From Cold Cloud to Hot Protostar

ngc3582_noao_big.jpg

Paradoxically, stars begin in the galaxy’s coolest places: the dense giant molecular clouds (or GMCs).

This is not quite the paradox it seems, as in the beginning, stars require little else but gravity to form. And that’s really quite lucky, because one thing they do need is regions of high density, and high density is unlikely to occur where temperatures are high.

And so stars begin in perhaps the most surprising of ways: as a high-density bundle of very cool gases within an equally cool interstellar cloud.

But they do heat up eventually. How? Continue reading

How are Stars Born?

Astronomers-Take-a-First-Glimpse-at-the-Birth-of-a-Triple-Star-System.jpg

Astronomers have discovered that the clouds of gas and dust—the interstellar medium (ISM)—found between the stars are made of the same materials as the stars themselves. In fact, hydrogen is the most common element in both stars and the ISM, followed closely by helium.

But it would be more accurate to say that stars are made of the same material as the ISM, not the other way around.

This is because all of the stars formed out of material in the ISM at some point millions to hundreds of billions of years ago. And when they die, they return that material—what’s left of it—to the ISM.

Specifically, stars form out of the giant molecular clouds (GMCs) of the ISM. But how? Continue reading

What is Coronal Gas?

planets_under_a_red_sun-800x533.jpg

Stars are hot. Space is cold. We’re all familiar with that, right?

Ok, good.

Technically, it’s more complicated than that. Space isn’t completely frigid—absolute zero, the temperature at which there is no heat whatsoever, is purely theoretical and not thought to exist in the universe. But it is pretty darn cold.

And stars aren’t always very hot—there is one newly discovered star that’s only as hot as fresh coffee. (It’s a brown dwarf, and if you go by the definition of a star as an object that’s ignited hydrogen fusion in its core, then it doesn’t actually count.)

In general, though, stars are pretty darn hot. Some special types of stars reach up to 200,000 K—that’s 359,540.33℉. Our own sun is about 5,778 K, which much cooler, but still almost ten thousand degrees Fahrenheit.

As a rule, we can think of stars as being much hotter than the space in between…except in the case of coronal gas. Continue reading