Reference terms from Wikipedia, the free encyclopedia

Stellar evolution

Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the age of the universe. The table shows the lifetimes of stars as a function of their masses. All stars are formed from collapsing clouds of gas and dust, often called nebulae or molecular clouds. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star.

Nuclear fusion powers a star for most of its existence. Initially the energy is generated by the fusion of hydrogen atoms at the core of the main-sequence star. Later, as the preponderance of atoms at the core becomes helium, stars like the Sun begin to fuse hydrogen along a spherical shell surrounding the core. This process causes the star to gradually grow in size, passing through the subgiant stage until it reaches the red-giant phase. Stars with at least half the mass of the Sun can also begin to generate energy through the fusion of helium at their core, whereas more-massive stars can fuse heavier elements along a series of concentric shells. Once a star like the Sun has exhausted its nuclear fuel, its core collapses into a dense white dwarf and the outer layers are expelled as a planetary nebula. Stars with around ten or more times the mass of the Sun can explode in a supernova as their inert iron cores collapse into an extremely dense neutron star or black hole. Although the universe is not old enough for any of the smallest red dwarfs to have reached the end of their existence, stellar models suggest they will slowly become brighter and hotter before running out of hydrogen fuel and becoming low-mass white dwarfs.

Stellar evolution is not studied by observing the life of a single star, as most stellar changes occur too slowly to be detected, even over many centuries. Instead, astrophysicists come to understand how stars evolve by observing numerous stars at various points in their lifetime, and by simulating stellar structure using computer models.

Note:   The above text is excerpted from the Wikipedia article Stellar evolution, which has been released under the GNU Free Documentation License.

Check out these latest Nanowerk Astronomy & Space News:


How do supermassive black holes get super massive?

Combined X-ray surveys and supercomputer simulations track 12 billion years of cosmic black-hole growth.

Wind from black holes may influence development of surrounding galaxies

The discovery helps illuminate the way active black holes can continuously shape their galaxies by spurring on or snuffing out the development of new stars.

Galactic bloodlines: Many nearby star clusters originate from only three 'families'

Supernova explosions from the formation history of these families also left traces on Earth.

Webb telescope reveals asteroid collision in neighboring star system

Astronomers have captured what appears to be a snapshot of a massive collision of giant asteroids in Beta Pictoris, a neighboring star system known for its early age and tumultuous planet-forming activity.

A Martian dawn reveals a view of the red planet's frosty, volcanic dew

Scientists have detected morning frost on some of the oldest and tallest volcanoes in the Solar System, on Mars, and estimate that up to 150,000 tonnes of ice could form on them.

The solar system may have passed through dense interstellar clouds 2 million years ago, altering Earth's climate

Astrophysicists calculate the likelihood that Earth was exposed to cold, harsh interstellar clouds, a phenomenon not previously considered in geologic climate models.

Exotic black holes could be a byproduct of dark matter

In the first quintillionth of a second, the universe may have sprouted microscopic black holes with enormous amounts of nuclear charge, physicists propose.

Planet-forming disks around very low-mass stars are different

JWST discovers a large variety of carbon-rich gases that serve as ingredients for future planets around a very low-mass star.

Earliest detection of metal challenges what we know about the first galaxies

Astronomers have detected carbon in a galaxy just 350 million years after the Big Bang, the earliest detection of any element in the universe other than hydrogen.

Researchers upend theory about the formation of the Milky Way Galaxy

New findings suggest that our galaxy's last major collision was billions of years later than previously thought.

Check out more of the latest Astronomy & Space News here.