Cygnus X-1, Cygnus X-3 and Sagittarius A* are examples of which type of star?
Neutron stars
Pulsars
Black holes
Red supergiants
Answers
Answer:
Cygnus X-1 (abbreviated Cyg X-1)[12] is a galactic X-ray source in the constellation Cygnus and was the first such source widely accepted to be a black hole.[13][14] It was discovered in 1964 during a rocket flight and is one of the strongest X-ray sources seen from Earth, producing a peak X-ray flux density of 2.3×10−23 Wm−2 Hz−1 (2.3×103 Jansky).[15][16] It remains among the most studied astronomical objects in its class. The compact object is now estimated to have a mass about 21.2 times the mass of the Sun[6][7] and has been shown to be too small to be any known kind of normal star, or other likely object besides a black hole.[17] If so, the radius of its event horizon has 300 km "as upper bound to the linear dimension of the source region" of occasional X-ray bursts lasting only for about 1 ms.[18]