On a dusty day, you can’t see the smog. At least that’s how it is for galaxies, which is why the detection of carbon in early galaxies is such a big deal.
Beryllium Sphere
Using an elemental trick, we can determine the age of our Milky Way galaxy.
Galaxy Quest
The categorization of galaxies was first made by Edwin Hubble in 1926, and became known as Hubble’s tuning fork. It was so-named because the variety of galaxies could be laid out along a scale of ellipticals which then branched into two types of spirals. When Hubble proposed this scheme, some suggested that it indicated the nature of galactic evolution, where round, elliptical galaxies gradually changed into flat, spiral galaxies. Hubble himself was cautious not to assume too much about the classification scheme. Still, it does raise an interesting question about these types of galaxies. Why do some become spirals and others not?
I’ll Fly Away
A couple days ago I wrote about how one of the properties of a galaxy is that its stars are gravitationally bound. This means that the stars don’t have enough speed to escape the gravitational attraction of the galaxy, and so a star by itself can’t escape the galaxy. But this doesn’t mean that stars can never escape their galaxy. In fact, given enough time, many of them will.
CANDELS in the Dark
If you look at different galaxies in the universe, you begin to notice that they seem to fall into some broad types. Edwin Hubble was the first to categorize galaxies into different types, and he divided them into ellipticals, spirals and irregulars. He then further broke these categories into subgroups, and arranged them into what is now known as Hubble’s Tuning Fork diagram.
Galaxy Wind
The Sun gives off a great deal of energy. As a result, ions from the upper atmosphere are pushed away from the Sun, producing what is known as the solar wind. With galaxies, a similar thing can occur. The center of many galaxies have the largest concentration of stars, and if that region is particularly active it can produce a “galactic wind” of molecules streaming away from the galactic center.
Hubble’s Tuning Fork
Edwin Hubble is perhaps most famous for discovering a relationship between the distance of a galaxy and the speed at which a galaxy moves away from us. This relation is now known as Hubble’s Law, and is evidence for the expansion of the universe. But Hubble’s primary interest was in galactic nebulae (what we now just call galaxies).
Spirals
Our Milky Way galaxy is a spiral galaxy. So are several galaxies in our neighborhood, like Andromeda, Triangulum, and the Pinwheel galaxy (seen above). About 70 percent of the galaxies in our corner of the universe are spiral galaxies.
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