Our sun is entering its middle age.
It has been shining in our sky for about 4.5 billion years and is likely to continue for another five billion or so.
Aging changes people and often you wake up one day and realize you are old. Sometimes these changes can be dramatic and sometimes they are subtle.
Like people, stars go through a similar aging process. There has been a recent discovery of a Jupiter-sized planet about 6,500 light years away with the ungainly name of MOA-2010-BLG-477Lb. The exoplanet (one outside our solar system) orbits a star that has reached old age and the planet was lucky to survive the experience. The discovery of this planet gives a preview of what is likely to happen in our own solar system, and the results are not pretty.
To understand what happens, you need to know a bit about the lifecycle of a typical star. How long a star lives and its eventual fate are all decided at its birth. It all depends upon the mass of the star.
Ironically, the larger the star, the shorter its lifespan. This is because larger stars burn hotter and use up their fuel faster than smaller stars.
Let’s look at a star like our sun. Hydrogen starts to clump due to some disturbance in the gas cloud and soon there is enough of the gas to start attracting more gas due to gravity. Eventually, there is enough pressure and heat at the proto-star’s core to start nuclear ignition — and a star is born.
The star will burn bright and hot for billions of years, slowly dimming as it uses up its fuel. When the fuel nears exhaustion, events become interesting.
Depending on its mass, a star could end up as a black hole, a neutron star, a white dwarf, or even a supernova. Our sun will end up as a white dwarf, slowly burning through what is left of its fuel for another few billion years.
Before it settles down into peaceful old age, it will follow the advice of poet Dylan Thomas and “rage, rage against the dying of the light” by puffing up to gigantic size.
This process will engulf the inner planets. Mercury, Venus and even the Earth will be gone. Mars will be scorched and also may disappear. Jupiter and the outer planets will survive.
This is the situation with MOA-2010-BLG-477Lb. Its parent star has gone through all of its fuel, expanded and then settled down as a white dwarf. It is probable that MOA-2010-BLG-477Lb barely survived the star’s death throes and easily could have been a casualty.
It is also suggestive of something else. We have a reasonable idea of how many white dwarf stars there are in the galaxy, but we thought there would only be debris left orbiting the dim star. The discovery of MOA-2010-BLG-477L shows that there may be many planets orbiting unseen, dim white dwarf stars. So., there may be many more planets in the galaxy than we had thought.
It was only in 1992 that we had our first confirmation of planets around other stars. I had thought we might never image them because it would be like trying to image a firefly around a searchlight 20 kilometres away. But special techniques have been developed that have allowed us to prove the existence of these exoplanets. As of last year, we have found 4,843 exoplanets in 3,579 planetary systems with 797 of them having more than one planet.
And the total increases every year. It is an exciting time to be a science enthusiast.
Tim Philp has enjoyed science since he was old enough to read. Having worked in technical fields all his life, he shares his love of science with readers weekly. He can be reached by e-mail at: email@example.com.