How do gamma rays affect life on Earth and why do we not meet in civilizations more advanced than us * Prof. Arnon Der
Prof. Arnon Dr
From the Technion magazine, 2001 courtesy of the Technion spokeswoman
The Cancer Nebula was created by a supernova explosion, the light of which reached Earth for the first time in 1054 AD. The explosion happened at a distance of 6000 light years from the Earth (that is, it took light 6000 years to reach from the place of the explosion to the Earth). In the center, the explosion left a bluish neutron star (pictured) emitting jets of radiation.
The neutron star rotates on its axis 30 times per second, and its light jet passes the Earth once per second. The image was obtained from the giant 10-meter telescope on Kechk, which is located on the summit of Hermauna Key in Hawaii at an altitude of 4.5 km.
Astrobiology at the Technion
by Prof. Arnon Dr
How did life begin on Earth? Does life exist elsewhere in the universe? How did life begin in the universe? What is the future of life on Earth and in the universe?
The search for scientific answers to these questions is at the center of astrobiology - a new interdisciplinary science that is developing very quickly in the world, and also at the Technion. Research in astrobiology carried out in recent years at the Faculty of Physics and the Space Research Institute at the Technion, by Professors Arnon Dar, Ari Laor, Shlomo Dado and Dr. Nir Shabiv in his doctoral thesis, in collaboration with foreign scientists from the European Research Center in Geneva and the Max Planck Institute in Munich, arouse interest Many scientists and receive coverage on television and in the international press. Among other things, they are included in a British documentary recently produced for the National Geographic television channels and screened in England.
These studies deal with one of the most fascinating puzzles in astrophysics - the origin of bursts of gamma radiation that reach us on average once a day from the edge of the universe, and their consequences for the development of life on Earth and in the entire universe.
Gamma radiation bursts were discovered by chance by the spy satellites launched by the United States in the 100s to check if the Soviet Union was conducting nuclear tests in space in violation of the treaty it had signed, which forbids their existence. The identity of gamma ray bursts, their exact location and the way they produce the massive fluxes of radiation were unknown until recently. But information gathered from satellites launched in recent years and from optical and radio telescopes, the largest ever built on Earth, indicates that gamma ray bursts occur in distant galaxies, once every XNUMX million years, in massive explosions called supernovae, where neutron stars and black holes are born. . Because of the large number of galaxies in the universe, these huge explosions, in which energy is released equal to the energy produced by all the stars in the universe at the same time, happen in the sky once or twice a day. Because of the great distances in the universe, the intensity of the radiation reaching us is usually small enough, so that it is absorbed by the Earth's atmosphere, which protects us from cosmic radiation.
Until recently, the exact generation mechanism of gamma radiation bursts was a matter of scientific controversy. Thousands of articles published in the professional literature over the past 30 years have proposed different and diverse mechanisms, which have been tested and failed.
However, a mechanism proposed by the Technion group, according to which bursts of gamma radiation are created by huge jets of matter ejected in supernova explosions during the birth of black holes, is being confirmed by
New observational evidence. Moreover, the creation mechanism of gamma radiation bursts explains how life on the surface of planets is almost completely wiped out once every 100 million years, and why we may not have detected signs of life from civilizations that are billions of years ahead of us until now.
Geological evidence shows that life on Earth began about 3,500 million years ago, after the formation of the solar system and the Earth. The origin of life on Earth is unclear and we do not yet know if the first living cells were created here or brought here by meteorites. The geological record of the development of life on Earth from its beginning until about 500 million years ago has been blurred by changes that have occurred on Earth. But the geological record of the last 500 million years is clearer.
The picture obtained from it is of an increasing hue over time of the types of flora and fauna, brutally interrupted from time to time by the almost complete extinction of all the types of life that had developed in the meantime on the continents and in the seas. Almost complete extinctions of life have occurred on average once every 100 million years in the last 500 million years. The last almost complete extinction happened about 65 million years ago. In the extinction, the dinosaurs that ruled the earth disappeared during the largest extinction in the history of the earth about 257 million years ago, until they were extinct about 65 million years ago. Along with the dinosaurs, about 70% of the life forms that inhabited the continents and oceans disappeared within a short period of time. These extinctions of life occurred, in part, when huge meteorites hit the earth, massive volcanic eruptions, the retreat of ocean water and drastic climatic changes.
The extinction of the dinosaurs, for example, coincides with the creation of a huge crater hidden under the Yucatan Peninsula and when Mexico was invaded by an asteroid with a diameter of about 20 km there about 65 million years ago. At the same time, one of the largest volcanic eruptions in the history of the earth also occurred, which covered a large part of India with 3 million cubic kilometers of lava and is known as the Deccan Traps. At that time, there were global climatic changes and a drastic retreat in the level of ocean water. The reason for the combination of all these events is still unknown.
The Technion group proposed that such combinations of events could be caused by the giant jets from the explosions that produce the bursts of gamma radiation, if the explosions happen in our galaxy and the jet from the explosion is facing us. The chance of this can be easily estimated from the number of galaxies in the universe and the observed rate of gamma ray bursts. This chance is one in 100 million years and corresponds to the frequency of the massive extinctions of life that happened in the last 500 million years on Earth.
According to the theory of the Technion group, very heavy stars quickly consume the nuclear fuel in their center. When the nuclear combustion ends there, the star cannot withstand its gravitational pressure and collapses. The resulting explosion manages to blow off its outer shell and causes the supernova phenomenon, which is observed from all directions. But the inner layers of the star do not go far in the explosion and are re-sucked back into the center by the force of gravity. They produce a black hole there, which emits projectiles of matter at a speed almost identical to the speed of light, along its axis of rotation. These jets reach the expanding mantle, penetrate it and produce the bursts of gamma radiation in the direction of the jet's movement in the tremendous collision.
The bursts of gamma radiation are observed from the Earth only if the jet is directed in the direction of the Earth. Such explosions happen in our galaxy once every 100 years, but the jets from the explosion only reach us once every 100 million years. The energy carried by the jet is so enormous that the jet plows through the interstellar medium and crosses our galaxy without deviating from its direction. If the jet passes through the solar system, it can deflect asteroids from the asteroid belt or the solar system's Oort cloud into a collision course with Earth. The gamma rays that precede the jet are so strong that they themselves can cause fatal changes in the Earth's atmosphere.
The jet that follows them causes the main destruction and the destruction of life on the earth, under the earth and in the oceans by penetrating radiations that it produces when it hits the earth's atmosphere. Are we in immediate danger from a gamma ray burst in our galaxy? The very heavy stars destined to end their lives in a supernova explosion and launch deadly cosmic jets in our galaxy are extremely bright stars that are relatively easy to observe. In our galaxy, three stars are known that within a relatively short cosmic period - about a million years - will produce such an explosion, but their axis of rotation and the jets they will emit will not be directed in the direction of the Earth. We will not be harmed by them, but other civilizations, if they exist on other planets in other solar systems on the path of progress of these jets and close enough to the place of explosion, will be annihilated.
Arnon Der, a partner in these studies, will not be surprised if the group's studies reveal an extreme cosmic irony - the solar system and the materials from which we and the Earth are made were created in a supernova explosion in our environment about 5 billion years ago. Jets from another supernova explosion in our galaxy
May, eventually, wipe out life on our planet that a previous supernova produced.
In the picture: two relativistic jets coming out in opposite directions from the black hole at the center of the quasar 175C3 (in the center) which is about 10 billion light years away from us. When the jets stop, after being propelled by the intergalactic medium along an orbit of about a million light years, they produce two bright lobes. The jet moving away from us is not visible because its radiation is concentrated into a cone that opens in the opposite direction from us.
The image was taken at a wavelength of 6 cm with the help of the largest radio telescope in the world, VLA, which is stationed on Earth in the state of New Mexico, USA.
