When late night sets in, countless flickering beacons appear in the dark sky. Those stars were “looking” at Earth top-down millions of years ago. Today we will describe how these cosmic “fireflies” are born.
A star is a huge ball that consists mainly of hydrogen and helium. It is formed in a gas-dust environment under the influence of gravitational forces.
Converting a molecular cloud into a celestial body requires suitable conditions and time.
It begins when the cloud, consisting mainly of interstellar gas and dust, becomes compressed and compacted by its own gravity. Such zones look like dark spots against a bright background that are easy to observe through optical telescopes. They are also called “giant complexes of molecular clouds” because the hydrogen they are made of occurs in molecular form. Those systems, along with spherical star clusters, are the largest structures in the galaxy. Their diameter sometimes reaches 1,300 light years.It is compression and compaction that leads to the formation of stars.
Younger stars are referred to as Population I. They appeared in the sky later than their predecessors, Population II stars. To be more precise, they were assembled from the remnants that arose after the flashes provoking a shock wave. The wave reaches a part of the nearest nebula that then shrinks. In parallel, another process takes place – the formation of Bok globules, rounded dense dark gas-dust clouds.
Who is Bok?
Bart Jan Bok (1906-1983) was an American astronomer who investigated the structure, dynamics, and evolution of the Galaxy. In his works he obtained estimates of the age of star clusters and studied the spatial distribution of stars. Together with E.F. Reilly Bok discovered strange dark nebulae in 1947. They had a rounded shape, strongly absorbed light and could only be seen against the background of bright diffuse nebulae. They were named globules.
Globule parameters:
size: from 10,000 AU up to 1-2 light years,
mass: 0.001 to 0.1 masses of the Sun.
A Bok globule acts like a sponge as it absorbs matter from neighboring areas by its gravity. The mass is getting larger and larger. The inside of the globule thickens faster than the outside, so the globule begins to warm up and rotate. After several hundred thousand years during which compression occurs, a proto-star is formed. But that’s still not the end.
Thanks to the same gravitational forces, the proto-star becomes like a ball surrounded by a dense gas-dust cloud. It occludes the view so it is completely impossible to see a proto-star even with the most powerful instruments.
It is important to say that the evolution of the proto-star is closely related to its mass: the heavier it is, the hotter it will be inside. Its mass increases further during the compression process. And then thermonuclear reactions begin, and hydrogen gets converted into helium.
At that point, equilibrium is established in the core of the body, and gravitational collapse stops. A star is born.
Events can still continue into a sort of magical star formation. The shock wave reaches a nebula and provokes the formation of new matter. This process is triggered by gas-dust clouds.
Construction Material
For a new star to shine in the night sky, hydrogen is necessary – the simplest of all existing molecules which consists of two atoms, and those in turn, comprise a nucleus with a single proton orbited by an electron in a quantum cloud.
The other component is deuterium featuring an extra neutron – an elementary particle without electric charge – in its nucleus.
Hydrogen is a substance that was one of the first to form after the Big Bang. Matter heated to incredible temperatures in the form of protons, neutrons, electrons and other elementary particles began to condense, and then hydrogen appeared.
A simulation of star formation
Scientists from the Royal Astronomical Society have created a simulation that takes into account the whole complex of physical phenomena that affect star formation.
“We appear to kind of know the basic history of star formation… but the devil is in the detail. If you really want to get the full picture, you just need to simulate it all,” says Mike Grudich, a theoretical astrophysicist at the Northwestern University in Evanston, Illinois.
The researchers simulated a huge cloud of cosmic gas – approximately 20 parsecs or 65 light years in cross-section – which collapses to form new stars. White areas indicate areas of denser gas, including young stars.
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