Two groups of scientists have dedicated themselves in the last 10 years to intensive SNe-Ia searches. The results of these so-called rival groups are crucial to what became known as The New Cosmology (e.g., Soares 2003). They are summarized here in terms of two Rips and one Hurrah.
1. The First Rip
In February 1995, Saul Perlmutter and a bunch of great cosmologists (Perlmutter et al. 1995) published a Letter in ApJ entitled ``A supernova at z=0.458 and implications for measuring the cosmological deceleration'' where they derive a deceleration parameter qo=0.1. They even explicitly quote on page L44 that it is a lower-limit determination since host galaxy extinction would increase qo. A confident decelerating universe!
2. The Second Rip
Four years later, Perlmutter and, again, a bunch of great cosmologists (Perlmutter et al. 1999) published a paper in ApJ entitled ``Measurements of omega and lambda from 42 high-redshfit supernovae''. The result was that qo<0. A confident accelerating universe!
Just a few other data, retrieved from the NASA Astrophysics Data System: in September 2002, the 1995 supernova paper had 44 citations and the 1999 paper had 431! In March 2004, the 1995 paper had 57 and the 1999 jumped to 1056 citations! These figures amongst other things show the relative strength of the first and second rips. But we have not yet the moral of the story. Let us go to the hurrah.
3. The Hurrah
In February 2004, Riess and yet another bunch of great cosmologists announced the publication in ApJ of a paper (Riess et al. 2004) entitled ``Type Ia supernova discoveries at z>1 from the Hubble Space Telescope: evidence for past deceleration and constraints on dark energy evolution''. The extraordinary result here, the amazing result here is that they found evidences for a transition between a decelerating and an accelerating phase of the universe!
And guess at which redshift this transition occurs? In their words: ``Using a simple model of the expansion history, the transition between the two epochs is constrained to be at z=0.46 ± 0.13.''
(Gee! I had bet another goose (see Soares 2003, end of section 2, and Soares 2004) on 0.458!... Holy Innocence! What did you expect from such damn (sorry) so-called rival groups! Did you expect any concordance, concordance, concordance?)
In any case there is something useful here: they have fixed a transition redshift! In an ocean of free parameters, THEY HAVE FIXED A TRANSITION REDSHIFT!!!
Anyhow.
4. Conclusion
Rip! Rip! Hurrah!
References
* Pun implied, of course. Those who are not updated with recent cosmological facts must be warned that the Author plays on words in the title and in the text. Accordingly, the "Hurrah" might fairly be taken as the "Big Rip" in "New Clues About the Nature of Dark Energy: Einstein May Have Been Right After All" (check at hubblesite.org/newscenter/newsdesk/archive/releases/2004/12/text/). Back.