<P> Black holes can be shaped differently . Some black holes are perfectly spherical - like a ball . Other black holes bulge in the middle . Black holes will be spherical if they do not rotate . Black holes will bulge in the middle if they rotate . </P> <P> Black holes are difficult to find because they do not let out any light . They can be found when black holes suck in other stars . When black holes suck in other stars, the black hole lets out X-rays, which can be seen by telescopes . </P> <P> In this chapter, Hawking talks about his bet with another scientist, Kip Thorne . Hawking bet that black holes did not exist, because he did not want his work on black holes to be wasted . He lost the bet . </P> <P> This chapter explains more about black holes . </P>

A brief history of time new york times book review