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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10,000 Black Holes at the Galactic Center

Hey, remember the super-massive black hole at the center of the galaxy?  Well, scientists have been thinking about it too, and they concluded that other black holes should sink into the middle of the galaxy near to the central monster.  To find out if this holds true, they utilized the Chandra X-Ray Observatory (an x-ray telescope located on a satellite in orbit around Earth) to observe stars near to the center of the galaxy.  Black holes can’t be detected on their own, but if they interact with nearby stars they produce esoteric x-rays which can be detected (so long as the x-ray telescope is outside of a planetary atmosphere, which absorbs x-rays, thank goodness).  Within the tiny (er, relatively tiny) three light year area which they scrutinized, the astronomers discovered dozens of black holes.  Extrapolating this data leads them to conclude there are more than 10,000 black holes at the center of our galaxy.  I wish I could contextualize this for you, but I just can’t… the concept of 10,000 super-dense gravity wells flattening and tearing all of the spacetime in the center of the galaxy into Swiss cheese is to disturbing for me to deal with (in any other way than blurting it out in a midnight blog).  I’m not sure this universe is safe at all. I am going to go lie down.

Quasars

During the 1950’s, astronomers using the first radio telescopes started discovering a mysterious class of heavenly objects.  Certain discreet points in the sky blazed brightly with low-frequency electromagnetic radiation–yet when the scientists looked at the spots through conventional optic telescopes, it was impossible to discover a source for this energy.  Some of these radio flares came from incredibly faint smudges and some issued from what seemed like empty space. Astronomers called the mystery flares “quasi-stellar radio sources” (QUASAR) because they believed such discreetly focused energy must come from stellar-like objects.  Further study revealed that the photons issuing from quasars were red-shifted, which meant that the quasars were rushing away from the solar system at high velocities.

An Artist's interpretation of a Quasar

Only in the 60’s did optical telescopes become powerful enough to associate certain quasars with the cores of extremely distant galaxies.  The reason no luminous objects were initially associated with quasars was because quasars turned out to be profoundly distant—the closest were billions of light years away.  They were visible to early radio telescopes only because of their immense energy output and their beam-like focus.

An X-ray image shows the quasar PKS 1127-145 (credit: NASA)

Scientific consensus concerning these massive energy flares did not fully coalesce until the 1980s.  Today astronomers believe that quasars are powered by accretion of material into super-massive black holes which lie at the center of dynamic young galaxies.  Such phenomena are called “active galactic nuclei” (AGN). As radio telescopes and time-space modeling grew more sophisticated it became obvious that quasars (which produce low-frequency radiation) were not the only energy flares associated with AGN.  Giant beams of different spectrums of electromagnetic radiation are possible depending on the galaxy.  Quasars and their ilk produce incomprehensible amounts of energy—the most luminous active galactic nuclei radiate exotic energy at a rate that can exceed the output of an average galaxy by a thousand times (equivalent to the energy from two trillion suns).  To produce such energy the brightest known quasars consume roughly 1000 solar masses of matter within an earth year (which is equivalent to swallowing/burning 600 Earths per minute).

Yikes

Galaxies change as they age. Today the Milky Way Galaxy is a mostly responsible middle aged galaxy (which only occasionally cuts lose with something crazy like the luminous blue hypergiant Eta Carinae) however there are reasons to think that in the past the Milky Way was a deeply troubled teen-aged galaxy ablaze with self-destructive fury just like the AGN galaxies we see at the far edges of space.  Assuming they exist, alien astronomers in galaxies billions of light years away probably see our galaxy as a blazing quasar–because they are looking at its distant violent past.

Active Galaxies Collide (painting by Don Dixon for "Scientific American")

Of course galaxies are not always quiescent.  Some astrophysicists theorize that in 3 to 5 billion years, when the Andromeda Galaxy collides with the Milky Way, the black holes in the center of one or both galaxies could begin swallowing up matter (or could merge) reigniting a super bright fountain of high energy particles again visible throughout the universe.