NEBULA

                                NEBULA

NEBULA

A nebula (from Latin: "cloud"; pl. nebulae  with ligature or nebulas) is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, nebula was a name for any diffuse astronomical object, including galaxies beyond the Milky Way. The Andromeda Galaxy, for instance, was referred to as the Andromeda Nebula(and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble, etal. Nebulae are often star-forming regions, such as in the Eagle Nebula. This nebula is depicted in one of NASA's most famous images, the "Pillars of Creation". In these regions the formations of gas, dust, and other materials "clump" together to form larger masses, which attract further matter, and eventually will become massive enough to form stars. The remaining materials are then believed to form planets, and other planetary system objects.

Many nebulae or stars form from the gravitational collapse of gas in the interstellar medium or ISM. As the material collapses under its own weight, massive stars may form in the center, and their ultraviolet radiation ionizes the surrounding gas, making it visible at optical wavelengths. Examples of these types of nebulae are the Rosette Nebula and the Pelican Nebula. The size of these nebulae, known as HII regions, varies depending on the size of the original cloud of gas. New stars are formed in the nebulas. The formed stars are sometimes known as a young, loose cluster.

Some nebulae are formed as the result of supernova explosions, the death throes of massive, short-lived stars. The materials thrown off from the supernova explosion are ionized by the energy and the compact object that it can produce. One of the best examples of this is the Crab Nebula, in Taurus. The supernova event was recorded in the year 1054 and is labelled SN 1054. The compact object that was created after the explosion lies in the center of the Crab Nebula and is a neutron star.

Other nebulae may form as planetary nebulae. This is the final stage of a low-mass star's life, like Earth's Sun. Stars with a mass up to 8–10 solar masses evolve into red giants and slowly lose their outer layers during pulsations in their atmospheres. When a star has lost enough material, its temperature increases and the ultraviolet radiation it emits can ionize the surrounding nebula that it has thrown off. The nebula is almost 97% hydrogen and 3% helium, plus trace amounts of other elements.

Types of nebulae

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  The Omega Nebula, an example of an emission nebula
 
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  The Horsehead Nebula, an example of a dark nebula.
 
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  The Cat's Eye Nebula, an example of a planetary nebula.
 
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  The Red Rectangle Nebula, an example of aprotoplanetary nebula.
 
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  The delicate shell of SNR B0509-67.5

  
  

Classical types

Objects named nebulae belong to four major groups. Before their nature was understood, galaxies ("spiral nebulae") and star clusterstoo distant to be resolved as stars were also classified as nebulae, but no longer are.

• H II regions, large diffuse nebulae containing ionized hydrogen
• Planetary nebulae
• Supernova remnant (e.g., Crab Nebula)
• Dark nebula

Not all cloud-like structures are named nebulae; Herbig–Haro objects are an example.

10 TERRIFYING PLANETS U DON''T WANT TO VISIT

10 TERRIFYING PLANETS U DON'T WANT TO VISIT

10

Carbon Planet

Our planet maintains a high ratio of oxygen to carbon. Carbon actually makes up only about 0.1 percent of earth’s bulk (hence the scarcity of carbon based materials like fossil fuels and diamonds). Near the center of our galaxy however, where carbon is more plentiful than oxygen, planet formation is very different. It is here that you find what cosmologists call carbon planets. The morning sky on a carbon world would be anything but crystal clear and blue. Picture a yellow haze with black clouds of soot. As you descend farther down into the atmosphere you find seas made of compounds like crude oil and tar. The surface of the planet bubbles with foul smelling methane pits and black ooze. The weather forecast doesn’t look good either: it’s raining gasoline and asphalt (…no smoking). But there would be an upside to this “oil-well hell.” You may have guessed it. Where carbon is plentiful you also find high quantities of diamond.

9

Neptune

On Neptune, one can find constant jet stream winds that whip around the planet at terrifying speeds. Neptune’s jet-stream winds push frozen clouds of natural gas past the north edge of the planet’s Great Dark Spot, an Earth-size hurricane, at a staggering 1,500 miles per hour. That is more than double the speed needed to break the sound barrier. Such wind forces are clearly beyond what a human could withstand. A person who happened to find himself on Neptune would be most likely be ripped apart and lost forever in these violent and perpetual wind currents. It remains a mystery as to how it gets the energy to drive the fastest planetary winds seen in the solar system, despite it being so far from the sun, at times farther from the sun than Pluto, and having relatively weak internal heat.

8

51 Pegasi b

Nick-named Bellerophon, in honor of the Greek hero who tamed the winged horse Pegasus, this gas giant is over 150 times as massive as earth and made mostly of hydrogen and helium. The problem is that Bellerophon roasts in the light of its star at over 1800 degrees F (1000 degrees C). Bellerophon’s star is over 100 times closer to it than the Sun is to Earth. For one thing, this heat creates an extremely windy atmosphere. As the hot air rises, cool air rushes down to replace it creating 1000 km per hour winds. The heat also ensures that no water vapor exists. However, that does not mean there is no rain. This leads us to Bellerophon’s main quirk. Such intense heat enables the iron composing the planet to be vaporized. As the vapor rises it forms iron vapor clouds, similar in concept to water vapor clouds here on Earth. The difference though, is that these clouds will then proceed to rain a relentless fury of molten iron down upon the planet (…don’t forget your umbrella).

7

COROT exo-3b

The densest and most massive exoplanet to date is a world known as COROT-exo-3b. It is about the size of Jupiter, but 20 times that planet’s mass. This makes COROT-exo-3b about twice as dense as lead. The degree of pressure put upon a human walking the surface of such a planet would be insurmountable. With a mass 20 times that of Jupiter, a human would weigh almost 50 times what they weigh on Earth. That means that a 180 pound man on Earth would weigh 9000 pounds! That amount of stress would crush a human beings skeletal system almost instantly. It would be the equivalent of an elephant sitting on your chest.

6

Mars

On Mars a dust storm can develop in a matter of hours and envelope the entire planet within a few days. They are the largest and most violent dust storms in our solar system. The Martian dust vortices tower over their earthly counterparts reaching the height of Mount Everest with winds in excess of 300 kilometers per hour. After developing, it can take months for a dust storm on Mars to completely expend itself. One theory as to why dust storms can grow so big on Mars starts with airborne dust particles absorbing sunlight, warming the Martian atmosphere in their vicinity. Warm pockets of air flow toward colder regions, generating winds. Strong winds lift more dust off the ground, which in turn heats the atmosphere, raising more wind and kicking up more dust. Surprisingly, many of the dust storms on the planet originate from one impact basin. Hellas Basin is the deepest impact crater in the Solar System. The temperatures at the bottom of the crater can be 10 degrees warmer than on the surface and the crater is deeply filled with dust. The difference in temperature fuels wind action that picks up the dust, then the storm emerges from the basin.

5

WASP-12b

Simply put, this planet is the hottest planet ever discovered. It measures in at about 4,000 degrees F (2,200 degrees C) and orbits its star closer than any other known world. It goes without saying that anything known to man, including man himself, would instantly incinerate in such an atmosphere. To put it in perspective, the planets’ surface is about half the temperature of the surface of our sun and twice as hot as lava. It also orbits its star at a blistering pace. It completes a full orbit once every Earth day at a distance of only about 2 million miles (3.4 million km).

4

Jupiter

Jupiter’s atmosphere brews storms twice as wide as the Earth itself. These goliaths generate 400 mph winds and titanic lightning bolts 100 times brighter than ones on Earth. Lurking underneath this frightening and dark atmosphere is a 25,000 mile deep ocean of liquid metallic hydrogen. Here on Earth, hydrogen is a colorless, transparent gas, but in the core of Jupiter, hydrogen transforms into something never seen on our planet. In Jupiter’s outer layers, hydrogen is a gas just like on Earth. But as you go deeper, the atmospheric pressure sky-rockets. Eventually the pressure becomes so great that it actually squeezes the electrons out of the hydrogen atoms. Under such extreme conditions, the hydrogen transforms into a liquid metal, conducting electricity as well as heat. Also, like a mirror, it reflects light. So if you were immersed in it, and caught under one of those ferocious lightning bolts, you wouldn’t be able to see anything.

3

Pluto

 Pluto is an extremely cold world where frozen nitrogen, carbon monoxide, and methane blanket the surface like snow during most of its 248 year plutonian year. These ices have been transformed from white to a pinkish-brown due to interactions with gamma rays from deep space and the distant Sun. On a clear day the sun provides about as much heat and light as a full moon does back on earth. With Pluto’s surface temperature of -378 to -396 F (-228 to -238 C) your body would freeze solid instantly.

2

CoRoT-7b

The temperatures on the star-facing side of this planet are so hot that they can vaporize rock. Scientists who modeled the atmosphere of CoRoT-7b determined that the planet likely has no volatile gases (carbon dioxide, water vapor, nitrogen), and is instead likely made up of what could be called vaporized rock. The atmosphere of CoRoT-7b could have weather systems that unlike the watery weather on Earth cause pebbles to condense out of the air and rain rocks onto the molten lava surface of the planet. And if the planet doesn’t already sound inhospitable to life, it also could be a volcanic nightmare. Evidence suggests that if CoRoT-7b’s orbit is not perfectly circular, gravitational tugs from one of its two sister planets could push and pull the surface, creating friction that heats the interior of the planet. This heating could cause extensive volcanism across the planet’s surface, with even more explosive activity than Jupiter’s moon Io, which has over 400 volcanoes.

1

Venus

Little was known about Venus (where the dense atmosphere is opaque to light at visible wavelengths) until the Soviets launched the Venera program back in the space race days. When the first probe touched down and began transmitting data back to Earth, the Soviets effectively achieved the only successful landing on the surface of Venus to this very day. The terrain was so incredibly volatile, the longest any of the probes lasted was 127 minutes before they were simultaneously crushed and melted. So, what would it be like to live on Venus, the most dangerous planet in our solar system? Well, almost instantly, you would be suffocated by the toxic air and although the gravity is only 90% of what we enjoy, you’d still be  crushed by the tremendous weight of the atmosphere. With pressures up to 100 times more than Earth’s, its 40 miles thick and so dense that walking on Venus’ surface would be like walking under 3,000 feet of water here on Earth. Simultaneously, you would be incinerated by the extreme 475 degree C temperatures, and eventually dissolved by the high concentration of sulfuric acid, which actually rains down on the surface of Venus.

SUPERNOVAS

                                                            SUPERNOVAS

One of the most energetic explosive events known is a supernova. These occur at the end of a star's lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy. If the star is particularly massive, then its core will collapse and in so doing will release a huge amount of energy. This will cause a blast wave that ejects the star's envelope into interstellar space. The result of the collapse may be, in some cases, a rapidly rotating neutron star that can be observed many years later as a radio pulsar.

While many supernovae have been seen in nearby galaxies, they are relatively rare events in our own galaxy. The last to be seen was Kepler's star in 1604. This remnant has been studied by many X-ray astronomy satellites, including ROSAT. There are, however, many remnants of Supernovae explosions in our galaxy, that are seen as X-ray shell like structures caused by the shock wave propagating out into the interstellar medium. Another famous remnant is the Crab Nebulawhich exploded in 1054. In this case a pulsar is seen which rotates 30 times a second and emits a rotating beam of X-rays (like a lighthouse). Another dramatic supernova remnant is the Cygnus Loop.

HISTORY

The supernova explosion that formed the Vela Supernova Remnant most likely occurred 10,000–20,000 years ago. In 1976, NASA astronomers suggested that inhabitants of the southern hemisphere may have witnessed this explosion and recorded it symbolically. A year later, archaeologist George Michanowsky recalled some incomprehensible ancient markings in Bolivia that were left by Native Americans. The carvings showed four small circles flanked by two larger circles. The smaller circles resemble stellar groupings in the constellations Vela and Carina. One of the larger circles may represent the star Capella. Another circle is located near the position of the supernova remnant, George Michanowsky suggested this may represent the supernova explosion as witnessed by the indigenous residents.

In 185 CE, Chinese astronomers recorded the appearance of a bright star in the sky, and observed that it took about eight months to fade from the sky. It was observed to sparkle like a star and did not move across the heavens like a comet. These observations are consistent with the appearance of a supernova, and this is believed to be the oldest confirmed record of a supernova event by humankind. SN 185 may have also possibly been recorded in Roman literature, though no re

cords have survived. The gaseous shell RCW 86 is suspected as being the remnant of this event, and recent X-ray studies show a good match for the expected age.

In 393 CE, the Chinese recorded the appearance of another "guest star", SN 393, in the modern constellation of Scorpius. Additional unconfirmed supernovae events may have been observed in 369 CE, 386 CE, 437 CE, 827 CE and 902 CE. However these have not yet been associated with a supernova remnant, and so they remain only candidates. Over a span of about 2,000 years, Chinese astronomers recorded a total of twenty such candidate events, including later explosions noted by Islamic, European, and possibly Indian and other observers.

The supernova SN 1006 appeared in the southern constellation of Lupus during the year 1006 CE. This was the brightest recorded star ever to appear in the night sky, and its presence was noted in China, Egypt, Iraq, Italy, Japan and Switzerland. It may also have been noted in France, Syria, and North America. Egyptian physician, astronomer and astrologer Ali ibn Ridwan gave the brightness of this star as one-quarter the brightness of the Moon. Modern astronomers have discovered the faint remnant of this explosion and determined that it was only 7,100 light-years from the Earth.

Supernova SN 1054 was another widely-observed event, with Arab, Chinese, and Japanese astronomers recording the star's appearance in 1054 CE. It may also have been recorded by the Anasazi as a petroglyph.This explosion appeared in the constellation of Taurus, where it produced the Crab Nebula remnant. At its peak, the luminosity of SN 1054 may have been four times as bright as Venus, and it remained visible in daylight for 23 days and was visible in the night sky for 653 days.

There are fewer records of supernova SN 1181, which occurred in the constellation Cassiopeia just over a century after SN 1054. It was noted by Chinese and Japanese astronomers, however. The pulsar 3C58 may be the stellar relic from this event.

The Danish astronomer Tycho Brahe was noted for his careful observations of the night sky from his observatory on the island of Hven. In 1572 he noted the appearance of a new star, also in the constellation Cassiopeia. Later called SN 1572, this supernova was associated with a remnant during the 1960s.

A common belief in Europe during this period was the Aristotelian idea that the world beyond the Moon and planets was immutable. So observers argued that the phenomenon was something in the Earth's atmosphere. However Tycho noted that the object remained stationary from night to night—never changing its parallax—so it must lie far away. He published his observations in the small book De nova et nullius aevi memoria prius visa stella (Latin for "Concerning the new and previously unseen star") in 1573. It is from the title of this book that the modern word nova for cataclysmic variable stars is derived.

The most recent supernova to be seen in the Milky Way galaxy was SN 1604, which was observed October 9, 1604. Several people noted the sudden appearance of this star, but it was Johannes Kepler who became noted for his systematic study of the object. He published his observations in the work De Stella nova in pede Serpentarii.

Galileo, like Tycho before him, tried in vain to measure the parallax of this new star, and then argued against the Aristotelian view of an immutable heavens.^[17] The remnant of this supernova was identified in 1941 at the Mount Wilson Observatory.