It is my pleasure to introduce Dr. Eric McKenzie, associate director for the department of astronomy at the University of Maryland.  He received his Ph.D. from the University of Florida, and his research has focused on galaxy evolution at specific wavelengths of redshifted light.  He also helped me get some of my facts straight for the Tomorrow News Network story “The Orion War.”

This week, he has answered some questions about galaxy evolution and what the early universe was like.  Today is the final installment of his interview.

James Pailly: If you could go back in time to visit a planet in one of these young galaxies, what do you think you’d find there?  Any chance you might meet an alien life form?

Dr. McKenzie: I’m no astrobiologist, so I’m speaking a little off-the-cuff, but here are some thoughts.

As mentioned earlier, there were fewer heavy elements in the early universe.  With hydrogen predominating, the population of planets would presumably favor gas giants like Jupiter rather than terrestrial planets like Earth.  Water would be relatively uncommon due to the need for oxygen atoms.  It’s a good guess that life would be carbon-based, like Earth’s. (Scientists have speculated that silicon-based life forms may be possible, but silicon would be quite rare in the early universe.)  Technology could be a challenge for early alien civilizations, since on average they would have smaller quantities of useful materials to work with.  Consider the conflicts that have been fought on Earth over scarce natural minerals – the problem would be exacerbated!

Early civilizations would also face the threat of an increased likelihood of supernovae.  With the early universe’s higher star formation rate, many stars were being born, but the largest ones were only living a few million years and dying in supernova explosions.  This wouldn’t be very healthy for civilizations living in nearby star systems, nor for emerging life which might one day result in a civilization.

It is my pleasure to introduce Dr. Eric McKenzie, associate director for the department of astronomy at the University of Maryland.  He received his Ph.D. from the University of Florida, and his research has focused on galaxy evolution at specific wavelengths of redshifted light.  He also helped me get some of my facts straight for the Tomorrow News Network story “The Orion War.”

This week, he will be answering questions about galaxy evolution and what the early universe was like.

James Pailly: What are quasars, how did they form, and what role did they play in galaxy evolution?

Dr. McKenzie: Quasars are the bright centers of galaxies where hot gas is swirling into giant black holes.  We believe that nearly all galaxies have massive black holes at their center; the Milky Way certainly does.  In most cases, these black holes are quiescent.  They’re not actively absorbing much material because the galaxy’s gas and stars are orbiting around the black hole without falling in.  However, a small fraction of galaxies have active black holes, where material is continuously spiraling inward.  The gas is moving very quickly in tight orbits and heating up due to friction between the gas particles.  The net result is a powerful blaze of energy – a quasar.  When the clump of gas is eventually consumed, the quasar will turn off again.

Quasars are a feature of the early universe – we don’t generally see them in nearby galaxies.  This may be because, at our present stage in the universe’s history, the massive black holes at the centers of galaxies have already cleaned out all of the ‘easy pickings’ of gas clouds.

The effects of quasars are potentially powerful enough to affect the evolution of their host galaxies.  As most of the nearby gas swirls into the black hole, angular momemtum effects cause a small fraction to be flung outward instead.  This outflow may push away other gas which is farther from the galaxy’s center, perhaps eventually cutting off the quasar’s food source.  On a larger scale, it may even reduce the galaxy’s ability to concentrate gas to form new stars.  This is a very active area of current research!

It is my pleasure to introduce Dr. Eric McKenzie, associate director for the department of astronomy at the University of Maryland.  He received his Ph.D. from the University of Florida, and his research has focused on galaxy evolution at specific wavelengths of redshifted light.  He also helped me get some of my facts straight for the Tomorrow News Network story “The Orion War.”

This week, he will be answering questions about galaxy evolution and what the early universe was like.

James Pailly: Were galaxies in the early universe different than the ones we see around us today?

Dr. McKenzie: Quite a bit!  They were generally smaller, for starters.  Because the universe was denser, they also collided with each other more frequently.  The larger galaxies that we see nowadays, including our own Milky Way, appear to have built up over time through mergers of smaller galaxies.  Modern galaxies often have orderly spiral or elliptical shapes, but it’s rare to see such galaxies in the early universe.

Early galaxies formed stars more quickly than modern galaxies do. The ‘global star formation rate’ has been steadily slowing over the past 5 billion years or so as the available gas gets converted into stars.  Some of the galaxy collisions caused massive waves of star formation because the galaxies’ gas got compressed by gravitational interactions; these galaxies are called ‘starbursting galaxies’.

Early galaxies also had fewer ‘metals,’ which in astronomy jargon means all the elements beyond the simplest ones, hydrogen and helium. The universe formed with essentially no heavy elements, including carbon, nitrogen, oxygen, iron, gold, uranium, and so on.  These were produced later by fusion within stars or during the violent supernova explosions that occur when the largest stars die.  (Pretty much all of the non-hydrogen atoms in our bodies originally came from stars.  The stars cast this material into space as their lives came to an end, and the atoms came to rest in the cloud of gas that later coalesced into our solar system.  I think that this is one of the most extraordinary discoveries of astronomy.)

It is my pleasure to introduce Dr. Eric McKenzie, associate director for the department of astronomy at the University of Maryland.  He received his Ph.D. from the University of Florida, and his research has focused on galaxy evolution at specific wavelengths of redshifted light.  He also helped me get some of my facts straight for the Tomorrow News Network story “The Orion War.”

This week, he will be answering questions about galaxy evolution and what the early universe was like.

James Pailly: Using redshifted light, you’ve peered back in time to see the formation and evolution of galaxies.  What is redshifted light, and how are we able to see so far into the distant past?

Dr. McKenzie: The wavelengths of light that we see from a moving object get shifted to the bluer or redder end of the spectrum because of the motion. The color shift depends on whether the motion is toward us or away from us.  Thus, stars and galaxies look bluer if they are moving toward us and redder if they are moving away from us.

This works just like the wavelengths of sound from a moving object.  Think of the sound when cars, trains, ambulances, etc. go past you.  When they come toward you, the sound is high in pitch (short wavelengths, high frequency).  When they pass you and are moving away, the sound quickly switches to low pitch.  If a car were driving past us at a significant fraction of the speed of light, we would see the visual color shift, as well: it would look first bluer, then redder!

Our universe is expanding: nearly all of the galaxies are moving away from us, and so their light is redshifted.  When we see the most distant galaxies, they are the reddest, because they are moving away the fastest.

By studying galaxies which are billions of light years away, we see what the universe was like at a younger time.  Because light travels at a finite speed, we never see anything as it looks ‘right now’.  The moon is 1 1/4 light seconds away, and so we see it as it was 1 1/4 seconds ago.  The sun is 8 light minutes away, and so we see it as it was 8 minutes ago.  (This leads to the slightly disconcerting thought that, if the sun winked out of existence right now, we would be happily oblivious for 8 minutes while the light rays continued to travel to us.)  Looking at distant galaxies gives us a picture of the early universe.  We can study how galaxy ‘demographics’ have been changing over time, such as their sizes, shapes, colors, and star/gas/dust content.