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A black hole is an object in space with an infinite density and no characteristic boundary - called a singularity. Thus a black hole does not have a "size" but it's size is based on it's event horizon, rather than it's physical properties.
A black hole with the mass of our Sun, would have a diameter of about 6 km. (The Earth's diameter for comparison is about 12,500 km)
Black holes at the centre of galaxies are enormous and can have a mass up to several billion Suns. So they could have a diameter as large as 12,000,000,000 km. Approximately 12 times larger than our own Sun.
These are called supermassive black holes, because they are so big.
As of November 2008:
OJ 287 [See related links], is a binary pair of black holes. It contains the most massive black hole known, with a mass estimated at 18 billion solar masses.
It is located in the constellation Cancer at a distance of more than 3.5 billion light years.
Those measurements are from our own perspective only. Strange things happen inside a blackhole and we can only guess. One thing that lately has been proposed is that the fabric of space-time falls apart inside of it. Woah!
What else can I help you with?
What were black holes before they turned into black holes?
stellar black holes were stars (these are large)primordial black holes were pieces of the big bang (these are microscopic)
Will the big bang make a black hole?
no black holes are stars
What have black holes got to do with the beginning of the universe?
The density of matter just after the big bang is calculated to be sufficient to have spontaneously created black holes; such are called primordial black holes, and searches for their existence are ongoing.
Why all dead big stars do not form black holes?
All dead big stars do not form black holes because sometimes the collapse of the star is stopped at a smaller size before it becomes a black hole.
Is there any chance of life in a black hole?
stellar black holes, no none at allhawking black holes, no none at allsuper massive black holes at galactic centers, no none at alluniversal black holes, yes we are an example, if the entire universe is indeed inside an ultra massive black hole as would be suggested by the combination of big bang theory and black hole theory
Is the universe being consumed by the galactic black holes?
Even though black holes suck through parts of the universe, the universe is inevitably big, and growing so as the universe is being sucked into another dimension by black holes, it is also expanding.
Is there such thing as big black holes?
While scientists have never actually SEEN a black hole (they are called "black holes" because their gravity is so great that not even light can escape!) we believe that super-massive black holes are at the hearts of most galaxies. These super-massive black holes might be the mass of a million stars the size of the Sun, or larger.
What is the connection between big bang theory and the blackhole?
One of the considerations for the eventual termination of the universe is that all matter will be pulled into black holes, and then these black holes would eventually evaporate.
What if black holes are actually planets with an atmosphere that does not reflect back any light?
Black holes aren't actually holes, they're just humongous 'objects' that are so big that they have huge gravitational pulls and therefore pull everything into themselves, hence the name 'holes'.
Is the amount of black holes in the universe relatively increasing and are the consequences of this a new creation big bang?
The amount of black holes are increasing because the fact that stars are dying and being reborn each second.
Were did a black hole come from?
Black holes came from old big stars that went supernova as it dies. Supernova causes the star to collapse into a black hole
Is the universe made of black holes?
No. It certainly has black holes, but it has other things as well.No. It certainly has black holes, but it has other things as well.No. It certainly has black holes, but it has other things as well.No. It certainly has black holes, but it has other things as well.
