the absorption or scattering of other colors.
Why do molecules, including H2 and more complex organic molecules, only form inside dark clouds? Why don't they fill all interstellar space?
H2 and complex organic molecules only form in dark clouds because the accumulation of dust blocks out starlight stopping ionization. They do not fill up space because the number of dust grains only account for a fraction of the volume of interstellar space.
Describe the characteristics of the various kinds of interstellar gas (HII regions, neutral hydrogen clouds, ultra-hot gas clouds, and molecular clouds).
Ionized hydrogen Region - near hot stars, after ionized hydrogen emits red color Neutral Hydrogen Clouds - Neutral state, doesn't emit visible wavelength, emits light with microwave wavelength. Ultra- Hot Gas Clouds - Temperature high, oxygen atoms ionized 5x emit X-rays, it's energy comes form massive stars at the end of their lives. Molecular Clouds - produce visible absorption lines and radiation in radio and infared wavelength. Produced when dust accumulates at a region and blocks infrared rays from stars to keep the molecules from ionizing.
Why do nebulae near hot stars look red? Why do dust clouds near stars usually look blue?
Nebulae near Hot stars look red because they absorb radiation and they emit a red color. Nebulae near Dust clouds look blue because the dust grain present in them scatters light from the nearest star and it looks blue because of their size.
List the different ways in which DUST can be detected in interstellar space.
• Blocking the light from distant stars • Reflecting the nearby star light • Emitting energy into the infrared part of the spectrum
List the different ways in which GAS can be detected in interstellar space.
• Light is emitted and absorbed by the ionized gases • Gravity gathers interstellar gas • Light from neutral interstellar gas are emitted by collision of atoms • Supernova Explosion heat the interstellar gas
