Throughout human history, the glow of the Milky Way stretching across the heaven
ID: 231421 • Letter: T
Question
Throughout human history, the glow of the Milky Way stretching across the heavens has been an inspiring sight, and thanks to hundreds of years of research, we now have a very detailed picture of the shape and content of our galaxy. Discuss the physical characteristics of the Milky Way, including a detailed sketch of the major structures and indications of their sizes in light years or parsecs. Be sure to discuss the content of these structures as well: Where do new stars form in the galaxy? Why don't new stars form everywhere? Where is the dark matter in the galaxy? What is the evidence for a super-massive black hole in the center of the galaxy?
Explanation / Answer
The Milky Way Galaxy is a huge spinwheel of stars and gas rotating within a giant cloud of invisible matter. Many generations of stars have formed and died within its disk, enriching our galaxy’s store of heavy elements. Before the disk formed, the future Milky Way probably existed as several distinct galaxies which fell together and fused.
The Earth orbits the Sun in the Solar System, and the Solar System is enclosed within this vast galaxy of stars. It is one of the hundreds of billions of galaxies in the Universe. It is called the Milky Way because the disk of the galaxy appears to be spanning the night sky like a misty band of bright white light. It is made up of a very large number of small, strongly grouped stars, and it seem to be cloudy patches because of their concentration and smallness. The Milky Way looks brightest toward the galactic center, in the direction of Sagittarius. Milky Way divides the night sky into two roughly equal parts specify that the Solar System lies near the galactic plane. The Milky Way has a comparatively low surface brightness due to the gases and dust that fills the galactic disk which prevent from seeing the bright galactic center or from seeing clearly what is on the other side of it.
Globular clusters group around the galactic center. The Milky Way has three main parts- bulge, disk, & halo. Our galaxy approximately contains 100,000,000,000 stars and it is around 100,000 light years side to side and it bulges at the middle and around 16,000 light years thick.
Our Milky Way is a barred spiral galaxy about 120,000 light-years across and around 1,000 light-years thick. The Milky Way was thought to have 4 spiral arms, but newer studies determined that it actually have 2 spiral arms, called Scutum Centaurus and Carina Sagittarius.
These spiral arms are produced from density waves that revolving around the Milky Way. As these density waves travel through an area, they condense the gas and dust and leading to a condition for active star formation for the region.
Astronomers approximate that there are around 100 and 400 billion stars in the Milky Way and each star has at least one planet, which means there may be hundreds of billions of planets in the Milky Way and at least 17 billion of these are likely to be the size and mass of the Earth.
Our Sun is situated in the Orion Arm, a region between the two major arms of the Milky Way, and around 27,000 light years from the galactic core. At the heart of the Milky Way is a super massive black hole called Sagittarius A. This is approximately more than 4 million times the mass of the Sun and is believed to have a diameter of 44 million kilometers.
Sun takes about 240 million years to revolve around the Milky Way once, it known as a galactic year (or cosmic year). The Milky Way is enclosed by a vast halo of dark matter, which accounts for around 90% of its mass. It determines how fast the galaxy rotates and other general characteristics. This dark matter helps to keep the galaxy from splitting itself apart as it rotates.
It is believed that our galaxy is formed due to the clash of smaller galaxies, early in the Universe and these fusions are still going on, and the Milky Way is likely to collide with the Andromeda galaxy in 3-4 billion years. The two galaxies will merge to form a huge elliptical galaxy, and their super-massive black holes may even merge.
The black hole that situated in the center of Milky Way is named as Sagittarius A* or Sgr A* for short. It is about 26,000 light-years from our Earth and Sgr A* is calculated to be about 14 million miles across. The lower mass limit of the black hole is calculated to be about more than 40,000 Suns. However, the radio-emitting part of Sgr A* is little bigger and it is about the size of the Earth’s orbit around the Sun (93 million miles), and weighs much, much more approximately 4 billion Suns. Black holes have a strong gravitational pull that nothing can escape from it. We think that black holes should be invisible because they don’t produce light, and attract everything in the vicinity, but it is actually be very bright, this is because of the fact that as matter grouped around them, friction causes the gas and dust to heat up and emit light. Sgr A*, will try to swallow anything that goes near it. But it is not destructive all of the time, the area around it is a good place for new stars to form. The black hole at the center of our Milky Way is very energetic, emitting out flares of gas from stars it has swallowed.
Astronomers have collected enough evidence from the observed motions of gas and stars that very huge lurk at the center of our galaxy. The first dynamical confirmation came from the motions of the ionized gas flags of the small spiral orbiting Sgr A*. Using the velocities of this gas calculated from the Doppler shift of spectral lines, astronomers estimated that a mass of six million solar masses must lie within 10 arcseconds of Sgr A*.
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