Black holes


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  • إن أي نجم يبلغ وزنه عشرين ضعف وزن شمسنا يمكنه في نهاية حياته أن يتحول إلى ثقب أسود، وذلك بسبب حقل الجاذبية الكبير وبسبب كتلته الكبيرة. ولكن النجم إذا كان صغيراً ونفد وقوده فإن قوة الجاذبية وبسبب كتلته الصغيرة وغير الكافية لضغطه حتى يتحول إلى ثقب أسود، في هذه الحالة يتحول إلى قزم أبيض white dwarf أي نجم ميت.حتى يتحول النجم إلى ثقب أسود في نهاية حياته يجب أن يتمتع بكتلة كبيرة، فالشمس مثلاً في نهاية حياتها سوف تستهلك وقودها النووي وتنطفئ بهدوء، ولن تتحول إلى ثقب أسود لأن وزنها غير كاف لذلك. وربما نجد في كتاب الله تعالى إشارة لطيفة إلى هذا التحول في قوله تعالى: (إذَا الشَّمْسُ كُوِّرَتْ) [التكوير: 1]. إذن ليس هنالك أي انهيار للشمس إنما انطفاء بطيء، وهذا ما عبّر عنه القرآن بكلمة (كُوِّرَتْ). ففي القاموس المحيط نجد كلمة (كوَّر) أي أدخل بعضه في بعض، وهذا ما سيحدث للشمس حيث تتداخل مادتها بعضها في بعض حتى تستهلك وقودها وتنطفئ.يتميز الثقب الأسود بجاذبية فائقة، ولذلك فإن أي غاز قريب منه سينجذب إليه ويدور في دوامه عنيفة مولداً حرارة عالية نتيجة هذا الدوران مثل الإعصار السريع، هذه الحرارة تبث الأشعة السينية باستمرار، وهذه الأشعة يمكن للفلكيين التقاطها بسهولة بواسطة أجهزتهم، ولذلك يعلمون بأن هذه المنطقة تحوي ثقباً أسود.
  • كي ندرك عظمة هذه النجوم الخانسة، تخيل أنك رميت حجراً وأنت تقف على الأرض سوف يرتد هذا الحجر عائداً بفعل جاذبية الأرض، ولكن إذا زادت سرعة هذا الحجر حتى تصل إلى 11.2 كيلو متراً في الثانية سوف يخرج خارج الغلاف الجوي ويفلت من جاذبية الأرض. بالنسبة للقمر سرعة الهروب فقط 2.4 كيلو متر في الثانية لأن جاذبيته أقل.It creates an immense gravitational pull not unlike an invisible cosmic vacuum cleaner. As it moves, it sucks in all matter in its way — not even light can escape.وهذا يعني:إنها - أي الثقوب السوداء – تخلق قوة جاذبية هائلة تعمل مثل مكنسة كونية لا تُرى، عندما تتحرك تبتلع كل ما تصادفه في طريقها، حتى الضوء لا يستطيع الهروب منها.وفي هذه الجملة نجد أن الكاتب اختصر حقيقة هذه الثقوب في ثلاثة أشياء:1- هذه الأجسام لا تُرى: invisible2- جاذبيتها فائقة تعمل مثل المكنسة: vacuum cleaner3- تسير وتتحرك باستمرار: moves
  • Michell (25 December 1724 – 29 April 1793) was an English natural philosopher and geologist whose work spanned a wide range of subjects from astronomy to geology, optics, and gravitation. He was both a theorist and an experimenter.
  • (Black holes were predicted as a theoretical object about a hundred years ago, long before there was any evidence that they actually existed. Nobody, not even Einstein, believed they could actually exist. Today we have abundant evidence that black holes are distributed throughout our Galaxy and other galaxies.) 
  • Event Horizon: The point at which no light can escape.
  • (Weight is a measure of the force of gravity. The more massive the object you are standing on (or near) is, the more gravitational force you would feel and the more you’d weigh. Gravitational force is based on the mass of the object and your distance from its center. The Sun has more mass than the Moon. YOUR mass does not change, just the force of gravity. You would still look the same. Let’s pretend that you weigh 150 pounds here on Earth. Can you jump up? On the moon, would it be easier or harder to jump up? )
  • (So where do the millions of black holes come from? Scientists have discovered and classified black holes into three categories. What does “stellar” mean? Yes, star-like. These black holes have masses comparable to the mass of stars. Supermassive: millions to billions of times the mass of the Sun And, the creatively named, “mid-mass”: between these two extremes. Where do we find each kind? ) 1-Stellar-mass:Black holes are made when a giant star, many times the mass of our Sun, dies. Most of the star’s atmosphere is blown into space as a supernova explosion. The star’s spent core collapses under its own weight. If the remaining mass is more than the mass of 3 Suns, it will collapse into a black hole. Where do black holes come from?((Most of the black holes are stellar-mass. How do they form? Are people born? Do we live our lives and then die? How about stars? Are stars born? Do they live their lives and die? There are two ways that a star might die. Stars around the mass of our Sun and smaller die, throw off much of its atmosphere as a nebula (planetary nebula) and the core becomes white dwarf. Stars with much more mass – about 8 times or more mass than the Sun die in a supernova explosion and leave a neutron star or what? Yes, a black hole! The millions of stellar-mass black holes spread throughout our galaxy are the corpses of massive stars. Additional Info: A star of 8 solar masses or larger will go supernova at the end of its life. If the REMAINING mass (the core mass not blown off the star during the supernova) is greater than 3 solar masses, the end object will become a black hole. Less than that and it will become a neutron star. Another analogy: You may instead want to communicate the “life” of stars to the length of their lives. The large, hot stars (stellar type: O) live very short lives, burning their fuel at a very rapid rate – these are roughly 50 times the mass of our Sun. A large commercial jet airplane (representing these large, hot stars) will burn 50 gallons of fuel in less than a minute during take-off. A small economy car (representing our Sun), traveling at 20 mph, can easily run for a couple of hours on just one gallon of fuel. O-type stars typically live only a few million years, whereas our Sun will continue for about 10 billion years. (Credit: European Southern Observatory)))2-Supermassive:Extremely massive black holes have been found in the centers of many galaxies - including our own!(Now, let’s look at the second classification of black holes: Supermassive. Found in the centers of most (and maybe all!) galaxies. Do we live in a galaxy? Yes, our Sun is one star in our Milky Way Galaxy of billions of stars. Are there many galaxies in the universe? Astronomers have found evidence for black holes that contain millions to billions of times the mass of our Sun at the centers of many galaxies. But we’re not sure how they formed in the first place – did the black hole form first and the Galaxy formed around it or did the black hole form after the galaxy was born? This is one of the questions NASA scientists are investigating. IMAGE: Central light year of the Milky Way taken in infrared light. Stars at the very center of this frame are orbiting the central black hole. (Credit: European Southern Observatory (ESO) - Very Large Telescope). )3-Mid-Mass:Scientists are finding these in the centers of large, dense star clusters. Like this globular star cluster, called M15, in our Galaxy. (Finally, astronomers have found some black holes with masses between stellar-mass and supermassive, creatively named “mid-mass” black holes. These appear to be found in the centers of large, dense star clusters. But, once again, scientists are not sure of the mechanism of how they formed. )
  • Note/from 200 billion stars, 22 billion are similar to our Sun. Currently only 100,000 or so are massive enough(Spectral Type O) to be candidates for future black holes.===============================
  • So… Let’s say you decide to travel to a stellar-mass black hole in a rocket ship (this could take a several hundred thousands of years, though, so it would be your descendants arriving). Starting several thousand miles from the black hole, you just turn off your rockets. The black hole’s event horizon would be about 35 miles in diameter (about 60 km), so the spaceship would have to be lot smaller.At first, you don't feel any gravitational forces at all. Since you're in free fall, every part of your body and your spaceship is being pulled in the same way, and so you feel weightless. (This is exactly the same thing that happens to astronauts in Earth orbit: even though both astronauts and space shuttle are being pulled by the Earth's gravity, they don't feel any gravitational force because everything is being pulled in exactly the same way.) As you get closer and closer to the black hole, within about 10,000 km (6000 miles – or within about 20 miles of the stadium in the small model), you start to feel "tidal" gravitational forces. The gravitational pull gets stronger as you get closer so the front of your spaceship is being pulled more strongly than the back of the spaceship. As a result you and your spaceship feel "stretched." (This force is called a tidal force because it is exactly like the forces that cause tides on earth.) These forces get more and more intense as you get closer to the black hole, and eventually they will rip your spaceship apart and the pieces will be pulled into the black hole The material pulled in will be compressed beyond recognition into the tiniest of its component particles and merge with the mass of the central black hole. The whole process, from the time you shut off your engines, takes just a few minutes. There is some speculation that a black hole is a portal to another part of the Universe (wormholes). Unfortunately neither you nor your spaceship would ever survive intact to find out. (peel the smashed spaceship off the table and hold it up)
  • (Our Milky Way galaxy is over 12 billion years old and the Solar System including Earth has been here over 4-1/2 billion years. How have we existed so long if black holes are so dangerous? )
  • If the Sun was replaced by a black hole of the same mass as the Sun, the Earth and all the planets would continue in their current orbits unaffected. Of course, there wouldn’t be any daylight - we would certainly get VERY cold! Gravitational force(قوة الجازبية) is based on 2 things: the mass of the object you are near and your distance from its center of mass. Did the mass of the object at the center of the Solar System change? No! Did the Earth’s distance from the center of the object change? No! So, the gravitational force does not change and we would continue orbiting as before.
  • Huh! Thank god So one reason we survive having all these black holes in our Galaxy is the vast distances between the stars. The other reason is that everything is orbiting!
  • This is a series of actual images showing the orbits of stars very close to the center of our galaxy over a period of 14 years: from 1992 through 2004 and projected to 2006 (watch the counter in the upper left corner) The red cross in the center marks the location of the invisible supermassive black hole in the center of our galaxy called Sagittarius A-star (Sgr A*). If we go back to our North America model of our Galaxy, The area we’re looking at would span about seven feet (a little over 2 meters) on a side around that central peppercorn black hole. See how fast the stars are moving as they pass by central black hole. Near the center of our galaxy, stars are much denser than out here where the Sun is. More interactions and deflections – easier for a star to get too close to black hole and have some of its material pulled into black hole. Let’s see what it looks like when gas is pulled into the central black hole. --- Additional Information: At closest approach, stars sweep around the black hole at 5000 kilometers per second! By contrast, the Sun orbits the center of our Galaxy at a relatively slow 220 km/sec - but we’re 26,000 light years from the center – roughly 650 miles on the quarter-North America scale. © Infrared and Submillimeter Astronomy Group at MPE Used with permission (Max-Planck-InstitutfürextraterrestrischePhysik) To find out more: © Infrared and Submillimeter Astronomy Group at MPE
  • when gas is pulled into the central black hole
  • التشكل والتطورتشكلت المجموعة الشمسية نتيجة انهيار في جاذبية سحابة جزيئية عملاقة قبل 4.568 مليار سنة.[13] ومن المرجح أن هذه السحابة الأولية عبرت العديد من السنين الضوئية ومن الممكن أنها ساهمت في ولادة العديد من النجوم.[14]تعرف المنطقة التي بدأت عندها تشكل المجموعة الشمسية بسديم الشمس الأولي،[15] عند انهيارها حافظت على العزم الزاوي ما جعلها تدور بشكل أسرع. تجمعت معظم الكتلة في المركز وازدادت درجة حرارة المركز بحيث أصبحت أعلى من محيط القرص.[14] وكلما تقلص السديم ازداد الدوران حتى بدأ يتسطح على شكل قرص كوكبي دوار بقطر 200 وحدة فلكية تقريبا ويبقى النجم الأولي الحار في المركز.[16][17] يعتقد أن الشمس عند هذه المرحلة كانت نجم تي الثور. تظهر الدراسات حول نجوم تي الثور أنها تترافق مع قرص من مواد الكوكب الأولي بكتلة تتراوح بين 0.001إلى 0.1 من كتلة الشمس، وهذا يدل على أن غالبية كنلة السديم بقيت في النجم نفسه.[18] ونتجت الكواكب من تنامي هذا القرص.[19]في غضون 50 مليون سنة، أصبح ضغط وكثافة الهيدروجين في قلب النجم الأولي كبير بما فيه الكفاية لبدأ تفاعلات الاندماج النووي.[20] ازدادت كل من درجة الحرارة ومعدل التفاعل والضغط والكثافة حتى وصلت إلى نقطةالتوازن الهيدروستاتيكي، بحيث أصبحت الطاقة الحرارية تعاكس قوة الجاذبية لتصبح الشمس في هذه المرحلة تتبع لتصنيف النسق.[21]دورة حياة الشمس.تبقى الشمس الموجودة اليوم حتى تبدأ بالتطور من مرحلة النسق الأساسي وفق تصنييف تصنيف هرتزشبرونج-راسل. فبعد أن تستنزف الشمس وقودها الهيدروجيني السطحي سيميل خرج الطاقة إلى الانخفاض مسببة انكماشها على تفسها، ممايؤدي إلى ازدياد الضغط ودرجة الحرارة في نواة الشمس، ونتيجة لذلك تصبح عملية الحرق أسرع ويزداد لمعانها بمعدل 10% كل 1.1 مليار سنة.[22]بعد حوالي 5.4 مليارات سنة من الآن، سيتحول كل الهيدروجين في قلب نواة الشمس إلى هيليوم لتنتهي مرحلة النسق الأساسي عندم تنتهي تفاعلات الهيدروجين. ستتقلص النواة أكثر، مسببة ازدياد في الضغط والحرارة مسببة تفاعلات نووية للهليوم، الذي يحترق في النواة عند درجة حرارة أعلى. ليصبح الخرج الحراري للشمس أكثر بكثير مما كان عليه في مرحلة النسق الأساسي. وفي هذا الوقت تتمدد الطبقة الخارجية للشمس حوالي 260 مرة من قطرها الأساسي، لتصبح الشمس عملاق أحمر. بسبب الازدياد الكبير في مساحة السطح، فإن حرارة سطح الشمس أقل بكثير مما كان عليه في مرحلة النسق الأساسي (2600 كلفن كحد أدنى).[23]أخيرا، يستنفز الهيلوم بشكل سريع في النواة بشكل أسرع بكثير مما كان يستنزف الهيدروجين، حتى أن مرحلة حرق الهيليوم تمثل جزء بسيط من وقت مرحلة حرق الهيدروجين. وبما أن الشمس غير كبيرة بما فيه الكفاية لحرق العناصر الأثقل من الهيليوم، يتضائل التفاعل النووي في قلب الشمس، وتتسرب الطبقة الخارجية منها بعيدا في الفضاء لتبقى الشمس كقزم أبيض ذو كثافة عالية. وتبقى الشمس بحوالي نصف كتلتها الأصلية ولكن بحجم يعادل حجم الأرض [24] أما الطبقات المتسربة فتشكل سديم كوكبي، فيما تعود بعض المواد التي شكلت الشمس إلى مواد ما بين نجمية.
  • Black holes

    1. 1. The Black Holes
    2. 2. Black holes are called“black” because we cannotsee them - no light comesout of them. No light canreflect off them.
    3. 3. THE GALAXY FULL OF BLACK HOLES It creates an immense gravitational pull not unlike an invisible cosmic vacuum cleaner. As it moves, it sucks in all matter in its
    4. 4. HISTORY• First postulated in 1783 by John Michel.• 1967: Term “Black Hole” coined.• 1970’s: Convincing evidence that black holes are real• Today: NASA space telescopes have discovered evidence for black holes throughout the universe.
    5. 5. WHAT DO YOU THINK?Our Milky Way Galaxy, as well as the other galaxies in theuniverse are full of black holes.• What is a Black Hole?• Are these(black holes) dangerous?• How are black holes made? Where are they, and how do we find them?• If we can’t see black holes, how do we know they are exist?• how do we survive in midst of all these Black Holes?
    6. 6. BLACK HOLESBlack holes: are the intense gravitational fields leftwhen a giant star collapses. It is called a black holebecause we can’t see them because not even light canescape!, The mass of the central black hole in ourGalaxy is over 3 million times the mass of the Sun!.
    7. 7. CONT.• Mass is so great in such a small volume that the velocity needed to escape is greater than the speed of light travels.• The density of a black hole is so great it would be like taking the whole Earth and crushing into a volume smaller than a 1” marble!.
    8. 8. A NONROTATING BLACK HOLE HAS ONLY A “CENTER” AND A “SURFACE”• The black hole is surrounded by an event horizon which is the sphere from which light cannot escape• The distance between the black hole and its event horizon is the Schwarzschild radius (RSch= 2GM/c2)• The center of the black hole is a point of infinite density and zero volume, called a singularity
    9. 9. SOME FACTSHow much would you “weigh”?• On Earth, let’s say you weigh 150 lbs.• On the Moon, you’d weigh 25 lbs.• On Jupiter, you’d weigh 350 lbs.• On the Sun, you’d weigh 4,000 lbs.• Near a Black Hole, you’d weigh over 20 TRILLON POUNDS!!!
    10. 10. Mid Mass Supermassive Stellar mass
    11. 11. THREE CLASSIFICATIONS OF BLACK HOLES:• Stellar-mass: 3 to 20 times the mass of our Sun• Supermassive: Black holes with millions to billions of times the mass of our Sun• Mid-mass: In between stellar-mass and supermassive.
    12. 12. ARE BLACK HOLES DANGER? What do you think?1. What happens to a spaceship that falls into a black hole?2. Will the black holes in our Galaxy eventually suck up everything in it - a cosmic vacuum cleaner?3. What would happen to Earth if the Sun was replaced by a black hole of the same mass?
    13. 13. CONT.• We can escape from the surface of Earth in a spaceship if the spaceship is accelerated fast enough (about 11 km/sec). you would need a force that could accelerate your spaceship to faster than the speed light travels to escape from a black hole - and nothing we know of can exceed the speed of light (speed light travels in a vacuum: 300,000 km/sec or 186,000 miles/sec) .
    15. 15. HOW HAVE WE SURVIVED?• There are 200 billion stars in our galaxy• There are also millions of black holes• Including one giant black hole at the very center How have we survived?
    16. 16. CONT.• How have we existed so long if black holes are so dangerous? The answer is two things in our favor:1. Great distances between the stars .2. All the stars are orbiting the center of the Galaxy.
    17. 17. CONT. Sun’s orbit >
    18. 18. WHAT WOULD HAPPEN IF THE SUN WAS…• Now let’s talk about what would happen if the Sun was replaced by a black hole of the small mass.• What do you suppose would happen to Earth and the other planets?
    19. 19. CONT.• If the Sun was replaced by a black hole of the same mass as the Sun, the Earth and all the planets would continue in their current orbits unaffected.• Of course, there wouldn’t be any daylight - we would certainly get VERY cold!• Gravitational force is based on 2 things: the mass of the object you are near and your distance from its center of mass. Did the mass of the object at the center of the Solar System change? No! Did the Earth’s distance from the center of the object change? No! So, the gravitational force does not change and we would continue orbiting as before .
    20. 20. CONT.So If Sun and the rest of the stars in our Galaxy were notorbiting, we’d all eventually get pulled in to central blackhole and the closer we got, the faster we’d be pulled.  So…we are quite safe
    21. 21. SO HOW DO WE FIND BLACK HOLES? There are three ways scientists can detect the presence of a black hole.• 1. If we see a star or stars orbiting an “unseen” object, this might be a binary (double) star system - that unseen object could be the remains of a massive star that used to be the companion star of the visible star - the companion died in a supernova explosion and now all that’s left is a black hole which the visible star is still orbiting.• 2. As a black hole pulls material from a closely orbiting companion star, the material heats up as it forms a swiftly rotating disk around the black hole. As it heats up, it gives off hot radiation in the form of x-rays.• 3. And sometimes hot jets of gas shoot out from the black hole. Very hot objects like the disk and the jets emit X-rays which we can detect with special telescopes out in space, like the orbiting Chandra X-Ray observatory.
    22. 22. Let’s see some interesting Slides
    23. 23. HOW DO WE KNOW IT’S THERE? Years “Weird” motions of objects nearbysupermassive black Orbits of stars very close to the center of our galaxy over a period of 14 years
    24. 24. Hot materialfalling into theblack hole.
    25. 25. when gas is pulled into the central black holeJets ofglowinggas
    27. 27. Thanks for listeningPeace be upon you allBy: Mohammed Gohdar (Michael Nur)
    28. 28. REFERENCES:1., Black Holes.2. Hawking, Stephen. A Brief History of Time, Bantam Publishing, 1996.3. 3- At the heart of every galaxy lurks a black hole, astronomers believe,, Jan. 14, 1997.4. No Escape: The Truth About Black Holes, www.amazing-space.stsci.edu5. www.kaheel7.com6. Hawking, Stephen. A Brief History of Time. Bantam Publishing, 1996.7. Novikov, Igor. Black Holes and the Universe. Cambridge University Press, 1995.8. Black Holes: The Deadliest Force in the Universe,, Aug. 28, 2006.9. Black Hole, www.nasa.gov10. www.wikipedia.com11.