Diamond stars

By Dana Wilde, BDN Staff
Posted May 21, 2011, at 6:03 p.m.

 A few years ago some astronomers announced some curious things they had learned about the white dwarf star BPM 37093, about 50 light-years away in the constellation Centaurus. The core of BPM 37093, they said, appears to be a diamond weighing about 10 billion trillion trillion carats.

How in the world does a star become a diamond?

In astroscience-speak, stars are likened to living beings. The formation of new stars is called “star birth.” It occurs in “stellar nurseries” where gas and dust twine together, attract more gas and dust, and eventually accrete to a mass that starts to contract and create heat. If it gets large enough, it ignites in nuclear fusion.

Over about 30 million years, a star the sun’s size matures from youth into a sort of middle-aged stability in which the star burns by fusing hydrogen in its core. For stars like the sun, this period of adulthood lasts about 10 billion years. Eventually, as in all life forms, the star starts to run out of energy — hydrogen fuel, to be exact. As this happens, a complex interplay of contraction and gravitation push the nuclear processes into the outer layers of the star, and it swells and in early old age becomes a red giant.

 

Elderly stars with masses about half again or more than the sun can die spectacular deaths. The core starts to contract, and the contraction becomes so enormous that the core implodes, triggering an inconceivably huge explosion called a supernova. The remains, in one scenario,  collapse into a ball roughly 10 miles wide with a mass greater than the sun. This neutron star spins wildly fast, emits radiation but no light, and eventually cools away and buckles. In stars three times or more larger than the sun, the remains of the supernova explosion become so dense they can’t stop collapsing. Their gravity becomes so concentrated that space and time are twisted out of all recognizable shape and even photons of light can’t escape. The star seems to disappear into itself and becomes a black hole.

 

Average-mass stars like the sun age more gracefully. They cool slowly over the billion or so years of the red giant stage. After a while, their outer layers become unstable and begin to disperse. What’s left shrinks and turns into a white dwarf, which is a star about the mass of the sun shrunken to about the size of the Earth. The remains of its life in the mainstream star sequence are densely packed, and stay hot but give off little in the way of energy. Over a few billion years the heat generated in their density radiates away, and eventually the white dwarf cools and fades into the night sky as a lonely chunk called a black dwarf.

In those last few billions of years before it cools and winks out, a white dwarf’s inner material can fuse into carbon and crystallize into diamond, which is apparently what happened to BPM 37093.

The vast majority of stars, like people, burn out and fade away into the heavens. It’s the natural process of life. Some stars are so large and powerful in their time that even after they’ve vanished from the visible world into a black hole of otherworld space-time, the invisible remains can serve as the central axis of a whole galaxy of living stars. And then there are stars that in their old age retire from their bright heydays as the centers of solar systems or — who knows? — points in constellations seen from faraway planets. They turn inward to their white-dwarf cores as if, now that the outer layers are shed, hardening and polishing what’s left into 10 billion trillion trillion carat diamonds.

There is a lot to be learned from these stars. There are not very many of them among the hundreds of billions in our galaxy, so you have to know what signs to look for, like the astronomers who identified BPM 37093. But what crystals they hold, if only you can understand them.

Watch for Dana Wilde’s collection of Amateur Naturalist writings, “The Other End of the Driveway,” available in June at www.booklocker.com.

 

naturalist@dwildepress.net

http://bangordailynews.com/2011/05/21/living/how-might-a-star-become-a-diamond/ printed on July 29, 2014