Cover Story: White Dwarfs by the Billions

Mercury, May/June 2001 Table of Contents

Copyright 2001 Lynette Cook

Astronomers have just identified a new class of white dwarf, which could number in the hundreds of billions and account for a significant portion of the galaxy’s dark matter.

by Ben R. Oppenheimer

Ancient. What images does that word suggest to you? Does it evoke visions of Egypt, with its pyramids and long lost gods? Does it remind you of Sumer, the first civilization? Or does it take you even further back, perhaps to the earliest cave paintings? Maybe it brings up images of Homo erectus or Triassic dinosaurs.

Compared to a human lifespan, these events occurred an eternity ago. But from an astronomical perspective, they occurred yesterday. To astronomers like myself, "ancient" means near the beginning of time itself. Fortunately, artifacts nearly as old as time exist, and we’re starting to find them in our own solar neighborhood. We are just beginning to study these artifacts, and we’re just beginning to realize that there could be tens of billions or even hundreds of billions in our galaxy, meaning they might outnumber the normal stars in the galaxy.

These artifacts are a breed of white dwarf, relics of our galaxy’s first stars. They are the cores of stars, born perhaps as long as 13 billion years ago, when the universe just began to resemble its present state, and our galaxy was no more structured than a lump of mashed potatoes. These stars presumably went through the various stages of stellar evolution in much the way that stars do today, eventually leaving behind white dwarfs, extremely dense spheres of carbon and oxygen with traces of hydrogen and helium.

Understanding these ancient white dwarfs, their temperatures, and how numerous they are, will ultimately reveal the age of the galaxy. Even more exciting is that the discovery of vast numbers of old white dwarfs challenges our conception of star formation, and may represent the first time astronomers have actually seen the so-called "dark matter."

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