Dust. Wind. Dude.

Contributed by
Oct 9, 2007

An interesting astronomical bit of research just came over the wire: black holes belch dust.

There are a handful of things that truly baffle astronomers. In general they are caused by two observations that contradict each other, or at least an observation that contradicts theory. For example, we know that dust grains -- complex aggregations of various minerals and compounds in space -- are created in red giants and supernovae. But we see a lot of dust way back in the early Universe, before it seems like there were stars old enough to make it.

A new observation using the Spitzer Space Telescope shows that black holes might be making that dust. Astronomers observed a quasar, a type of galaxy with an extra-bright nucleus, about 8 billion light years away, and specifically the black hole in the center of that quasar. All big galaxies have supermassive black holes in their centers; the one in the Milky Way is about 4 million times the mass of the Sun, but some can be a billion solar masses! If that black hole is gobbling down matter, it can actually wind up spewing a lot of that material back out. The material can be very bright, making it easy to study.

Astronomers took a look at the material coming out of the central black hole in quasar PG2112+059 and found it had a lot more complex dust in it than was previously thought (including the materials that make up sapphires and rubies!). Normally, that kind of dust is generated in stars but is quickly destroyed by nearby bright stars -- their UV light can break down the materials -- so seeing this much of it implies strongly that it's coming from the black hole wind itself.

The spectrum of the galaxy shows the presence of all kinds of stuff, including corundum, which is a basic ingredient of sapphires and rubies! The observed spectrum is in white/beige, and the models of the spectra of the other materials are in the different colors. They all add up together to make the observed spectrum, and the fit is pretty good.

This galaxy isn't really considered to be in the "early" Universe: at 8 billion light years away, we see it as it was when it was only a little more than half the age of the Universe now. But we know these supermassive black holes were around farther back in time, and that in turn means they could have been the source of the dust that has been dogging astronomers.

This is hardly proof, but it does indicate that when astronomers are confronted with a paradox of sorts, they look -- and usually find -- the knife that cuts the Gordian knot. The next step is to look for these minerals in more quasars, and more distant ones, too.

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