![]() The star Cygnus X-1 is a strong X-ray source and is considered to be a good candidate for a black hole. The superheated materials emit X-rays, which can be detected by X-ray telescopes such as the orbiting Chandra X-ray Observatory. When material falls into a black hole from a companion star, it gets heated to millions of degrees Kelvin and accelerated. Therefore, it was concluded that a black hole had passed between Earth and the object. When the Hubble Space Telescope looked at the object, it saw two images of the object close together, which indicated a gravitational lens effect. In the image, the brightening of MACHO-96-BL5 happened when a gravitational lens passed between it and the Earth. Photo courtesy NASA/Space Telescope Science Institute Credit: NASA and Dave Bennett (University of Notre Dame) These images show the brightening of MACHO-96-BL5 from ground-based telescopes (left) and the Hubble Space Telescope (right). This effect can be seen in the image below. 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. ![]() The star's position shifted because the light from the star was bent by the sun's gravity. This was later confirmed during a solar eclipse when a star's position was measured before, during and after the eclipse. Gravity LensĮinstein's General Theory of Relativity predicted that gravity could bend space. Such a huge mass for a disk might indicate that a black hole is present within the disk. The disk is about the size of our solar system, but weighs 1.2 billion times as much as the sun. You then estimate the mass of the black hole by looking at the effect it has on the visible object.įor example, in the core of galaxy NGC 4261, there is a brown, spiral-shaped disk that is rotating. For example, if a visible star or disk of gas has a "wobbling" motion or spinning AND there is not a visible reason for this motion AND the invisible reason has an effect that appears to be caused by an object with a mass greater than three solar masses (too big to be a neutron star), then it is possible that a black hole is causing the motion. ![]() What you look for is a star or a disk of gas that is behaving as though there were a large mass nearby. The radius of the event horizon is called the Schwarzschild radius, named after astronomer Karl Schwarzschild, whose work led to the theory of black holes. Once inside the event horizon, all "events" (points in space-time) stop, and nothing (even light) can escape. Once something passes the event horizon, it is gone for good. You can think of the event horizon as the mouth of the black hole. The opening of the hole is called the event horizon. ![]() The core becomes the central part of the black hole called the singularity. Because the core's gravity is so strong, the core sinks through the fabric of space-time, creating a hole in space-time - this is why the object is called a black hole. This object is now a black hole and literally disappears from view. The core's gravity is so strong that even light cannot escape. What remains is the highly compressed, and extremely massive,core. As the core compresses, it heats up and eventually creates a supernova explosion in which the material and radiation blasts out into space. At the same time, the star's gravity pulls material inward and compresses the core. As the star dies, the nuclear fusion reactions stop because the fuel for these reactions gets burned up. ![]()
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