Novas

Neutron stars are the remnants of massive stars that have gone supernova. While they are no longer actively undergoing nuclear fusion like main sequence stars, they are not truly "dead" as they continue to emit radiation and have incredibly strong gravitational fields.

The explosion of a supernova. Some astrophysicists don't believe that even THAT would suffice to make some of the very heavy elements such as gold or uranium; they believe that only the collision of two neutron stars would release enough energy to do that.

The problem is the "packing fraction" curve. Two atomic nuclei can smash into each other at high energy and release a little bit of energy as the nuclei come together, or "fuse". When two or more hydrogen atoms smash into each other in the cores of stars, they fuse into helium, and we call this "nuclear fusion".

As we smash heavier and heavier elements together, they release smaller and smaller amounts of energy in fusing - until we get to iron. Once you start fusing elements together to get stuff heavier than iron, you have to PROVIDE energy to complete the reaction. Think of the packing fraction curve as a valley, with iron at the bottom of the valley. As you roll your bike down the hill from one side, you can coast because gravity is providing energy. Once you pass iron (at the bottom of the hill) you need to start putting in your OWN energy, by pedaling.

Yes, supernova explosions that occur in a star cluster can happen during the first 100 million years of the universe's existence. Supernovae play a key role in the evolution of star clusters and galaxies, shaping the cosmic landscape in the early universe. The explosions can trigger further star formation and affect the chemical makeup of the surrounding environment.

As a white dwarf cools, its radius will not change significantly because the pressure created by the electrons in its core prevents gravitational collapse. The pressure supports the white dwarf against further compression, maintaining its size even as it cools and emits radiation.

A black dwarf stage is a theoretical phase that is projected to last for an extremely long time, possibly longer than the current age of the Universe. It is the final stage in the evolution of a white dwarf star, where it cools down to become a cold, dark object with no nuclear fusion activity. The exact duration of this stage is uncertain due to the vast timescales involved, but it is thought to extend for trillions or even quadrillions of years.

"Beetlejuice" is a common nickname for Betelgeuse, a red supergiant star in the constellation of Orion.

There are no known explosive objects within our solar system. Explosions in space are typically associated with events like supernovae in distant galaxies, rather than occurring within our own solar system.

Some stars explode as supernovae when they run out of the hydrogen which they depend on to stay hot. Another way is due to binaries - when a particularly large star, e.g. a red giant, attracts a smaller star due to gravitational pull, and they orbit each other. The star cannot bear the heat and explodes in a massive amount of heat and light - that is how novae happen. A supernova has a much larger effect than a mere nova, and they happen when the star collapses due to reduction of fuel before the spontaneous explosion, and thus causing it to be much larger and brighter.

Because for a star to fuse elements heavy elements (iron and heavier) it would actually consume energy rather than liberate it. That doesn't work well to keep the star "alive." The explosion of the supernova itself can create these heavier elements because of the heat of the blast.

Probably both; at the end of its life, a very massive star like Rigel or Betelgeuse will experience a titanic explosion that will crush the core of the star into a black hole, while blasting the outer layers of the star into space. The supernova will shine for several months, and fade into obscurity, but the black hole will probably exist forever.

At least, if our mathematical theories concerning black holes is correct, which is always open to debate. It is at least remotely possible that everything we think we know about black holes will turn out to be incorrect, and that we will have to refine our theories on the basis of new discoveries as we venture forth into the universe.

No, the sun is not a nova. The sun, being roughly 5 billion years old, is what is known as a main sequence star. This is the stable stage of a star's life, where hydrostatic equalibrium is maintained (radiation pressure pushing out balances gravity pulling in). Novae occurs at the end of a star's life, and can come in several different forms (depending on the size of the star in question, whether it is a multiple star system, etc). The sun, with our current understanding of astrophysics, is unlikely to go nova (or supernova), but will die as a white dwarf that casts off its outer atmosphere in what's known as a planetary nebula.

In 5 billion years time, our Sun will turn into a white dwarf.

That depends exactly how you interpret the term "strong". In its vicinity, the black hole distorts space more than anything that is NOT a black hole; so much that nothing can get out of the black hole. But at some standard distance, a galaxy, for example, would have more gravitational attraction than a black hole, simply because it has more mass. At least, so far no black hole of the mass of an entire galaxy has been found.

That depends exactly how you interpret the term "strong". In its vicinity, the black hole distorts space more than anything that is NOT a black hole; so much that nothing can get out of the black hole. But at some standard distance, a galaxy, for example, would have more gravitational attraction than a black hole, simply because it has more mass. At least, so far no black hole of the mass of an entire galaxy has been found.

That depends exactly how you interpret the term "strong". In its vicinity, the black hole distorts space more than anything that is NOT a black hole; so much that nothing can get out of the black hole. But at some standard distance, a galaxy, for example, would have more gravitational attraction than a black hole, simply because it has more mass. At least, so far no black hole of the mass of an entire galaxy has been found.

That depends exactly how you interpret the term "strong". In its vicinity, the black hole distorts space more than anything that is NOT a black hole; so much that nothing can get out of the black hole. But at some standard distance, a galaxy, for example, would have more gravitational attraction than a black hole, simply because it has more mass. At least, so far no black hole of the mass of an entire galaxy has been found.

Our Sun is not massive enough to end in a supernova explosion. When it nears the end of its life, it will shed its outer layers as a planetary nebula and eventually collapse into a white dwarf. Supernova explosions typically occur in massive stars that have exhausted their nuclear fuel and undergo a catastrophic collapse.

Actually before the rise of visible light there is a surge in neutrinos that can give a warning of a super-nova by as much as five days.

Then comes the light flash in all forms of electromagnetic radiation (including visible light).

Many people were involved in the current spectral classes.

The person who first realised that the spectral sequence then categorised was in fact temperature, was Cecilia Payne.

See related link for more information on her.

Stars explode into supernovae, which can leave behind remnants like neutron stars or black holes. During the explosion, elements heavier than iron are forged through nucleosynthesis and dispersed into space, enriching the interstellar medium with these elements.

Hydrogen and helium are primarily formed inside stars through nuclear fusion processes. As stars age and go through various stages of stellar evolution, they can also produce heavier elements such as carbon, oxygen, and iron through fusion reactions in their cores.

Yes, due to the extreme density of matter within a white dwarf star, a teaspoon of material can indeed have a mass equivalent to several tons. This is a result of the immense gravitational forces present in white dwarfs, causing matter to be densely packed.

Generally, no. The lighter elements are made by nuclear fusion in the cores of stars. The heavier elements are made in the supernova explosions that take place at the end of a large star's life cycle.

Polaris A is a white supergiant.

There are records of visual observations dating back as far as 185 CE. Since observation technology has increased, more and more stellar remnants are observed

In 2008 an actual supernova explosion was caught on camera.

Supernova only occur about once every fifty years, so they are not that common.

See link for more information.

D. white dwarfs. Most stars in the Milky Way, including our Sun, will eventually end their lives as white dwarfs. This occurs after the star has exhausted its nuclear fuel and shed its outer layers.