The Universe is passing through the stelliferous era --its peak of star formation--but appears to be still peaking in its formation of planets, according to Dimitar Sasselov, Professor of Astronomy at Harvard University and director of the Harvard Origins of Life Initiative. There are more stars in the Universe than there are grains of sand on Earth and there are an equal number of planets.
There are 200 billion stars in the Milky Way and 90% are small enough and old enough to have planets in orbit. And only 10% of these stars were formed with enough heavy elements to have Earth-like planets with 2% of these --or 100 million super-Earths and Earths-- will orbit within their star's habitable zone.
Differing from Sasselov, an important study by an international team of astronomers has established that the rate of formation of new stars in the Universe is now only 1/30th of its peak and that this decline is only set to continue.
The accepted model for the evolution of the Universe predicts that stars began to form about 13.4 billion years ago, or around three hundred million years after the Big Bang. Many of these first stars are thought to have been monsters by today's standards, and were probably hundreds of times more massive than our Sun. Such beasts aged very quickly, exhausted their fuel, and exploded as supernovae within a million years or so. Lower mass stars in contrast have much longer lives and last for billions of years. Much of the dust and gas from stellar explosions was (and is still) recycled to form newer and newer generations of stars.
Our Sun, for example, is thought to be a third generation star, and has a very typical mass by today's standards. But regardless of their mass and properties, stars are key ingredients of galaxies like our own Milky Way. Unveiling the history of star formation across cosmic time is fundamental to understanding how galaxies form and evolve. Enlarge This diagram indicates the changing ‘GDP’ of the Universe over time.
The results, reported by a team led by David Sobral of the University of Leiden in the Netherlands, are published in the journal Monthly Notices of the Royal Astronomical Society. Their findings indicate that, measured by mass, the production rate of stars has dropped by 97% since its peak 11 billion years ago.