Welcome readers!
This week was a slower week, for most of my work consisted of reading up on how to determine the Hubble Constant. This was valuable though because I found out what to do with the data once I receive it. I've come to realize, however, that I have not properly discussed what I need to do to find the rate at which the universe is expanding. I will do my best to explain it in a way that won't be dry.
There are a few ways to measure the universe's rate of expansion, including the use of supernovae or cepheid variable stars. In case you don't know, a supernova is an explosion of a star while cepheid variable stars are stars that have periods of luminosity (similar to a slow flicker of a lightbulb). Astronomers use these objects because of the amount of light that they emit. Supernovae are one of the brightest objects in the sky. One was recorded as 20 times brighter than the combined amount of light from the Milky Way galaxy's 100 billion stars! Because they can be so bright, making them easier to observe, they are optimal for finding distance. In order to find the distance of the stars, astronomers need to know their apparent magnitude (how bright they look to us) and absolute magnitude (how bright they are with a standard distance of 32.6 light-years), and/or luminosity (the amount of energy emitted from the star). Once researchers have found the apparent magnitude (m) and absolute magnitude (M), they can plug it into the equation d = 10^{[(m-M) + 5]/5}.
To find the velocity of the star, or galaxy, astronomers need to determine the redshift. When objects move away from us, light shifts toward the red end of the spectrum, meaning that wavelengths get longer. Some have described this by relating it to a police siren. As the siren approaches, the pitch gets higher, but as it passes, their is a sudden decrease in the pitch. This arises because the sound waves are closer together when moving towards the listener, but the sounds waves stretch once they make their way past the listener. This is known as the Doppler Effect! Galaxies have the same effect. Because most galaxies are moving away from us, the light is stretched. Redshift can be described, in other words, as the shift in wavelengths of light. The equation for this is z = (observed wavelength - rest wavelength)/(rest wavelength). Rest wavelength is the wavelength of a star, or galaxy, not moving. If we have the redshift (z), we can multiply it by the speed of light, which is 300,000 km/s, to find the velocity of the object.
Now that we have both the velocity and distance, we can find the Hubble Constant. The Hubble Constant is the relationship between both velocity and distance. With both values, we can plot them on a graph. If we do this using several supernovae, we can determine the slope. The slope is the value of the Hubble Constant. The Constant is defined in terms of km/s/Mpc. Mpc is an abbreviation for Mega parsecs, a distance value. That tells us how far the object is. The km/s tells us how fast that object is receding from us.
I hope this cleared up any questions you had about how I am approaching this problem. If there are any questions, feel free to leave them below. Hope you guys have a good weekend!
This week was a slower week, for most of my work consisted of reading up on how to determine the Hubble Constant. This was valuable though because I found out what to do with the data once I receive it. I've come to realize, however, that I have not properly discussed what I need to do to find the rate at which the universe is expanding. I will do my best to explain it in a way that won't be dry.
There are a few ways to measure the universe's rate of expansion, including the use of supernovae or cepheid variable stars. In case you don't know, a supernova is an explosion of a star while cepheid variable stars are stars that have periods of luminosity (similar to a slow flicker of a lightbulb). Astronomers use these objects because of the amount of light that they emit. Supernovae are one of the brightest objects in the sky. One was recorded as 20 times brighter than the combined amount of light from the Milky Way galaxy's 100 billion stars! Because they can be so bright, making them easier to observe, they are optimal for finding distance. In order to find the distance of the stars, astronomers need to know their apparent magnitude (how bright they look to us) and absolute magnitude (how bright they are with a standard distance of 32.6 light-years), and/or luminosity (the amount of energy emitted from the star). Once researchers have found the apparent magnitude (m) and absolute magnitude (M), they can plug it into the equation d = 10^{[(m-M) + 5]/5}.
To find the velocity of the star, or galaxy, astronomers need to determine the redshift. When objects move away from us, light shifts toward the red end of the spectrum, meaning that wavelengths get longer. Some have described this by relating it to a police siren. As the siren approaches, the pitch gets higher, but as it passes, their is a sudden decrease in the pitch. This arises because the sound waves are closer together when moving towards the listener, but the sounds waves stretch once they make their way past the listener. This is known as the Doppler Effect! Galaxies have the same effect. Because most galaxies are moving away from us, the light is stretched. Redshift can be described, in other words, as the shift in wavelengths of light. The equation for this is z = (observed wavelength - rest wavelength)/(rest wavelength). Rest wavelength is the wavelength of a star, or galaxy, not moving. If we have the redshift (z), we can multiply it by the speed of light, which is 300,000 km/s, to find the velocity of the object.
Now that we have both the velocity and distance, we can find the Hubble Constant. The Hubble Constant is the relationship between both velocity and distance. With both values, we can plot them on a graph. If we do this using several supernovae, we can determine the slope. The slope is the value of the Hubble Constant. The Constant is defined in terms of km/s/Mpc. Mpc is an abbreviation for Mega parsecs, a distance value. That tells us how far the object is. The km/s tells us how fast that object is receding from us.
I hope this cleared up any questions you had about how I am approaching this problem. If there are any questions, feel free to leave them below. Hope you guys have a good weekend!
Thank you for thoroughly explaining the process! You have some work set out for yourself and I wish you all the best. Hope everything goes smoothly!
ReplyDeleteYou did a good job explaining something so complex in simple terms, so clearly you really understand this! I'm excited to see what you do with the data you receive, best of luck!
ReplyDeletey= mx+c is everywhere...... :)
ReplyDelete