The Mysterious Case of Epsilon Aurigae

By Dennis Mammana

November 2, 2017 4 min read

Week of Nov. 5-11, 2017

Ever since I was a youngster, I've been fascinated by how crime scene investigators can reconstruct a crime with such amazing accuracy from relatively scant evidence. They don't have the luxury of watching the crime occur, and they often don't even have an eyewitness. Instead, they must work backward from their own observations and measurements — using such tools as physics, chemistry and biology — to logically reconstruct what must have happened and produce the evidence as it now appears.

Astronomers are often faced with the same problem. They must determine complex physical mechanisms by observing and measuring only the tiniest flickers of starlight coming from many trillions of miles away. And the stories carried to our eyes and telescopes by starlight are really quite remarkable.

One such story comes from a relatively obscure star in the constellation Auriga, the charioteer, low in the northeastern sky shortly after dark on autumn evenings.

Now, I know that beginning stargazers are tempted to search the skies for an outline of a charioteer. That is, after all, the constellation's namesake. But I think you'll find it much easier to trace among its stars a pentagon that emanates from the bright star Capella.

Along Auriga's northwesternmost side you'll see three relatively faint stars form a tiny triangle. The brightest of these three, which is also closest to Capella, is known to astronomers as Epsilon Aurigae, or Almaaz.

Viewing this star with the eye, binoculars or even a small telescope gives no hint as to how unusual it may be. The flickers of starlight tell us that the star may be 12,000,000,000,000,000 miles (that's twelve thousand trillion miles) from Earth, so distant that its light requires some two millennia to reach us. They also suggest that its mass is about 15 to 20 times larger than the sun, and that its size is perhaps 300 times wider than the sun.

If this isn't amazing enough, astronomers have long known that since its brightness dips every 27 years or so, it is regularly eclipsed by something orbiting nearby. Many so-called eclipsing binaries exist around the sky, and their eclipses often take a few hours or days. This one, however, lasts about two years. Whatever is eclipsing this star seems to be significantly larger than Almaaz itself — perhaps a thick, doughnut-shaped ring of dust as large as the orbit of Saturn that passes in front of Almaaz from time to time.

During the most recent eclipse of Almaaz, from 2009 to 2011, astronomers compiled more evidence from ground-based and space-borne telescopes to devise some competing theories that explain its faint flickers of starlight.

One is that Almaaz may be a massive supergiant star that is periodically eclipsed by two tightly bound stars inside a swirling, dusty disc. Another is that it might be a relatively large dying star with a low mass that is periodically eclipsed by a single star inside a disc; it also follows that Almaaz will blast its atmosphere into space sometime in the next few thousand years.

Of course, no one knows for certain what's happening there, and astronomers will surely be debating the evidence until its next eclipse, around 2036.

So, much like a complex crime scene, the investigation continues.

 Learn about the mysterious case of Epsilon Aurigae this week.
Learn about the mysterious case of Epsilon Aurigae this week.

Visit Dennis Mammana at www.dennismammana.com. To read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

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