There’s a lot of gas and dust in the universe. Some of it has coalesced into dark nebulae, such as bok globules that almost look like holes in the starry night. We can observe these by the background light they absorb. Some clouds of dust are close enough to a star that light reflects off them, creating reflection nebulae such as the one near T Tauri. But sometimes a cloud of gas and dust is near a hot star, but too diffuse to scatter light much. In this case it can produce a faint nebula known as an emission nebula.
Island Universe
The visible universe is vast. It is 93 billion light years across, and contains more than 100 billion galaxies. The average galaxy contains about 100 billion stars, and untold numbers of planets. Yet a century ago there was serious doubt among many astronomers that the universe was much more than 100,000 light years across. Arguments about whether the universe was small or large became known as the Great Debate.
Going Rogue
A rogue planet is a planet-sized object that doesn’t orbit a star. Instead these objects move through the galaxy just as stars do. They’ve long been thought to exist, but their small size and low temperatures made them difficult to observe.
Three is a Magic Number
Yesterday I talked about the star T Tauri, a red star that is transitioning into a main sequence star. The image yesterday was a composite of visible and near infrared images. The image below is a high resolution image at an infrared wavelength known as the K-band. You can see the visible star labeled as T Tau N (T Tauri North). You can also see two smaller stars, labeled Sa and Sb. These two stars don’t emit much light in the visible, so they can only be observed in the infrared. Earlier images didn’t resolve the binary pair, and instead only saw it as a single star (T Tauri South). It has only been in the past few years that we’ve seen them as a binary.
Winds of Change
The image above is of a star known as T Tauri. T Tauri is the prototype (primary example) of T Tauri type stars. In many ways T Tauri is a star in the making. Not quite a main sequence star, but more than a protostar.
Battle of the Bands
When light passes through gas and dust in the interstellar medium, some of the light is absorbed. Since the gas and dust only absorb certain wavelengths or colors of light, by by looking at these absorption bands we can determine the type of material that makes up the interstellar media. Well, most of the time. It turns out there are a range of absorption bands that we haven’t been able to identify. They are known as diffuse interstellar bands.
Violence Inherent in the System
The Orion Nebula has been in the news recently due to a new set of pictures such as this one from Astronomy Picture of the Day. It is an image of high velocity “bullets.”
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