Question

What happens after a nebula contracts and its temperature increases to 10 million \(K\) ? A) a black hole forms B) a supernova occurs C) fusion begins D) a white dwarf forms

Short answer

C) Fusion begins.

Step-by-step solution

Understanding the Nebula

A nebula is a vast cloud of dust and gas in space. It is the starting point for star formation. As gravity pulls the particles together, the nebula begins to contract.

Gravitational Contraction and Temperature Increase

As the nebula contracts, the particles collide more frequently, transforming kinetic energy into thermal energy. This process leads to a significant increase in the temperature of the core of the nebula.

Reaching Critical Temperature for Fusion

When the core temperature of the contracting nebula reaches around 10 million Kelvin (\(10^7 K\)), it becomes hot enough for nuclear fusion to commence.

Starting Nuclear Fusion

At this point, hydrogen nuclei in the core start fusing to form helium nuclei. This process releases a vast amount of energy and marks the birth of a new star. Fusion is a critical step in star formation.

Key concepts

Nebula Contraction

A nebula is a majestic and gigantic collection of gas and dust sprawled across space. Often serving as the cradle of star formation, a nebula is a cosmic nursery teeming with potential.
As time passes, the gravitational forces acting within the nebula start to shape its future, drawing the particles inward. This contracting process, known as nebula contraction, is a monumental step towards star birth.
Gravity plays a leading role here, continually pulling particles closer together, pushing them to squeeze into a smaller volume, and setting the stage for what's to come next.

Star Formation

The transformation from a nebula to a star is a fascinating process filled with physical and chemical marvels. As the nebula contracts, it gives birth to various stages of star evolution, culminating in the star’s formation.
As the particles of gas and dust draw closer, the ever-increasing pressure and heat mark the early phases of a star’s lifecycle. Eventually, the pressure generated by the gravitational forces becomes sufficient to initiate nuclear reactions.
These nuclear reactions serve as crucial elements in the star formation process. It's at this point, with the heat of a newborn sun, that a star officially forms, blazing with the light of life in the universe.

Gravitational Contraction

Gravitational contraction is a key player in the orchestration of star creation, heralding a cascade of changes within the contracting nebula. As the particles are coaxed closer together by gravity, each collision turns kinetic energy into thermal energy.
This continuous build-up of heat is pivotal, causing the nebula to compress further and reach higher temperatures deep within its core.
Over time, the heat becomes substantial enough to create a hot and dense environment, setting the stage for nuclear fusion and a stellar phenomenon.

Critical Temperature for Fusion

At the heart of stellar formation lies a thermal milestone known as the critical temperature for fusion. This is the tipping point where temperatures peak around 10 million Kelvin ( 10^7 K ). Reaching this astronomical temperature is critical in allowing the gaseous nebula to transform into a star.
At this fevered temperature, hydrogen nuclei possess enough kinetic energy to overcome repulsive forces and collide.
The resultant fusion of hydrogen into helium releases an enormous amount of energy, heralding the birth of a star and marking the commencement of nuclear fusion within the core.
This reaction not only gives rise to a shining star but fuels the stellar furnace continuously, supporting the star throughout its lifetime.