Black Holes Anoushka jp anoushka jp VIA Chinmaya Vidyalaya New Delhi
What are Black Holes <ul><li>Black holes are the cold remnants of former stars, so dense that no matter—not even light—is able to escape their powerful gravitational pull. </li></ul>anoushka jp VIA Chinmaya Vidyalaya New Delhi
How big are they? <ul><li>While most stars end up as white dwarfs or neutron stars , black holes are the last evolutionary stage in the lifetimes of enormous stars that had been at least 10 or 15 times as massive as our own sun. Extremely large black holes may exist at the center of some galaxies—including our own Milky Way. These massive features may have the mass of 10 to 100 billion suns. They are similar to smaller black holes but grow to enormous size because there is so much matter in the center of the galaxy for them to add. Black holes can accrue limitless amounts of matter; they simply become even denser as their mass increases. </li></ul>anoushka jp VIA Chinmaya Vidyalaya New Delhi
Spheres or Funnel shaped? The gravity you feel from an object depends on two things: the object’s mass, and your distance from that object. This means that anyone at a given distance from a massive object — say, a million kilometers — would feel the same force of gravity from it. That distance defines a sphere around an object: anyone on that sphere’s surface would feel the same gravity from the object at the center. The size of an event horizon of a black hole depends on the gravity, so really the event horizon is a sphere surrounding the black hole. From the outside, if you could figure out how to see the event horizon in the first place, it would look like a pitch black sphere. anoushka jp VIA Chinmaya Vidyalaya New Delhi
Are Black holes Black/dark? Matter falling into a black hole would rarely if ever just fall straight in and disappear. As more matter falls in, all this junk can pile up around the hole. Because of the way rotating objects behave, this matter will create a disk of material whirling madly around the hole, and because the gravity of the hole changes so rapidly with distance, matter close in will be orbiting much faster than stuff farther out. This matter literally rubs together, generating heat through friction. This stuff can get really hot, like millions of degrees hot. Matter that hot glows with intense brightness… which means that near the black hole, this matter can be seriously luminous. anoushka jp VIA Chinmaya Vidyalaya New Delhi
Are Black Holes Dangerous? Most people think the Earth would fall in, sucked inexorably down by the black hole’s powerful gravity. But remember, the gravity you feel from an object depends on the mass of the object and your distance from it. The black hole has the same mass as the Sun. And the Earth’s distance hasn’t changed. So the gravity we’d feel from here, 150 million kilometers away, would be exactly the same! So the Earth would orbit the solar black hole just as nicely as it orbits the Sun now. But, we might possibly freeze to death! Anoushka JP VIA Chinmaya Vidyalaya New Delhi
anoushka jp VIA Chinmaya Vidyalaya New Delhi How do astronomers detect where the Black Holes are? Black holes can detected by their gravitational effects on nearby stars or by the intense core of light they produce in the centre of galaxies when astronomers study the speed of the gases in the cores of such galaxies.
Conclusion <ul><li>When we look into the Universe today, we see that pretty much every large galaxy has a super massive black hole in its heart. Even the Milky Way has a black hole at its core with a mass of four millions times that of the Sun. </li></ul><ul><ul><li>Black Holes are a long way off at least 26,000 light years (260 quadrillion kilometers) </li></ul></ul><ul><ul><li>Its mass is still very small compared to the 200 billion solar masses of our galaxy so it can’t really harm us. </li></ul></ul><ul><ul><li>Unless it starts actively feeding. Which it isn’t. But it might start sometime, if something falls into it. Though we don’t know of anything that can fall into it soon! </li></ul></ul><ul><ul><li>Even though black holes can cause death and destruction on a major scale, they also help galaxies themselves form! So we owe our existence to them. </li></ul></ul><ul><li>Thank You </li></ul><ul><li>Anoushka jp VI A </li></ul>anoushka jp VIA Chinmaya Vidyalaya New Delhi