with guest Dr. Alex Filippenko, University of California at Berkeley
From time to time "guest stars" have appeared in the sky, at times shining bright enough to see during the daytime. We now know the "guest stars" are gigantic stellar explosions called supernovae. A supernova is the final explosion of a giant star coming to the end of its life. In a desire to understand supernovae, astronomers seek them out, hoping to learn more about how the universe is seeded with the raw materials needed for new stars, planets, and ultimately life.
In this special two-part edition of Astronomy Behind the Headlines we talk with Dr. Alex Filippenko about some current research and findings about supernovae.
Listen to Part 1
Listen to Part 2
Download Transcript (pdf)
Produced by Loch Ness Productions for the Astronomical Society of the Pacific
Written and narrated by Carolyn Collins Petersen
Soundtrack and original music by Mark C. Petersen
Additional resource materials by Andrew Fraknoi
Special thanks to Dr. Alex Filippenko.
Fraknoi (Foothill College & ASP)
Not all stars end their lives in the same way. When a massive star dies, its end produces one of the most spectacular explosions in the universe. When the core of such a gargantuan star collapses, its powerful gravity forces it to produce one of two extremely bizarre and compressed objects -- either a neutron star or a black hole. In most cases, the rest of the star then blows up, in a mind-boggling explosion called a supernova. These explosions produce so much energy that the star can briefly become brighter than the entire galaxy in which it is located (brighter than 100 billion Suns).
In addition to their brilliance, supernovae play an essential role in "recycling" the elements that stars spend their lives making. As part of what keeps them shining, massive stars produce heaver and heavier elements, fusing them together from smaller atoms in their hot centers. When a supernova happens, the violence of the explosion itself briefly makes even heavier elements in its cataclysmic cauldron. Then all these elements are flung outward into space at great speed and join the raw material (gas and dust) already there between the stars. It is this enriched raw material that later gives rise to new stars, new planets, and perhaps new astronomy students. Most of the atoms in your body are the recycled products of earlier generations of supernova explosions.
More recently, astronomers have discovered another kind of star death that can lead to a supernova explosion. Unlike the Sun, many stars live out their lives with a companion star at their side. If one member of such a couple has too little mass to make a neutron star or black hole, it will die by collapsing into a white dwarf -- a star corpse which squeezes something like the total mass of the Sun into a ball only twice the size of Earth. If the white dwarf were alone, that would be the end of the excitement. It would then just fade away as it cools and become a dark remnant of what it once was.
But if the white dwarf has a companion star nearby, and that companion expands its size (as all stars do late in life), material from the companion star will fall onto the surface of the white dwarf. Since the gravity there is about a million times that on the surface of the Earth (really, a million times!), that falling material is pulled in with a lot of speed. As more and more material falls onto the white dwarf, the energy released is enough to "re-ignite" the dead star, and, pretty quickly, to cause it to explode. (Astronomers call this kind of supernova a Type Ia -- not exactly a picturesque name.) Type Ia supernovae are much in the news these days, since they allow astronomers to measure the expansion of the universe in remarkable detail and have led to the discovery that this expansion is (mysteriously) speeding up.
The most famous supernova in history was seen in July 1054. Records of it still survive, from China all the way to North American Indian lore. Seen today, roughly a thousand years later, its remnant, called the Crab Nebula, is one of the most interesting objects in the sky. It can be found with good binoculars or small telescopes in the constellation of Taurus, the Bull, and looks impressively chaotic through our largest telescopes. Another important "supernova fossil" is the one left by a 1987 explosion in the Large Magellanic Cloud, a close neighbor galaxy. A number of other supernova remnants are also known, and are being studied with interest by astronomers.
This list is a sample of the many resources that are available on this topic. Also, many general books and web sites on astronomy will have sections on supernovae.
Articles on Supernovae in General
A Few Articles on Specific Supernova Remnants
Articles on Observing Supernovae
Supernovae and Cosmology
Some Web Resources for Formal and Informal Educators
The Crab Nebula, the remnant of the 1054 supernova explosion, photographed by the Hubble Space Telescope (NASA/ESA/STScI)
Marschall, Laurence The Supernova Story, 2nd ed. 1994, Princeton U. Press. The introduction of choice to supernovae and Supernova 1987A.
Wheeler, J. Craig Cosmic Catastrophes: Supernovae, Gamma-ray Bursts, and Adventures in Hyperspace, 2nd ed.2007, Cambridge U. Press. This is a fine introduction to violent events in the universe by a noted astronomer.
Kirshner, Robert The Extravagant Universe: Exploding Stars, Dark Energy, and the Accelerating Cosmos. 2002, Princeton U. Press. Non-technical primer to the use of supernovae in figuring out the fate of the universe.
Filippenko, A. "A Supernova with an Identity Crisis" in Sky & Telescope, Dec. 1993, p. 30. Good review of supernovae in general, and of the one called 1993J in galaxy M81.
Garlick, M. "The Supernova Menace" in Sky & Telescope, Mar. 2007, p. 26. On the effects of nearby supernova explosions on the Earth.
Hillebrandt, W., et al. "How To Blow Up a Star" in Scientific American, Oct. 2006, p. 42. On supernova mechanisms. On the web at:
Reddy, F. "The Supernova Next Door" in Astronomy, June 2007, p. 32. About Eta Carinae, a massive star which will someday make a spectacular supernova.
Two separate remnants of supernova explosions in a neighbor galaxy, seen with the Gemini South Telescope (Image from P. Michaud, S. Fisher, and R. Carrasco from Gemini and T. Rector from the Univ. of Alaska)
Reddy, F. "What Makes Stars Explode" in Astronomy, Mar. 2007, p. 38. Computer simulations of the mechanisms that lead to supernovae.
Soderberg, A. "X-Rays Mark the Spot: A Newborn Supernova" in Sky & Telescope, Nov. 2008, p. 26. The story of catching a supernova explosion just as it begins, using an x-ray telescope, and what the discovery helped us learn.
Stevenson, D. "A Bigger Bang" in Sky & Telescope, Jul. 2007, p. 32. On Type Ia supernovae and a particularly intriguing example.
Talcott, R. "Supernova 1987A: 20 Years Later" in Astronomy, Oct. 2007, p. 26. Good review of the famous supernova in one of the nearest galaxies, and what the last 20 years of observing it have taught us.
Kirshner, R. "Supernova: The Death of a Star" in National Geographic, May 1988, p. 618. Excellent introduction for beginners on SN 1987A.
Kirshner, R."Supernova 1987A: The First Ten Years" in Sky & Telescope, Feb. 1997, p. 35.
Shubinski, R. "All About the Crab Nebula" in Astronomy, Jan. 2007, p. 70. Introduction to historical and current observations of the remnant of the supernova of 1054 CE.
Zimmerman, R. "Into the Maelstrom" in Astronomy, Nov. 1998, p. 44. On the Crab Nebula.
Gottlieb, S. "How to Observe Exploded Stars" in Astronomy, Sep. 2006, p. 64. An observing guide for amateur astronomers for finding some of the brightest supernova remnants.
Rich, D. "How to Search for Supernovae" in Astronomy, Mar. 2007, p. 70. A primer for amateur astronomers who want to find exploding stars.
Glowing x-rays (seen in false color) from the remnant of a supernova that was seen to explode in the year 1006. (Image from the XMM and the Chandra X-ray Observatories)
Appell, D. "Dark Forces at Work" in Scientific American, May 2008, p. 100. A profile of Saul Perlmutter, the leader of one of the teams whose work with supernovae led to the discovery of the universe's acceleration.
Finkbeiner, A. "Cosmic Yardsticks: Supernovae and the Fate of the Universe" in Sky & Telescope, Sep. 1998, p. 38. Early discussion of using supernovae to figure out changes in how the universe is expanding.
Irion, R. "Exploding Stars Tell All" in Astronomy, Nov. 98, p. 50. Using supernovae as standard bulbs to learn about cosmology; another early report.
Riess, A. & Turner, M. "From Slowdown to Speedup" in Scientific American, Feb. 2004, p. 62. On observations of supernovae and what they tell us about the acceleration of the universe's expansion.
The Crab Nebula Story:
A short, introduction to the history and science of best known super-nova remnant.
Hubble Observations of Supernova 1987A:
Cornell University Ask An Astronomer Supernovae Page:
NASA Goddard Imagine the Universe Supernova Pages:
Chandra Mission Introduction and Background:
http://chandra.harvard.edu/edu/formal/snr/bg.html (note this site starts out, on the first page, specifically about one supernova remnant, but if you go down through all the pages, it is nice introduction to supernovae in general)
Starry Lives, Starry Skies:
http://www.pbs.org/seeinginthedark/pdfs/starry_lives_starry_skies.pdf (Organize the life stages of a star into categories and then find objects in the night sky that are in each category)
Let's Make A Supernova:
http://nightsky.jpl.nasa.gov/download-view.cfm?Doc_ID=339 (A movement activity to show what happens in a supernova explosion.)
A Universe Without Supernovae:
http://nightsky.jpl.nasa.gov/download-view.cfm?Doc_ID=344 (Participants get to think about all the ways that supernovae are essential for the universe)
The Crab Nebula Through Time Activity:
http://chandra.harvard.edu/edu/formal/crab_time/ (from the Chandra X-ray Observatory Mission; students construct a time-line for how this supernova remnant evolved)