Question No.  186 :
Recently I read about some profound stuff on things on astronomy, and inside the book it mentioned black matter. I would like to know what that is. Isn't matter just matter?

According to Newton's law of gravitation, the more distant a star is from the centre of a spiral galaxy, the lower its orbiting velocity. However, observations showed that even stars in the far periphery of a galaxy orbited at nearly the same speed as those closer to the centre. To our eyes, galactic mass appears concentrated towards the centre and diminishes towards the periphery. And yet the stars at the periphery move as if they are embedded in much greater mass. Astronomers had to come to terms with the fact that what they had seen through their telescopes was only a very small part of the universe. The unseen matter, by inference, must be a major component of galaxies. This came to be known as "dark matter." This nonluminous matter has not been confirmed by observations at any electromagnetic wavelength and constitutes at least 90 percent of the universe. In physics, baryons is the collective term for heavy particles such as protons and neutrons. Stars, planets, and interstellar dust and gas are all made of baryons. Matters composed of protons and neutrons are known as baryonic matters. Some dark matter is baryonic. However, its presence is not detected because the radiation that this matter emits or absorbs might be too insubstantial. It is estimated that more than 90 percent of dark matter is not baryonic. Some of this dark matter may consist of light particles such as the neutrino which interact with other particles of matter only very rarely. This form is referred to as hot dark matter because such particles would have emerged from the Big Bang at high velocity. Relatively heavy, slow-moving particles would be called cold dark matter. Dark matter might also exist in a number of other forms. Weakly interacting massive particles (WIMPs) have been proposed on theoretical ground. Cold dark matter would presumably be made of WIMPs. If cold dark matter particles really exist, they interact with ordinary matter only on rare occasions. There have been numerous different theories about what this non-baryonic dark matter might be made of, and all of them have encountered difficulties. Question Asked By:

Name: Nigel

Age Group: 13 to 20

Occupation Type: Student

Education Level: Others