Laying down under a bright sky with falling stars in the sahara nearby Erg Chebbi in Merzouga, Morocco I heard some people trying to describe the Milky Way.
What is it ?

Milky Way
Milky Way

If you look up into the sky on a clear dark night, far from the intrusive glow of streetlights, you will see a faint band of light running across the heavens. This is the Milky Way, our own galaxy. It contains about two hundred billion stars and countless other objects besides. The Milky way viewed through binoculars is a magnificent sight, with thousands of stars in each field of view. The image on the left was taken at the Anglo Australian Observatory and shows the centre of the Milky Way, in the constellation of Sagittarius. Like the constellations and planets, the Milky Way was important in mythology, and many stories were told to explain it. Our galaxy is only one of billions of other galaxies in the universe, but it is special to us, because it is home to Earth and our solar system. The Milky Way has been studied extensively by astronomers, and today our ideas about it’s nature are set on a more firm foundation. Here I set out to examine what this faint band of light is, where it came from, and where Earth and the Sun fit into the picture.

The birth of our Galaxy

Long before the Sun and the solar system formed, before the galaxy existed, the universe was filled with gas – mainly hydrogen, with some helium. This gas was eventually to be turned into stars, planets and people. But before these things could happen, the galaxy had to form. Astronomers believe that the galaxy formed out of a large, fairly spherical cloud of cold gas, rotating slowly in space. At some point in time, the cloud began to collapse in on itself, or condense, in the same way that the clouds which formed individual stars also condensed. Initially, some stars may have formed as the gas cloud began to fragment around the edges, with each fragment condensing further to form a star or group of stars. Because the cloud was spherical at that time, we do see some very old stars distributed in a spherical halo around the outside of the galaxy today. At such early times, these stars consisted only of the hydrogen and helium gas which made up the cloud.

The cloud continued to collapase, with more and more stars being formed as it did so. Since the cloud was rotating, the spherical shape began to flatten out into a disc, and the stars which were formed at this time filled the disc regions. Once again we see this shape today in the main body of the galaxy. As the formation of new stars continued, some of those which had been created earlier had enough time to evolve to the end of their active lifetimes, and these stars began to shed their atmospheres or explode in huge supernova events. In the process, these older citizens of the still young galaxy enriched the gas in the cloud with the new, heavier elements which they had formed, and the new stars being created in the disc regions contained the heavier elements. Astronomers call these younger, enriched stars population 1 stars, and the older stars population 2. This process of star formation, then manufacturing heavier elements inside stars and finally returning these elements into the gas between the stars (called the interstellar medium) continued, as it still does today, all the time enriching the medium so that today the gas within our galaxy consists not only of Hydrogen and Helium, but also the other elements which are needed to form the Earth and the rest of the universe we see around us.

The Milky Way today

The Milky Way galaxy in which we now live is a very different place to the cold gas from which it formed over 16 billion years ago. No longer is it a spherical mass of hydrogen; today astronomers with radio telescopes have charted the clouds of gas and have found that the Milky Way is a Spiral Galaxy, one of countless others. Whilst we can’t “stand back” and see our galaxy as a whole, we can look out into space and see other galaxies which we think may be similar to our own.

Read More
New Planet
New Planet

The planet (left) is about five times the size of our Jupiter. European and American scientists say they have photographed a planet outside the Solar System for the first time. The European Southern Observatory group said the red image is the first direct shot of a planet around another star. The planet, known as 2M1207b, is about five times the size of Jupiter and is orbiting at a distance nearly twice as far as Neptune is from our Sun. The parent star and planet are more than 200 light-years away near the southern constellation of Hydra. There has been a lot of competition among astronomers to secure the first direct picture of an exoplanet. When the ESO group first released the picture last September there was doubt over whether the star and planet were gravitationally bound. But follow-up images taken at the Very Large Telescope facility in Chile show the two objects are moving together. “Our new images are quite convincing,” said Gael Chauvin, an Eso astronomer. “This really is a planet – the first planet that has ever been imaged outside of our Solar System,” he added.
Tough task
It is extremely difficult for current technology to detect exoplanets – let alone get a clear shot of one. All of the 130 or so exoplanets so far discovered have been found using indirect methods – looking for changes in the properties of stars (their brightness or way they move) that can be explained only by the presence of a planet. Now we have a direct observation, the Eso team says. The star has the uninspiring catalogue number 2M1207A. It is a brown dwarf, or “failed star” – an object whose mass of hydrogen and helium has failed to trigger the nuclear reactions that would make it shine brightly like normal stars. At the time of 2M1207b’s discovery, it was impossible to prove that the red speck caught in the original images was not a background object, such as an unusual galaxy or a peculiar cool star.

The new observations show with high confidence that the two objects are moving together and hence are gravitationally bound. “The two objects – the giant planet and the young brown dwarf – are moving together; we have observed them for a year, and the new images essentially confirm our 2004 finding,” said Benjamin Zuckerman, a University of California-Los Angeles (UCLA) professor of physics and astronomy. Anne-Marie Lagrange, another member of the team from the Grenoble Observatory in France, looks towards the future: “Our discovery represents a first step towards one of the most important holy grails of modern astrophysics: to characterise the physical structure and chemical composition of giant and, eventually, terrestrial-like planets.”

Alien worlds
Alien worlds
Dr Chauvin added: “Given the rather unusual properties of the 2M1207 system, the giant planet most probably did not form like the planets in our Solar System.” “Instead it must have formed the same way our Sun formed, by gravitational collapse of a cloud of gas and dust.” As a consequence, there are bound to be some scientists who will still question if 2M1207b really is a planet. Lynne Hillenbrand, an assistant professor of astronomy at the California Institute of Technology, told the Associated Press news agency: “The claim of an object being a planet is subject to one’s definition of planet, and there are different camps on what that definition is.” What everybody wants is a direct image of a rocky planet like Earth circling another star. But this will not come until we get the next generation of super-telescopes capable of resolving such small, faint objects. The latest research has been accepted in Astronomy and Astrophysics, a premier journal in astronomy.

Read More