What is Astrophysics: Definition and 819 Discussions

Astrophysics is a science that employs the methods and principles of physics in the study of astronomical objects and phenomena. Among the subjects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background. Emissions from these objects are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including classical mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
In practice, modern astronomical research often involves a substantial amount of work in the realms of theoretical and observational physics. Some areas of study for astrophysicists include their attempts to determine the properties of dark matter, dark energy, black holes, and other celestial bodies; and the origin and ultimate fate of the universe. Topics also studied by theoretical astrophysicists include Solar System formation and evolution; stellar dynamics and evolution; galaxy formation and evolution; magnetohydrodynamics; large-scale structure of matter in the universe; origin of cosmic rays; general relativity, special relativity, quantum and physical cosmology, including string cosmology and astroparticle physics.

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  1. S

    I Dark Energy contribution to plasma temperature in galaxy clusters?

    I have a question about this work called "Dark energy and key physical parameters of clusters of galaxies"* There, towards the end, the authors talk about the isothermal velocities and tempreature parameters of the gas and particles circulating between galaxies in clusters. In particular they...
  2. Mahsum

    Dark Matter Density Distribution

    Hello, I have asked a similar question before, but this time I want to ask it a bit differently to be understood better. I am a physics student at a university and this semester I am going to make a term project about Dark Matter Density Distribution by using rotation curves. However, I am a...
  3. S

    I Tidal effects of galaxies orbiting one another with dark energy?

    I recently found a question in a physics discussion site [1] about whether there was a "distance" between two galaxies where both the gravitational force and the influence of dark energy would be balanced. The answers and comments seem to indicate that there is indeed such a "radius" around a...
  4. AndreasC

    Astrophysics Up to date astrophysics and astronomy books for physicists

    With all the recent debates about CDM vs MOND etc, I decided I need some more background on astrophysics and phenomenology. I have the physics background, I prefer concise books even if they are harder. I was considering something like this for phenomenology...
  5. M

    I Inquiry Regarding the Determination of the Galactic Disk's Outer Bound

    I have recently read research papers that mention that disk stars have been found up to distances as far as 25 kpc from the milky way galactic center and possibly even up to distances as far as 31 kpc. I was wondering if there is a particular distance (or distance range) observed where the...
  6. S

    I Would there be any way to avoid gravitational wave emissions?

    In principle every object orbiting another (e.g. a planet revolving around a star) would emit gravitational waves, relaxing the orbit over time. However, this would not happen if the orbits had a time-invariant and symmetric quadrupole moment. As it is indicated in this question (), it appears...
  7. T

    I Star cluster in the Milky Way appears to be as old as the Universe

    https://www.sciencenews.org/article/star-cluster-milky-way-old-universe https://doi.org/10.48550/arXiv.2306.02180 Cheers, Tom
  8. FeatherGlow

    I Is Fluorescence Possible in Twilight?

    Earlier this year I saw what appeared to be a large glowing bird at twilight. The normal explanation for this is bioluminescent fungus contaminating a bird. I’m wondering if the effect might actually be a blue light effect where a fluorescent bird only appeared to glow because of the lighting...
  9. S

    I Thoughts on this article: The Universe Is More in Our Hands Than Ever Before

  10. A

    I Star with quadrupole in a binary system violates Newton's 3rd Law?

    Assume that, in a binary system, one (and only one) of the two stars has a non-zero quadrupole moment. Then the other star feels the usual gravity force $F_g$ plus an additional force $F_q$ coming from the quadrupole potential. On the other hand, the first star feels only the usual gravity force...
  11. DaveC426913

    B Sorry to hear you lost your 'Planet' Status, Earth

    The International Astronomical Union (IAU) defined in August 2006 that, in the Solar System,[1] a planet is a celestial body that: is in orbit around the Sun, has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and has "cleared the neighbourhood" around its orbit...
  12. ZX.Liang

    I What are the conditions under which stars can radiate coherent light?

    Some papers mention the coherent radiation of stars, such as this one: https://iopscience.iop.org/article/10.1086/519790/pdf I want to know under what conditions can a star exhibit coherent radiation?
  13. F

    Admissions Profile evaluation for astronomy Phd applicant in the fall 2023 cycle

    I will apply for a Ph.D. in Astronomy in the fall of 2023. I want to have a realistic evaluation of my profile to see if I am over-ambitious or not. I think I am out of reach for the "big four" universities. I will donate money to two of them only and will be targeting other top schools...
  14. RyanJ

    Astrophysics Book Around the Subjects of Supernovae and Stellar Remenants

    Hi all! It has been quite a while since I last posted here. Again. I'm currently interested in supernovae and the exotic stellar remnants that are left behind from such events. I'm interested in the physics and science surrounding this subject, it's something that I currently have an interest...
  15. warhammer

    Physics Are many Physics Students entering into Astrophysics?

    Maybe it is my present circle but I see a lot of students pursuing Astrophysics and related domains in terms of projects, Master's Degree etc. and I wonder what are the reasons for the same. Is the field extremely "hot" or is it just saturation caused by excessive Pop Sci influence? Full...
  16. waglebivu

    A To set up parameters for the sherpa tool

    How to set the parameters - photon index and metal abundance in the CIAO-sherpa tool for an x-ray source?
  17. tanaygupta2000

    Astrophysics research at ISRO in India?

    TL;DR Summary: Theoretical astrophysics research status in ISRO, India I am from India and want to be an astrophysicist serving my nation. Whenever I check about any ISRO news, it is always about some engineering achievements, like the launch vehicle and never about pure theoretical research...
  18. S

    I Expansion-Collapse cycle in cosmological structures?

    Concerning cosmological structures (like galaxies, clusters of galaxies, gas bodies, superclusters...etc) if the elements that make them are close enough they will be attracted towards each other by gravity. Contrarily, if they are sufficiently far apart they will get further away following the...
  19. S

    I Hubble flow kinetic energy into other types of energy?

    Spacetime expands at an accelerated rate and the particles with movement associated to this expansion are coupled to the Hubble flow. In many papers that I've read, objects coupled to the Hubble flow are treated as if they have some velocity and kinetic energy associated with it. However, can...
  20. Kyuubi

    Most relevant topics and math for astrophysics

    Helloz. I want to become an astrophysicist and was wondering if there topics in math that are HEAVILY used in astrophysics so that I can start focusing on them from early on. I understand that A LOT of different aspects of math are used in almost every field of physics, but I want to know which...
  21. D

    Calculations using the Standard Solar Model & Solar Equations of State

    Assuming the Sun’s core has a mass of 0.35 Msolar_mass and taking values for other quantities from a internet background search or from the following figures (i.e.: Radius "solar core" = 0.25 Rsolar_radius ): ------------------------------------------------------------------------...
  22. Thai

    Which Major Should I Choose for Astrophysics Professor Career?

    Summary: Should I major in math, physics, or astrophysics? Hello. I want to be an astrophysics professor someday. Does anyone have experience on whether I should be a math major, or a physics major, or an astrophysics major? And whether I should get B.A or a B.S? Thank you.
  23. cosmologyscience

    I Orbital Velocities and Mass Distribution in Galaxies

    Has anyone looked into the details of stellar orbital speeds and required (visible) mass distribution in the Milky Way? Doing some math here - if the local mass density is significantly higher in the inner 10-15% of the galaxy, and then lower and gradually thinning outwards in the disk, we will...
  24. Delta2

    I Earth's orbit not perfect ellipse

    Listen to the following arguments: Earth's orbit isn't perfect ellipse because classically there is the gravitational field of moon and possibly of Mars and Venus which affect it According to general relativity isn't perfect ellipse because there is the curvature of space time which doesn't...
  25. A

    What is the best free website for publishing my articles on astrophysics?

    Summary: best publishing sites Hello. I have a theory on astrophysics. I want to find the best free website or platform to publish my articles on it. I want the website to be completely free, not asking for fee from me or the readers in any ways, and not having hidden fees either. please...
  26. S

    Astrophysics question (Star Magnitude)

    My attempt has been attached.
  27. megapiano

    Need help with N-body simulation

    Many years ago, for my high school senior project, I wrote a solver for the N-body problem that is performance-optimized using the Barnes-Hut algorithm. (the optimization algorithm is not relevant to my question.) In one particular simulation, I simulated a spiral galaxy. The simulation is not...
  28. Snako73

    Best Colleges for Astrophysics

    I was wondering what the best colleges for astronomy/astrophysics are? I'm specifically interested in universities with opportunities for a lot of undergrad research. I've heard good things about University of Colorado Boulder and Michigan State, what's your take and them and what other ones...
  29. ergospherical

    Courses Switching to Astrophysics

    I've recently become curious about switching to an astrophysics course for my third and fourth years of undergrad. This course is available to students who have completed two years of either mathematics or physics, and is said to be more mathematically demanding than the standard physics course...
  30. Haorong Wu

    I How is light modeled in astrophysics?

    Suppose a light beam is sent from a distant star. When the light beam hit a telescope orbiting around the Earth. How is the light beam modeled? I have searched for many keywords without success. In my opinion, since the beam has gone so far, it can be viewed as parallel rays, with a decaying...
  31. ergospherical

    Astrophysics Cosmology and Astrophysics through problems: Padmanabhan

    I’ve really been struggling with this book since I started it a couple of days ago. It’s essentially a problem book designed to teach you about astrophysics, structure formation, radiation, fluid dynamics, etc. through a curated set of questions. Some of the questions take a ridiculously long...
  32. Mikkel

    Deep Learning for Image Recognition in Astrophysics

    Summary:: I'm looking for some great books on deep learning related to image recognition that I can use in astrophysics. Hello, I'm about to start my master thesis, where I, in short, will be comparing snapshots of young binary stars from simulations to observations using deep learning -...
  33. D

    Star Opacity and Balmer Break

    I am not sure where to start for this. Considering it needs to be demonstrate Balmer Break, I am assuming it needs to be wavelength based. As a result I am assuming I cannot use mean (Kramers) Opacity but rather express in terms of Opacity k= n*sigma/rho. My thoughts are to use Boltzmann...
  34. F

    A Cl's : sum into a chi^2 when we have a sum of chi^2

    1) If I take as definition of ##a_{lm}## following a normal distribution with mean equal to zero and ##C_\ell=\langle a_{lm}^2 \rangle=\text{Var}(a_{lm})##, and if I have a sum of ##\chi^2##, can I write the 2 lines below (We use ##\stackrel{d}{=}## to denote equality in distribution)...
  35. G

    Admissions (international) My chances of getting into top Astrophysics programs?

    Dear All. I am an international student who is planning to apply for the Ph.D. in astrophysics in the US in the coming application cycle. I am aiming for the top astrophysics school in the US. For the top, I mean CALTECH, Princeton, MIT, Columba, JHU, Cornell ... e.t.c. I would kindly ask for...
  36. Viii

    Interplanetary cruise problem

    Summary:: You have a spacecraft the size of a cube (2x2x2 m^3, m=3000 kg. It has 24 thrusters (2N each) and one main engine. For preparing your spacecraft for maneuvers, you want to rotate by 180 degrees. For the rotation, you'll use n=4 attitude thrusters per burn. What am I doing wrong...
  37. Mikkel

    Ultra high energy cosmic ray deflection angle causes by magnetic field

    I'm given an ultra-high energy cosmic ray with energy 10^20 eV. It is coming from a source 10 Mpc away with an extragalactic magnetic field with strength B = 10^-9 G. I am to determine the maximum angular deflection of this cosmic ray, so it hits Earth. I don't have an attempt of the solution...
  38. K

    Astrophysics Looking for an Advanced Introduction to Astrophysics text

    I'm a physicist familiar with QM, QFT and GR etc but I've never really sat down and learned astrophysics properly. Would Steven Weinberg's new book be considered a good advanced introduction or would people recommend another text. Half tempted to get it anyway to complete the Weinberg collection.
  39. F

    A Computing a variance in astrophysics context

    Below the error on photometric galaxy clustering under the form of covariance : $$ \Delta C_{i j}^{A B}(\ell)=\sqrt{\frac{2}{(2 \ell+1) f_{\mathrm{sky}} \Delta \ell}}\left[C_{i j}^{A B}(\ell)+N_{i j}^{A B}(\ell)\right] $$ where ##_{\text {sky }}## is the fraction of surveyed sky and ##A, B##...
  40. S

    Astrophysics Redshift Question

    I have attempted to link the equations, but I don't really understand how the data given fits. Does the angular radius get plugged in as the deflection angle?
  41. petha1

    Some homework questions in astrophysics (Kepler's Laws, Newton's Laws)

    1. Keplers third law (and the asumption that M1+M2 ~ M1) gives that M_Mars = 4*Pi^2*a^3/(G*T^2) With numerical values inserted Mmars = 4*3.14^2*(9400*1000+3396.97*1000)^3/((6.67*10^-11*(7*60*60+39*60)^2) 2. Phobos needs 7h39 minutes to complete a circle, this gives a speed of...
  42. V

    Programs Astrophysics or planetary science?

    Hi I am a computer science undergraduate working as a data scientist. I generally love studying physics and planetary science. I am aspiring to research in biomarkers and bio signatures in planets. If I have to choose this research path should I study masters in, astrophysics or...
  43. R0dr1go

    B Is the Universe spinning?

    Hello all, I recently did a thought experiment and thought, "what if the universe as a whole is spinning?" This could solve the dark energy problem, as if the universe was spinning, there would be outward pull, and therefore keep the universe expanding. And, I don't know if this means anything...
  44. N

    What topics in a Physics degree don't appear in an Astrophysics degree?

    Summary:: Looking for advice on what Physics topics, which may be dropped, to brush up on whilst studying an Astrophysics focussed degree I'm embarking on an part-time distance learning BSc in Astronomy at UCLAN. I was originally torn between this degree and the BSc Physics at the Open...
  45. A

    I Gravitational lensing: deriving magnification of lensed image

    In gravitational lensing, the image magnification is defined as the image area over the source area. But many texts also give it as the inverse of the determinant of the jacobian, A, of the of the lens equation. My question is how these are equivalent. The lens equation is...
  46. Mikkel

    Measure the distance to a star using magnitude and extinction

    Hello, I'm struggling with this question A star is observed close to the center of the Milky Way and from its spectrum we find that it is a type A3 star. Its observed magnitude is m_v = 25. There is only a diffusive gas between us and the star, so we can assume an extinction, of 1 magnitude per...
  47. M

    Astrophysics Looking for Books on Astronomy and Astrophysics

    What are some good textbooks for astronomy and astrophysics? I know of fundamental astronomy and the principles of astrophysics. I would prefer it if it were good for self-study. Also, are there any books that are free?
  48. koroshii

    I Acquiring a Small Dataset of a pulsar signal

    I am taking a class in signal processing. We have a final project in which we seek out "real-world" signal data and process and analyze it, and write a report on what we figured out. I thought it would be interesting to put my own interests into it and try to analyze a pulsar signal. My idea is...
  49. Q

    B Why is Carbon considered volatile?

    Carbon is considered volatile by planetary science, eg Moon lacks volatiles and thus lacks carbon. However volatiles are defined as "elements or substances with low boiling point", but Carbon boiling point is very high! Its sublimation point is 3900K, so it should be refractory and not volatile...
  50. Astronuc

    B Phys.org - Carbon creation finding set to rock astrophysics

    https://phys.org/news/2020-10-carbon-creation-astrophysics.html Back in 2016 - Recent results in nuclear astrophysics https://arxiv.org/abs/1605.07810 From the abstract -