The Nucleus of a Galaxy

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  • 0:01 A Dormant Volcano
  • 0:27 The Nucleus of Our Galaxy
  • 1:34 What's Inside the Nucleus
  • 4:18 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will explore our galaxy's nucleus. Namely, we will find out how we can peer inside using radio waves and infrared, and what that and X-rays tell us about the cool thing that's located inside of it.

A Dormant Volcano

A dormant volcano is a volcano that hasn't erupted in a long time. It may have been a big and powerful rumbling thing back in its day, but no longer is, although it may become active again. At the center of our galaxy, the Milky Way, there is something big, rumbling in its own way, and it is considered to be dormant. This lesson will tell you what that thing is as we look inside the nucleus of our galaxy.

The Nucleus of Our Galaxy

Our galaxy is a barred spiral galaxy, a type of galaxy that has a bar-like elongated nucleus with spiral arms jutting out from the bar. About two-thirds of all spiral galaxies are barred spiral galaxies. The very center of our galaxy is called the nucleus, or central bulge. There is some pretty crazy stuff that happens here. And if you've seen other lessons on galaxies you're probably too aware of the fact that we can't see much of it. At least not with any visible light - that kind of stinks.

The reason we can't see it is for the same reason you can't see very far in a dust storm. Just picture riding through a desert when one kicks up. It'll become almost as dark as night even if the sun is still shining. When light travels through space, it also encounters space dust and gas. This stuff will block and scatter light. In fact, the amount that's blocked is insane. If a trillion photons of light left the center of our galaxy, guess how many would reach Earth? One puny photon, that's it.

What's Inside The Nucleus?

This means we must use a sort of X-ray vision to see through all of this dust, except it's not always X-ray vision; it's also radio vision and infrared vision. What I mean is, we use radio waves and infrared to see through the dust. Short-wavelength X-rays can penetrate the interstellar matter (the dust and the gas) as well. The reason we can't see through the dust using visible light is because wavelengths about the same size as the diameter of a speck of dust, like that of visible light, will be scattered or absorbed by the dust. Longer wavelengths will be able to pass right through.

Observations using infrared and radio waves show us that the nucleus has a lot of crowded stars orbiting at a high velocity. There are so many stars, they heat up the surrounding dust, which then emits very strong infrared radiation. Furthermore, radio maps of the center of our galaxy revealed a lot of different radio sources, but one stood out above the rest. It is Sagittarius A*, or Sgr A*. A very powerful radio source lying in the galactic nucleus.

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