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Fewer New Stars

February 26, 2015

One of the busiest stellar nurseries in the galaxy stands about half way up the southern sky at nightfall right now. The Orion Nebula has given birth to thousands of stars, with many more taking shape even now.

As the universe has aged, sights like the Orion Nebula have become less common — far fewer stars are born today than when the universe was young.

In fact, the rate at which new stars are born reached its peak billions of years ago, and has been dropping ever since. According to a study published a couple of years ago, the universe is giving birth to only one-thirtieth as many stars today as it did about 11 billion years ago. In fact, the study says that 95 percent of all the stars that will ever be born have already taken shape.

In part, the drop in the stellar birth rate is because much of the original supply of gas for making stars has been used up. The universe is also bigger now, so the gas for making new stars is more spread out. And hot gas around giant black holes creates radiation that may shut down the process of starbirth in many galaxies. Yet these ideas can’t fully account for the dramatic drop in starbirth — leaving astronomers to ponder why so few stars are born today.

Stars are still being born in the Orion Nebula, though. Look for it below the three stars of Orion’s Belt. Under dark skies, the nebula looks like a large but fuzzy star — a massive stellar nursery less than 1400 light-years away.


Script by Damond Benningfield, Copyright 2014

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