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answers:
Raymond say: In science, precise definitions are important.
A "black hole" is a region in space, from which the escape speed is greater than the speed of light. It is possible that some black holes are the result of stars that have collapsed so much (often due to catastrophic events) that its remaining mass has compressed into a small enough volume. However, it is also possible that large black holes are simply the coming together of what would otherwise be "normal matter"... just LOTS of it.
A "black star" (other than in movies) would be a star that is no longer shining. When the Sun reaches the end of its "life" on the main sequence (when it is still fusing hydrogen into helium), in 5 billion years, it will turn into a red giant and, eventually, shed its outer layers. What will be left behind is the core (40% of present mass) which will shine just from the accumulated heat (millions of degrees).
Over many billions of years, this dwarf star will still shine white, then yellow, then red and, eventually, will become too cool to shine. THEN it will be a black dwarf. The process is expected to take almost a hundred billion years (much longer than the present age of the Observable Universe).
The two objects, black holes and black stars, are very different objects, that are formed in totally opposite manners.
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poornakumar b say: same
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CarolOklaNola say: No. Supposedly the Universe isn't old enough for low mass stars like the Sun to to turn into black stars.How do you explain the visible light from the accretion discs and Hawking radiation and x-rays from the event horizon's of black holes, or the super massive black holes in the centers of most, bot all , galaxies?. What about micro black holes. that evaporate in a few billionths of second. We've creating micro black holes in linear accelerators for YEARS.