University Lowbrow Astronomers

A COSMOLOGICAL CONUNDRUM.

by Lorna Simmons
Printed in Reflections:  November, 1999.

Is it or isn’t it?  Cosmological accelerated expansion of course?  Do the standard candles lie?  What is going on?  Can’t those guys get it together?

It seems that the Supernova Cosmology Project is going full steam ahead, all engines revved.  The High-z Supernova Search Team folks are gently tweaking the cosmological machine, perhaps throwing a monkey wrench into the works.  These two world-encompassing teams of astronomers, astrophysicists, cosmologists, particle physicists, engineers, you name it (cosmetologists?), are now, seemingly, temporarily at odds about this question.  Is the universe, after all, accelerating in its expansion?

Let us backtrack for a minute to get our bearings straight.  Just what is all of this fuss about?  It appears that when Saul Perlmutter and Carl Pennypacker (of the Lawrence Berkeley Laboratory) initially began their study approximately 12 years ago, they were seeking to determine the rate of slowing of the universe.  They then believed that the universe was decelerating in its expansion.  Because of the great distances involved, they used the type Ia supernovae as “standard candles.”  Type Ia supernovae become violent bombs when white dwarf stars, in close binary relationships, accrete material from their binary companion stars onto their own accretion disks, thereby forcing the white dwarf stars eventually to reach the Chandrasekhar limit for white dwarfs of 1.44 solar masses.  That means “curtains” for the white dwarf stars.  Perhaps it also means “curtains” for the companion stars.

Saul Perlmutter and Carl Pennypacker’s initial problem was in getting enough telescope time for their project which seemed to have little chance of succeeding, because these astrophysicists had the difficult task of finding the type Ia supernovae explosions (stellar bombs) which occur infrequently, perhaps once a century at most, in each galaxy.  Certainly not an everyday occurrence!  Saul Perlmutter and Carl Pennypacker came up with a method for taking a great swath of the sky beginning shortly before the new moon (sound familiar?) in order to take advantage of the dark sky.  Steve Holland, team leader for the Supernova Cosmology Project, devised a highly resistive chip which was much thicker than normal chips and which mimics the electrical properties of an exceedingly thin chip.  In this way, they would be able to image the brightening before and the dimming afterward of a great number of supernovae explosions.  This method proved to be successful, and to accomplish that task, they did not need so much telescope time for each event, because they could take a great number of type Ia supernovae images simultaneously.

Two worldwide groups were formed in order to have checks and balances on the findings.  This gentle challenging of groups would offer the scientific community the assurance of controls over this study.  The large group of researchers which included Saul Perlmutter, Carl Pennypacker, and Peter Nugent was named “The Supernova Cosmology Project” (using Cerro Tololo, Keck II, and a third telescope which was designed and engineered at Berkeley Lab specifically for this singular purpose of recording, simultaneously, a large number of type Ia supernovae events).  The other group, “The High-z Supernova Search Team” (using Mount Stromlo Observatory and Siding Spring Observatory) was composed of Brian Schmidt, David Reiss and Adam Riess, in addition to a large additional number of researchers, with the purpose of making the same kind of study of type Ia supernovae.

Well, surprises of surprises, they were wrong.  The data coming in showed that, far from decelerating as expected, the universe was, instead, expanding and, to make things worse, accelerating in that expansion!  For crying out loud!  Back to the drawing board!  They checked and rechecked their data, but the answer was very clear.  Acceleration was “in”; deceleration was “out”!  By that time, they were getting more and more telescope time (naturally, because they were onto something big) and were able to develop a method for viewing a great number of these stellar bombs at one time.  Remember, the white dwarfs all went supernova at 1.44 solar masses (the Chandrasekhar limit for white dwarf stars), so the supernovae should be recorded as having an extreme sameness in that respect.  Also, the astrophysicists took spectra of the composition of the material in the explosions to be even more certain.  Same results.  Conclusion:  They just could not escape the evidence for an accelerating universe.

In comes theorist Michael Turner of the University of Chicago with his long-held theory, suggesting the possibility of a cosmological constant, lambda (named after Einstein’s “Lambda” and greatest blunder), as a candidate for explaining the non-zero acceleration.  Lambda was considered to be energy density and a repulsive force, as opposed to gravity which was mass density and an attractive force.  This interesting theory gave a foundation for the observations of the two teams.

To the blaring of trumpets, the issue of “Science” for 18 December 1998, pronounced the “Accelerating Universe” as the “Discovery of the Year”!  Ta da!

Now, hold on a minute.  There is now a fly in that ointment.  Members of the High-z Supernova Search Team came up with some interesting observations.  It seems that there is a discrepancy.  Slight variations which had previously gone unnoticed were seen among the type Ia exploding stars.  When members of the High-z team took a close look at the early phase of ten nearby type Ia supernovae explosions they found that it took more than 2 days longer to reach their highest brightness level than it took for the average of the far distant supernovae.  These unexplained differences in the near type Ia supernovae have called the new theory of the expansion of the universe over time into question.  The explosions which had been thought to flare to nearly the same luminosity each time, therefore serving as a measure of their distance, are now showing seemingly strong discrepancies in their rate of brightening.  On the other hand, the members of the Supernova Cosmology Project, who have not yet come to the end of their own study and have not yet begun to prepare their findings for the scientific community, are, therefore, unready to respond to these emerging data.  Others feel that, while the data are pretty strongly discrepant, they are extremely interesting.  Type Ia supernovae are getting the ultimate test for their accuracy as standard candles, and whether push actually comes to shove, the outcome will be always interesting and beneficial to the astrophysical/cosmological science.

New calibrations might be in the works.  Correcting for leftover differences in brightness could be the result of these latest findings.  Nobody knows if the difference in the “rise times” of distant type Ia supernovae will provide difficulties in the value of their use as standard candles.

If distant type Ia Supernovae, which have been found to be unexpectedly dim, are indeed intrinsically different from nearby type Ia supernovae, there goes one great standard candle right down the drain!  And then again, nothing about measuring the universe is perfect, and the type Ia supernovae provide the best game in town for distant objects.  Nobody is ready to throw anything away.  Right now, however, the data must be placed on hold, awaiting new findings of the Supernova Cosmology Project which might be some time in coming.

The suspense is unnerving...

Addendum:

Do not worry.  The sun, which is expected to become an eventual white dwarf, cannot go type Ia supernova, because it is not in a binary relationship.  Therefore you can go back to sleep and forget about all of this nonsense.

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