Stellar Evolution

They are called "sunspots".

They are areas where concentrated tangled magnetic flux lines exit through the photosphere of the sun (locally cooling it, resulting in the dark appearance), propelling solar plasma outward as coronal loops (prominences), solar flares, and coronal mass ejections. Sunspots always occur in pairs, one being a "north" magnetic pole and the other a "south" magnetic pole.

Scientist believe that stellar evolution contained only hydrogen and then helium.

Beta Herculis is actually a binary system. The main star, of the two, is yellow.

No.

They're mainly burning gasses, just like our sun.

The first stage of stellar evolution is nebula.

Since white dwarves concentrate a large part of the mass of the original star into a much smaller volume, the conservation of angular momentum should demand that they spin much faster than the original star did. However, observations of the surface layers of white dwarves show that they typically spin much slower. It is not known at this time whether it's just the surface spinning slowly, while the interior rotates more rapidly, or if the star has somehow managed to shed angular momentum during its evolution.

Sound travels through air. Between the Earth and any star, there are long stretches of distances with hardly any particles--not nearly enough to carry sound.

The stars with an A-type spectrum are the hottest common stars, but early-stage stars with a B-type spectrum are even hotter.

The order of temperature is B-A-F-G-K-M for common stars. The M-type stars are the coolest common stars and they definitely look red, e.g. Antares, Betelgeuse.

Remember the order by learning this: Be A Fine Girl, Kiss Me!

Stars are often born in nebulae composed of interstellar gases called stellar nurseries.

Star of one stellar mass, red giant, white dwarf, planetary nebula

Mostly lighter elements, such as hydrogen (one proton) and helium (two protons). The helium found in young stars comes from nuclear fusion reactions where 2 hydrogens fuse to make a helium atom.

I don't know, but I need an answer!

Scientists calculated indirectly the mass of a black hole by the behavior of matter around it, from which its gravitational pull can be determined, and with an accurate measure of its distance, its mass can then be inferred. In some cases an upper limit can be calculated by the closest approach of a visible object observed near it; in this case, its size is a result of a direct relation to its mass since the radius of the event horizon is directly proportional to the black hole's mass.

we cant see lower mass stars because were blind.... :)

Stars like the Sun are not massive enough to become a black hole. Instead, in several billion years, the Sun will form a white dwarf. Black holes can be formed if the remaining core of a star after it had gone supernova is very massive (more than 2.5 times the mass of the Sun).

It isn't; heavier elements can be, and are, produced by DYING stars.

The reason is the "packing fraction curve". As atomic nuclei would fuse together within the cores of normal stars, hydrogen atoms as "fuel" would fuse into helium "ash"; when the star became old, the core of the stars would heat up and become more dense as the star began to collapse into itself. The denser stellar core material would heat up and begin to fuse into heavier elements; carbon, oxygen, and heavier elements, releasing a little energy every time a new atom was formed by fusing together lighter ones - UNTIL they got to iron.

Once you get to iron, any additional fusion sucks energy OUT of the star's core, and every fusion from there on sucks even MORE energy out of the star, leading to the star's quick collapse. This is one scenario for how a "nova" might occur.

If a star EXPLODES in a supernova, then there's LOTS of energy to crash even heavy elements together into even HEAVIER elements. So all of the gold, uranium, lead, and every atom heavier than iron, was formed in a supernova explosion.

Here is an answer based on a typical star like our Sun. It's slightly simplified.

If you need more detail Wikipedia's "Stellar Evolution" is useful, but a bit complicated.

An easier introduction is given by NASA in the "Sources and related links" below. Just click on that link if you wish.

All stars will eventually exhaust their supply of hydrogen, the main fuel of every star in the universe (and most abundant element in the universe). The main process of fusion that powers all stars converts hydrogen into the heavier element helium (see "fusion" for more details).

For a star with the mass of our Sun, each second millions of tons of hydrogen (600 million) are converted to helium, slowly depleting the remaining hydrogen (our Sun started with about 11-13 billion years of hydrogen "fuel").

When the hydrogen supply runs low, the Sun will expand, reaching the "red giant" stage of its life.

Eventually the core will become hot enough to fuse helium. The process of fusion will then continue with the helium, along with some remaining hydrogen.

The helium will be converted to carbon, continuing to power the star.

A quite complicated situation arises with hydrogen and helium "burning" at different levels in the star.

Fusion stops after producing oxygen nuclei, because the Sun's temperatures will not be high enough to produce heavier elements.

As the last fuel is exhausted, the star's outer layers will be expelled by the imbalance in pressure from fusion versus the gravity holding the star together. As these outer layers are expelled, the core of carbon and oxygen nuclei will be the remnant, a white dwarf star.

In the beginning there will be a super hot white dwarf emitting light until it cools down and no longer emits light and becomes a black dwarf.

High mass stars, after going supernova, become neutron stars or become black holes, if they're massive enough.

You cannot determine the age of a star based on it's luminosity or spectral class.

However, you can make *assumptions*.

OB and A stars are massive and will have a short lifespan in the millions of years.
FG and K stars have a longer life period - in the billions of years.
KMWLY and T stars are stars those that cause problems.

Most stars in this class are red dwarfs, stars that are so low in mass that they have a low rate of nuclear fusion and last for tens of billions of years.

In general - and I mean in general - a redder shift, should indicate an older star but you cannot use the HR- Diagram to determine this.

To say that black holes have infinite gravity is somewhat misleading. Theoretically, the strength of gravity at the singularity is infinite, but it diminishes with distance. While technically there is some gravitational attraction, even across light years of space, the effect is tiny at such distances.

That is not known exactly, since even at such a relatively short distance, many red dwarves will go undetected. You can check the Wikipedia article "List of nearest stars and brown dwarfs" for known stars up to a distance of about 16 light-years, and extrapolate. That is, just assume that a larger volume has proportionally more stars. Note that due to the difficulty of detecting red dwarves, this should give you a MORE RELIABLE figure than actually counting all the known stars up to a distance of 50 light-years (since it is likely that up to a distance of 16 light-years, the detection rate for red dwarves is higher). As a reminder, the volume of a sphere is proportional to the cube of its radius. That is, a sphere of 50 light-years has approximately 29 times as much volume as one of radius 16.3 light-years, so you would expect it to have approximately 29 times as many stars.

You would see very little, unless you could stand very still for some 434 years - that's the time light takes to travel from Polaris to Sol.

The supermassive black hole at the center of our Milky Way galaxy may not have a formal name yet, but takes its identification from a powerful radio source "Sagittarius A*" (where the asterisk is part of the name). Because of the discovery of this energy source it's commonly believed a black hole must be located there, powering the emissions perhaps because of the black hole's accretion disk or relativistic jets.

The least massive stars, i.e., the red dwarves. More massive stars get more pressure and temperature, and therefore burn their fuel up faster. For comparison, while a red dwarf might shine for trillions of years, the most massive stars run out of fuel after just a few millions of years.