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contenidos

  1. The trip of the photon

  2. Planet formation

  3. How stars are born

  4. A cosmic dance

  5. The ages of the Universe

  6. The sky and its stars

  7. Wenulewfv the word that dream us

  8. The observation of Light

  9. A window to the Universe

  10. An astrophotographer in Santiago Chile

  11. Mysteries of the Cosmos

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editorial

THE MEMORY OF THE RIVERS
While the sweet scent of the canelo
and the laurel medicine trees
rose to the skies
the Parents of my Parents glimmered
as they gazed at the Southern Cross.

Elicura Chihuailaf
Translation: Camila Yver

Cities gather us in different ways, we dwell them, walk around its streets and avenues attending our own eagerness. Many cities have rise over us with huge buildings that show the ability of societies to overcome our scale, and so in a display of phenomenal energy, cities keep moving.

Now days, electric light seems to be a primary need for todays society. Cities and their lights shine over the night sky, blinding our eyes of the ordinary exercise of looking to the starry night that practice our ancestors. Those who have been in the Atacama Desert know that once is late night, looking at the stars there is a different experience, from the one we are used to when we look at the stars from our “shining” cities. This thought becomes most significant while we start to think about our everyday experience. Have we lost something in the way?

Our culture as human beings, have always been related to the night sky observation. Today, new planetary systems are discovered weekly, observation tools and instruments are increasingly sophisticated; we can look at the origin of the Universe and make an image of it. We live in a fast and fascinating era in which we can dazzle with images of supernova’s explosions, nebula clouds and faraway galaxies. The understanding of what “surround us” changes radically and Astronomy raises new questions, challenging the limits of our comprehension. Now we can look farther and farther and so wider the horizon becomes.

Facing this prospect, we propose to add different points of view. Contributing to the astronomical reflection from different angles, being the scientific perspective one in many others possible. Because we are interested in poetry, music, art and design, also in casual conversation, laughter, awkwardness and contradictions, in things that move and those who stay quiet, we are interested in large and small questions of humanity.

This first edition of Galatic Magazine is the number cero and has as main subject the Birth, the origin of things and also the origin of this project. This is a starting point of a conversation that we hope will spread in time, and so will convene many voices and many views.

Javier Quintana

Galactic Magazine
02

Planet formation

TEXT Nicolás Rojas

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Star hd 142 527
Disc of gas and cosmic dust around the young star, showing vast streams of gas flowing across the gap in the disc. Credits: ALMA (ESO / NAOJ / NRAO), Simón Casassus et al.

Sebastián Pérez works at Millenium Nucleus for Protoplanetary Disk Research (MAD) at alma, chaired by Simon Casassus, astronomer at the Astronomy department in the University of Chile. This team made an important discovery published by Nature magazine, they observed gas fluids channelled by giant planets in formation in the star HG 142 527, located more than 450 light-years away from the Earth. The finding was possible thanks to the joined work of the 16 radio telescopes of the Atacama Large Millimeter/submillimeter Array (alma), located 5000 metres high in the Atacama desert.

Pérez, bachellor degree in physics from the University of Chile and PhD in astrophysics from Oxford University, tells us how the study was developed and also put forward the project’s future investigations for when alma is fully equipped with more than 60 antennas in operation.

the origin
In 2006 an article was published with an infrared image of the star HG 142 527, which showed a disk with a cavity, which according to the current models, indicated that there might be a planet forming. Thanks to the resolution and sensitivity of alma, the international team led by doctor Cassassus were able to observe hundreds of planets’ formation patterns.

The alma observatory uses the principle of interferometry to obtain good quality data. “Light is an electromagnetic wave. When it gets to the Earth, alma antennas combine to obtain a high-resolution image” explained Sebastian. Since November of 2013 the set of 66 high-precision antennas are working together, therefore, the observable range is comparable to a 16 km diameter telescope.

formation of a giant planet
A molecular cloud collapses due to its own gravity. Because of the conservation of movement quantity (angular momentum) a star is formed and a gas and dust disk settles rotating around it. Material is added to this disk which then generates a planetary embryo that will continue growing like a snow ball. Then, it will be able to capture gas and maybe even form an atmosphere. There two proposed processes to explain its origin:

Plantesimal theory: Molecules and dust cluster together and form larger and larger bodies in a process that begins enlarging objects exponentially until reaching sizes as big as large asteroids. “This theory has various shortcomings, since it is difficult for a cluster to grows to a size bigger than one metre in diameter” clarifies Pérez.
Gravitational instability theory: this one shares the formation principle of stars. A certain amount of material collapses gravitationally, thus deriving the formation of an object. In protoplanetary disks there is enough material, mass and gravitational potential for the disk to break up, collapse gravitationally and form giant planets (or Jovian planets).

“As more planetary systems are discovered, you realise that there is a wide variety of processes and lots of nuances. It is believed rocky planets are formed with the progressive growth of dust clusters, whereas Jovian planets are formed because of gravitational instability: closer to the way a star is formed”, says Pérez from his office at the National Astronomic Observatory of the University of Chile.

What characteristics should an object have to be considered a planet?
It must have certain orbit and size characteristics according to the International Astronomy Union. It must be in a planetary system and orbit around a star, also this orbit must be coplanar with the rest of the orbits. Additionally, it must have enough mass to be in hydrostatic equilibrium (it must be round) and must have cleared the neighbourhood of its orbit.

Star hd 142 527
This artist’s impression shows the disk of gas and cosmic dust. Credits: ALMA (ESO / NAOJ / NRAO), M. Kornmesser (ESO).

How could we imagine the formation of a planet?
The starting point is a protoplanetary disk that, depending on the region of the galaxy where it is formed, will be rich in certain chemical elements. Those particles start getting together and growing. After some centimetres they can’t grow more because the clash between particles is very violent. We reported a new discovery about the HG 142 527, which is the presence of a vortex made of gas in the protoplanetary disk; here the conditions are much better for the dust clusters to grow to a size bigger than one metre. Later, they will continue growing until becoming a planet’s inner core. All this process has to happen in the first few million years of a star’s life because gas disperses rapidly. Hence, these clusters must grow quickly in order to grab this gas and obtain an atmosphere. Then, we have a planet as we know it.

So, the formation of the Earth originated from a sun-generated disk?
Sure, it’s the easiest explanation.

Is the protoplanetary disk separated from the star at any given time?
When a proplanetary nucleus is formed and that material starts to acquire more and more material, that object clears its neighbouring orbit and generates a gap in the disk. This is a key moment, when it is large enough to be able to clear its orbit; the star will control the dissipation of the disk with its solar wind. It should not take more than 10 million years to achieve this.

What are the projections of this research?
Two material fluids that come out from the external disk were observed. We believe these fluids are being channelled by a pair of giant planets in formation. Now with the 66 antennas from alma, we will be able to see what’s going on in there.

Are there other researchs that the members of mad are into?
There are dozens of young stars that are close enough to the Solar System so as to be observed in detail and investigated by the telescope. We focus on the star HD 142 527 and other similar objects that show interesting characteristics. Disks are very asymmetric, they have spiral arms. If vortexes make the dust dynamic enough to accumulate efficiently and form these protoplanetary nuclei, we will be solving a part of this theory. We focus on studying horseshoe-like vortexes, as well as doing hydrodynamic simulations of interaction between a planet and protoplanetary disks.

Is research about these objects being done anywhere else in the world?
This area of the astronomic community is focused on exploring the cavities and dust traps that form these vortexes. The protoplanetary community is working together at the same time to explore these new elements. There are many theories and different groups in Japan, Holland, France and the United States observing these processes of planetary formation.

Sebastián Pérez finishes the conversation highlighting that “the formation of planets has many nuances. It’s not a simple or clean process. It’s full of details. Less than 20 years ago the first exoplanet was discovered. Before that the only planets that existed for humanity were in our Solar System, now there are thousands. What surprises me the most is the diversity of phenomena; every planetary system is incredibly varied in planets, sizes, and chemical composition. There are planets in binary star systems and a whole lot of very dynamic phenomena. You should never focus on the general impression, the magic is in the details.”