Around 4.5 billion years ago, our Sun and all the other bodies that object around it were born from an enormous cloud of interstellar gas and dust, similar to the glowing emission nebulae we see scattered across today’s night sky. Astronomers have understood this basic picture as the birth of the Solar System for a long time, but the details of how the process happened have only become clear much more recently – and now, new theories, discoveries and computer models are showing that the story is still far from complete. Today, it seems that not only did the planets form in a far more sudden and dynamic way than previously suspected, but also that the young solar system was rather different from that we know now.

Much of what we know about the birth of our solar system comes from observing other star systems. The so- called ‘nebular hypothesis- the idea that our solar system arose from a collapsing cloud of gas and dust has a long history.As early as 1734, Swedish philosopher named Emanuel Swedenborg suggested that the planets are born from clouds of material ejected by the Sun while the 1775 German thinker Immanuel Kant suggested that both the Sun and planets formed alongside each other from a more extensive cloud collapsing under its own gravity. In 1796, French mathematician Pierre- Simon Laplace produced a more detailed version of the Solar System formed from an initially shapeless cloud. Collisions within the cloud caused it to flatten out into a spinning disc, while the concentration of mass towards the centre caused it to spin faster.

In broad strokes described above, Laplace’s model is now known to be more or less correct, but he certainly got some details wrong, and left some crucial questions unanswered- just how and why did the planets arise from the nebula? And why didn’t the sun, concentrating more than 99 per cent of the Solar system’s mass at the very centre of the system, spin much faster than it does? Solutions to these problems wouldn’t come until the late 20th Century, and some of them are still causing doubts even today.

Stars are born in and around huge glowing clouds of gas and dust, tens of light years across, called emission nebulae (well known examples include Orion Nebulae, the Lagoon Nebulae in Sagittarius, etc). The nebulae glow in a similar way to a neon lamp, energized by radiation from the hottest, brightest and most massive stars within them and remains active for perhaps a few million years, during which time they may give rise to hundreds of stars forming a loose cluster. Since the brilliant, massive stars age and die rapidly, it’s only the more sedate and lower mass stars like our own Sun that outlive both the nebula and show disintegration of the star cluster.

Star birth nebulae develop from the vast amounts of normally unseen, dark gas and dust that forms the skeleton of our Milky Way Galaxy, and subside as the fierce radiation from their most massive stars literally blow them apart. The initial collapse that kick- starts formation can be triggered in several ways- for instance by a shockwave from a nearby exploding supernova, or by tides raised during close encounters with other stars. However, the biggest waves of star birth are triggered when materials orbiting in our galaxy have flattened outer disc drift through a spiral shaped region of compression that extends from the galactic hub and gave rise to our galaxy’s characteristic shape.

Thus, our solar system grew from the various theories provided by many theoretical astronomers. The exact reason of the birth of our Solar System is unknown. New theories turn old theories and newer theories turn new theories. No exact reason behind the formation is known till date.

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