Surf's Up! In a BIG Way!

 As stars go, our sun is rather average in size. The smallest stars, called red dwarf stars, can be less than one-tenth the mass of our sun. The largest stars are fifty times our sun’s mass or more. Most stars are not single, like our sun. NASA estimates that more than half of all stars have one or more partners, where two or more stars are in orbit around each other. Some astronomers calculate that as many as 85% of stars in the universe are in multiple star systems.

Sometimes stars in a double star system can orbit quite close to each other. That can cause some strange effects.

When you hear the words tides and waves, you probably picture an ocean beach, perhaps with surfers. On Earth, our tides are caused by the gravitational pull of the Moon. But our tides are rather gentle, with the ocean’s edge slowly creeping up and down the beach twice a day.

If two stars orbiting each other come close together, each can pull tides on its companion. If those stars are really large, they can pull big tides. 

Stars orbiting close together can pull large tides on each other. Credit NASA, JPL

Astronomers describe a binary system in which the two stars have elongated orbits as “heartbeat stars.” Because of their orbits, the distance between the stars can vary dramatically. When the two stars are closest, they can cause huge tidal forces on each other, which causes large, regular brightness changes in the stars, such as a heartbeat might do on an electrocardiogram.

A heartbeat star (center of each image). Credit: NASA ESA CSA I. Labbé Swinburne University Of Technology Image Processing

One such binary star was first detected in the 1990s during a project known as MACHO which stands for Massive Compact Halo Objects. The ‘smaller’ star is ten times as massive as our sun, while the larger one is 35 times as massive as our sun and 24 times wider than our sun. The tidal force between them doesn’t just create gently moving tides as on Earth. The smaller star pulls tides on the larger star so hard it creates waves 3 times taller than the diameter of our sun.

"Each crash of the star's towering tidal waves releases enough energy to disintegrate our entire planet several hundred times over," says astrophysicist Morgan MacLeod, from the Harvard-Smithsonian Center for Astrophysics who studied the binary pair. "These are really big waves." The smaller star also makes tidal waves, but, being smaller, the waves on its surface are much smaller.

The energy of these gargantuan tides causes the two stars to slowly spiral closer together. Eventually, they will crash into each other and merge into one even larger star. The star system sits in the Large Magellanic Cloud, a satellite galaxy of your Milky Way 160,000 light years away. Too bad, as that collision would be a dramatic sight if it were closer.

Surfers may be desirous of such waves, but they would need to use a lot of sunscreen. The surface temperature of such stars can easily exceed 37 million degrees.

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

 This is reprinted with permission from the Oklahoman and www.Oklahoman.com.