What are 3 characteristics of main sequence stars?

Answer 1

Main Sequence stars are an average size, and as the surface temperatures of the star increase, the luminosity increases. The luminosity increases from red to blue-white is mostly related to an increase in star size and the resulting higher temperatures.

Answer 2

A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas and plasma ejected during the asymptotic giant branch phase of certain types of stars late in their life.[1] This name originated with their first discovery in the 18th[2] century because of their similarity in appearance to giant planets when viewed through small optical telescopes, and is otherwise unrelated to the planets of the solar system.[3] They are a relatively short-lived phenomenon, lasting a few tens of thousands of years, compared to a typical stellar lifetime of several billion years.

At the end of the star's life, during the red giant phase, the outer layers of the star are expelled via pulsations and strong stellar winds. Without these opaque layers, the hot, luminous core emits ultraviolet radiation that ionizes[1] the ejected outer layers of the star. This energized shell radiates as a planetary nebula.

Planetary nebulae play a crucial role in the chemical evolution of the galaxy, returning material to the interstellar medium that has been enriched in heavy elements and other products of nucleosynthesis (such as carbon, nitrogen, oxygen and calcium). In more distant galaxies, planetary nebulae may be the only objects that can be resolved to yield useful information about chemical abundances.

In recent years, Hubble Space Telescope images have revealed many planetary nebulae to have extremely complex and varied morphologies. About a fifth are roughly spherical, but the majority are not spherically symmetric. The mechanisms which produce such a wide variety of shapes and features are not yet well understood, but binary central stars, stellar winds and magnetic fields may all play a role.

Planetary nebulae are generally faint objects, and none is visible to the naked eye. The first planetary nebula discovered was the Dumbbell Nebula in the constellation of Vulpecula, observed by Charles Messier in 1764 and listed as M27 in his catalogue of nebulous objects.[4] To early observers with low-resolution telescopes, M27 and subsequently discovered planetary nebulae somewhat resembled the giant planets like Uranus, and William Herschel, discoverer of this planet, eventually coined[4] the term 'planetary nebula' for them, although, as we now know, they are very different from planets.[5]NGC 7293, The Helix Nebula

Credit: NASA, ESA, and C.R. O'Dell (Vanderbilt University)

The nature of planetary nebulae was unknown until the first spectroscopic observations were made in the mid-19th century. William Huggins was one of the earliest astronomers to study the optical spectra of astronomical objects, using a prism to disperse their light.[5] On August 29, 1864, Huggins was the first to take the spectrum of a planetary nebula when he analyzed NGC 6543.[4] His observations of stars showed that their spectra consisted of a continuum with many dark lines superimposed on them, and he later found that many nebulous objects such as the Andromeda Nebula (as it was then known) had spectra which were quite similar to this-these nebulae were later shown to be galaxies.

However, when he looked at the Cat's Eye Nebula, he found a very different spectrum. Rather than a strong continuum with absorption lines superimposed, the Cat's Eye Nebula and other similar objects showed only a small number of emission lines.[5] The brightest of these was at a wavelength of 500.7 nanometres, which did not correspond with a line of any known element.[6] At first it was hypothesized that the line might be due to an unknown element, which was named nebulium-a similar idea had led to the discovery of helium through analysis of the Sun's spectrum in 1868.[4]NGC 2392, The Eskimo Nebula

Credit: NASA, ESA, Andrew Fruchter (STScI), and the ERO team (STScI + ST-ECF)

While helium was isolated on earth soon after its discovery in the spectrum of the sun, nebulium was not. In the early 20th century Henry Norris Russell proposed that rather than being a new element, the line at 500.7 nm was due to a familiar element in unfamiliar conditions.[4]

Physicists showed in the 1920s that in gas at extremely low densities, electrons can populate excited metastable energy levels in atoms and ions which at higher densities are rapidly de-excited by collisions.[7] Electron transitions from these levels in nitrogen and oxygen ions (O2+ or OIII, O+ and N+) give rise to the 500.7 nm line and other lines.[4] These spectral lines, which can only be seen in very low density gases, are called forbidden lines. Spectroscopic observations thus showed that nebulae were made of extremely rarefied gas.[8]

The central stars of planetary nebulae are very hot.[1] Only once a star has exhausted all its nuclear fuel can it collapse to such a small size, and so planetary nebulae came to be understood as a final stage of stellar evolution. Spectroscopic observations show that all planetary nebulae are expanding. This led to the idea that planetary nebulae were caused by a star's outer layers being thrown into space at the end of its life.[4]

Towards the end of the 20th century, technological improvements helped to further the study of planetary nebulae.[2] Space telescopes allowed astronomers to study light emitted beyond the visible spectrum which is not detectable from ground-based observatories (because only radio waves and visible light penetrate the Earth's atmosphere). Infrared and ultraviolet studies of planetary nebulae allowed much more accurate determinations of nebular temperatures, densities and abundances.[9][10] Charge-coupled device technology allowed much fainter spectral lines to be measured accurately than had previously been possible. The Hubble Space Telescope also showed that while many nebulae appear to have simple and regular structures from the ground, the very high optical resolution achievable by a telescope above the Earth's atmosphere reveals extremely complex morphologies.[11][12]

Under the Morgan-Keenan spectral classification scheme, planetary nebulae are classified as Type-P, although this notation is seldom used in practice.[13]

Origins

Answer 3

1. Main sequence stars are the most common type of star.
2. They fuse hydrogen and helium in their cores.
3. They show a strong relationship between color, temperature, luminosity, and mass.

Answer 4

1. Extremely low temperature. ( -1,000,000,000,000 C and below)

2. Collapse and for a black hole.

3. Combine another stars to make a new stars.

Answer 5

Whats elements are they composed of and what elements they are "burning" and at which part of their life they are at.