Astronomy C

[Giantpants]

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?

Okay I was waiting for someone else to answer, but it’s been almost 2 months since this was posted so I’ll just give it a shot lol
1. 1 Solar Mass
2. So with E = mc^2, for E I get 1.79E47 J, and since gravitational waves move at the speed of light, for the time it would take to get from there to earth was 4.4E16 seconds. Dividing the two, I get 4.07E30 W, and accounting dividing by earths surface area (which I got as 5.10E14 with a radius of 6378 km), the expected flux at earth is 7.98E15 W/m^2
3. So I found that 1E44 J is the energy released by a 1a supernova, redoing all the previous math, I get 4.46E12 W/m^2, which is 5.5E-4 times larger than the flux from the GW event.
4. So I found it should take 2.46E13 seconds to equalize the difference, which should get me to 4.07E30 W, so if I multiply that by 3E8, I get 7.37E21 m, or 7.79E5 ly, which is also 5.5E-4 times farther than the GW event.
That may have been completely wrong, but even if it was, hopefully I can learn from it lol. I figured the questions weren’t doing anyone any good if they stayed unanswered!

[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?

Okay I was waiting for someone else to answer, but it’s been almost 2 months since this was posted so I’ll just give it a shot lol
1. 1 Solar Mass
2. So with E = mc^2, for E I get 1.79E47 J, and since gravitational waves move at the speed of light, for the time it would take to get from there to earth was 4.4E16 seconds. Dividing the two, I get 4.07E30 W, and accounting dividing by earths surface area (which I got as 5.10E14 with a radius of 6378 km), the expected flux at earth is 7.98E15 W/m^2
3. So I found that 1E44 J is the energy released by a 1a supernova, redoing all the previous math, I get 4.46E12 W/m^2, which is 5.5E-4 times larger than the flux from the GW event.
4. So I found it should take 2.46E13 seconds to equalize the difference, which should get me to 4.07E30 W, so if I multiply that by 3E8, I get 7.37E21 m, or 7.79E5 ly, which is also 5.5E-4 times farther than the GW event.
That may have been completely wrong, but even if it was, hopefully I can learn from it lol. I figured the questions weren’t doing anyone any good if they stayed unanswered!

Ok so when I originally wrote this question, I included assume all energy is released in one second. I forgot to include that lol but your assumption states that energy is being released over about a billion years, which is not the case. But because I forgot to say and your assumption is reasonable because I forgot to say, I'll go with it. Now we have 4E30 W. Now is where I'm confused, why is it divided by earth's SA? Earth's SA shouldn't even matter because flux is watts/m^2 so it should equal 4E30/(4/3*pi*(1.4E9*9.461E15)^2) (just dividing by the SA of the distance to it). Also a flux of 8E15 is unrealistic, we'd all be dead.
Apply same logic for 3 (sorry to dead to actually do it rn)
I'll just take your answer of 5.5E-4 times larger flux. The flux released is 1818.18182x greater from the GW. Apply inverse sqare law, the GW is 42.6401433 times further away or the SNe is 0.0234520788x further away in order for fluxes to be equal.

Your turn

[64015197]

The small angle formula is D= theta (angular diatance)/ 206265. you forgot to divide in the end right?

[ganiates]

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?

Hey, thanks for the questions. I haven't really worked much on concepts as I have been doing only DSOs so far.
1) They form into clusters of galaxies which in turn become superclusters.
2) Don't know, need to study that one. Though my best guess would be something to do with a galaxy not relying on other gravitational bodies / interactions / collisions to grow, so they, when cold dark matter formed wells early on in life, purely relied on the forces provided by it
3) Mass and distance. and the other I'd say the distribution of dark matter.
Again, sorry if I'm wrong, and thanks for the questions.

[RiverWalker88]

Okay, let's finish July with a little more astronomy.

Some things on stars and stellar evolution:

1. 1. What causes granlulation in the sun's surface?
   2. A similar pattern to granulation is seen in the photosphere of the sun, and is of the same cause. What is the name of this pattern?
2. Where is convection the main transfer of heat in a 0.25 solar mass main-sequence star? A 1 solar mass main-sequence star? A 2 solar mass main sequence star?
3. 1. What is the effect of the helium flash on a star's luminosity?
   2. Why is this?

[Aimer]

Okay, let's finish July with a little more astronomy.

Some things on stars and stellar evolution:

1. 1. What causes granlulation in the sun's surface?
   2. A similar pattern to granulation is seen in the photosphere of the sun, and is of the same cause. What is the name of this pattern?
2. Where is convection the main transfer of heat in a 0.25 solar mass main-sequence star? A 1 solar mass main-sequence star? A 2 solar mass main sequence star?
3. 1. What is the effect of the helium flash on a star's luminosity?
   2. Why is this?

1a. Granulation is caused by the Sun's convection currents located in its convective zone.
1b. a boiling pattern? not sure about this one
2. 0.25 solar mass: Convective zone spans the entire interior of the star.
1 solar mass: Surface convective zone is located outside of the central radiative zone.
2 solar mass: Convective zone is located at the core and is surrounded by the surface radiative zone.
3a. The helium flash has little to no effect on a star's luminosity.
3b. The energy released in the helium flash is used to bring the core out of degeneracy and is absorbed by the outer, non-degenerate layers, so an observer outside of the star wouldn't see much change in the luminosity of the star.

[RiverWalker88]

Okay, let's finish July with a little more astronomy.

Some things on stars and stellar evolution:

1. 1. What causes granlulation in the sun's surface?
   2. A similar pattern to granulation is seen in the photosphere of the sun, and is of the same cause. What is the name of this pattern?
2. Where is convection the main transfer of heat in a 0.25 solar mass main-sequence star? A 1 solar mass main-sequence star? A 2 solar mass main sequence star?
3. 1. What is the effect of the helium flash on a star's luminosity?
   2. Why is this?

1a. Granulation is caused by the Sun's convection currents located in its convective zone.
1b. a boiling pattern? not sure about this one
2. 0.25 solar mass: Convective zone spans the entire interior of the star.
1 solar mass: Surface convective zone is located outside of the central radiative zone.
2 solar mass: Convective zone is located at the core and is surrounded by the surface radiative zone.
3a. The helium flash has little to no effect on a star's luminosity.
3b. The energy released in the helium flash is used to bring the core out of degeneracy and is absorbed by the outer, non-degenerate layers, so an observer outside of the star wouldn't see much change in the luminosity of the star.

1a. Yep!
1b. Supergranulation was the answer I was looking for.
2. Yep!
3a. The helium flash actually decreases a star's luminosity (according to what I've read, anyway)
3b. The luminosity decreases because the expanding of the core causes contraction in the outer layers (once again, according to what I've read, I may be wrong about that)

Your turn!

[Aimer]

1. How long would it take for a 5.4 solar mass black hole to evaporate due to Hawking radiation? Assume the black hole receives no outside mass or energy.
2. Why would this black hole be unable to evaporate in reality?
3. Briefly explain the black hole information paradox, and how it relates to Hawking radiation.

[nobodynobody]

1. How long would it take for a 5.4 solar mass black hole to evaporate due to Hawking radiation? Assume the black hole receives no outside mass or energy.
2. Why would this black hole be unable to evaporate in reality?
3. Briefly explain the black hole information paradox, and how it relates to Hawking radiation.

ouf super rusty but :
1. 3.40074705e69 years
2. The only thing I'm aware of is that it'll gain mass before it can evaporate (?)
3. Information cannot be created or destroyed, and the paradox is that when information goes into a black hole, it gets "destroyed" in a way where it becomes unretrievable, but hawking radiation might (or does idk) allow for information to come back out. (i think)

[Aimer]

1. How long would it take for a 5.4 solar mass black hole to evaporate due to Hawking radiation? Assume the black hole receives no outside mass or energy.
2. Why would this black hole be unable to evaporate in reality?
3. Briefly explain the black hole information paradox, and how it relates to Hawking radiation.

ouf super rusty but :
1. 3.40074705e69 years
2. The only thing I'm aware of is that it'll gain mass before it can evaporate (?)
3. Information cannot be created or destroyed, and the paradox is that when information goes into a black hole, it gets "destroyed" in a way where it becomes unretrievable, but hawking radiation might (or does idk) allow for information to come back out. (i think)

1. yup!
2. You're correct, a more specific answer is that the CMB radiation prevents any black hole above the mass of the Moon from evaporating due to the black hole gaining energy from the radiation.
3. yup! The theory that Hawking radiation somehow carries information back out of the black hole is one of the proposed solutions to the paradox although I don't believe they know for sure (might be wrong on this). I believe there was a resolution to the paradox discovered in 2019, at least for simple gravity theories. Your turn!