Daily Archives: February 13, 2009

astronomy, physics

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Exploring the Superlative Universe

The Space Shuttle: how fast is it? How fast could it go? (Artwork depiction courtesy National Geograhic.)
The Space Shuttle: how fast is it? How fast could it go?

Do you want to know what the fastest things are in the universe?  The most explosive?  The biggest and smallest? What objects do you think are faster, bigger, smaller, or most explosive?  For the fastest, I figured maybe it would be the high-speed, relativistic jets coming out from the centers of galaxies, where black holes live and snarf up surrounding matter.

For biggest and smallest, I figured superclusters of galaxies and sub-atomic particles, respectively. And, most explosive?  It would have to be the Big Bang, right?

All those things are examples of superlative things (from a Middle English perversion of a late French term superlatif, which came from the Latin superlatus, meaning “lifted up to the highest degree, most eminent”, etc.).

An asteroid the size of Manhattan may have contributed greatly to the death of the dinosaurs some 65 million years ago. Is that the biggest explosion in the cosmos?
An asteroid the size of Manhattan may have contributed greatly to the death of the dinosaurs some 65 million years ago. Is that the biggest explosion in the cosmos? (Artwork depiction courtesy National Geograhic.)

Superlatives in the cosmos are the topic of a series of three programs being shown on National Geographic beginning this weekend called Known Universe. I’ve been watching a preview copy of the series (thanks to the NatGeo folks!) and even I’ve learned some new things.  Like, what do you think the fastest object to be rocketed into space?  It turns out to be the new Horizons spacecraft which is traveling at toward a rendezvous with Pluto in 2015 at around 18 kilometers per second.  The series is chock-full of facts like that.

So, why study superlatives in the cosmos?

Because, so far as we know the biggest and smallest and fastest and slowest and most explosive things all obey the same laws of physics, throughout the universe. They teach us about conditions in other places, and how planets and galaxies and stars can change and evolve. These things help us understand the universe a bit better, even if what we’ve learned is the smallness of the atoms in a strand of hair or the speed of particles as they are accelerated in a physics experiment. In other words, superlatives help us understand the common places as well as the exotic in the cosmos.  That’s part of the message of this series. Maybe as you watch it, you’ll discover new things yourself.  Go check it out — starting Sunday night, January 15th on National Geographic Channel (in the U.S.).

galaxies

Does Size Matter?

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It Might for Galaxies in the Early Universe

We live in a region of the Milky Way Galaxy where our neighbors are pretty few and far between. The closest star is 4.5 light-years away and even if we had a good interstellar space ship that could travel at oh, say, a tenth the speed of light (roughly 300,000,000 meters per second), it would take centuries to get there. It would appear that living the galactic sticks is part and parcel of being in our spiral galaxy.

The large image shows a star field imaged by Dr. Michael Hilker, using the 2.5-meter Du Pont Telescope at Las Campanas, Chile. The inset boxes are close-ups made using HST of two ultra compact disk galaxies, courtesy Michael Drinkwater of the University of Queensland. (Click to biggenate.)
The large image shows a star field imaged by Dr. Michael Hilker, using the 2.5-meter Du Pont Telescope at Las Campanas, Chile. The inset boxes are close-ups made using HST of two ultra compact dwarf galaxies, courtesy Michael Drinkwater of the University of Queensland. (Click to exframulate.)

But, what if we lived in a galaxy that was perhaps 1/1000 the diameter of the Milky Way? Say something like an Ultra Compact Dwarf Galaxy? Such objects existed in the early universe and they had stars jam-packed together in a region only about 60 light-years across!  The bright star Aldebaran in the constellation Taurus is around 60 light-years away. Imagine packing a whole galaxy into the space between us and Aldebaran!

So, does a galaxy’s size matter?  It could, depending on what you want to know about it.

For one thing, if there were any planets around these stars (and that’s probably doubtful), the “light pollution” from all the nearby stars would drown out our view of the more distant ones. For another, these objects were most likely formed when more “normal” galaxies collided and mingled stars a few billion years after the Big Bang. That means that they’ve experienced some major transformations and evolution since then.

Actually, what really matters about these UCDs (as they are often referred to) is their masses. They seem to have way more matter than their starlight implies.  Could they be full of massive stars or dark matter?  Or something else?

A team of astronomers led by Professor Pavel Kroupa and graduate student Joerg Dabringhousen of the University of Bonn has been looking at UCDs to figure out what they’re made of. They think that each UCD was incredibly packed with stars — maybe as many as a million in each cubic light -year of space. For comparison, in our part of the Milky Way, that number is closer 1 star per cubic light-year.  Think of cramming a million stars within a cubic light-year of the solar system. The sky would literally glow.

Having stars crammed together that closely in the UCDs means that over time, they could merge together to build hugely massive stars — the kind that live fast and die young as supernovae.  What’s left of these massive stars at that point are superdense neutron stars or the occasional black hole. Both of which are incredibly dense without being bright.

So in today’s UCDs, much of their mass is sunk into these dark remnants that you can think of as fossils pointing the way to a more dramatic and active past. Billions of years ago they must have looked absolutely stunningly bright. And, if you were inside one, on a hypothethical planet, your sky would be nothing but stars making it as bright as a sunny day here on Earth.