Roaming the Cosmos – Vega

Fourteen thousand years ago, the North Star wasn’t the North Star.

The night sky in the northern hemisphere currently turns around Polaris, the brightest star in the Little Dipper. But that changes, ever so slowly, because the Earth is not a perfect sphere. Its spin gives it a slight bulge at the equator. Gravitational forces from both sun and moon apply a gentle torque to this bulge, causing the pole to move in a circle. This movement is called axial precession and it takes 26,000 years to complete one circle.

1024px-precession_nThe North Pole circles a huge swath of the sky over that time, allowing many different stars to be the North Star. But the brightest by far is Vega.

Vega is the second-brightest star in the northern celestial hemisphere and the fifth-brightest star in any sky visible from Earth. That’s because it’s both big and close. At twenty-five light years away, it’s in the stellar neighborhood and it’s a burning hot blue giant more than twice the size of the sun and fifty-eight times brighter.

In summer in the northern hemisphere, Vega is located nearly straight overhead at night. But fourteen thousand years ago the north pole pointed right at it and the night sky spun around Vega all-year long.

Let’s travel to the star itself. If you’re expecting an orderly system with planets at regular intervals, you will be quite surprised.

Excess infrared flux coming from Vega indicates that the star is surrounded by a massive, disc-shaped cloud of debris that’s as big as our solar solar system.

Lots of stars have protoplanetary discs around them right after they form, but Vega is not a newly-formed star. It’s been around for millions of years. For that much debris to be circling Vega, there has to be a continual source of replenishment. The inner-part of the disc, close to Vega, must have an extremely high dust production rate, since stellar wind pressure should have pushed out all small grains long ago. Where does this big cloud come from?

The quickest way to get a cloud of dust in space is by smashing big things together. There must be a tremendous amount of bombardment going on. One possible explanation would be the migration of giant planets in Vega’s outer disc. The cloud is very uneven, indicating the potential presence of large objects.

Either from one big collision between planets or many small collisions from smaller planetoids (or both), Vega is surrounded by chaos. If you stood on a crumbling world near Vega, you could see the dust of the system lacing the sky.

Through this haze, the sun would be visible. Our sun, that is. Twenty-five light years is a great distance, but not so far as to change the stars in the sky too much. Roughly the same constellations could be seen from the Vega system. The sun would be a faint star in the Columba constellation.

We view the Vega system top down. It’s one of the reasons why this disc of debris is so easy to see. Because we are located directly above Vega, the sun might be the North Star of a planet in the Vega system.

Or, if not, we might become the North Star at some point. After all, guiding stars change all the time.

Sources/Additional Reading:

Vega: The Once and Future North StarSpace.com

Vega’s StardustCNRS International Magazine

New evidence for Solar-like planetary system around nearby star – Royal Observatory, Edinburgh

The Vega Debris Disk: A Surprise from Spitzer – Cornell University Library

Precession chart created by Wikipedia user Tauʻolunga.

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