Interstellar Medium

1. After the universe's supply of H is depleted, can stars still be born from the enriched interstellar medium?

A star does not return all its gas to its interstellar medium, as it leaves behind a degenerate remnant (a white dwarf, neutron star, or black hole, depending on its mass.) Although some of its mass is recycled, this only prolongs the lifetime of star formation by a small factor, and it is predicted that, even if recycling is taken into account, star formation in this galaxy will cease in at most 10^14 (100 trillion) years, leaving behind a galaxy composed of degenerate remnants and very thin gas which is too diffuse to form stars.

2. How can we see through the interstellar medium?

I think there's another way of understanding your question. Perhaps you already know that interstellar space is virtually empty. But maybe you think light needs a medium to propagate, like sound. Sound waves don't propagate in a vaccuum, but light waves (and all forms of electromagnetic radiation) do. So that's how we can see through the 'medium' even though the medium is empty.

3. About what percent of the interstellar medium is dust?

Whoa. both of those numbers are waaay too high. The second author read About 99% of the ISM is gas (hydrogen and helium), the remaining one percent consist of heavier elements and dust at their link but forgot the heavier elements part. Jsut because something is carbon or oxygen or sulfur (or neon!) does not mean it will all deplete out of a gaseous state onto dust grains. First, the mass of the universe is only 1% things other than hydrogen and helium, so that is the amount of raw material one has to make up dust in the ISM. It isn't all dust, however; a large fraction of it will be in a gaseous state. In our relatively heavy element enriched galaxy, almost 2%of the mass is elements other than hydrogen and helium. Finally, different parts of the ISM will have different densities of dust. Obviously in a dense molecular cloud (or the envelope of a cool star) where there is a) more opportunity for the scant numbers of heavier atoms to interact and stick together and b) less heat and hard radiation to sputter atoms from dust grains eroding them, you will find higher concentrations of dust than just outside the photosphere of a 15,000K O star! As a rule of thumb, never more than 1%, and usually substantially less.

4. What are some ways in which winds from red-giant stars are linked to the interstellar medium?

Interstellar medium makes up between 10 to 15% of the visible mass of the Milky Way. About 99% of the material is gas and the rest is ``dust''. The dust is made of thin, highly flattened flakes or needles of graphite and silicates coated with ice. Each dust flake is roughly the size of the wavelength of blue light or smaller. It is thought to be formed in the cool outer layers of red giant stars and dispersed in the red giant winds.

5. Is the interstellar medium involved in any way with star formation?

ISM has everything to do with star formation. In fact, the whole star is made of interstellar materials (molecules and dusts). In addition, the new star also carries some of the angular momentum and magnetic fields originated in ISM, thus the rotation and sunspots

6. About how dense is the interstellar medium?

About 1 atom per cm^3, in our galaxy. This is almost all hydrogen gas. Near our sun (within about 100 light years), the density is about 1/10 that value. Between galaxies, the density is even less, by a factor of many billions. One estimate is 1 atom per 10^11 cm^3.

7. Describe how the ultra-cold material in the interstellar medium eventually gets hot enough (about 6 million de

8. What parts of the interstellar medium can be obersved in the x-ray region of the elctromagnetic spectrum?

After UV come X-rays. Hard X-rays have shorter wavelengths than soft X-rays. X-rays are used for seeing through some things and not others, as well as for high-energy physics and astronomy. Neutron stars and accretion disks around black holes emit X-rays, which enable us to study them. X-rays will pass through most substances, and this makes them useful in medicine and industry. X-rays are given off by stars, and strongly by some types of nebulae. An X-ray machine works by firing a beam of electrons at a target. If we fire the electrons with enough energy, X-rays will be produced. http://en.wikipedia.org/wiki/Electromagnetic_spectrum http://en.wikipedia.org/wiki/X-rays http://en.wikipedia.org/wiki/X-ray_astronomy

9. THe interstellar medium dims starlight by about 1.9 magnitude / 1000pc. What fraction of photons survive a tri

1.9 magnitudes represents a brightness difference of about 5.755. (2.511886 ^ 1.9). So if its that much dimmer, that's 17.4% of its original brightness. 100^(1.9/5) also works. 1.9 is the only variable in this equasion.

10. Is the extinction of starlight due to the interstellar medium greater for violet or red part of the spectrum?

Violet. Red, or longer wavelengths, are more penetrating of the interstellar medium. That's why we use radio frequencies, (long waves), to see through it.

11. How is the interstellar medium heated?

It isn't actually heated because it's almost a total vacuum. The only temperature the interstellar medium (..space..) has is the remnant temperature from the Big Bang which created our universe. Space itself first came into existence at the moment of the Big Bang and so was filled with the BB's immense temperature. Over many billions of years that temperature of space has fallen as space expanded until today its very close to absolute zero.

12. what evidence do we have that the interstellar medium contains both gas and dust?

Evidance for interstellar gas::::: Hydrogen is there in interstellar medium. It is in many much greater proportion than other elements.. It can be found by taking spectrum of that area.. Evidance for interstellar dust::::: Many times, dust in space affects observation,, Such conditions are very less but it comes in observation, It cannot be tracked through normal telescope, but its evidance can be experienced from large telesopes like HST, VLT....

13. What is interstellar medium?

Outer space, pretty much - specifically, the space between stars, but still within a given galaxy. The space between galaxies is more accurately termed the intergalactic medium. There's not much there - about a million atoms of hydrogen per cubic meter, with trace amounts of heavier elements. Sounds like a lot. It isn't. There's also plenty of gauge bosons flitting about the place, but they don't much contribute to the mass of the medium itself.

14. How would our view of the night sky be different if there were no dust grains in the interstellar medium?

Our view from Earth would be nearly unchanged. With most optics. Dust particles spinning in the interstellar medium radiate electromagnetic waves, they also emit longitudinal plasma waves. For very small grains with an intrinsic electric dipole moment, it is, in most interstellar environments, orders of magnitude shorter than the usual slowing-down time due to collisional friction.

15. The interstellar medium dims starlight by about 1.9 magnitudes/1000PC?

On the surface, the answer you are looking for is: L=L0[10^(-1.9/2.5)] = 0.17, so 17% of the photons survived. In reality, it is more complicated as the photons would be absorbed and re-emitted at a different (and longer) wavelength.

16. What propels the interstellar medium towards the sun, at at what speed?

Nothing propels it. The sun is moving around the galaxy, relative to the interstellar medium. Therefore, the medium is also moving with relation to the sun. It's like a car being driven on a calm day. The car is thought of as moving, but the air it's being driven through is moving towards the car also.

17. can someone tell me about the formation of stars from clouds of gas and dust in the interstellar medium?

Stars are born within clouds of dust (nebula). The cloud collapses as gravity causes the dust to clump together. Warmer than the surrounding area, this dense region (called a protostar) becomes more massive and heats up even more. At some point, as its internal pressure increases, nuclear reactions ignite at its core and the star lights up (begins to shine and radiate energy out into space) and begins converting hydrogen to helium in its core, through nuclear fusion. The moment this happens is when the star is born.

18. What are three ways that we are able to detect interstellar matter?

1. Reflection of starlight 2. Absorption of starlight 3. Emission of it's own light Reflection: Interstellar matter is often found in the vicinity of young stars. The light passing through the gas and dust around these young stars is bluish. These clouds are called reflection nebulae and are detected visually. Absorbtion:The presence of matter blocks light reaching us from distant stars. This would appear visually as a dark cloud in a region of the sky. Sometimes referred to as extinction of starlight. Emission: Interstellar gas may be heated by the ultraviolet light of hot stars. This causes the gas of the clouds to visibly glow. In such a case, the ionized hydrogen molecules emit a red light. Called emission nebulae. When not heated, cold interstellar matter (composed mainly of neutral hydrogen gas) emits light at a wavelength of 21cm. Giant molecular hydrogen clouds are accompanied by carbon monoxide molecules which emit radiation at 2.6mm. These would be measurable in the electromagnetic spectrum.

19. The interstellar medium dims starlight by about 1.9 magnitudes/1000 pc. What fraction of photons survive?

each magnitude corresponds to a ratio of 10^(-.2), so you want to multiply the (-.2) by (1.9) and look at 10 to that power. This gives the fraction of photons that make the trip. Homework and repeat question.

20. The interstellar medium dims starlight by about 1.9 magnitudes. What fraction of photons survive a trip of 100

Your question is very incomplete. The interstellar medium dims starlight by 1.9 magnitudes over what distance? Then, how long is that trip? 100 what? The actual extinction is about 2 magnitudes per kiloparsec. One magnitude difference is a ratio of 10^(-.2), so a 2 magnitude difference would correspond to a ratio of 10^(-.4)=.398 (Magnitude is a logarithmic scale). Thus, about 40% of the photons survive a trip of 1000 parsecs. The rest get absorbed by the interstellar medium.