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Why Can’t We See the Center of the Milky Way?

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Posted April 30, 2015

Shouldn’t there be a great big glowing ball at the center of the galaxy? Why can’t we see it in the night sky?

Admire the majesty that is the Milky Way. It’s our celestial home. See all the detail in this gorgeous photo. Look at all those stars, gas and beautiful glowing space dust.

The Milky Way Galaxy. Credit: NASA

The Milky Way Galaxy. Credit: NASA

Can you imagine what went into taking this photo? What marvels of human engineering to get a camera to photograph the whole Milky Way all at once. Of course you can, you’re smart. Let’s walk through this together.

First, you’d need to have a camera that worked in space and a big wide field of view. Sure, we can build those. Then you’d need to take that camera and place it just outside the Milky Way pointing back at Earth. Like if you were taking a picture of a house, you’d need to stand in the street out front. So we figure to be out on the street in front of the Milky Way, you’d need to be about 100,000 light years above it. That’s not so far. Some galaxies are millions of light years away.

So, how did we get a camera this sophisticated that far out above the Milky Way? You know, the galaxy we’re inside of. This is where the “photo of the Milky Way” curtain comes down. By our current propulsion technology, it would take us 2.2 billion years to get to that sweet spot. Truth is, that’s not a photo. It’s an artist’s illustration of the Milky Way.

NGC 6744. Credit: ESO

NGC 6744. Credit: ESO

Here’s a photograph of a galaxy that sort of looks like what you’d see if you were outside the Milky Way. This is NGC 6744, a galaxy that many astronomers think looks pretty similar to the Milky Way.

See the swirling arms? Bright core surrounded by dark lanes of gas and dust? The blobs of active star formation? Hold it in your mind. Here’s an actual photo of the Milky Way.

Right here is the core, the brightest, densest spot; stars are packed so close together it’s hard to tell them apart. Also the location of our galaxy’s supermassive black hole, a region that contains 4.1 million times the mass of the Sun.

The center of the Milky Way in infrared. Credit: NASA, ESA, and Q.D. Wang (University of Massachusetts, Amherst), Jet Propulsion Laboratory, and S. Stolovy (Spitzer Science Center/Caltech)

The center of the Milky Way in infrared. Credit: NASA, ESA, and Q.D. Wang (University of Massachusetts, Amherst), Jet Propulsion Laboratory, and S. Stolovy (Spitzer Science Center/Caltech)

Stars swirl around this region like comets going around a star. Don’t see it? I promise, that’s the spot. Compare this to what it looks like when you peer away from the core, towards the outer disk of the Milky Way.

Man, those photos sure are different and by that I mean, shouldn’t one those nearly identical pictures have a giant glowing ball in the middle? Why can’t we see it… it’s right there-ish? It’s dust. Interstellar dust.

Back to the image of NGC 6744. See the dust lanes surrounding the core of the galaxy? From our position within the galaxy, that thick dust totally obscures our view. The dust is created by stars, as they fuse material and create energy. It collects together by gravity into formations that obscure our view.

Fortunately, astronomers have a few additional wavelengths they can use to see into the galaxy. When you look at the core of the galaxy in infrared, like with the Spitzer Space Telescope, it looks like this.

In fact, in the infrared, you can slice right through that dust and see the environment around the supermassive black hole at the heart of the galaxy. Dr. Andrea Ghez and her team used this technique to find stars whipping around. Nothing could be this dense and dark, except a supermassive black hole.

Astronomers have a name for the region of sky obscured by the Milky Way: the Zone of Avoidance. See now, that’s a cool name. It’s a little 1950’s but it’s way better than “Water Reclamation System”.

Back in the days that astronomers could only make visual observations, the Zone of Avoidance took up about 20% of the night sky.

But by observing in other wavelengths, like infrared, x-ray, gamma rays, and especially radio waves, astronomers can see all but about 10% of the sky. What’s on the other side of that 10% is mostly a mystery.

Thanks dust, for ruining our view to one of the most beautiful objects in the night sky. I suppose we should thank you for giving us some beautiful nebulae to look at. I guess you’re not all that bad, just get out of my sinuses already.

What’s your favorite dark nebula? Tell us in the comments below.

Source: Universe Today, written by Fraser Cain

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