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Elijah Evans
Elijah Evans

Buy A Star Nasa !!HOT!!

Astronomers believe that molecular clouds, dense clouds of gas located primarily in thespiral arms of galaxies are the birthplace of stars. Denseregions in the clouds collapse and form "protostars". Initially, thegravitational energy of the collapsing star is the source of its energy. Once the starcontracts enough that its central core can burn hydrogen to helium, it becomes a"main sequence" star.

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Main sequence stars are stars, like our Sun, that fuse hydrogen atoms together to makehelium atoms in their cores. For a given chemical composition and stellar age, a stars'luminosity, the total energy radiated by the star per unit time, depends only on its mass.Stars that are ten times more massive than the Sun are over a thousand times more luminousthan the Sun. However, we should not be too embarrassed by the Sun's low luminosity: it isten times brighter than a star half its mass. The more massive a main sequence star, thebrighter and bluer it is. For example, Sirius, the dog star, located to the lower left ofthe constellation Orion, is more massive than the Sun, and is noticeably bluer. On theother hand, Proxima Centauri, our nearest neighbor, is less massive than the Sun, and isthus redder and less luminous.

Since stars have a limited supply of hydrogen in their cores, they have a limitedlifetime as main sequence stars. This lifetime is proportional to f M /L, where f is the fraction of the total mass of the star, M, available for nuclear burning in the core and Lis the average luminosity of the star during its main sequence lifetime. Because of thestrong dependence of luminosity on mass, stellar lifetimes depend sensitively on mass.Thus, it is fortunate that our Sun is not more massive than it is since high mass starsrapidly exhaust their core hydrogen supply. Once a star exhausts its core hydrogen supply,the star becomes redder, larger, and more luminous: it becomes a red giant star. Thisrelationship between mass and lifetime enables astronomers to put a lower limit on the age of the universe.

After a low mass star like the Sun exhausts the supply of hydrogen in its core, there is no longer any source of heat to support the core against gravity. Hydrogen burning continues in a shell around the core and the star evolves into a red giant. When the Sun becomes a red giant, its atmosphere will envelope the Earth and our planet will be consumed in a fiery death.

Meanwhile, the core of the star collapses under gravity's pull until it reaches a high enough density to start burning helium to carbon. The helium burning phase will last about 100 million years, until the helium is exhausted in the core and the star becomes a red supergiant. At this stage, the Sun will have an outer envelope extending out towards Jupiter. During this brief phase of its existence, which lasts only a few tens of thousands of years, the Sun will lose mass in a powerful wind. Eventually, the Sun will lose all of the mass in its envelope and leave behind a hot core of carbon embedded in a nebula of expelled gas. Radiation from this hot core will ionize the nebula, producing a striking "planetary nebula", much like the nebulae seen around the remnants of other stars. The carbon core will eventually cool and become a white dwarf, the dense dim remnant of a once bright star.

Massive stars burn brighter and perish more dramatically than most. When a star tentimes more massive than Sun exhaust the helium in the core, the nuclear burning cyclecontinues. The carbon core contracts further and reaches high enough temperature to burncarbon to oxygen, neon, silicon, sulfur and finally to iron. Iron is the most stable formof nuclear matter and there is no energy to be gained by burning it to any heavierelement. Without any source of heat to balance the gravity, the iron core collapses untilit reaches nuclear densities. This high density core resists further collapse causing theinfalling matter to "bounce" off the core. This sudden core bounce (whichincludes the release of energetic neutrinos from the core) produces a supernova explosion.For one brilliant month, a single star burns brighter than a whole galaxy of a billionstars. Supernova explosions inject carbon, oxygen, silicon and other heavy elements up toiron into interstellar space. They are also the site where most of the elements heavierthan iron are produced. This heavy element enriched gas will be incorporated into futuregenerations of stars and planets. Without supernova, the fiery death of massive stars,there would be no carbon, oxygen or other elements that make life possible.

The fate of the hot neutron core depends upon the mass of the progenitor star. If theprogenitor mass is around ten times the mass of the Sun, the neutron star core will coolto form a neutron star. Neutron stars are potentially detectable as "pulsars",powerful beacons of radio emission. If the progenitor mass is larger, then the resultantcore is so heavy that not even nuclear forces can resist the pull of gravity and the corecollapses to form a black hole.

Our Sun (a star) and all the planets around it are part of a galaxy known as the Milky Way Galaxy. A galaxy is a large group of stars, gas, and dust bound together by gravity. They come in a variety of shapes and sizes. The Milky Way is a large barred spiral galaxy. All the stars we see in the night sky are in our own Milky Way Galaxy. Our galaxy is called the Milky Way because it appears as a milky band of light in the sky when you see it in a really dark area.

The first clue to the shape of the Milky Way comes from the bright band of stars that stretches across the sky (and, as mentioned above, is how the Milky Way got its name). This band of stars can be seen with the naked eye in places with dark night skies. That band comes from seeing the disk of stars that forms the Milky Way from inside the disk, and tells us that our galaxy is basically flat.

Several different telescopes, both on the ground and in space, have taken images of the disk of the Milky Way by taking a series of pictures in different directions – a bit like taking a panoramic picture with your camera or phone. The concentration of stars in a band adds to the evidence that the Milky Way is a spiral galaxy. If we lived in an elliptical galaxy, we would see the stars of our galaxy spread out all around the sky, not in a single band.

Another clue comes when astronomers map young, bright stars and clouds of ionized hydrogen in the Milky Way's disk. These clouds, called HII regions, are ionized by young, hot stars and are basically free protons and electrons. These are both important marker of spiral arms in other spiral galaxies we see, so mapping them in our own galaxy can give a clue about the spiral nature of the Milky Way. There are bright enough that we can see them through the disk of our galaxy, except where the region at the center of our galaxy gets in the way.

At the start of the VIM, the two Voyager spacecraft had been in flight for over 12 years having been launched in August (Voyager 2) and September (Voyager 1), 1977. Voyager 1 was at a distance of approximately 40 AU (Astronomical Unit - mean distance of Earth from the Sun, 150 million kilometers) from the Sun, and Voyager 2 was at a distance of approximately 31 AU.

While this image is spectacular, there are actually stars that Hubble can't see inside those pillars of dust. And that's because the visible light emitted by those stars is being obscured by the dust. But what if we used a telescope sensitive to infrared light to look at this nebula?

The Pillars of Creation in the Eagle Nebula captured in infrared light by Hubble. The light from young stars being formed pierce the clouds of dust and gas in the infrared. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

The next image is another Hubble view, but this time in near-infrared. In the infrared more structure within the dust clouds is revealed and hidden stars have now become apparent. (And if Hubble, which is optimized for visible light, can capture a near-infrared image like this, imagine what Webb, which is optimized for near-infrared and 100x more powerful than Hubble, will do!)

ALMA image of the young star HL Tau and its protoplanetary disk. This best image ever of planet formation reveals multiple rings and gaps that herald the presence of emerging planets as they sweep their orbits clear of dust and gas. Credit: ALMA (NRAO/ESO/NAOJ); C. Brogan, B. Saxton (NRAO/AUI/NSF)

Webb's amazing imaging and spectroscopy capabilities will allow us to study stars as they are forming in their dusty cocoons. Additionally, it will be able to image disks of heated material around these young stars, which can indicate the beginnings of planetary systems, and study organic molecules that are important for life to develop.

  • Webb will address several key questions to help us unravel the story of the star and planet formation: How do clouds of gas and dust collapse to form stars?

  • Why do most stars form in groups?

  • Exactly how do planetary systems form?

How do stars evolve and release the heavy elements they produce back into space for recycling into new generations of stars and planets?

To unravel the birth and early evolution of stars and planets, we need to be able to peer into the hearts of dense and dusty cloud cores where star formation begins. These regions cannot be observed at visible light wavelengths as the dust would make such regions opaque and must be observed at infrared wavelengths.

Stars, like our Sun, can be thought of as "basic particles" of the Universe, just as atoms are "basic particles" of matter. Groups of stars make up galaxies, while planets and ultimately life arise around stars. Although stars have been the main topic of astronomy for thousands of years, we have begun to understand them in detail only in recent times through the advent of powerful telescopes and computers.

A hundred years ago, scientists did not know that stars are powered by nuclear fusion, and 50 years ago they did not know that stars are continually forming in the Universe. Researchers still do not know the details of how clouds of gas and dust collapse to form stars, or why most stars form in groups, or exactly how planetary systems form. Young stars within a star-forming region interact with each other in complex ways. The details of how they evolve and release the heavy elements they produce back into space for recycling into new generations of stars and planets remains to be determined through a combination of observation and theory. 041b061a72


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