Black holes appear black for what basic reason?They appear in starless, dark areas of the Milky Way.They "shine" by blackbody radiation and are easily detected.    They are invisible and can never be detected by astronomers.Light cannot escape them.

A method for identifying a black hole is toGroup of answer choicessearch for radio waves from the accretion disk.look for their effects on nearby companions.locate a visible star that disappears when the black hole passes in front of it.look for voids in the star fields.search for their pulsar signal.

The ‘Black Hole’ theory waspropounded by [UPPCS (Mains) 2016UPPCS (Pre) 1996](A) C.V. Raman(B) H.J. Bhabha(C) S. Chandrashekhar(D) Hargovind Khurana8. A ‘black hole’ is a body in spacewhich does not allow any typeof radiation to come out. Thisproperty is due to its [IAS (Pre) 2000](A) Very small size(B) Very large size(C) High density(D) Very low density9. The terms ‘Event Horizon’,‘Singularity’, ‘String Theory’ and‘Standard Model’ are sometimesseen in the news in the context of[IAS (Pre) 2017](A) Observation and understandingof the Universe(B) Study of the solar and the lunareclipses(C) Placing satellites in the orbit ofthe Earth(D) Origin and evolution of livingorganisms on the Earth10. ‘Super Nova’ is[UP Lower Sub. (Mains) 2015](A) An asteroid (B) A black hole(C) A comet (D) A dyning star11. How many constellations are in ourSpace? [44th BPSC (Pre) 2000](A) 87 (B) 88(C) 89 (D) 9012. Which one of the following is not anAstronomical object?[UPPCS (Pre) 1996IAS (Pre) 1993](A) Pulsar (B) Brittle star(C) Black hole (D) Quasar13. A group of stars arranged in aparticular shape, is called[UPPCS (Pre) 2013](A) Milky Way (B) Constellation(C) Andromeda (D) Solar system

What is a black hole?

Black holes have played an important part in astrophysics for the last half-century.  A black hole is a region of space where the force of gravity is especially strong and gravitational potential energy U is very large.  Analogous to the electrostatic potential energy associated with electrical charges, U is defined as the work required to move an object of mass m from an infinite distance to a point at radial distance r within the gravitational field of a second mass M as given byU=−GMmr𝑈=-𝐺𝑀𝑚𝑟Equation 1where G is the gravitational constant.  Near a black hole, the gravitational potential energy can become so negative that not even light has enough energy to escape the black hole's gravity.Escape velocity can be determined by launching an object of mass m with velocity v to an infinite radial distance from the surface of a central mass M (eg, a star or a planet) with radius R.  For a black hole to exist, the escape velocity must be equal to the speed of light.Scientists have thoroughly studied the physics of black holes.  Stars near the center of our galaxy have been observed to orbit an extremely massive, invisible object (millions of times more massive than our Sun) that is almost certainly a black hole.  The orbital angular velocity ω of a star is defined asω=360°⋅f𝜔=360°⋅𝑓Equation 2where f is the frequency of rotation in hertz (Hz).  Likewise, black holes are not merely static masses but are often observed to rotate about their own axis.  The interaction between the rotation of a black hole and matter falling into the hole is suspected to form powerful beams (jets) of ionized matter that project away from the black hole along its axis of rotation.  Nevertheless, many aspects of how these jets are formed remains a mystery.  Black holes will remain a fruitful area for research far into the future. Question 12A star orbiting a supermassive black hole makes two approximately circular revolutions around the black hole every 20 hours.  What is the approximate angular velocity of the star?A.5.0 × 10-3 degrees/secondB.1.0 × 10-2 degrees/secondC.3.0 × 10-1 degrees/secondD.6.0 × 10-1 degrees/second

It can be concluded from paragraph 3 that light1 pointA. destroys a black holeB. can barely reveal a black holeC. does not exist near a black holeD. originates in spacetime