A nebula is a giant cloud of dust and gas in space. Some nebulae more than one nebula come from the gas and dust thrown out by the explosion of a dying star, such as a supernova. Other nebulae are regions where new stars are beginning to form. For this reason, some nebulae are called "star nurseries. These towers of cosmic dust and gas make up part of the Eagle Nebula.
These so-called Pillars of Creation are part of an active star-forming region within the nebula. Sometimes they are spread out wide like butterfly wings. Reflection nebulae are clouds of interstellar dust that have a star or stars close enough to shine light on them to make them visible to astronomers.
When a massive star reaches the end of its life, sometimes it explodes as a supernova. When this happens, the star expels lots of the material that used to be part of the star. Also known as plerions, pulsar wind nebulae are often found inside the shells of supernova remnants. They have also been found around older pulsars whose supernova remnants have disappeared.
Also known as absorption nebulae, dark nebulae are interstellar clouds so dense that they hide the light behind them. They are like thick storm clouds on Earth. These small areas can usually be found within larger H II regions.
There are millions and millions of Nebulas in the Universe, some more notable than others. It was first discovered by William Herschel in , and it was the first planetary nebula to be observed with a spectroscope in , giving astronomers insight into what makes up planetary nebulae.
In , scientists began to realize it was created by a supernova when Carl Otto Lampland noticed he had seen changes in its structure over time. The Horsehead Nebula also gets featured in photos because, being a dark nebula, it shows up very well against the surrounding portions of the Orion Complex.
It gets its name from its shape, like many nebulae. One of the easiest nebulae to see for the amateur observer, the Orion Nebula is known by a few other designations: Messier 42, M42, and NGC We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. However, you may visit "Cookie Settings" to provide a controlled consent. Read more on our privacy policy here.
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These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may affect your browsing experience. Necessary Necessary. Necessary cookies are absolutely essential for the website to function properly. Stellar Evolution Stars are not static objects. As a star consumes fuel in its nuclear reactions, its structure and composition changes, affecting its color and luminosity.
Thus, the H-R diagram not only shows us the colors and luminosities of many stars, it shows these stars at different stages in their evolutionary histories. All stars on the main sequence have interiors hot enough fuse four hydrogen atoms into one helium atom, and this one helium atom is 0. The lost mass is converted into energy, and this energy is released, providing the star's luminosity. Over billions of years, however, the residual helium in the star's core accumulates. When enough helium has accumulated, the helium can also undergo nuclear reaction.
In this reaction, three helium atoms are converted into one carbon atom. The helium-burning nuclear reaction can occur only when the star's interior reaches a higher temperature, and this higher temperature causes the star's outer surface to expand to a much larger size than it was while it remained on the main sequence.
Even though the core of the star is much hotter, the surface is now cooler, making the star redder. Thus, over time, a star becomes a red giant, moving from the main sequence area in the center of the H-R diagram to the red giant area in the upper right. The evolution from main sequence to red giant occurs at different times for different stars. Stars that are much heavier and hotter, like O-stars, become red giants in only 10 million years.
Cooler, lighter stars like our sun take 10 billion years to become red giants. This fact actually provides a way of testing how old a group of stars is - jut make an H-R diagram for the stars, and see which classes of stars have evolved off the main sequence! Eventually, all the helium in the core of the star is used up. At this point, what happens next depends on the mass of the star. The heaviest stars, over six to eight times as massive as our sun, have enough pressure in their cores to start fusing carbon.
Once carbon is gone, they explode as supernovae, leaving behind neutron stars or a black holes. Less massive stars simply burn out, shedding their outer layers into beautiful planetary nebulae, and leaving the core as a hot white dwarf. White dwarfs lie in the lower left corner of the H-R diagram, a cosmic burial ground for dead stars. An H-R diagram showing the evolutionary track of a sun-like star. Nebulae Originally, the word "nebula" referred to almost any extended astronomical object other than planets and comets.
The word "nebula" comes from the Greek word for "cloud. The solar wind from the star will eventually blow away all of the excess dust and gas. Sometimes other smaller clumps of matter around the star may form planets. This is the beginning of a new solar system. Several nebulae have been found to be stellar nurseries.
The Eagle Nebula, and the Orion Nebula are both sites of active star formation. There are a few nebulae that can be seen with the naked eye and many more that can be detected with a good pair of binoculars. A telescope is required to bring our fine details. Unfortunately, the human eye is not sensitive enough to bring out the rich colors of most nebulae. It is the photograph that does the most justice to these incredible objects. Until recently, time exposures on film were the best way to bring a nebula's true colors.
Today, digital photography has simplified the process. New tools like the Hubble space telescope are giving us views of nebulae that have never been seen before. Areas of active star formation have been identified in many galaxies that were once thought to be inert. Perhaps the most well known nebulae is the Orion Nebula, also known as M It is one of the very few that can be seen with the naked eye.
It is a bright emission nebula over 30 light-years in diameter. The nebula is illuminated by a group of stars at its center known as the trapezium. Another popular favorite is the Lagoon Nebula, M8. It is much larger than the Orion Nebula, reaching over light-years across the heavens.
The Trifid Nebula, M20, is one of the most colorful. This reflection nebula contains a combination of elements that render it in rich hues of red, blue, and pink. Dark lanes of dust divide it into three distinct parts, giving rise to its name. One of the most famous planetary nebulae is the Ring Nebula, M This is a beautiful object that resembles a circular rainbow around a small central star.
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