Questions tagged [astrophysics]

Questions involving the physics of the universe, especially the nature of astronomical objects, energy fields, and/or regions, rather than their positions or motions in space.

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Open problems in astronomy that a BSc. could contribute / attempt to solve?

From this related question: Open problems in astronomy that an amateur (with a PhD in some other field) would have a chance of solving? What are some open problems in astronomy that an amateur would ...
nuwe's user avatar
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8 votes
6 answers
4k views

Why don't we just unshift the IR photos from Webb?

I’ve been going back and forth with peers on why image processing is done the way it is on the Webb Telescope. Based off some article, my understanding is that they have various filters that represent ...
lumenhippo's user avatar
0 votes
0 answers
19 views

Deriving Faber-Jackson Relation from Milgrom's Law

I am reading Famaey & McGaugh 2011, a review paper on Modified Newtonian Dynamics. My question concerns bullet 3 in Sec 5.2, where the authors try to explain how Faber-Jackson Relation can be ...
Ambica Govind's user avatar
1 vote
1 answer
66 views

For detection of distant galaxies by gravitational lensing-induced magnification, roughly what are the distance ratios from the lensing systems?

Discussion in comments under the question Does seeing a gravitationally lensed/magnified galaxy imply that they could also see us as well? have got me wondering about the geometry behind detection of ...
uhoh's user avatar
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0 votes
0 answers
30 views

How to obtain the distance to a particular stellar cluster from GAIADR3 data? [closed]

I am trying to obtain distance towards a Galactic IR bubble. I took the data of all stars in that region from the GAIADR3 catalogue and tried to figure out if there are any stellar clusters. I found ...
Rian's user avatar
  • 503
-2 votes
1 answer
153 views

Why is v lowercase and D uppercase in $v=H_0D$?

Why is v almost always written in lowercase and D in uppercase in $v=H_0D$? OK, v is in lowercase, as usual, but then why is D in uppercase? What's so different/special about it? In my physics school ...
Curious Cat's user avatar
4 votes
1 answer
169 views

Mysterious factor of 30 in Coulomb cross section for electron–electron collisions

I’m a bit stuck trying to understand where a numerical constant in an old paper comes from. The number in question is in eq. (A1) in Shull & van Steenberg (1985) (which gives the cross section for ...
Socob's user avatar
  • 273
0 votes
1 answer
87 views

Does a cosmological redshift occur within our local group, of galaxies?

I know that it is not supposed to be expanding but space is space and it is expanding everywhere else outside it so why not inside it too, and gravity just holds everything back. I suppose if it is, ...
Curious Cat's user avatar
1 vote
2 answers
1k views

How can Hubble's original data show that the universe is expanding?

The diagram from Hubble's original data only goes from 0 to 2 Mpc (see here), and yet our Local Group is not supposed to be expanding and it is 1.5 Mpc in radius. How can the data show that the ...
Curious Cat's user avatar
2 votes
2 answers
228 views

Fractal structure of the universe

I decided to return to the question first written here after some time, since a short and succinct phrase had formed in my head that described the phenomenon that I was trying to understand. What are ...
dtn's user avatar
  • 705
2 votes
1 answer
127 views

Why are distant type Ia supernovae dimmer than expected?

Why are the (extremely) distant type Ia supernovae dimmer than expected? Relative to what? Their cosmological red shift? Well, what else. Please don't just say "Because the expansion is ...
Curious Cat's user avatar
1 vote
0 answers
107 views

Determining Time Based on Arc Seconds

So our arc day starts at 20°41'32 which is midnight (0:00) and ends 24 hours later at 21°42'42. According to my calculations it traveled 0 degrees, 59 minutes, and 30 seconds or 3570 arc seconds in 24 ...
dimitri33's user avatar
  • 127
4 votes
1 answer
247 views

How to calculate the number density of electrons?

I am trying to calculate the number density of electrons (number of electrons/m^3) for a white dwarf, knowing these parameters : the mass and radius of the white dwarf (therefore its density (kg/m^3))...
Jean Pégoud's user avatar
0 votes
0 answers
63 views

Flux from the Sun on the Earth using the Stefan-Boltzmann law

What is wrong with this computation, plase? I am getting the result of 4291.65 W m^{-2} instead of 1361 W m^{-2}. Thank you very much ...
Anna-Kat's user avatar
  • 505
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0 answers
43 views

Consistent values for density of galaxies between degree squared and steradian

I have a table of densities of galaxies : Expected number density of galaxies for photometric survey per unit area and redshift intervals, $\mathrm{d} N / \mathrm{d} \Omega \mathrm{d} z\left[\mathrm{...
guizmo133's user avatar
2 votes
1 answer
110 views

Hierarchy of gravitational interactions of astronomical objects: from single to large-scale structures

Hierarchical structure is clearly visible in the Universe. The "observable universe" includes almost empty voids, between which lie large cosmic filaments. The filaments consist of galactic ...
dtn's user avatar
  • 705
2 votes
1 answer
220 views

The Poynting Robertson Effect

In the Poynting Robertson effect, it says in general, the Poynting Robertson effect is caused by the fact that objects like dust re-emit the light they absorb. Is that correct? Is this effect weak? ...
A Curious Mind 's user avatar
1 vote
0 answers
22 views

What would be the new Equation of motion if the magnetic field's origin is shifted from the origin of a co-rotating spherical polar coordinates?

The equation of motions due to the dipole magnetic force of a planet in a frame corotating with the planet and origin at the centre of planet assumed to be sphere components wise are given as below: \...
Lunthang Peter's user avatar
0 votes
2 answers
135 views

What happens to a binary star system when one of the stars explodes and loses a lot of mass

If one star of a binary system explodes and leaves a remnant. The remnant would still have the velocity but lack the mass of the original star.
Michael Mcgarry's user avatar
0 votes
0 answers
25 views

How to plot different curves in the same polar cordinates in matplotlib?

I tried to plot the paths of particle of different sizes in the same polar coordinate using the code given below using matplotlib. somewhat like this: Instead I got this plot: while the path for ...
Lunthang Peter's user avatar
4 votes
1 answer
107 views

How do various astrophysical models deal with so many orders of magnitude in scale? Are there completely different models for different scales?

If we just model our solar system's dynamics, one could use a straightforward numerical integrator with all n(n-1)/2 gravitational interactions along with some torques and non-gravitational forces. ...
uhoh's user avatar
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2 votes
0 answers
67 views

How is an index of n=0 possible for the Lane-Emden equation?

I was recently showing that an index of $n=0$ for the Lane-Emden equation results in constant density throughout the star. However, in my calculations I had to use the constant $\alpha$ which can be ...
Kian31's user avatar
  • 21
1 vote
1 answer
327 views

Would water freeze on Neptune?

Someone told me that water would boil on Neptune because of the pressure. But this seems suspect to me. Given a temperature of -353 Fahrenheit, I'd expect water to freeze pretty much instantly. So ...
PhysicsNoob's user avatar
3 votes
1 answer
86 views

If a cluster of stars in dynamical equilibrium falls into a much larger blob of dark matter, will it get hotter and expand? Will it stop?

This question is inspired by ProfRob's inspiring answer to Are there really confined Globular Clusters? in which he invokes the concept of "virialization" where a dynamical system reaches ...
uhoh's user avatar
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1 vote
1 answer
74 views

Gas mass and velocity in galaxy

I was going through the SPARC data on galaxies (http://astroweb.cwru.edu/SPARC/) The velocity of gas in the SPARC data is in http://astroweb.cwru.edu/SPARC/MassModels_Lelli2016c.mrt The gas velocity ...
Angela's user avatar
  • 201
1 vote
0 answers
34 views

What is value of charge by mass ratio (q/m) for a spherical micro charged particle with surface potential 6 volts in S.I units and in e/amu units?

In Liu and Ip (2014),The Astrophysical Journal, 786:34 (8pp), the value of q/m is derived as follows : "for a dust grain with radius 'a', from $\phi = \frac{4\pi q}{\varepsilon_0 a}$ we have $\...
Lunthang Peter's user avatar
0 votes
0 answers
42 views

Crop a FITS file in shape of another

I have a FITS file, let us say file A. I have another FITS file, file B. File B has a smaller footprint than file A. I want to crop file A in shape of file B. How do I go about doing that?
SlightDecoy's user avatar
2 votes
1 answer
57 views

When analyzing a particle moving at Kepler speed, √(GM/R) in a planetary magnetic field, do we need to convert it to angular speed, √(GM/R^3)?

A charged particle is moving in a planetary magnetic field, in a spherical polar coordinates which is corotating with the magnetic field. To solve the equations of motion numerically what would be the ...
Lunthang Peter's user avatar
3 votes
1 answer
269 views

Can a star have one forbidden line or does it have to have many?

My question is: Can a star have one forbidden line, or does it have to have multiple? Some Examples I'll be using the O ᴠɪɪ line as an example. ζ Puppis is a well studied O4Ief star with the O ᴠɪɪ ...
Neil Iyer's user avatar
  • 133
1 vote
1 answer
53 views

Is the magnetic permeability (mu_0) necessary in the expression for planetary magnetic field?

To numerically analyse the Lorentz effect due to the magnetic field, say, radial component on a charge particles which of the expression would be correct, $\{ B_r = \frac{2R}{r^3} g_1^0 \cos(\theta) \}...
Lunthang Peter's user avatar
0 votes
0 answers
40 views

calculating mass of galaxy from luminosity

A very elementary question, just to make sure I got this thing right. Suppose we are given that the mass to luminosity ratio of a galaxy is $2 \frac{M_{\odot}}{L_{\odot}}$. Let us say, that the ...
Angela's user avatar
  • 201
1 vote
0 answers
97 views

Formula for "gravity assist"

I am familiar with the concept of "gravity assist" by which a space probe or other object, passing near a moving planet, can pick up some of the planet's orbital velocity. I presume that ...
Mike Stone's user avatar
5 votes
1 answer
154 views

Why is nuclear pasta the strongest part of a neutron star?

From my very rudimentary understanding of neutron stars taken from the abstract to "Elasticity of Nuclear Pasta", nuclear pasta is the strongest substance, hence the strongest part of a ...
Ben A.'s user avatar
  • 153
3 votes
2 answers
3k views

Why can't dark energy be considered a 5th fundamental force?

So I have recently been researching for multiple articles about fundamental forces, currently there are just 4 forces: Gravity Electromagnetism Strong nuclear force Weak nuclear force So far there ...
Furious Arcturus's user avatar
2 votes
0 answers
53 views

What could these LMC objects in this color-color diagram be?

I have performed a color-color and colour-magnitude plot of various sources detected in an LMC image (JWST NIRCAM F200W, F150W and F115W filters). I then also queried SIMBAD to collect relevant ...
KBo's user avatar
  • 21
1 vote
1 answer
43 views

Elliptical galaxy classification

The elliptical galaxy (Hubble) classification goes from E0 to E7, with E0 being spherical and E7 being the most flattened. I understand that the angle at which the elliptical is viewed affects this ...
user374355's user avatar
2 votes
1 answer
154 views

Core radius of King's model

I've been learning about the King's model for globular clusters and have been taught that it assumes a core radius: $$r_c = \sqrt \frac{9\sigma^2}{4\pi \rho_0 G} \ (1)$$ where $r_c$ is the core radius ...
user374355's user avatar
1 vote
2 answers
148 views

Public data for calculating equilibrium temperature of exoplanets

I am a high school student beginning a simple independent project to calculate the equilibrium temperature of exoplanets. I'm curious to see how many exoplanets have a similar equilibrium temperature ...
HSStudent's user avatar
6 votes
3 answers
1k views

Concerning a binary system of stars/planets/black holes could one of them be ejected before eventually merging or colliding?

I was having a discussion with an undergraduate student of physics about binaries and their interactions with external celestial bodies (which could cause the ejection of one of the members in the ...
vengaq's user avatar
  • 827
1 vote
2 answers
166 views

is there any direct method to calculate gravitational wave frequency if the source mass is known?

Suppose we have neutron stars of 8 and 9 solar masses, they both merge and produce a GW. How does one find the frequency of the GW? Is there any specific formulae to compute it? What I want to know is ...
Astrophile_Sanju's user avatar
1 vote
0 answers
91 views

Is there such a thing as a map that shows the current (not observed) positions of celestial objects?

As I understand it, maps of the sky and three-dimensional maps of the universe all show the observed positions of celestial objects. Are there any maps that show our best guess at their current ...
John Wu's user avatar
  • 111
3 votes
0 answers
66 views

Gravitational recoil with stars/planets...?

When two black holes are merging, the resulting merge can be ejected if one of the black holes had less mass than the other one, so the gravitational waves emitted by both of them is unbalanced, and ...
vengaq's user avatar
  • 827
-5 votes
1 answer
111 views

How long would it take for a black hole of the mass of mercury to evaporate? [closed]

Mass of mercury, formula of time taken to evaporate by a black hole
Astrophile 's user avatar
1 vote
3 answers
250 views

Why is final kinetic energy zero for escape energy calculations?

When the question is about the minimum speed to reach a certain point, we would usually use conservation of momentum, i.e. $\mathrm{E_k + E_p}$(initial) = $\mathrm{E_k(0) + E_p}$(final). I am curious ...
Just want to know more's user avatar
5 votes
1 answer
194 views

Can rings last around planets indefinitely?

Apparently, Saturn is losing its rings (https://weather.com/en-IN/india/space/news/2023-05-04-saturn-is-losing-its-rings-webb-may-tell-us-how-long-they-have-left) However, is there any way or ...
vengaq's user avatar
  • 827
3 votes
1 answer
139 views

Do all orbits emit gravitational waves?

In principle, all orbits in the universe should progressively decay due to the emission of gravitational waves. However, does this always happen? Are there any kind of orbits that do not decay as they ...
vengaq's user avatar
  • 827
1 vote
0 answers
207 views

Typical astronomical and astrophysical problems in various programming languages

As a rule, work in the field of observational astronomy and astrophysics requires knowledge of such programming languages as: C/C++ and the principles of OOP, MPI, CUDA. Sometimes additional ...
dtn's user avatar
  • 705
2 votes
0 answers
32 views

Could rogue planets with cold nucleus have winds or water currents/waves due to the planet's rotation?

Are there any types of wind or waves caused and produced only and exclusively by a planet's rotation? Not influenced by the planet's rotation, but produced solely by it? In the case of waves, are ...
vengaq's user avatar
  • 827
3 votes
1 answer
146 views

Why is the dark matter component of MOND important in central regions?

A lot of papers say that even the theory of MOND requires the existence of dark matter, particularly in the central regions. However this is a bit counterintuitive to me considering that rotation ...
Ambica Govind's user avatar
0 votes
0 answers
44 views

What are the primary astrophysical implications of a proposed mass of about 11 M⊙ for the SN 2023ixf progenitor?

The abstract of the arXiv preprint SN 2023ixf in Messier 101: A Variable Red Supergiant as the Progenitor Candidate to a Type II Supernova (itself recently "discovered" in the observatory) ...
uhoh's user avatar
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