Astronomy C

[Name]

1. Gravitational lensing results from large amounts of mass, more than we observe directly in galaxies, implying the existence of dark matter; the alternative gravity theory fails to explain lensing.
2. They passed through each other slowed but relatively undisturbed. The gas was separated from the galaxies due to strong interaction. Dark matter, however, stuck with the galaxies, as it's theorized to be weakly interacting.
3. Since without dark matter, gravitational lensing would occur around the greatest concentrations of baryonic matter - the gas - but calculations have shown the matter to be concentrated with the galaxies, not the gas.

Correct! Your turn.

[Steuben42]

Great!

Apologies since these aren't all directly related, but...
1. On a large scale, how are galaxies distributed across the universe (what structures do they form)?
2. What does the term "secular evolution" refer to in galactic evolution?
3. The Virial Theorem can be used to calculate one unobservable characteristic of a galaxy through two measurable factors. What are those three factors, and which is unobservable?

[Giantpants]

1. On a large scale, how are galaxies distributed across the universe (what structures do they form)?
2. What does the term "secular evolution" refer to in galactic evolution?
3. The Virial Theorem can be used to calculate one unobservable characteristic of a galaxy through two measurable factors. What are those three factors, and which is unobservable?

1. Into clusters...? Lol
2. Not so sure, like the development of a galaxy, forming disk galaxies and it happens in spiral galaxies too
3. Calculates its unobservable gravitational potential energy through mass and velocity.

[Steuben42]

1. On a large scale, how are galaxies distributed across the universe (what structures do they form)?
2. What does the term "secular evolution" refer to in galactic evolution?
3. The Virial Theorem can be used to calculate one unobservable characteristic of a galaxy through two measurable factors. What are those three factors, and which is unobservable?

1. Into clusters...? Lol
2. Not so sure, like the development of a galaxy, forming disk galaxies and it happens in spiral galaxies too
3. Calculates its unobservable gravitational potential energy through mass and velocity.

1. I wasn't super clear what I was asking, but my idea for the answer was 'filaments,' like if you look at those pictures of the universe at large - although that might be a bit too large scale for what tests will cover
2. Secular evolution's something I found researching galactic evolution last year, and it's when a spiral galaxy evolves in color, luminosity, and morphology by internal processes and not external influences
3. That seems right to me

Your turn!

[Giantpants]

Alright!
A star has the same radius as the sun, but 1.5 times greater temperature. Assuming the temperature of the sun is 5500 K...

A. What is the luminosity of the star?
B. What is the absolute magnitude of the star?
C. What is the B-V color index for the star? (I'll accept answers within a range because I couldn't seem to find a consistent formula, so if anyone has one I'd love to see it haha)

[Name]

Alright!
A star has the same radius as the sun, but 1.5 times greater temperature. Assuming the temperature of the sun is 5500 K...

A. What is the luminosity of the star?
B. What is the absolute magnitude of the star?
C. What is the B-V color index for the star? (I'll accept answers within a range because I couldn't seem to find a consistent formula, so if anyone has one I'd love to see it haha)

A. 5.0625 solar lumo
B. 3.069087
C. B is at 440 nm, visual is 550 nm. Plugging into the full plank equation and dividing I get 0.92370184907
So blue is 0.92370184907x dimmer then visual. Subtracting abs magnitudes I got 0.08617?
https://en.wikipedia.org/wiki/Color_index has another equation relating to temp/B-V. Solving that equation gives .73 B-V which is probably the answer?

[Giantpants]

A. 5.0625 solar lumo
B. 3.069087
C. B is at 440 nm, visual is 550 nm. Plugging into the full plank equation and dividing I get 0.92370184907
So blue is 0.92370184907x dimmer then visual. Subtracting abs magnitudes I got 0.08617?
https://en.wikipedia.org/wiki/Color_index has another equation relating to temp/B-V. Solving that equation gives .73 B-V which is probably the answer?

For A I got 1.5969E27 W, or 4.17 solar luminosities using L = 4pi * r^2 * Stefan Boltzmann constant * T^4? Which means that for B I got 3.27789, but the number you got is right for your answer, so you’re good!
For C, I’m not sure. I found http://astro.physics.uiowa.edu/ITU/labs ... uster.html, which gives a formula relating B-V and temperature and for that my answer was 0.15939? I plugged that value into the formula on Wikipedia and got a temperature of near value to the original 8250 K? So idk I figured that made sense. What formula did you use? You might be right considering 0.08617 isn’t too far off? Idk lol.

[Name]

A. 5.0625 solar lumo
B. 3.069087
C. B is at 440 nm, visual is 550 nm. Plugging into the full plank equation and dividing I get 0.92370184907
So blue is 0.92370184907x dimmer then visual. Subtracting abs magnitudes I got 0.08617?
https://en.wikipedia.org/wiki/Color_index has another equation relating to temp/B-V. Solving that equation gives .73 B-V which is probably the answer?

For A I got 1.5969E27 W, or 4.17 solar luminosities using L = 4pi * r^2 * Stefan Boltzmann constant * T^4? Which means that for B I got 3.27789, but the number you got is right for your answer, so you’re good!
For C, I’m not sure. I found http://astro.physics.uiowa.edu/ITU/labs ... uster.html, which gives a formula relating B-V and temperature and for that my answer was 0.15939? I plugged that value into the formula on Wikipedia and got a temperature of near value to the original 8250 K? So idk I figured that made sense. What formula did you use? You might be right considering 0.08617 isn’t too far off? Idk lol.

For A I used the relationship to compare two stars. Luminosity*(1/temperature)^4=radius^2 (all in solar units because we're comparing to the sun). I think this is a simplified version of your equation.

For C I accidentaly used 5500 instead of 8250. Solving with the wiki equation and a graphing calc I got .189 which is close enough. The chart on the wikipedia page for color index also indicates a slightly positive B-V. The wiki equation does have two solutions though, the other one being -1.5
On the other hand, the plank formula got screwed up with the new temperature where the B-V became negative implying blue is more luminous. The second negative solution doesn't account for this possible answer because their way too far off from each other. I don't even know if this method is even valid, it was the only thing I could think of using to find luminosities at different wavelengths before googling alternative equations. A website for the plank calculator can be found here https://ncc.nesdis.noaa.gov/data/planck.html
Its also possible the wavelength filters of B and V were off by a bit, different telescopes have their B and V filters at slightly different values although this doesn't account for (I got around a -1, depending on the filter used)

However plugging 8250 k into wien's law to find the peak emission wavelength, I got 351.2 nm. This is below every single B and V filter wavelength i've found. Because B has a shorter wavelength it should be closer to the peak wavelength and therefore the star should be more blue, implying the B-V should be negative.

So basically both B-V equations check out, but disagree with the planks law method which is then supported by wiens law.

I think your equation and wikis equation is correct, but idk why the plank equation is wrong and why wiens law seems to support the solution to the plank equation

[Giantpants]

So basically both B-V equations check out, but disagree with the planks law method which is then supported by wiens law.

I think your equation and wikis equation is correct, but idk why the plank equation is wrong and why wiens law seems to support the solution to the plank equation

Yeah I’m not sure either. Ig it’s good we found some consistency at least lol
Anyway, your turn?

[Name]

GW 151226 resulted from the merger of two black holes, which weighed 14.2 and 7.5 SM. However, the measured mass of the final merged black hole was less then the combined masses of the two smaller black holes. The mass lost was believed to have been released as gravitational waves.

1. How much mass was lost to gravitational waves? Assume all mass loss is due to GWs.
2. Assuming a perfect mass energy conversion, what is the expected flux at earth of GWs?
3. Now lets compare this to 1a SNes. How many times larger is the flux from a 1a SNes at the same distance?
4. How many times further away would the 1a SNe have to be to have the same expected flux?