Stellar Astronomy
AREA DE ASTRONOMIA

DIF-FUS Universidad de sonora

In transparent and dark nights that prevail in the top of 'CerroAzul', the Carl Sagan observatory will have a strong astronomical activity. The almost ideal conditions of this observatory, will enable investigations to take place contributing on new cientific knowledge. These investigations will focused on the study of certain type of stars in explosion known as Ia type supernovas, which have proven to be extremely useful to discover global properties of the universe.

All the stars that we see in the firmament, shine, because they have a source of fusionable material inside of it. But this nuclear fuel will be one day totaly exhausted. When this happens, the star no longer counts on the pressure necessary to support the weight of its own atmospheric layers and the star is contracted. In the case of our star, in about 5000 million years the sun will suffer great changes. First, it will became giant red star and later began a process in which it will lose its atmosphere. The only thing that will left of our sun it will be an extremely dense object, that will continue radiating light by a long time due to the stored heat, but that no longer will be able to continue producing  nuclear fusion energy.

In astronomy an object with these features is known as a white 'dwarfed' star.

In the 1930's Chandrasekhar, an hindi astrophysic proved that any white dwarf with a mass superior to 1.4 times the solar mass could no longer exist. This limit mass is of an extreme interest in astronomy. If by some reason some white dwarf receives enough mass to arrive at Chandrasekhar's limit, this star is destroyed totally, in an event known as supernova of type IA.

What does that you supernovas Ia are so important for astronomia, is that all of them shine the same way. This is becaus phyisic mechanism that produced it  is always the same one (the destruction of 1.4 solar masses).

The similarity and the great brightness of a supernovate Ia, turns them into ideal candidates for measurements of distances (what the astronomers denominate candles standard) to distant galaxies.

Beside of the distance also is possible to measure the speed with which each galaxy moves radially with respect to us. In order to make this measurement the Doppler effect is used. Somehow or another we al have seen in action the operation of the Doppler effect when approaching or moving away of us a siren of a train or an ambulance. When the siren comes towards us, we observed that its sound becomes but acute. which means that the wavelength diminishes.

Because the Doppler effect is an undulatory phenomena. This ocurred with sound and light waves. In the case of a light source. The light is blueshifted or redshifted, depending on if the source approaches or moves away of us. This way, the Doppler effect has allowed the astronomos to know speeds for hundreds of thousands of galaxies.

Once the distances and speeds are known with precision for a great number of galaxies, it is possible to learn much more on the global structure of the universe. By the end of the 1920's Edwin Hubble only counted on very rudimentary data of parameter, nevertheless, these were enough to do one of the great discoveries of this century (or of the millenium, now that this word this so fashionable), that the universe is expanding, when he finds out that the speed and the distance obey a linear relation. The discovery of the expansion of the universe, was the first base that the Big Bang theory had, this thery says that the universe originate with a great explosion about 14 billion years ago.

By the end of the year of 1998, two groups of astronomers working independently using distances obtained studying supernovate Ia, they show that universe is not only expanding but this expansion is accelerating itself. Among other things, this says that the universe is never going to be contracted again, but it will continue growing in size and decreasing in density.

The only way to explain the acceleration of the expansion of the universe, is to accept that the famous cosmologic constant  introduced y Albert Einstein more than 80 years ago is in fact different from zero, like Einstain was proposed at first. It is interesting that Einstein retract of the previous when he finds out the expansion of the universe, was then when he says his famous phrase ' is the greatest error in my life'. If the cosmologic constant is different from zero, as the observations seems to indicate, it means that the first conclusion of Einstein was the right one.

The news on the acceleration of the expansion of the universe was considered by the Science magazine the most important scientific discovery of the year 1998. Doubtlessly, the selection of Science magazine was very guessed right due to the relevance of the subject. Nevertheless, in spite of the care which the works made show by both groups, this does not mean that already all has been said on the matter. 

The distances to galaxies that are to great distances, are measured with calibrations that take control of near galaxies.  There is much more to make to have precise calibrations. For this it is very important to discover and to study as soon as possible a greater number of near Ia supernovas. Until now, almost all the calibrations have been made considering data of supernovas wich the explison had took place a couple of days ago. 

With the Carl Sagan Observatory every night hundreds of galaxies will be observed, with the purpose to look for new supernovas. When this happens, this will pronounced as a very shining star that havenīt been notice in previous images of the same galaxy. Of course, it would be very rewarding to be able to discover a new supernova. Nevertheless, the success of our program does not depend on it, since part of the time of observation will be dedicated to the study of supernovas reported by other observatories. In it completes instance, the important thing is to contribute with own data that provide new information for this type of studies. Besides this, same images taken for the study of supernovas, will be for the asteroids and comets search. As well as the study variable stars of different types. 

With no doubt about it, the observation of the nicht sky with the telescope of the Carl Sagan Observatory, promises to be extremely motivative from the scientific point of view. 

But this is not everything, but the exciting thing for us is that most of the discoveries that will take place in this observatory will be done by Junior and High school kids and youths of the state. To promote a scientific culture in the state is also one of the great goal of the OCS. 

INVEST IN THE FUTURE...

Last Update: August 04, 1999.