with guest Dr. Shep Doeleman from MIT's Haystack Observatory
The Milky Way Galaxy has a black hole at its heart -- an object called Sagittarius A* (pronounced A-star). We can't see it visually, but radio astronomers can easily spot it. A group led by Dr. Shep Doeleman at MIT's Haystack Observatory made a startling measurement of the accretion disk around Sagittarius A*. In this edition of Astronomy Behind the Headlines we talked with Dr. Doeleman about his team's discovery.
Listen (mp3, 8.5 MB)
Download Transcript (pdf)
Produced by the Astronomical Society of the Pacific
Written and narrated by Carolyn Collins Petersen
Original music by Geodesium
Soundtrack production by Loch Ness Productions
Web page materials by Andrew Fraknoi
Special thanks to Dr. Shep Doeleman.
Fraknoi (Foothill College & ASP)
Among the most fascinating objects that astronomers today can study are the bizarre, collapsed corpses of massive stars that have come to be called black holes. Around these incredibly dense star-remnants, gravity becomes so strong that nothing, not even light, can escape. (The theoretical framework for black holes was established in Einstein's new ideas about gravity -- called the theory of general relativity.)
In the last few decades, new instruments on the ground and in space have enabled astronomers to detect the presence of black holes for the first time. Being black and very small, these objects are hard to "see" directly, but we can sometimes find them by watching them "eat". Smaller black holes are found when they are caught having their companion stars for lunch. At the centers of galaxies, much larger black holes are often seen consuming their "neighborhood," pulling in large quantities of gas, dust, and larger bodies into swirling disks around the black hole. In the process, excess "food" is also "spit out into" vast jets extending in opposite directions, which can signal the presence of the central black hole to great distances.
The list below is a selection of non-technical resources that you may find useful if you want to begin exploring the world of black holes in more detail. Some are very basic and others are full of exotic details about these mind-boggling objects.
A4. A Few Articles on Super-massive Black Holes in General (see the next section for the one in the middle of our Galaxy)
Artist's Close-Up of a Black Hole with an Accretion Disk (NASA)
Begelman, Mitchell & Rees, Martin Gravity's Fatal Attraction: Black Holes in the Universe. 1996, Scientific American Library. Nice book on the astronomical aspects of black holes. (A second edition is coming in 2010.)
Ferguson, Kitty Prisons of Light: Black Holes. 1996, Cambridge U. Press. A science writer provides a basic, non-threatening overview.
Greenstein, George Frozen Star. 1984, Freundlich Books. Eloquent introduction to the death of stars in general.
Kaufmann, William Cosmic Frontiers of General Relativity. 1977, Little Brown. For those who want more non-technical details about the different types of black holes; out of print, but well worth searching out.
Thorne, Kip Black Holes and Time Warps. 1994, W. W. Norton. The long, definitive introduction by one of the leading scientists in the field; a bit technical in places.
Wheeler, J. Craig Cosmic Catastrophes: Exploding Stars, Black Holes, and Mapping the Universe, 2nd ed. 2007, Cambridge U. Press. Well-written book has some good basic chapters on black holes.
Wheeler, John A Journey Into Gravity and Spacetime. 1990, Scientific American Library. A brilliant, but demanding introduction by one of the foremost scientists of our time (the man who helped coin the word "black hole".)
Will, C. Was Einstein Right? -- Putting General Relativity to the Test. 1986, Basic Books. Introduction to the experiments that confirm the theory.
Zee, A. An Old Man's Toy: Gravity in Einstein's Universe. 1989, Macmillan. Good, non-technical primer by a physicist.
LoPresto, J. "The Geometry of Space and Time" in Astronomy, Oct. 1987, p. 6.
Gefter, A. "Putting Einstein to the Test" in Sky & Telescope, July 2005, p. 32. Nice review of experimental tests of general relativity.
Trefil, J. "Relativity's Infinite Beauty" in Astronomy, Feb. 2005, p. 46. On current and future tests. (Part of a special issue on the centennial of relativity theory.)
Blaes, O. "A Universe of Disks" in Scientific American, Oct. 2004, p. 48. On accretion disks and jets around young stars and black holes.
Charles, P. & Wagner, R. "Black Holes in Binary Stars: Weighing the Evidence" in Sky & Telescope, May 1996, p. 38. Excellent review of how we find stellar-mass black holes.
Jayawardhana, Ray "Beyond Black" in Astronomy, June 2002, p. 28. On finding evidence of the existence of event horizons and thus black holes.
Nadis, S. "Black Holes: Seeing the Unseeable" in Astronomy, Apr. 2007, p. 26. A brief history of black hole idea and an introduction to potential new ways to observe them.
Parker, B. "In and Around Black Holes" in Astronomy, Oct. 1986, p. 6.
Rees, M. "To the Edge of Space and Time" in Astronomy, July 1998, p. 48. Good quick overview.
Bartusiak, M. "A Beast in the Core" in Astronomy, July 1998, p. 42. Nice discussion of giant black holes being uncovered at the centers of many galaxies.
Ford, H. & Tsvetanov, Z. "Massive Black Holes at the Hearts of Galaxies" in Sky & Telescope, June 1996, p. 28. Nice overview.
Irion, Robert "A Quasar in Every Galaxy?" in Sky & Telescope, July 2006, p. 40. Discusses how supermassive black holes powering the centers of galaxies may be more common than thought.
Nadis, Steve "Here, There, and Everywhere" in Astronomy, Feb. 2001, p. 34. On Hubble observations showing how common supermassive black holes are in galaxies.
Rees, M. "Black Holes in Galactic Centers" in Scientific American, Nov. 1990, p. 56. One of the astronomers most involved in explaining how giant black holes can form and power active galaxies explains the key ideas in the field.
Wanjek, Christopher "How Black Holes Helped Build the Universe" in Sky & Telescope, Jan. 2007, p. 42. On the energy and outflow from disks around supermassive black holes; nice introduction.
A diagram showing the observations of the center of our Galaxy made by Shep Doleman and his team (MIT / NASA / CXC / JHU / Univ. of Illinois)
Dvorak, J. "Journey to the Heart of the Milky Way" in Astronomy, Feb. 2008, p. 28. Measuring nearby stars to determine the properties of the black hole at the center.
Freedman, D. "The Mysterious Middle of the Milky Way" in Discover, Nov. 1998, p. 66. A journalist explains the evidence that our own galaxy harbors a massive black hole in the center.
Irion, Robert "Homing in on Black Holes" in Smithsonian Magazine, Apr. 2008. On how astronomers probe the large black hole at the center of our Milky Way Galaxy. Available on the web at: http://www.smithsonianmag.com/science-nature/black-holes.html
Jayawardhana, R. "Destination: Galactic Center" in Sky & Telescope, June 1995, p. 26.
Schulkin, B. "Does a Monster Lurk Nearby?" in Astronomy, Sep. 1997, p. 42.
Tanner, A: "A Trip to the Galactic Center" in Sky & Telescope, Apr. 2003, p. 44. Nice introduction with observations pointing to the presence of a black hole. (see also: http://www.astro.ucla.edu/~ghezgroup/gc/journey/ )
An artist’s conception of a black hole with matter spiraling in (A. Simonnet/Sonoma State U./NASA)
Hubble Space Telescope Black Hole Encyclopedia (a good introduction for beginners):
Frequently Asked Questions about Black Holes (written by University of Richmond physicists Ted Bunn in 1995, while he was a graduate student at Berkeley; a bit dated, but still good):
Chandra X-Ray Observatory Field Guide to Black Holes:
StarDate's Introduction to Black Holes:
87 Questions and Answers about Black Holes from astronomer Sten Odenwald's Astronomy Café:
Monster of the Milky Way (companion site to the PBS-TV NOVA episode on the black hole at the center of our Galaxy):
For a set of black hole information guides and demonstration activities from the ASP's and JPL's Night Sky Network, go to the link below and check the box on black holes:
The Universe in the Classroom (The ASP's Newsletter on Teaching Astronomy) Issue on Black Holes by John Percy:
No Escape: The Truth about Black Holes (teacher lesson from the Space Telescope Science Institute):
Gravity and Black Holes (A Teacher Guide from the Adler Planetarium):
Black Hole Math (a nice introductory booklet at the high-school math level by astronomer Sten Odenwald):
The Anatomy of Black Holes (from NASA's Imagine the Universe site):
Benford, Gregory Eater. 2000, Eos/HarperCollins. An ancient intelligent black hole comes to our solar system.
Brin, David "The Crystal Spheres" in The River of Time. 1987, Bantam. Advanced races use black holes to bear with the loneliness of a universe in which life is still rare.
Johnson, Bill "Meet Me at Apogee" in Carr, T., ed. The Best Science Fiction of the Year 12. 1983, Pocket Books. Posits a future in which people (with alien help) organize levels of descent near a black hole; so the two-month level is where one day of experienced time for the traveler equals two months in the outside universe. Prospectors and people with incurable disease hire pilots to take them down to lower levels.
Landis, Geoffrey "Approaching Perimelasma" in Impact Parameter. 2001, Golden Gryphon. In the far future, a virtual human is dropped into a black hole and makes an interesting discovery about space and time.
McDevitt, Jack & Shara, Michael "Lighthouse" in Cryptic: The Best Short Fiction of Jack McDevitt. (2009, Subterranean Press) [also on the web at: http://www.webscription.net/chapters/1596061958/1596061958___8.htm] An alien race decides, as a public service, to mark the location of unaccompanied black holes in the Galaxy by putting very strange brown dwarfs around them that could not exist in nature. Shara is an astronomer.
Niven, Larry World Out of Time. 1976, Ballantine. Protagonist uses a supermassive black hole to travel into distant future.
Pohl, Fred Gateway. 1977, Ballantine. Enjoyable novel with rotating black holes, event horizons, and "black hole guilt".
Willis, Connie "Schwarzschild Radius" in Preiss, Byron & Fraknoi, Andrew, eds. The Universe. 1987, Bantam. Haunting story combining episodes from the life of Karl Schwarzschild and black hole images.