In most of the galaxy , the stars are not uniformly distributed , but instead are arranged in certain patterns. The most frequent ones are spiral galaxies .The center of such galaxies is thick with several old , red shining stars. A flat disc stretcher all around this centre in wich the individual arms of the spiral are present. It has a thickness of just about 100 light years, which is very thin as compared to the size of a galaxy. The spiral arms contain a lot of young bright blue stars. If a sprial galaxy . other types of galaxies are the egg-shaped “elliptical galaxies ” and the irregular galaxies , which are completely disordered.
The most popular theory of our universe’s origin centers on a cosmic cataclysm unmatched in all of history—the big bang. This theory was born of the observation that other galaxies are moving away from our own at great speed, in all directions, as if they had all been propelled by an ancient explosive force.
Before the big bang, scientists believe, the entire vastness of the observable universe, including all of its matter and radiation, was compressed into a hot, dense mass just a few millimeters across. This nearly incomprehensible state is theorized to have existed for just a fraction of the first second of time.
Big bang proponents suggest that some 10 billion to 20 billion years ago, a massive blast allowed all the universe’s known matter and energy—even space and time themselves—to spring from some ancient and unknown type of energy.
The theory maintains that, in the instant—a trillion-trillionth of a second—after the big bang, the universe expanded with incomprehensible speed from its pebble-size origin to astronomical scope. Expansion has apparently continued, but much more slowly, over the ensuing billions of years.
Scientists can’t be sure exactly how the universe evolved after the big bang. Many believe that as time passed and matter cooled, more diverse kinds of atoms began to form, and they eventually condensed into the stars and galaxies of our present universe.
Origins of the Theory
A Belgian priest named Georges Lemaître first suggested the big bang theory in the 1920s when he theorized that the universe began from a single primordial atom. The idea subsequently received major boosts by Edwin Hubble’s observations that galaxies are speeding away from us in all directions, and from the discovery of cosmic microwave radiation by Arno Penzias and Robert Wilson.
The glow of cosmic microwave background radiation, which is found throughout the universe, is thought to be a tangible remnant of leftover light from the big bang. The radiation is akin to that used to transmit TV signals via antennas. But it is the oldest radiation known and may hold many secrets about the universe’s earliest moments.
The big bang theory leaves several major questions unanswered. One is the original cause of the big bang itself. Several answers have been proposed to address this fundamental question, but none has been proven—and even adequately testing them has proven to be a formidable challenge.
Neutron stars are ancient remnants of stars that have reached the end of their evolutionary journey through space and time.
These interesting objects are born from once-large stars that grew to four to eight times the size of our own sun before exploding in catastrophic supernovae. After such an explosion blows a star’s outer layers into space, the core remains—but it no longer produces nuclear fusion. With no outward pressure from fusion to counterbalance gravity’s inward pull, the star condenses and collapses in upon itself.
Despite their small diameters—about 12.5 miles (20 kilometers)—neutron stars boast nearly 1.5 times the mass of our sun, and are thus incredibly dense. Just a sugar cube of neutron star matter would weigh about one hundred million tons on Earth.
A neutron star’s almost incomprehensible density causes protons and electrons to combine into neutrons—the process that gives such stars their name. The composition of their cores is unknown, but they may consist of a neutron superfluid or some unknown state of matter.
Neutron stars pack an extremely strong gravitational pull, much greater than Earth’s. This gravitational strength is particularly impressive because of the stars’ small size.
When they are formed, neutron stars rotate in space. As they compress and shrink, this spinning speeds up because of the conservation of angular momentum—the same principle that causes a spinning skater to speed up when she pulls in her arms.
These stars gradually slow down over the eons, but those bodies that are still spinning rapidly may emit radiation that from Earth appears to blink on and off as the star spins, like the beam of light from a turning lighthouse. This “pulsing” appearance gives some neutron stars the name pulsars.
After spinning for several million years pulsars are drained of their energy and become normal neutron stars. Few of the known existing neutron stars are pulsars. Only about 1,000 pulsars are known to exist, though there may be hundreds of millions of old neutron stars in the galaxy.
The staggering pressures that exist at the core of neutron stars may be like those that existed at the time of the big bang, but these states cannot be simulated on Earth.
Black holes are the cold remnants of former stars, so dense that no matter—not even light—is able to escape their powerful gravitational pull.
The origin of the Moon refers to any of the various explanations for the formation of the Moon, Earth’s natural satellite. The leading theory has been the giant-impact hypothesis Continue reading “ORIGIN OF MOON”
During the stages of the Earth formation, ash, lava, carbon dioxide and water vapour discharged onto the surface of the planet by constant volcanic eruption.the water forms the oceans, wile carbon dioxide entered the atmosphere or was dissolved in the ocrans. Cloud,formed of water droplets,reflected some of the sun’radiation back into space. The Earth’s temprature stabilizing and early life forms began to emerge,converting carbon dioxied into life -giving oxygen.
It is taught that the gases that make up the earth’s atmosphere originated deep within the interior , and were realised many milloon of years ago during intense valcanic activity, similar to this eruption at mout st.helens
MILLIONS OF OBJESTS , remnannts of planetry formation, circle the sun in a zone lying between mars and jupiter: the asteroid belt. Fragments of asteriods break of to form meteorides , which can reach the Earth’s surface. Comets,conposed of ice and dust, originated outside our solar system. their elliptical orbit brings them close to sun and into the inner solar systm. Meteor crater in Arizona is 4200 feet (1300m) wide and 660 feet (200m) deep. It was formed over 10,ooo years ago. The orbit of halley’s comet brings it close to the EARTH every 76 years. It’s last visit was on 1986.