June 3, 1998

By observing distant supernovae, such as the three shown in the above image, astronomers have found that the expansion of the universe, which has been known since the 1920s, is likely to continue forever. The gravity by which the matter in the universe exerts an attractive force on all other matter is insufficient to bring the expansion to a halt and reverse it. The expansion is believed to have resulted from the primordial explosion, the Big Bang, some 12 to 15 billion years ago, when the universe and all it contains came into existence.

Supernovae are exploding stars that are among the brightest objects in the universe, exceeding the brightness of the Sun by factors of up to 10 billion. Due to their intrinsic brightness, they can be seen to great distances.

The three supernovae shown above are so distant that when the light rays that produced the images started on their journeys toward us, the solar system had not yet been born. The light from the explosion in the left image was sent on its way 7 billion years ago. The light from the other two started out approximately 5 billion years ago. The age of the solar system, in comparison, is 4.5 billion years. (Note: Light travels 5.9 trillion miles per year.)

By comparing the supernovae's apparent brightnesses (i.e., the actual, observed brightnesses, which diminish with distance) with the supernovae's intrinsic brightnesses (which for the type of supernovae shown above are well known), astronomers can estimate their distances. By examining the wavelength distribution of the light from the supernovae, astronomers can determine how fast they are receding from us.

These two kinds of data -- distances and recession speeds of distant supernovae -- allow astronomers to calculate the rate at which the expansion of the universe is slowing.

The bottom line: We live in a universe that will be expanding forever and whose basic building blocks, namely clusters of galaxies, will in due time disperse to infinity.

More Cool Stuff

We obtained the above images from a press release of the Space Telescope Science Institute of January 8, 1998:

http://oposite.stsci.edu/pubinfo/pr/1998/02/a-js.html

The research reported here was carried out by the High-Z Supernova Search Team, whose homepage is at:

http://cfa-www.harvard.edu/cfa/oir/Research/supernova/HighZ.html

In addition to the HST, the High-Z Supernova Search Team uses the Canada-France-Hawaii Telescope (CFHT) on Mauna Kea, HI, the Keck Observatory, also on Mauna Kea, the joint Smithsonian Institution-University of Arizona Multiple Mirror Telescope Observatory (MMTO) on Mt. Hopkins, AZ, and the Cerro Tololo Inter-American Observatory (CTIO) in Chile, which is funded by the National Science Foundation:

http://www.cfht.hawaii.edu/ (CFHT)

http://www2.keck.hawaii.edu:3636/ (Keck Observatory)

http://sculptor.as.arizona.edu/foltz/www/mmt.html (MMTO)

http://www.ctio.noao.edu/ctio.html (CTIO)

As part of its Learning Technologies Project (LTP), NASA supports a number of educational Web sites that have excellent material on the space sciences:

http://observe.ivv.nasa.gov/nasa/education/edu/edudocs/topic_space.html