Blue and New; Red and Dead; Ocher and Croaker(?): The Shapes and Colors of Galaxies

Sometimes if you aren’t watching the heavens (or the news) closely enough, you miss a major astronomical discovery.  For example last summer, astronomers discovered a galaxy which formed only one or two billion years after the Big Bang (so I guess it is unclear whethter I missed this story by one year or by 12 billion).  At any rate, the galaxy hunters used the Hubble space telescope to peer through a powerful gravitational lense far away in space.  Gravitational lenses are areas where timespace is warped like a huge lense by high-gravity phenomena, and a viewer can use them like a huge lense to see far-away objects.  By using the Hubble telescope together with the gravitational lense they were able to see back a dozen billion years in time to the edge of the universe…as it once was not long after creation.  What they saw perplexed them.

There is a fundamental difference between galaxies.  Galaxies where stars are being formed tend to be blue and spiral shaped (like our own beloved Milky Way!).  Galaxies where stars have largely stopped forming are “red and dead” since the remaining stars tend to be long lived red dwarf stars and the bright young (short-lived) blue stars are mostly gone.  These red galaxies are not shaped like spirals, but tend to be elliptical shaped (like an egg or a football, not like one of those evil gym machines).

The ancient galaxy at the edge of the universe was neither of those colors or shapes. It was a dense yellow disk.  Stars formed in an (enormous) accretion disk but then, for some reason, new star formation stopped.  The blue stars burned out (“the light that shines twice as bright etc, etc..”), but the yellow middle aged stars were still burning.   The galaxy had three times the mass of the Milky Way but scrunched into a pancake of much smaller area.

So do galaxies always form as disks and then either become self-renewing blue spirals (maybe by colliding with other galaxies or clouds of dust)or dead red footballs?  Or was this early yellow disk galaxy an abberation? Or is our own galaxy truly new (well…newish…being only a few billion years old)?  I do not understand astrophysics well enough to answer these questions or even formulate them properly (although I get the sense some of these questions may not yet be answered by anyone in any comprehensive way), but I would love to hear what people can add to this rudimentary yet compelling story of shapes and colors.

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The Comet Storm of Fomalhaut

A Comparison of the relative sizes of the Fomalhaut system and the solar system (image created by NASA and ESA)

Fomalhaut is a star with twice the mass of the sun located approximately 25 light-years from Earth in the constellation Piscis Austrinus.  It is a bright young star 100 to 300 million years old (out of a projected lifespan of 1 billion years). Coinicientally  the name Fomalhaut is Arabic and means “mouth of the Southern fish.”  Fomalhaut has at least one planet—Fomalhaut b, which is believed to be approximately the same size as Jupiter (but could be anywhere from the size of Neptune to 3 times as large as Jupiter).  Just as Saturn is surrounded by a ring of debris, the entire star system of Fomalhaut is surrounded by a giant toroidal circumstellar disk.   This torus is vastly greater in diameter than our entire solar system (including the Oort Belt) and is made up of somewhere between 260 billion and 83 trillion comets which are constantly colliding and annihilating each other!  The Herschel Space Observatory recently captured an infrared image of this immense comet storm.

An infrared image of the Fomalhaut system--and its huge cloud of disintegrating comets) captured by the Herschel Space Observatory (credit: ESA)