Unit 2: Very Small and Far Away: Measuring and Observing Extremes Resembling a gigantic hubcap in space, a 3,700-light-year- wide dust disk encircles a 300-million- solar-mass black hole in the center of the elliptical galaxy NGC Roeland P. van der Marel (STScI), Frank C. van den Bosch (Univ. of Washington), and NASA Pictures-/Hubble-Uncovers-Dust-Disk-arou.htm Listeria virus 5337 (host: Listeria monocytogenes) Micrograph prepared by Hans Ackermann, Department of Microbiology, Medical Faculty, Laval University,Quebec, Canada. Specimen stained with 2 % PTA.The bar represents 100 nm. Primary magnification 29,700 x. Micrographs were taken with a Philips EM 300 electron microscope operated at 60 kV. ttp:// 02.htm

What is a black hole? Artistic rendering of a Black Hole (NASA)

What is a black hole? Artistic rendering of a Black Hole (NASA) A black hole is a theoretical entity predicted by the equations of general relativity. A black hole is formed when a star of sufficient mass undergoes gravitational collapse, with most or all of its mass compressed into a sufficiently small area of space, causing infinite spacetime curvature at that point (a "singularity"). Such a massive spacetime curvature allows nothing, not even light, to escape from the "event horizon," or border.

Timespace and Wormholes?

1. What is the biggest obstacle to proving that black holes really do exist? An optical image of the peculiar elliptical galaxy Centaurus A. The white glow is from stars, the dark band is absorption from interstellar dust. (Image from

2. What kinds of evidence are there that they do?

Their gravitational effects on other objects: Artist impression of a binary system with an accretion disk around a compact object being fed by material from the companion star.

2. What kinds of evidence are there that they do? Their gravitational effects on other objects (also known as spaghettification): An illustration of the effect that extreme gravitational forces would have on an astronaut as he approaches the black hole event horizon.

2. What kinds of evidence are there that they do? X-ray radiation from material falling into the black hole: An X-ray image of Cygnus X-1 (in Sagittarius in the Milky Way) from the EXOSAT satellite An optical image of the peculiar elliptical galaxy Centaurus A. The white glow is from stars, the dark band is absorption from interstellar dust. The same image, with the radio jets superposed.

3. Given what you know about scientific inquiry, why is the lack of direct evidence for black holes a problem for scientists?

4. Why might black holes be important?

5. How is the search for black holes similar to the quest to view microscopic objects?

Bohr model of the atom (a disproven theory) The solar system