Fossil Stars and Their Luminosity

Articles “Astronomers find Fossil Stars from the Beginning of our Galaxy” and “Star Brightness Versus Star Luminosity”

In the first article I found “Astronomers find Fossil Stars from the Beginning of our Galaxy” relates to our eighth conceptual objective “I can explain how astronomers determine the luminosity, the temperature, and sizes of stars”, explains a recent story of how there is a system called Terzan-5 that is located in the center of our Milky Way galaxy. Scientists have now been able to figure out exactly how old the system is. It is exactly 12 billion years in age and is much older than our system. The article explains that we still do not know very much about this ancient fossil of a system but the more research is done the more we will eventually know. This story fits perfectly with this objective because they used a system called the color- magnitude diagram which uses color and the luminosity. It’s then in turn used to find the age of the star. After finding the age scientists then use the information to find the surface temperature and mass of each of the stars.

In class we learned that there are three specific properties that scientists study about stars which are luminosity, mass, and temperature. We did several lecture tutorials of this material in finding a star’s temperature and mass and how it can help to discover its luminosity and also its brightness. According to the second article nearly every star that you see with the unaided eye is larger and more luminous than our sun, and that the majority of stars that are seen at night with just our eyes are millions of times farther away than our own star. These long distant stars can be seen from here on Earth though because they are much more luminous than the sun. So what exactly is a star’s luminosity? according to the definition in our book it is “the total power output of an object, usually measured in watts or in units of solar luminosities.” basically how much power and light it gives off and is measured by units of our sun. In order to find the exact calculations of a star’s luminosity, scientists have to combine and add its surface temperature, mass, and distance from us in the Milky Way. The star shows to be more luminous to us here on Earth if it is much hotter, closer, and appears more blue in the sky. When the star is less luminous it tends to be the opposites such as being further away, much cooler, and more red in color. The less luminous stars also tend to be smaller than those who are more luminous and outshine the others. Sometimes however this is not always the case. There are some stars that could appear to have more luminosity even though they are cooler but are still bigger than others just because they are closer to us. Another unique situation that can break the rules as mentioned earlier is that if there are two stars that happen to be the same mass and distance away even though one is hotter than the other, they can be equally luminous to us here. A great in class example that you can view and try out in your own home is the stove experiment. In one of our lecture tutorials we learned that if you have a stove and two burners one being large but not as hot and one that is small but super hot and you tried to cook a pot of spaghetti on each one, the spaghetti on the super hot small burner would cook faster despite its size because of the super hot temperature. Not only is temperature found on stoves and can be measured and used for spaghetti but it can also be measured on stars. This is measuring of surface temperature and can be directly taken. In order to find the star’s surface temperature you can start by observing the color radiating from it. Scientists learn from doing this all the time. As was mentioned earlier stars that are the hottest are colors such as blue, white, or even purple. Medium temperatured stars like our own are generally more yellow or orange while cool stars are red. The next part for scientists to be able to have an exact knowledge of surface temperature is being able to measure the star’s spectral lines. Spectral lines are by definition in our book as, “the bright or dark lines that appear in an object’s spectrum, which we can see when we pass the object’s light through a prism like device that spreads out the light like a rainbow.”

Image result for spectral lines

In the picture above you can see how each one of the colors is represented and scientists use color scales like these in order to get the temperature to an exact degree. There are however different types of these spectra which include continuous spectrum, emission line spectrum, and absorption line spectrum. Each of these spectrums are a little different like how continuous spectrum is typically your incandescent light bulb because its wavelengths are broad and are without interruption. Emission line spectrum is usually blocked light slightly by a gas cloud and only emits light at certain wavelengths that depend on its composition and temperature. Finally there is absorption line spectrum where if there is a cloud of gas we are still able to see most of the continuous spectrum but some of the specific wavelengths do get absorbed.

Image result for continuous line spectrum

Certain stars that have spectral lines that are made of highly ionized elements are hotter because atoms have to have a higher temperature to ionize. While other stars whose spectral lines have molecules are cooler because the molecules will break apart into separate atoms if and when the temperature is not cold enough. When scientists are finished with their studying of spectral lines, they then classify the stars based on their chemical composition of the spectral lines and their spectral types. After classifying these two things the last portion is measuring mass. This task can be very difficult considering the star is so far away so scientists use Newton’s version of Kepler’s third law to accomplish this. Newton’s law has a catch however, it can only be applied when there are two objects and one object orbits the other. Since this is the case most of the time scientists are usually only able to measure the mass of stars within a binary system (a two star system that orbits one another). When scientists are able to get the mass of a star, they find it by measuring its velocity, orbital distance, and orbital speed. By adding and combining these three things together and Kepler’s third law with Newton’s they are able to calculate the star’s mass.

This objective was probably one of my tougher ones but I ended up learning a lot from it. One of my favorite things about this unit that I learned was about how scientists are able to get the exact measurements of stars by their color and spectral lines. I have always known that fire at least has a color range when it comes to its temperature and how the reddest ember is the coolest part of the fire while the blue and white center of a flame is the hottest (even though you don’t want to touch either of them) but I did not know it was the same for stars for the longest time. It is very interesting to now know that. The articles I read for this objective had a lot to say and helped me learn quite a bit about this objective on another level which is great. They were well written and were interesting to read. I believe this objective was one of my most helpful ones and will definitely be great to use for other objectives and who knows it may pop up again sometime outside of class and now I will know that much more about the universe. This was a very interesting and fun objective and I look forward to our next unit.






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