Evgenya Shkolnik on four stars with surprisingly tight orbit

An astronomer has found four stars in a tight orbit that might help unlock secrets of how stars evolve. The system is BD -22 5866, and astronomers thought it was one star.

Evgenya Shkolnik: I’ve looked at many, many spectra in my career, and I’ve never seen anything like this before, and I thought, wow, this is really neat.

That’s Evgenya Shkolnik at the University of Hawaii. She found there are four stars here whose very fast mutual orbit carries them no farther from each other than Jupiter is from our sun.

Evgenya Shkolnik: The tightest binary sytems are orbiting about 133 kilometers per second, which equals about 300,000 miles per hour. So it’s very fast, and that would get you from Honolulu to New York in less than a minute.

Some binary stars take thousands of years to orbit each other. But astronomers can watch this whole system go around in less than a decade. That means they can use mathematics and physics to pin down properties of the stars.

Evgenya Shkolnik: We can spend a lot of time at the telescope analyzing the entire system in many different techniques, and that would give us the true masses and the true inclinations of each of the orbits, and the true periods and distances between the stars. So if we can completely characterize the system, then we can plug those into the evolutionary models and figure out where the evolutionary models are wrong or right.

This four-star system is located 166 light-years away.

Astronomers are describing this four-star system as having the shape of a ‘dumbbell.’ The whole dumbbell spins around and returns to its original position in nine years. Jupiter, in a similar orbit around the sun, needs nearly 12 years to complete an orbit.

While groupings of stars moving around each other are fairly common, only 1 in 2,000 consists of so many stars in such a relatively small space, according to Shkolnik.

Evgenya Shkolnik: In astronomy, when we look at a star, just one star, it’s very hard to determine its mass. Surprisingly hard. So we really don’t know the masses of single stars all that well. However, if you have a binary system, two stars moving around each other, we can use the laws of gravity to stars determining what their masses are.

An alternate catalog name for this system is NLTT 53279.

Our thanks to:
Evgenya Shkolnik
NASA Astrobiology Institute
Institute for Astronomy
University of Hawaii at Manoa

March 28, 2008

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