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The Eagle Nebula is about 6500 light years (lys) away in the constellation Serpens. Its 'wings' span 20 light years. The 'claws' at the bottom are known as the "Pillars of Creation" (see next slide). It is designated as Messier object M16 and named the Eagle Nebula for its obvious resemblance to a soaring eagle. Its true interest to astronomers is shown in the next slide, however.
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Pillars of Creation
The Pillars of Creation sounds like James Cameron’s latest 3-D epic. But it is in fact a massive cosmic structure that is a cauldron of star creation. Located in the Eagle Nebula, the Pillars, forming the eagle's talons, are as much as four light years in length.
The name was earned because these massive structures of dust and hydrogen gas are creating new stars on a continuing basis. The ‘Pillars’ are incredibly dense for such celestial gas clouds. Because they are so dense, they collapse under their own weight, and as this happens, the collapsing gas forms protostars. As the stars form, they accrete more material from the cloud and grow into full-fledged stars.
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The constellation of Orion is one of the most visible in the northern sky. It climbs well above the horizon in the winter, when seeing with a telescope is best in the cold still air. It is readily apparent by two unique features--the three star forming the hunter's belt (in the center of the photograph) and the three stars in the sword hanging from the belt. It is the second fuzzy 'star' that most interests astronomers, because that fuzzy object is not a star. It is a giant nebula, also a stellar nursery like the Pillars. Only 1500 lys from Earth, it is much easier studied, as the next slide shows.
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The Great Nebula in Orion
In this Hubble image, more than 3000 new stars are being formed. Many have surrounding accretion disks that contain protoplanets, giving astronomers more evidence that planetary formation is normal throughout the universe. There are also many brown dwarfs, failed stars that never accreted sufficient material to sustain their nuclear furnace. Most of the more recent stars began forming about 300,000 years ago. The Orion Nebula is 13 lys across, making it perhaps the most compact star birthplace in the galaxy.
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The Crab Nebula
Many nebulae, including Orion, are the result of a star that exploded as a nova or supernova, expelling its mass into space. The Crab Nebula is the remains of a star that was only about 10 times the mass of our Sun. The light of its life ending reached Earth on July 4, 1054 when its explosion as a supernova, 6500 years earlier, was seen clearly. (If you're a history buff, you know 1054 was a significant date in English history.) Sky watchers of the day, from Europe to the Orient, recorded the event. In the center of the nebula is a tiny neutron star, about the size of a small town, but as massive as the Sun.
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A New Stellar Explosion
The Stingray Nebula, so named for its obvious resemblance to the ocean creature, was not even known until Hubble snapped its picture. It is the youngest known planetary nebula—twenty-five years ago, the gas surrounding the dying star at the center was not hot enough to glow.
This image shows a rare moment in the final stages of a star's life where a shell of gas is cast off by a dying star, which then begins to glow like a neon light bulb. Images of planetary nebulae in their formative years like this can yield new insights into the last moments of ordinary stars like our Sun.
The nebula is one-tenth the size of most planetary nebulae and is 18,000 light-years away in the direction of the southern constellation Ara (the Altar).
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Not all 'nebula' are star formers—at first anyhow. There are huge clouds of dust and large molecules that obscure our vision of the Universe beyond them. This one, some 9500 lys away in the constellation Cassiopeia is unique in that there are newly formed stars around it that are pulling it apart. Called Bok globules after the astronomer who first hypothesized their existence, these dark clouds can sometimes hold together to become stellar nurseries, but often, like this one, eventually are torn apart by the radiation and gravitation forces of surrounding stars. They are formed from huge dust clouds hundreds of light years in size, their mass concentrating them into the smaller globules. This one is a little more than 13 lys in width.
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A Ball of Thousands of Stars
Globular clusters are gravitationally bound swarms of typically up to a million stars. There are more than 200 globular clusters in our Milky Way Galaxy. Astronomers have found evidence for a medium-size black hole at the core of Omega Centauri, one of the largest and most massive globular star clusters orbiting our Milky Way galaxy.
The intermediate-mass black hole is estimated to be roughly 40,000 times the mass of the Sun. For comparison, the supermassive black hole at the center of the Milky Way is billions of solar masses. The ancient cluster is located 17,000 light-years from Earth.
Astronomers measuring the speed of the stars swirling near the cluster's center found that the stars closer to the core are moving faster than the stars farther away. The measurement implies that some unseen matter at the core is tugging on stars near it.
By comparing these results with standard models, astronomers determined that the most likely cause of this accelerating stellar traffic jam is the gravitational pull of a massive, dense object. They also used models to calculate the black hole's mass. This is precisely the way in which the supermassive black holes at the center of galaxies were detected.
How globular clusters could exist had been a mystery for hundreds of years. Hubble may have found the answer.
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Into the Universe
If we could see our Milky Way galaxy from above, it would look something like this, M74 (Messier 74), also called NGC 628. This is a pure spiral galaxy viewed nearly face-on from Earth. Its perfectly symmetrical spiral arms emanate from the central nucleus and are dotted with clusters of young blue stars and glowing pink regions of ionized hydrogen (hydrogen atoms that have lost their electrons).
These regions of star formation show an excess of light at ultraviolet wavelengths. Tracing along the spiral arms are winding dust lanes that also begin very near the galaxy's nucleus and follow along the length of the spiral arms, very similar to dust lanes in our galaxy.
M74 is roughly 32 million light-years away in the direction of the constellation Pisces. It is the dominant member of a small group of about half a dozen galaxies, the M74 galaxy group. It is estimated that M74 is home to about 100 billion stars, making it slightly smaller than our Milky Way.
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More Stars Than You Can Count
The Coma Cluster of Galaxies, one of the densest known galaxy collections in the universe. Spanning several million light-years across the entire cluster contains thousands of galaxies. The cluster has a spherical shape more than 20 million light-years in diameter.
It is named after the constellation Coma Berenices, Bernice's Hair, which is near the Milky Way's north pole. This places the Coma Cluster in an area unobscured by dust and gas from the plane of the Milky Way, and easily visible from Earth. Most of the galaxies that inhabit the central portion of the Coma Cluster are ellipticals. Both dwarf, as well as giant ellipticals are found in abundance in the Coma Cluster.
Farther out from the center of the cluster are several spiral galaxies. These galaxies have clouds of cold gas that are giving birth to new stars. Spiral arms and dust lanes "accessorize" these bright bluish-white galaxies that show a distinctive disk structure.
In between the ellipticals and spirals is a morphological class of objects known as S0 (S-zero) galaxies. They are made up of older stars and show little evidence of recent star formation, however, they do show some semblence of structure—perhaps a bar or a ring, which may give rise to a more disk-like feature.
This Hubble image consists of a section of the cluster that is roughly one-third of the way out from the center of the cluster.
In the entire Coma Cluster, there are more stars in all its galaxies than there are grains of sand on all the beaches in all the world.
- Personal knowledge
- The Pillars of Creation: Brighthub Space Channel http://www.brighthub.com/science/space/articles/68542.aspx
- NASA, ESA, and the Hubble Heritage Team (STScI/AURA)