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Unit 2 Seminar. SC300 Eric Bliss. Black Holes: What Are They?. Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun. If a star that massive undergoes a supernova explosion, it may leave behind a fairly massive burned out stellar remnant.

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unit 2 seminar

Unit 2 Seminar

SC300

Eric Bliss

black holes what are they
Black Holes: What Are They?
  • Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun.
  • If a star that massive undergoes a supernova explosion, it may leave behind a fairly massive burned out stellar remnant.
    • With no outward forces to oppose gravitational forces, the remnant will collapse in on itself.
black holes what are they1
Black Holes: What Are They?
  • The star eventually collapses to the point of zero volume and infinite density, creating what is known as a " singularity".
  • Around the singularity is a region where the force of gravity is so strong that not even light can escape.
    • Thus, no information can reach us from this region. It is therefore called a black hole,
      • and its surface is called the “event horizon ".
      • http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html
if we can t see them how do we know they re there
If We Can't See Them, How Do We Know They're There?
  • Since black holes are small, and light that would allow us to see them cannot escape, a black hole floating alone in space would be hard, if not impossible, to see.
    • the photograph below shows the optical companion star to the (invisible) black hole Cygnus X-1.
if we can t see them how do we know they re there1
If We Can't See Them, How Do We Know They're There?
  • If a black hole passes through a cloud of interstellar matter, or is close to another "normal" star, the black hole can pull matter into itself.
slide7
Astrophysicists generally agree that when the compact object in an X-ray binary system is shown to be more massive than about 3 times the mass of the Sun, then this compact object is a black hole beyond reasonable doubt.
  • http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/011120a.html
slide9
There is good observational evidence from X-ray observations and from the Hubble Space Telescope that there are massive black holes (with masses more than a million times that of the Sun) exist in the centers of some galaxies.
  • http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970805b.html
slide10
Given what you know about scientific inquiry, why is the lack of direct evidence for black holes a problem for scientists?
  • Steps of the scientific method…
      • 1. Name the problem or question
      • 2. Form an educated guess (hypothesis) of the cause of the problem and make predictions based upon the hypothesis
      • 3. Test your hypothesis by doing an experiment or study (with proper controls)
      • 4. Check and interpret your results
      • 5. Report your results to the scientific community
slide11
Why might black holes be important?
  • “If I have seen further, it is by standing on the shoulders of giants.” Sir Isaac Newton
  • Culture of exploration?
if we can t see them how do we know they re there2
If We Can't See Them, How Do We Know They're There?
  • As the matter falls or is pulled towards the black hole, it gains kinetic energy, heats up and is squeezed by tidal forces.
    • The heating ionizes the atoms and they emit x-rays The X-rays are sent off into space before the matter crosses the Schwarzschild radius and crashes into the singularity.
        • Thus we can see this X-ray emission.
references
References
  • http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html
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