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Planets Orbiting Other Stars | Dead Stars and Black Holes |
| Dead Stars and Black Holes | |
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Image
on left: An artist's impression of the Earth after the Sun has expanded to become a red giant.
Image source: Wikimedia Commons / Fsgregs After a star has finished burning through all of its fuel, it is called a dead star. As discussed in the Stars section, some stars explode as they die, while some stars have a much quieter death. It all depends on how much material, or mass, a star had to begin with. What happens to life on any planets that orbit around the star when it dies? In short, life on any nearby planets would die. All of the stars grow to become red giants or supergiants before they die. If a planet is too close when this happens, the planet would burn up as the star grows to swallow them. If a planet is far enough away, then it would still safely orbit the star, but the planet would be much hotter and get much more energy now that the surface of the star is so much closer to it. After a star has finished the red giant or supergiant phase, it will either explode or simply let go of its outer layers. If the star explodes, it will destroy any planets that are still orbiting around it. If the outer layers simply lift away instead, the planets wouldn't be destroyed, but they would no longer get any light or heat from the star as it dies. |
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Black Holes Image on left: Still image of a black hole animation. Magnetic fields stream radiation out of the poles of the black hole while material spirals into it. Image source: NASA / ESA /SSM-Newton When an extremely massive star explodes in a supernova, sometimes the core of the star collapses so much that it can form a black hole. Because so much material is packed into such a small space, black holes have very strong gravity. The gravity of a black hole is so strong that nothing can escape once it gets too close--not even light can escape. Black holes can come in many different sizes. Most black holes form from the death of one very massive star, but there are some very large black holes that are called supermassive black holes. Supermassive black holes are hundreds to millions of times more massive than a star. Many astronomers believe that most, if not all, galaxies have a supermassive black hole at their centres. Does a black hole suck up everything in the universe? Only if you get too close. If the Sun somehow magically shrank until it turned into a black hole, the Earth and other planets would still stay in their orbits. It is only once you get too close to a black hole that you wouldn't be able to escape. What happens if you go into a black hole? Anything falling into a black hole gets pulled apart piece by piece thanks to the strong gravity. If the black hole is spinning, astronomers think it might be possible to find a safe way to swing around the black hole and come out of it in a different part of space and time. However, the technology needed to do this is very far in the future, as we would need to be able to travel faster than light to make it possible. What are the parts of a black hole? The accretion disc is a disc of any material around the black hole that is being pulled in. Here, the material is pulled apart piece by piece as it falls into the black hole. The event horizon is the point of no return. It surrounds the black hole, and marks the distance where where things can no longer escape from a black hole. The singularity is the black hole itself, or the place where all of the material has been packed together so tightly that it is pulling everything into it. |
  | Neutron Stars and Pulsars Images on left: An artist's impression of a neutron star, showing the two beams of radiation and other material that spirals around the strong magnetic field. Image source: NASA. The Vela pulsar appears to blink as it spins, sweeping its beams into our eyes. Image source: NASA / DOE /Fermi LAT When a star much more massive than our Sun explodes in a supernova, sometimes the core isn't massive enough to become a black hole. Instead, the material from the core gets packed together very tightly in a small space, but not as small as a black hole. Instead of a black hole, the tightly-packed material is called a neutron star. Neutron stars are usually only a few km wide, but one spoonful of neutron star material would weigh as much as all of the cars on Earth put together. What is a neutron star like? Neutron stars spin extremely quickly and have two huge beams of radiation that come out of their poles. They have extremely strong gravity, but not as strong as a black hole's gravity. If a neutron star is lined up the right way, we can sometimes see the 'blinking' of the beams as the star spins to shine the beam at us and then away from us again. What is the difference between a neutron star and a pulsar? A neutron star and a pulsar is really the same thing. Some are just called pulsars because we see them appear to 'blink' on and off. This happens because some of the neutron stars spin so that their beams of light swing around to shine at the Earth and then away again. We see this beam of light shine at us, then away from us over and over again as the star spins. This causes us to see the 'blinking' effect, and astronomers then call it a pulsar. How quickly do neutron stars spin? Very quickly! For example, the neutron star at the centre of the Crab Nebula spins 30 times a second. The faster neutron stars can spin up to 600 times per second. |
 | White Dwarfs Image on left: A white dwarf star can be seen in the middle of the Eight-Burst Nebula. The outer layers of the star have lifted away to create the nebula, leaving behind the core of the star as a white dwarf. Image source: NASA / ESA Stars about as massive as our Sun don't explode in a supernova. Instead, the outer layers gently lift away and the core gets left behind. The leftover core of the star is then called a white dwarf. A white dwarf star is a small object of very tightly-packed material, but the material isn't as packed as a neutron star or black hole. A white dwarf is about the size of the Earth, and a spoonful of white dwarf material would weight about as much as a car. White dwarfs are much like a hot cinder. They are very hot, but aren't actively burning fuel anymore. Over billions of years, the white dwarfs eventually cool down. What happens to us when our Sun becomes a white dwarf?: Hopefully we will have found a new place to live long before then. Before the Sun becomes a white dwarf, it will expand so much that the surface of the Sun will reach all the way to where the Earth currently orbits. This would kill all life on Earth if our planet stays in that orbit. Once the Sun finally becomes a white dwarf, it will no longer give enough light or heat to support life anywhere in the Solar System. |
 | Advanced
Ideas (intended
for
high school ages and older) Image on left: An artist's impression of a black hole moving between us and a background galaxy. As the black hole moves past the galaxy, it bends the light of the galaxy around it. Image source: Wikimedia Commons / Urbane Legend How do astronomers detect black holes? It is difficult to detect a black hole itself, since astronomers rely on light, heat, or some other kind of radiation to detect objects in space. Black holes allow none of this to escape. Instead, the material that is swirling into the black hole allows astronomers to detect them. The material speeds up faster and faster as it falls in and emits a lot of radiation. Just outside the event horizon, it is still possible for this radiation to escape into space, so this is what astronomers search for. There is so much energy coming from this material that it is detected as x-rays. Astronomers can also use an different effect, called gravitational lensing, to find possible black holes. Light from space bends as it passes by a very massive object. By finding places where the light from a background object is obviously bent, astronomers can begin to learn about how much gravity it takes to bend the light that much. This can also lead them to say that the object bending the light may be a black hole. |
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For Primary and Intermediate Schools General Information about Stars: http://www.windows2universe.org/the_universe/BH.html&edu=mid http://www.windows2universe.org/the_universe/NS.html&edu=mid http://www.windows2universe.org/the_universe/WD.html&edu=mid Images and Movies: http://hubblesite.org/gallery/album/exotic/black_hole/ http://www.esa.int/esa-mmg/mmg.pl?topic=Astronomy+targets&subtopic=Black+holes http://hubblesite.org/gallery/album/star/pulsar/ http://www.esa.int/esa-mmg/mmg.pl?topic=Astronomy+targets&subtopic=Neutron http://hubblesite.org/gallery/album/star/white_dwarf/ http://hubblesite.org/gallery/album/nebula/planetary/ http://www.esa.int/esa-mmg/mmg.pl?topic=Astronomy+targets&subtopic=Planetary+nebulae For High Schools and Older General Information about Stars: http://hubblesite.org/explore_astronomy/black_holes/home.html http://science.howstuffworks.com/dictionary/astronomy-terms/black-hole1.htm http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html http://www.daviddarling.info/encyclopedia/P/pulsar.html http://www.daviddarling.info/encyclopedia/N/neutronstar.html http://www.daviddarling.info/encyclopedia/W/whitedwarf.html Images and Movies: http://www.esa.int/esa-mmg/mmg.pl?topic=Astronomy+targets&subtopic=Black+holes http://hubblesite.org/gallery/album/exotic/black_hole/ http://hubblesite.org/gallery/album/star/pulsar/ http://www.esa.int/esa-mmg/mmg.pl?topic=Astronomy+targets&subtopic=Neutron http://hubblesite.org/gallery/album/star/white_dwarf/ http://hubblesite.org/gallery/album/nebula/planetary/ http://www.esa.int/esa-mmg/mmg.pl?topic=Astronomy+targets&subtopic=Planetary+nebulae |