# astrophysics

1. ### Courses What is it like to work as an Astrophysicist or an Aerospace Engineer?

Hi all. I'm currently an aerospace engineering undergraduate student in my second year, but I'm going through a very confusing process of second guessings and would greatly appreciate advice from older people who work in the Aerospace or in the Physics/Astronomy fields to help me compare the...
2. ### I What are the potential effects on electricity due to Earth's magnetic field reversal?

What is/are the potential or theoretical effect on electricity due to reversal of planetary magnetic field? Would circuitry continue to function or would knowledge and understanding need re-evaluating as a result of a reversal of our magnetic field on planet Earth? Note: this is not a homework...
3. ### B What is the black that we see in the night sky?

Summary: Can black means many thing? The black we see in night sky has to mean many things First of all, from point of views of human eyes then the photons can't reach our eyes so it appears black. Secondly, the objects appear smaller as we go farther from that object. So, at some point object...
4. ### A Derivation of radial momentum equation in Kerr geometry

I am trying to derive the radial momentum equation in the equatorial Kerr geometry obtained from the equation $$(P+\rho)u^\nu u^r_{;\nu}+(g^{r\nu}+u^ru^\nu)P_{,r}=0 \qquad$$. Expressing the first term in the equation as $$(P+\rho)u^\nu u^r_{;\nu}=(P+\rho)u^r u^r_{;r}$$ I obtained the...
5. ### B Intensity of Spherical Shell of Stars

Given that L is the luminosity of a single star and there are n stars evenly distributed throughout this thin spherical shell of radius r with thickness dr, what is the total intensity from this shell of stars? My calculations were as follows: Intensity is the power per unit area per steradian...
6. ### Setup for Spherical Astronomy Problem

My apologies for not detailing my attempts at a solution; I'm not sure how to to digitally illustrate or describe the various setups I attempted before looking at the solution to this problem. I am also ONLY asking about the setup, though I included the full question for context. The solution to...
7. ### Mass Transfer in a Binary Star System

Homework Statement: A binary star system consists of M1 and M2 separated by a distance D. M1 and M2 are revolving with an angular velocity w in circular orbits about their common center of mass. Mass is continuously being transferred from one star to the other. This transfer of mass causes...
8. ### B What’s more “important": GR or QM?

Let’s say to the average Astronomer conducting research; generalizing the research to “astronomy” ; which would be more useful for the “average” Astronomer on a day to day basis: Quantum Mechanics or General Relativity? Obviously most are, but which so more? Which would be referred to more?
9. ### B How well should Astronomers know General Relativity?

I know that it would vary depending on the type of research a specific astronomer would be doing ( Astrophysics/Cosmology research versus an Astronomer researching exoplanets ) ; but in your opinion, “how much” or “how well” should an Astronomer with a graduate degree in Astronomy know General...
10. ### Schools What are the best Colleges for Astrophysics?

I just finished my Junior year in high school in Houston. I am currently pursuing a degree in Astrophysics. I have been looking at Rice and Cal-tech as my best options, but in case I cant make it into those school I am considering Texas A&M, University of Texas for being in state. As well as...
11. ### B Black holes and the first law of thermodynamics

The first law of thermodynamics states that matter can only be transferred from one state to another, and cannot be truly destroyed. What happens to matter consumed by a black hole? What happens to it and where does it go? Does the first law still hold true?
12. ### How can we determine the distance to the Galactic center?

Problem Statement: We can use "spectroscopic line shift of S2" and "its proper motion", but I don't have any idea what dose this sentences mean. please show me details!! Relevant Equations: spectroscopic line shift
13. ### Courses What undergrad topics do astronomy grad programs expect you to have taken?

I was speaking with my prof about the requirements for the applied physics major track offered at my school, and she said some very surprising things. Just for context, I’m interested in pursuing observational astrophysics/astronomy in grad school later. She said that I can skip diff equations...
14. ### I Gaussian probability distribution of formation PBH

Hello. If we consider PBH formation from collapse of large density perturbation in the early Universe, a mass PBH depends on density contrast as And δ must be larger then . Also we have β — an abundance of black holes, it's the ratio of the PBH energy density to the total energy density, this...
15. ### A Abundance and mass spectrum of PBH

Hello. I'm trying to study primordial black holes for my work, but I still can't understand what are abundance and mass spectrum? Could you explain? Thanks in advance.
16. ### A What does the image of the black hole say about general relativity?

We all heard about the "photo of black hole". My question is: did this image show any hints of physics beyond general relativity? I read once (not sure where) that the apparent size of black hole shadow is very sensitive to corrections to general relativity. Add some minor correction and the...
17. ### How to use the Bremsstrahlung flux to analyse a medium?

I don't know where to even begin?
18. ### I The Confinement Radius of a Cosmic Ray (Galactic vs. Extra-galactic)

If we want to show whether or not a specific Cosmic Ray particle is confined to our galaxy we must use the Larmor radius (relativistic version), r = γmc / qB Considering a 10^14 eV proton and assuming the galactic magnetic field strength is 10^−11 T, show that the particle is confined to the...
19. ### Courses What undergrad electives should be taken when pursuing astrophysics?

Hi, I go to a small liberal arts college and I'm majoring in physics. The college I attend has a VERY unique academic curriculum, with few required core courses, and one can have an oxford style tutorial in almost any area in physics, no matter how advanced. I want to pursue graduate school in...
20. ### Programs Diploma thesis - Neural Network Application in Physical Problems

Hello everybody. I am currently on my last year of Computational Physics education. More and more I am interested in Machine Learning and Neural Network. Time has come for me to choose diploma work thesis, so I am searching for interesting ideas where I can merge my interest in neural networks...
21. ### Observing galaxies: area of sky would I need to survey

1. Homework Statement Given that there are 10-2 Ellipticals per Mpc3 and my garden telescope can reach to 14 mag. How large an area of sky would I need to survey to find 100 Elliptical galaxies ? (assume the typical absolute magnitude for an Elliptical galaxy is -21 mag). 2. Homework...
22. ### About initial mass function and mean mass in stellar cluster

1. Homework Statement Assuming a Salpeter IMF with upper and lower mass limits of 0.1 and 20 M⊙ respectively, calculate: (i) the mass point at which half the mass formed in a stellar cluster lies in more massive systems and half in less massive systems. ii) the mass point at which half the...
23. ### Admissions Applying to European PhD Programs with a US Masters

I know this topic has been discussed a lot on this forum, but I had trouble finding an answer to my precise question. Current Understanding: I have read up on the differences between the US and European graduate systems. I understand US merges MS and PhD programs resulting in an average...
24. ### Importance of uncertainty and probability in research papers

As someone who is interested in astrophysics, I always get emphasized on the importance of knowing statistics and error analysis in results of a calculation. However when I read about real physics papers, I never see any numerical solutions, just equations that demonstrate phenomena. I know that...
25. ### Physics Should I switch to astrophysics?

Like many of you, I have always enjoyed physics and math throughout high school. When applying to universities, I was quite unsure about my goals, so I applied to both engineering and science majors. I have always been deeply fascinated by astronomy, but I enjoyed environmental science as well...
26. ### A Notes on Cosmic rays - wave interactions in plasmas

Dear community, I am Pedro de la Torre, now doing my PhD on Cosmic ray propagation. Now, I have started to study reacceleration due to interactions of CR with plasma waves. My problem is that I do not find neither a good book or any kind of review with a detailed demonstration on the...
27. ### On the convergence of the three body disturbing function

For the three-body-disturbing function expanded in multipolar orders with respect to the ratio of the semi major axes, the function converges for small ratios, how to check the convergence for a certain set of parameters? I'm using the work of the Laskar in his paper "Explicit expansion of the...
28. ### A Is there any astro-field that uses QM or GR frequently?

Hi all! Happy New year! I will select my supervisor soon but i want to involve in the field that uses QM or GR frequently I love physics and i want to apply physics to explain astrophysical phenomenon. I know that Compact objects and Astrochemistry use such physics but i wonder to know more...
29. ### Programs PhysicsREU statement

Hello everyone, I am currently applying for physics REUs. I am looking for people who would help me proofread my essay and criticize it as much as you'd like please. Beginning It was my junior year of high school when I first harbored an interest for physics above other subjects. When I first...
30. ### Hello from UK!

I am more of a budding (sorry) botanist / plant scientist, but I have an interest in astrophysics, how planets came to be the way they are and how this can help us understand what makes a habitable planet. I'm also starting something of a novel regarding a failing terraformed utopia. I won't...