Astrophysics

When a red giant runs out of its fuel - helium - it will blow off its outer layers while the inner core collapses to form a white dwarf. The latter will gradually radiate away its energy to become a black dwarf.

No, that is not likely to happen. At some point, a significant part of each galaxy will be absorbed by the supergalactic black hole in the center; but it is impossible that those black holes all come together, considering that most galaxies are moving away from one another.

The main alternatives is to eat in not-so-quick restaurants, or to cook yourself.

Normally not, since there is no surface on which you might stand, where you would feel its gravity. Of course, you can calculate the gravitational acceleration at any point, but the distance to the black hole would have to be specified.

From a position outside the star, such as a planet orbiting it, gravity does not change. It is only within the original radius of the star that there is a noticeable increase in gravity. After the collapse is finished, the gravity at a distance is actually reduced, as the supernova resulting from the collapse blasts away the star's outer layers, reducing the object's overall mass.

The strength of gravity for any object is proportional to the object's mass and inversely proportional to the square of your distance from it. So at a distance, the gravitational pull of a black hole can be no greater than that of the object that collapsed to form it.

For a stellar mass black hole, the gravitationaly pull at most distances is no different than that of a large star. It is only when you get within a few hundred thousand miles of it that the gravitational pull becomes abnormally strong.

A black hole can a few times the mass of our Sun, starting out at perhaps 2-3 times the mass of the Sun. Larger black holes (supermassive black holes, in the center of most larger galaxies) can have masses of millions or even billions of solar masses. There are also intermediate-mass black holes in star clusters, with a few thousand solar masses.

The size and color, at sometime, it will get too old and blow up, like a nova or supernova.

A young star is mostly hydrogen, undergoing nuclear fusion to form helium. As the star gets older, it has steadily more helium. Eventually, when it begins to run out of hydrogen, the helium will undergo fusion to form progressively heavier elements. By looking at the light from the star through a spectroscope, you can see markers that indicate the proportion of different elements, allowing you to estimate the star's age.

In order to protect our delicate human body from the destructive effects of
gamma rays, our tissues must be shielded from the gamma rays, by some kind
of material that absorbs them.

The Earth's atmosphere is a better gamma ray shield than a spacecraft is.
At least it's a better shield than any spacecraft that could be built without
a ridiculous weight, requiring a ridiculous and completely impractical amount
of fuel and money to propel it to anywhere.

There is no special machine that measures that directly. Astronomers have to observe objects known to be close to the black hole (most black holes observed are part of a binary or multiple system, simply because those are easier to detect), and use one of the usual methods used in astronomy to calculate distances.

Researchers determined that the black hole V404 Cygni (Nova Cygni 1989, GS 2023+338) is the closest at approximately 7,800 light-years (or 2400 parsecs) from Earth, in the constellation Cygnus. It is measured to have a diameter of roughly 37-56 miles (60-90 km) and is 10 to 15 times the mass of Earth's Sun.

As you say, in theory, if it were possible.......

This is the heart of the matter. It is not really possible. But as an analogy, if you think of a whirlpool, you can't see or paint that either, what you see and can paint is the effects of the whirlpool on water and things floating or living in the water and their behaviour as they are attracted to and sucked into the whirlpool.

A black hole is a place of infinite gravity where even light cannot escape - so there is nothing to see. But all known and observable black holes have a huge accretion disk where the matter and energy being sucked in speeds up to incredibly high speeds and covers vast areas of space.

The black hole in the centre of our galaxy is not active (feeding) and has no accretion disc but can be observed by the very odd behaviour of the stars around where the black hole is believed to be.

I hope this helps a bit.

It is (kind of) - I believe such anthropomorphic analogies to be misleading and inappropriate; i.e. black holes do not eat. Instead the immense gravitational forces of a black hole tend to attract and compact all matter. And this is currently happening with the black hole at the center of our Milky Way galaxy.

Note: Such misleading imagry presents an inaccurate perspective of cosmological interactions. The misunderstood consideration of matter being engulfed into a hole and deficated as Hawking radiation presents a fictional consideration of natural forces, similar to the deification of nature to identify with mythological deities.

It you define the size of a black hole by the size of its event horizon then yes, the sun is larger than most black holes. The sun has a radius of just under 700,000 kilometers, while a stellar mass black hole would have an event horizon between 8.8 and 44 kilometers. Supermassive black holes are a different matter. The black hole at out galaxy's center, at 3.7 million solar masses, would have a radius of about 10 million kilometers. A black hole of 12 billion solar masses, which likely does exist, would have a radius of 35 billion kilometers, about 5 times wider than the orbit of Pluto.

Yes, the Apollo 8 mission of December 1968 was a success. It had the first manned spacecraft to leave earth orbit, the first manned spacecraft to reach the moon and to orbit another celestial body; enabled the first direct views of the far side of the moon, and generated one of spaceflights most famous photographs, that of earthrise during lunar orbit. It paved the way for remaining missions in the Apollo program including the later lunar landing of Apollo 11. The three crew, Borman, Lovell and Anders, completed mission objectives and returned safely to Earth.

If a rogue black hole were headed towards Earth, astute astronomical observation - such as those scanning for near earth objects, like asteroids - could notice gravitational lensing effects of the black hole due to its ability to bend light; perterbations of orbits of objects in the solar system might be noticed, or possibly electromagnetic emissions such as those around x-ray energies caused by its accretion disk could be detected.

There have been some efforts to statistically predict the probability that a black hole might encounter earth, results indicate the event to be extremely unlikely although not entirely impossible.

There are currently space-born science packages that are searching for this very event - detection of such has not been successful to date but NASA's FGST gamma ray telescope launched in 2008 is looking for what is believed to be the characteristic light flash from them.

To my knowledge there is no college offering Msc Astrophysics in Chennai, but in Kodaikanal, Tamilnadu, Mother Teresa Women`s University.

Probably the most important characteristic of Earth in its support for life is the significant percentage of the surface covered with liquid water. This would not be possible except for Earth's favorable distance from the Sun where water can easily be liquid; and other characteristics like Earth's liquid core and magnetic field strong enough to protect the oceans from being evaporated into space by energetic particles and radiation from the Sun. The tidal effect of the moon is thought to have significant influence also.

The possibility of life elsewhere in the solar system where liquid water can exist (for example, in gas giant moons' oceans kept liquid by tidal heating effects) has not been entirely eliminated; nor has the possibility of life outside the solar system. Given the large number of earth-like planets just within our own galaxy (possibly as many as 40 billion), many consider the possibility statistically likely.

One other effect is of note - microscopic life and spores which have made their way into the upper atmosphere are thought to be pushed constantly outwards from the orbit of earth into the solar system; if they can survive the hostile freezing, desiccation and radiation of interplanetary space (like tardygrades) and land on a favorable environment it would be conceivable that micro-populations could thrive on bodies other than Earth.

Zathura is a fictional black hole created for the movie "Zathura: A Space Adventure." Real black holes are astronomical objects in space with immense gravitational pull, whereas the one depicted in the movie is part of a fictional story.

Adverb: "A black hole forms when a supermassive star collapses after a supernova explosion."

No. A black hole can be a very condensed star. It's also possible for "mini" black holes of less than stellar mass to exist. But in no case would it be possible to describe one as an "expanded" star.

poles

It's hard to compare. Probably the hypernova. According to the Wikipedia article on supernovae, a supernova can influence Earth's biosphere even at a distance of 3000 light-years. And a hypernova is supposed to be a some sort of "super-supernova". On the other hand, while most black holes are fairly harmless if they are just a few light-years away, a quasar emits typically has a brightness of over 10 million million times that of the Sun; that means that at a distance of about 50 light-years, it would look about as bright as the Sun does to us. I would guess that at a distance of 3000 light-years a quasar would be fairly harmless, unless you happen to be right in the main particle beam.

A black hole isn't a hole in the sense that it is a "drain" that funnels things out of the universe. Think of it more as a trash compactor. Everything a black hole sucks in contributes to the mass of the black hole and sits there at a impossibly small focus called a singularity. However, with the evidence of hawking radiation, (small particles that escape a black hole's event horizon periodically). It is now understoon that black holes have a "memory" of everything they've eaten. For example, if a black hole were to suck you up, your matter wouldn't disappear. Over the course of trillions of years, you would be spat out, particle by particle. So black holes will increase in density until there is nothing left to suck up around them, and then in an incredibly slow process (trillions and trillions of years) a black hole will lose density particle at a time until it is completely evaporated!

You would be long dead before you even reached it a black hole has so much gravity you would be long dead before you even got there. Although saying you did survive you would get sucked in like a noodel than hit the core made of the densist pact atoms in the universe.