GALACTIC DUST AND CLOUDSBRYAN NOZALEDA

What is the interstellar medium?

is the matter that exists within galaxies, between and among—but not including—the stars. Almost all of the interstellar medium is comprised of gas and microscopic dust particles.

How much interstellar medium is there in galaxies?

About one percent of the luminous mass of a galaxy like the Milky Way (that is, excluding the non-baryonic dark matter) is interstellar medium.

How dense is the interstellar medium?

The interstellar medium in our region of the Milky Way galaxy has a density of about one atom of gas per cubic centimeter. By contrast, Earth’s atmosphere at sea level contains about 1019 gas molecules per cubic centimeter. There is also about one dust particle per 10,000,000 cubic meters in the local interstellar medium.

What does the interstellar medium look like?

It can appear in an amazing variety of forms and colors. Much of the interstellar medium is invisible; in fact, it will block the view of distant astronomical objects.

What is a molecular cloud?

A molecular cloud is a cloud that contains molecules—constructs of multiple atoms.

Are molecules in the interstellar medium only found in molecular clouds?

No. They exist in the interstellar environments surrounding stars, too. Gas molecules in space, however, are much more fragile than atomic gas.

If the interstellar medium is so thin,how can we see nebulae at all?

Even though interstellar gas clouds are incredibly thin by terrestrial standards, they make up in size what they lack in density. Interstellar nebulae can be many light-years wide, so the total amount of gas we see from a distance can far exceed even the thickest cloud in Earth’s atmosphere, making them quite visible.

How big are molecular clouds?

Molecular clouds can be enormous compared to stars. The largest ones are called “giant molecular clouds” and can be many light-years millions of times as much mass as the Sun across. Giant molecular clouds can contain thousands or even; they may also contain a number of dense core regions, each with 100 to 1,000 Suns’ worth of gas.

Where can the interstellar medium be found in galaxies?

In most galaxies, the majority of their interstellar gas and dust collects in the disks of the galaxies rather than in bulges or halos.

How does the interstellar medium affect astronomical observations?

The interstellar medium is, of course, itself a target for astronomical study. However, it can also complicate astronomical observations substantially. This effect of dust is called extinction, and it both changes the observed colors of astronomical objects and obscures them from view.

Is interstellar dust similar to household dust?

No. Interstellar dust is typically much smaller, and it is made of very different material, compared to house dust here on Earth. While house dust typically is made up of things like dirt, sand, cloth fibers, crumbs, animal and plant residue, and even microscopic living creatures, interstellar dust is composed primarily of carbon and silicate (silicon, oxygen, and metallic ions) material, which is sometimes mixed with frozen water, ammonia, and carbon dioxide.

Why is the interstellar medium important?

To make things like stars, planets, plants, and people, enough of the interstellar medium has to come together and interact—physically, chemically, and even biologically—to create them.