Black holes emit no light. However, scientists can find them if they are located close to another star. The enormous gravitational pull of the black hole will tear gas from the star, pulling in streams of material. This gas will circle the black hole with such force that its temperature can exceed 100 million °C. This is so hot that x-rays will be released. Satellites such as the RXTE are used by astronomers to detect these x-rays.
Einstein’s General Theory of Relativity predicted that gravity could bend space. This was later confirmed during a solar eclipse when a star’s position was measured before, during and after the eclipse. The star’s position shifted because the light from the star was bent by the sun’s gravity. Therefore, an object with immense gravity (like a galaxy or black hole) between the Earth and a distant object could bend the light from the distant object into a focus, much like a lens can.
A gravitational lens passed between it and the Earth. When the Hubble Space Telescope looked at the object, it saw two images of the object close together, which indicated a gravitational lens effect. The intervening object was unseen. Therefore, it was concluded that a black hole had passed between Earth and the object.
When material falls into a black hole from a companion star, it gets heated to millions of degrees Kelvin and accelerated. The superheated materials emit X-rays, which can be detected by X-ray telescopes such as the orbiting Chandra X-ray Observatory.
The star Cygnus X-1 is a strong X-ray source and is considered to be a good candidate for a black hole. Stellar winds from the companion star, blow material onto the accretion disk surrounding the black hole. As this material falls into the black hole, In addition to X-rays, black holes can also eject materials at high speeds to form jets. Many galaxies have been observed with such jets. Currently, it is thought that these galaxies have supermassive black holes (billions of solar masses) at their centers that produce the jets as well as strong radio emissions.
It is important to remember that black holes are not cosmic vacuum cleaners — they will not consume everything. So although we cannot see black holes, there is indirect evidence that they exist. They have been associated with time travel and worm holes and remain fascinating objects in the universe.
Picture Credit : Google
