Answer 32-35 with explanation 32. The main sequence turn-off point in the H-R di
ID: 288219 • Letter: A
Question
Answer 32-35 with explanation
32. The main sequence turn-off point in the H-R diagram of a star cluster reveals the of the cluster. a) total stellar mass b) chemical composition c) total star number 0 age 33· The Pleiades is an example of a a) open cluster Dplanetary nebula c) globular cluster d) supernova remnant 34. The object at the center of the Crab nebula supernova remnant is a a) white dwarf black hole planetary nebula b) neutron star s. According to Einstein's theory of special relativity, the speed of light is the same for all observers. a) TRUE b FALSEExplanation / Answer
The turnoff point for a star refers to the point on the Hertzsprung-Russell diagram where it leaves the main sequence after the exhaustion of its main fuel. Sun-like stars will enter the red giant branch as subgiants.
By plotting the turnoff point of the stars in star clusters, one can estimate the cluster's age.
Star clusters provide us with a lot of information that is relevant to the study of stars in general. The main reason is that we assume that all stars in a cluster formed almost simultaneously from the same cloud of interstellar gas, which means that the stars in the cluster should be very homogeneous in their properties. This means that the only significant difference between stars in a cluster is their mass, but if we measure the properties of one star (age, distance, composition, etc.), we can assume that the properties of the rest of the stars in the cluster will be very similar.
In reality, some stars in the cluster form earlier than others, but compared to their lifetimes, the spread in their formation times is small and can be ignored. We also assume that the stars in a cluster are all the same distance away from us. Again, there is in fact a spread in distance, but, in most cases, this spread is much smaller than the distance to the cluster, so it can be ignored. For example, the outermost stars in the globular cluster M13 are about 50 parsecs from the center of the cluster, but the cluster is about 7,700 parsecs away from us. Finally, we assume that the chemical composition of all of the stars in a particular cluster should be very similar because the cloud of gas from which they formed is expected to have been well mixed, so the individual cloud fragments that formed individual stars should all have contained the same mix of elements and molecules.
When stars form out of a molecular cloud, very high mass stars (perhaps up to about 100 times the mass of the Sun) all the way down to low mass, brown dwarf objects (about 0.08 solar masses) are formed. Observations of newly formed populations of stars have shown us that very few high mass stars form, while many low mass stars form. The drop-off is very steep as you get to higher masses, as well. If you were to survey the stars near the Sun, you would find that about 90% of all stars in our Solar Neighborhood are less than or equal to the Sun's mass. Most of the rest are less than twice the mass of the Sun, and only about 0.5% of all nearby stars are more massive than 8 times the mass of the Sun. Remarkably, observations of star formation in many different locations in the universe seem to indicate that the relative ratios of stars of different masses that form is a universal law. That is, the same relative proportion of high mass compared to low mass stars always forms regardless of the size of the star forming region, the environment in which the star forming region resides, and how long ago the stars formed. Therefore, if we can determine how one cluster of stars formed, we can generalize our findings to apply to all clusters. This idea of a relationship between the number of stars formed in a star forming region and their mass is referred to as the stellar initial mass function.
Let us follow the evolution of an entire cluster of stars through several stages of its lifetime. Click on the "Advance in time" button in the Flash animation below to step through the evolution
33) he Pleiades have inspired a wealth of mythology and legends: fascinating as these are the reality the star cluster is profoundly more wonderful. Historically, the Pleiades were seen as a group of 'seven' stars – its brightest stars: Alcyone, Atlas, Electra, Maia, Merope, Taygeta and Pleione are visible to the keen naked eye. However modern observations show that this most famous of open clusters is comprised of several hundred stars wreathed in intricately structured nebulosity.
At a distance of about 440 light years from the Earth, the Pleiades are one of the nearest galactic open clusters. The brightest stars in the cluster (Alcyone is magnitude +2.8, and Pleione +5.1) are distributed over about seven light years and although faint to naked sight these stars are from 40 to 1000 times brighter than our Sun. From the Earth the cluster's apparent size is 110 minutes of arc (almost 2°) in the plane of the ecliptic: in comparison, the diameter of a full Moon is about 0.5°.
The cluster has an apparent motion relative to the Earth of an angular rate of just over five seconds of arc per century towards the star lambda Tauri, that is, in a south-easterly direction. Thus the Pleiades takes some 60,000 years to traverse one degree.
The Pleiades exhibits one of the finest and nearest examples of a reflection nebula associated with a cluster of young stars. The nebulosity seen here is light reflected from the particles in an interstellar cloud of cold gas and dust into which the cluster has drifted. The apparent blue colour is due to the preferential scattering of blue light by these tiny interstellar particles and is 'streaky' in structure since the particles have been aligned by the magnetic fields between the stars.
A supernova remnant forms when the pressure inside of a star is stronger than the gravity that holds it together, and the star explodes. As the gas rushes outward, it fills the space around it. The material ejected from the Crab Nebula is moving at more than 3 million mph (4.8 million kph). [Supernova Photos: Great Images of Star Explosions]
The nebula stretches 10 light-years across, though it continues to expand. It lies approximately 6,300 light-years from Earth, in the constellation of Taurus. M1 can be seen with the naked eye in a dark sky, but only barely. A pair of binoculars will turn up a dim patch, while more of the identifying features of the nebula become visible with a low-magnification telescope. A higher-grade, 16-inch telescope will begin to refine more of the nebula.
A bright source In the summer of 1967, U.S. Air Force officer Charles Schisler was on radar duty at Clear Air Force Base in Alaska when he noticed a fluctuating radio source. The source appeared over the course of several days, and Schisler noticed that its position coincided with the Crab Nebula. However, the findings weren't published by the Air Force at the time, and the discovery went unrealized until 2007.
A year later, astronomers in Puerto Rico discovered the same pulsing radio source. Determined to be a pulsar, the object is a rapidly-rotating, town-sized star that flashes about 30 times a second. Known as NP0532, or the Crab Pulsar, the neutron star is 100,000 times more energetic than the sun. Though only a few tens of miles across, it shines about as brightly as our nearest sun.
Two objects exert a force of attraction on one another known as "gravity." Sir Isaac Newton quantified the gravity between two objects when he formulated his three laws of motion. The force tugging between two bodies depends on how massive each one is and how far apart the two lie. Even as the center of the Earth is pulling you toward it (keeping you firmly lodged on the ground), your center of mass is pulling back at the Earth. But the more massive body barely feels the tug from you, while with your much smaller mass you find yourself firmly rooted thanks to that same force. Yet Newton's laws assume that gravity is an innate force of an object that can act over a distance.
Albert Einstein, in his theory of special relativity, determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels. As a result, he found that space and time were interwoven into a single continuum known as space-time. Events that occur at the same time for one observer could occur at different times for another.
As he worked out the equations for his general theory of relativity, Einstein realized that massive objects caused a distortion in space-time. Imagine setting a large body in the center of a trampoline. The body would press down into the fabric, causing it to dimple. A marble rolled around the edge would spiral inward toward the body, pulled in much the same way that the gravity of a planet pulls at rocks in space.