Bad Astronomy | Many early dark galaxies were buried by dust

When you think of a galaxy, you probably see some gorgeous, giant spiral-armed disk filled with bright blue stars and pink/red clouds of gas dotted with arms. And in fact many galaxies are just like that, including our galaxywhile others are elliptical, or irregular, or even peculiar,

The common denominator is that they are filled with stars, millions or billions of them, so numerous that from afar they blur together in a milky glow.

but recently Astronomers Found Some Galaxies That Don’t Look Like This at All, Located billions of light-years away from Earth, they seem to violate what we know about galaxy structure. Almost no stellar light is seen in them, and the light they emit is at very long wavelengths, far beyond what the human eye can see. They’re dusty—that is, they have clouds made up of grains of iron, rocky, or sooty (carbonaceous) material—but that dust is much cooler than a typical galaxy.

These strange galaxies have been a mystery for some time, but now a team of astronomers thinks they have the answer: These galaxies aren’t just dusty, they choked up With dust, so much so that they completely block out the starlight coming from inside them. In fact, these galaxies are positively bursting with star formation, but are so deeply buried in opaque dust that these galaxies are dark in the kind of light we see. If they didn’t have all that dust, these galaxies would be blazing bright [link to paper],

Galaxies were found in deep survey observations of the sky. They are practically invisible even when viewed in the near-infrared, just outside the visible spectrum, but at progressively longer wavelengths, from mid-infrared to radio waves, they become brighter. If these were normal galaxies in which a normal amount of stars make light and heat the dust around them, they would be brighter in the shorter wavelengths of the infrared. But they are not.

Four such galaxies were previously known. Astronomers saw six more, all far away; It took about 12 billion years for their light to reach Earth. Typically, to measure the properties of galaxies, astronomers make some basic assumptions. For example, they believe that the dust in star-forming clouds is thick enough to block visible light, but let infrared light through. This is usually a decent assumption.

But when they did, they found paradoxes and physical properties that make no sense for these 10 galaxies. This is usually a good sign that one or more of the assumptions you made are wrong. So he changed that assumption, and did the math by assuming that the dust is very, very thick; So dense that even infrared light cannot escape.

And suddenly physics began to make sense.

These galaxies are completely filled with dust, even in the infrared we can only see the surface of these clouds. It’s not that these galaxies have more dust than usual, but they are smaller, so density There is more dust. Normally infrared light can also escape from within the dust cloud, but in this case they are so dense that they are opaque to it.

And that in turn means that to explain the light we see, these galaxies are cranking Outer stars, dozens of times faster than the Milky Way’s formation rate. These are true starburst galaxies, even though oddly, they emit no optical light that we can see. They are dark galaxies.

OK, so this is just objectively good; Galaxies are so thick with dust that they hide what they are doing inside. But it is really important to understand this. We measure the star formation rates of galaxies in a variety of ways, but this is a great way to understand what the galaxy is doing, how much gas and dust it contains, and more. The rate at which stars are born tells us a lot about the galaxy… and also what the universe itself was doing when the light we see left that galaxy, so sometimes past deepens in.

The fact that galaxies are singularly churning stars, yet completely overlooked because they are dark means we have missed a large piece of the early universe; Astronomers estimate that 10% of all dusty galaxies in the early universe are so dusty that they are in the dark.

The next question to answer is why are they that way. Are these examples of colliding galaxies in the early universe? Do stars there form under different conditions than in the surrounding universe, such that they make more dust? With only 10 sample galaxies this is not clear.

what Is What is clear is that we are still learning what the distant, early universe was like, and that sometimes what we want to see remains hidden from us until we find a clever way to see it. In this case a large part of the star-forming galaxies were invisible. What else is there that we have overlooked?

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