What is Astrophysics: Definition and 856 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. Somoth Ergai

    I New Paradox Discovered, I Think

    User New here but this conundrum is something that occurred to me as I was watching a physics video and I have run out of ways to ask about this. So here I am. Ok first principle. the setup. let's say we have invented a perfect telescope on earth. such that we can resolve any object no matter...
  2. N

    A Friedmann-Lemaitre-Robertson-Walker model

    I am a math student conducting a study on the stability analysis of the FLRW model using the Lyapunov direct function. To do that, I need to find the equilibrium points of FLRW and create a Lyapunov function to carry out the study. Do i find the equilibrium points by setting time derivatives to...
  3. S

    I The Evolution of Galactic Scale Cosmic Voids

    According to some papers I've found [1], [2] expanding voids can be found inside clouds of denser materials that can cause them to eventually collapse. I have a question about this: Overdensities generally expand up to a given turnaround radius and then collapse. However, as the elements in the...
  4. P

    Astrophisics maniac

    Hi! I'm a student from korea. If there is anything wrong with my grammer, please kindly understand and if you can, answer my question! I like astrophysics. If you like it too, please try to chat with me. thank you.
  5. DaveC426913

    B Astro science in a TV show

    I know, I know, I'm committing the cardinal sin of putting any stock in the technobabble of a TV show, but this one seems egregious. Lewis (English WhoDunnit-in-Oxford on Britbox) Season 8 Episode 2 "The Lions of Nemea" had an astro physics professor who said this: "... and so we see that one...
  6. Sciencemaster

    I Observational Astronomy Project Ideas to Show Special Relativity

    This semester, I'm taking a class on Observational Astronomy which requires us to perform observations for a final project over the course of roughly a month (mid-March to Mid-april, although it could be a bit longer or shorter). As we get to choose the project, I'd like to take this opportunity...
  7. I

    B Questions about dark matter/energy

    Does the astrophysics community really think dark energy/matter is real, or that we just haven't figured out the actual physics of what is happening and this just makes it work out (to our current understanding).
  8. S

    I Avoiding structure collapse due to dark energy?

    I had a question about this paper (https://arxiv.org/abs/1401.3742) There, the authors indicate that dark energy competes against gravity in oversdensities and can slow down or even prevent their collapse. I have a simple question about this: Galaxies will in principle evaporate their outer...
  9. S

    I Dark energy and the kinematic Sunyaev-Zeldovich effect?

    I was reading this interesting article about possible effects of dark energy in the formation of large-scale structures which should have an impact on the Sunyaev-Zeldovich effect ("Dark energy imprints on the kinematic Sunyaev-Zel'dovich signal" (https://arxiv.org/abs/1309.1163))There, the...
  10. 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...
  11. 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...
  12. 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...
  13. K

    How to Effectively Seek and Provide Homework Help in Engineering and Comp Sci?

    Hello, Im a student in astrophysics and space technology!
  14. 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...
  15. 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...
  16. 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...
  17. P

    Everything physics

    Just a thread to discuss ideas and questions of physics. I plan on becoming a theoretical physicist after I graduate, and feel that enriching discussions here will help further that cause.
  18. JessPlaysGames

    I haven't studied physics for a while, and looking to get back into it

    I’m Jessica, a (nearly) 25 year old trans woman from the UK. I studied Physics and Astrophysics at university before dropping out. I dropped out for mental health reasons which were later diagnosed as Gender Dysphoria. After a few years away, I have now begun tutoring Physics to a friend in...
  19. Calculus007

    How can I become an astrophysicist? Welcome to PF!

    I want to become an astrophysicist and hope to learn a lot about physics from this forum.
  20. 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
  21. 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...
  22. S

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

    https://www.theatlantic.com/science/archive/2023/01/astrophysics-fusion-experimentation-supernovas/672625
  23. 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...
  24. 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...
  25. 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?
  26. nbktremblay

    New to the forums!

    Hey everyone, I'm brand new here! I absolutely love Physics, specifically Astrophysics, I'm actually looking to study black holes and stellar evolution. I'm preparing to go to University this fall to get my bachelors in Science with a major in Physics and a minor in either Mathematics or...
  27. 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...
  28. 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...
  29. 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...
  30. 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?
  31. 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...
  32. 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...
  33. 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...
  34. 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...
  35. 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 ): ------------------------------------------------------------------------...
  36. 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.
  37. 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...
  38. 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...
  39. 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...
  40. S

    Astrophysics question (Star Magnitude)

    My attempt has been attached.
  41. Thelamon

    Mechanical engineer and scientific researcher.

    Hi, I'm Dutch, not any kind of Quark ;-) (so excuse me for any bad English) and I'm very curious about "how the universe works". Cosmology/astrophysics and modern physics (quantum, relativity). I find it all mighty intersting. Actually all physics and also how it's all developed and "evolved"...
  42. 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...
  43. 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...
  44. ergospherical

    Courses Is switching to astrophysics a better option for my future career?

    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...
  45. 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...
  46. 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...
  47. 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 -...
  48. 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...
  49. 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)...
  50. 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...
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