Young Stellar Objects and Protostellar Disks Video

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  • 0:02 An Example of Star Formation
  • 0:35 Protostars & Young…
  • 2:40 Protostellar Disks
  • 3:47 Bipolar Flows &…
  • 4:27 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
Birth lines, bipolar flows, protostellar disks, and young stellar objects. What do these have to do with star formation? How do they clue us into planetary formation? Check this lesson out for that and lots more info.

An Example of Star Formation

Let's pretend for a second you're a pizza chef. If you take a ball of dough, stick it on your index finder and start spinning that ball around, what would happen?

As plenty of videos online can show you, the dough would flatten out into a disk or pancake shape. Another thing you'll notice is that the index finger juts out of the spinning disk of dough just a bit on either side of the disk's center. The pizza dough has demonstrated a couple of interesting concepts involved in the formation of stars, as you'll learn in just a second.

Protostars and Young Stellar Objects

When stars are being born, they form from dense molecular clouds located in the interstellar medium. Think of dense molecular clouds as regions of space filled with lots of ingredients to make a star. Just like you need flour, eggs and milk to make some good pizza dough, stars need atoms, like hydrogen and helium.

These clouds, triggered to contract thanks to shock waves rippling through space, begin to condense and spin in order to one day become a fully formed, full-fledged, main sequence star like our sun. This earliest stage of formation of a star is like taking the ingredients for pizza, mixing them, condensing them into a ball, sticking the ball on your finger and starting to spin the dough in preparation for making the final product.

As the molecular gas clouds condense, they form the earliest versions of a star, called a protostar. This protostar is surrounded by a cocoon that makes the protostar invisible to the unaided eye, meaning we can't see it at visible wavelengths of light.

With time, this cocoon disappears and a later stage of protostellar development, one where the forming star has lost its cocoon and becomes detectable at visible wavelengths but is not yet a main sequence star, is known as a young stellar object (YSO). On the famous H-R diagram, the line where these pre-main sequence stars become visible is known as the birth line, and the stars, as they form, will move towards the main sequence from there.

You might be wondering how long it takes for a star to fully develop into a main sequence star from the molecular cloud. Well, the more massive the star is, the faster it contracts into a star due to a stronger force of gravity. Our sun took about 30 million years to form. Stars far more massive than the sun can take tens of thousands of years to take shape, while stars far smaller than our sun will take a billion years to reach the main sequence.

Protostellar Disks

So, back to our pizza thingy. Remember that I said that as the molecular cloud contracts to form a protostar, like you force together the pizza ingredients into a compact dough ball, it spins. This is like you taking that pizza dough ball and sticking it on your finger. As the protostar spins, as the pizza dough ball spins, both flatten out into a disk shape. In the center of this disk, the protostar continues to form and take shape. The disks that form around protostars are called, quite simply, protostellar disks.

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