Sunday, November 29, 2015
Sooo Hot!
In September of this year, the galaxy's hottest white dwarf was discovered by astronomers from the universities of Potsdam and Tübingen. This came from analysis of spectra analyzing the edge of the Milky Way, in which they discovered a relatively small, but very hot star in its cooling phase. This star (RX J0439.8-6809) was measured to be around 250,000K, although it is estimated that at its peak the temperature was around 400,000K. A star of such low density and such high temperature is indicative of something originating very far from us; indeed, this was found to be a part of a larger gas cloud moving towards the Magellenic cloud structure. Not much is known about the formation of this unusual star beyond that.
Thursday, November 5, 2015
Space Elevator Part 2: Elevation time, come on!
Reach for the stars! No, really, reach! They are right there above you!
As mentioned in part one of this blog post, lifting yourself up off of the ground will require a lot of energy, as part of whatever system one tries to lift will be redundant weight of fuel, which of course may only last so long. The thought arises that there must be another way. Looking simply at Newton's third law, there are more ways to dissipate lifting energy than through the air. Rather than having fuel provide thrust up into the atmosphere, why not push off of the ground to launch something into orbit.
There are many ways of doing this: from cables on satellites to towers, using already in place physical systems could be an ideal way of lifting something out of the atmosphere. So, what are our options here?
First, let's look at a cable, as it is one of the simpler examples. In order to escape the atmosphere, an object should be able to travel about 50km into the air. In
As mentioned in part one of this blog post, lifting yourself up off of the ground will require a lot of energy, as part of whatever system one tries to lift will be redundant weight of fuel, which of course may only last so long. The thought arises that there must be another way. Looking simply at Newton's third law, there are more ways to dissipate lifting energy than through the air. Rather than having fuel provide thrust up into the atmosphere, why not push off of the ground to launch something into orbit.
There are many ways of doing this: from cables on satellites to towers, using already in place physical systems could be an ideal way of lifting something out of the atmosphere. So, what are our options here?
First, let's look at a cable, as it is one of the simpler examples. In order to escape the atmosphere, an object should be able to travel about 50km into the air. In
Tuesday, November 3, 2015
Space Elevator Part 1: Burn Baby Burn
One of the largest hurdles in any technological advancement is the provision of power. As new technology comes out, it must overcome the transport and size of power. Space travel is no exception to this dilemma. Any self-propelled vessel must contain something internal to provide force. The success of any space program has hinged upon the ability to make the power-to-weight ratio as large as possible. If this ratio may be limited, then the ship will have an easier time lifting itself from earth's orbit.
Let's look at a simple example:
A ship weighs 50000 kg, and carries 500 kg of gasoline.
Burning gasoline provides about 50Mj/kg, so burning all of this fuel will provide about 25,000 Mega-Joules of energy.
Now, since we cannot burn all of this at once (lest one wishes to explode), so lets burn all of this over a rate of about a minute. So now we get a rate around 500MJ every second. This still sounds like a lot of energy!
But the force of gravity alone on our rocket ship is about 500000 Newtons. This means simply to negate our gravity , it would take about 500000 Joules, or about .5 MJ. This is not very much at all! We have 1000 of those! But force is an acceleration, so it takes more than that to overcome inertia. Lifting this machine will take much more than the amount of prescribed gasoline.
Just doing some approximations, we can expend about 45MJ a second towards lifting the craft up and out of the atmosphere. which thus would exert about
Gas is really heavy, so people have used plenty of alternative fuel sources, and compressed forms of certain elements burn with incredible energy and can do all of the heavy lifting, but they overlook something else entirely: why must the world burn?
That method of chemical energy transmission means carrying your own fuel source, which can be impractical. People have proposed many mechanical solutions, such as catapults and slingshots, but one theoretical marvel stands out in my imagination: the space elevator.
The basic premise of this apparatus would be an object that had one mechanical point in space, and one which reached to the ground. This seems simple enough, but the feat of engineering which comes with it would involve some intensive structural and materials engineering. All of which will be looked at in the riveting part two of this blog post!
Let's look at a simple example:
A ship weighs 50000 kg, and carries 500 kg of gasoline.
Burning gasoline provides about 50Mj/kg, so burning all of this fuel will provide about 25,000 Mega-Joules of energy.
Now, since we cannot burn all of this at once (lest one wishes to explode), so lets burn all of this over a rate of about a minute. So now we get a rate around 500MJ every second. This still sounds like a lot of energy!
But the force of gravity alone on our rocket ship is about 500000 Newtons. This means simply to negate our gravity , it would take about 500000 Joules, or about .5 MJ. This is not very much at all! We have 1000 of those! But force is an acceleration, so it takes more than that to overcome inertia. Lifting this machine will take much more than the amount of prescribed gasoline.
Just doing some approximations, we can expend about 45MJ a second towards lifting the craft up and out of the atmosphere. which thus would exert about
Gas is really heavy, so people have used plenty of alternative fuel sources, and compressed forms of certain elements burn with incredible energy and can do all of the heavy lifting, but they overlook something else entirely: why must the world burn?
That method of chemical energy transmission means carrying your own fuel source, which can be impractical. People have proposed many mechanical solutions, such as catapults and slingshots, but one theoretical marvel stands out in my imagination: the space elevator.
The basic premise of this apparatus would be an object that had one mechanical point in space, and one which reached to the ground. This seems simple enough, but the feat of engineering which comes with it would involve some intensive structural and materials engineering. All of which will be looked at in the riveting part two of this blog post!
Monday, October 5, 2015
Week 1: Galaxy Density
Today during class, I mistakenly heard Prof. Siana make a comment that the Milky Way was a particularly dense galaxy. Although I misheard (he said that galaxies, in general are dense compared to space), this prompted me to ask him afterward about the measurement of galaxy density. The methods he described to me, in a quick recap, involved using the make-up of stars in the galaxy (by percent of different stars in the galaxy) and the luminosity of the galaxy. From that, astronomers can extrapolate how roughly how many massive stars are in the galaxy. Then, using the size (as determined by parallax measurments), they can determine the density of the galaxy.
There are some major innacuracies in this, of course; some objects in the galaxy are contributing to the overall mass of the galaxy, but are not inherently luminous. The largest of these, it seems, would be dark matter clusters. This can be slightly corrected by gravitational lensing. In my research for this blog, I came across an article from 2013: a paper highlighting techniques used by astronomers at numerous research institutions collaborating to measure data on the density of dark matter distribution among multiple galaxies.What they saw lined up well with current CDM, or cold dark matter, theories.
The methods, which are more comprehensively discussed in the linked article, seem to present improved ways on accounting for the density of dark matter when dealing with galaxy density.
Here is a link to the academic article, and a link to the article that led me to it. Hope everyone is having a good start to school, and good luck on the assignment.
-Aaron
P.S. Just a random occurrence. As I was re-doing problem four tonight (on Comet Lovejoy), I was shuffling through old music, when a song by the same name started playing. I thought it was a weird coincidence. I have it linked here, for any of you who would appreciate random jazz/hip hop instrumentals. I don't think it has anything to do with the comet itself, but it is still a good song. The whole album is pretty good, actually, if you are interested.
There are some major innacuracies in this, of course; some objects in the galaxy are contributing to the overall mass of the galaxy, but are not inherently luminous. The largest of these, it seems, would be dark matter clusters. This can be slightly corrected by gravitational lensing. In my research for this blog, I came across an article from 2013: a paper highlighting techniques used by astronomers at numerous research institutions collaborating to measure data on the density of dark matter distribution among multiple galaxies.What they saw lined up well with current CDM, or cold dark matter, theories.
The methods, which are more comprehensively discussed in the linked article, seem to present improved ways on accounting for the density of dark matter when dealing with galaxy density.
Here is a link to the academic article, and a link to the article that led me to it. Hope everyone is having a good start to school, and good luck on the assignment.
-Aaron
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