Remains of Dead Star Systems Teach About Earth's Future

Scientists from the University of Cambridge say they've examined two dead star systems that offer a glimpse of what Earth's own solar system may look like, say, in a few billion years.

It's then, they suspect, when the sun will expand outwards as its nuclear fuel is nearly spent and blows off its external layers. Some of the closer planets will be devoured by the process while asteroids will be pushed out of their orbits.

The work was recently published in the Monthly Notices of the Royal Astronomical Society.

The new analysis has also offered researchers new ideas about where planets might be found in the earth's own Milky Way Galaxy.

The pair of dead stars in question are located amid the Hyades cluster, in the Constellation Taurus, approximately 150 light-years from Earth.

The two are so-called white dwarfs, burned-out cores of average-sized stars similar to the sun.

Using the Hubble Space Telescope's powerful Cosmic Origins Spectrograph to examine the chemical remains of the dwarfs, the university team found the burnt-out solar systems abundant with silicon, the same element found in the rocky material that makes up the earth, the other inner planets in our solar system and its asteroids.

"Stuff must be falling on to [each] star at a very high rate," Dr. Jay Farihi of Cambridge's Institute of Astronomy, told BBC News.

"We can calculate the number of grams per second. That turns out to be something like a small river's worth of material," he said. "Based on the whole phenomenon of polluted white dwarfs and what we've learnt in the last few years, we know that there's a disc of material that must be feeding the star's atmosphere with this silicon-rich material."

That disc of material, he added, had to have originated from "some disrupted, torn-apart planetesimal."

Computer models show as aging stars throw off their outer layers and lose mass, they destabilize the environments around them.

Clusters like Hyades are where many stars are born and live relatively close by to each other. But very few planets have yet been detected there.

Of the estimated 800 planets catalogued beyond our solar system, only four are known to orbit stars clustered with other stars, maybe because such areas are very energetic, therefore making it difficult to pinpoint other planets with current observation techniques.

The latest research nevertheless stars in clusters almost certainly do have planets.

"The body responsible for [the silicon materials] we see must have been an asteroid about 50-100km in size," Farihi explained. "Asteroids or big rocks are really the building blocks of planets, so the fact that we're seeing giant rocks at these stars means that terrestrial planets were built during the stars' energy-producing lifetime.

The question is "whether they retain those planets to this day," he said. "I would venture to say 'yes,' because we need large planets to push these rocks around so that they can get close to the star and pollute its atmosphere."