Discovering a Supernova

Using a search technique that enables scientists to see violent explosions of dying stars "on demand," Saul Perlmutter of Lawrence Berkeley National Laboratory led a team to the surprising discovery that the expansion of the universe is accelerating, and thus is likely to continue doing so forever. The discovery was based on the identification and measurement during the 1990s of the most distant supernovas ever observed. Observations of rare type Ia supernovas—astronomical "standard candles" that all have the same intrinsic brightness—placed them much farther away than would be expected based on standard analyses of their emitted light. By comparing the distance to these exploding stars with the distance of their home galaxies, researchers calculated how fast the universe was expanding at different times in history. To ensure that supernovas were seen during limited telescope time, the team devised a strategy of imaging patches of sky just after a new moon, when the sky is dark, and then again three weeks later when supernovas show up as bright points of light. The discovery was selected by the journal Science as the top breakthrough of 1998.

Scientific Impact: This work overturned the common assumption that the expansion of the universe was slowing down because of gravity. The results also provided strong evidence of a mysterious, self-repelling property of empty space—the cosmological constant first proposed by Albert Einstein—which may represent much of the total mass-energy density of the universe.

Social Impact: SOCIAL IMPACT: These findings raise profound questions about the ultimate fate of the universe and the Earth, with the promise of as-yet-unimagined impacts on human society.

Reference: S. Perlmutter et al. (1998), presentation at the January 1998 Meeting of the American Astronomical Society, Washington, D.C., LBL Report Number LBL-42230; referenced in B.A.A.S., Volume 29, page 1351 (1997); astro-ph/9812473; S. Perlmutter et al., Astrophysical Journal, 517: 565-586 (1999); astro-ph/9812133.

URL: http://www.supernova.lbl.gov/

Technical Contact: Dr. Saul Perlmutter, sperlmutter@lbl.gov

Press Contact: Jeff Sherwood, DOE Office of Public Affairs, 202-586-5806

SC-Funding Office: Office of High Energy and Nuclear Physics