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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What is the unit for 'magnitude' in terms of the Isophotal diameter of a galaxy?

Every site and AI and Google say that one way of measuring a galaxy's diameter is in terms of its isophotal diameter, using the blue D25 standard, using units of, "25 mag per arcsec2". But ...
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Question on two planets orbiting a sun

I’ve come up with an astronomy question that I cannot seem to resolve and could really use some help. I’m working on a problem involving two planets orbiting a star in circular orbits. The star has a ...
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Relation between density and mass of a galaxy

The Tully-Fisher relation provides the relation between the terminal velocity of stars and the mass of a galaxy. On similar lines, is there a relation between the density of stars (and gasses) in a ...
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1 vote
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Do voids expand faster at dark energy domination era or not?

I asked one of the authors of a paper about the expansion of voids and filaments in the cosmic web whether voids expand faster when dark energy started to dominate in the universe. But I am confused ...
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Does the expansion of space imply anything about the dimensionality of the Universe?

I have read that we should visualize the expansion of the Universe as something like a balloon expanding with the Universe, which apparently is 3 dimensional, not being the balloon itself, but rather ...
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Would an asteroid spherical field emit gravitational waves?

A moon orbiting around a planet will emit graviational waves as they create an non-invariant quadrupole moment, meaning that, as there is an unequal distribution of mass in orbit around that planet, ...
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Who - if anyone - predicted the emission of gamma rays from jetted active galaxies? An historiographical inquiry

We know that the relativistic electrons that produce synchrotron radiation in the jets of active galaxies also produce gamma radiation via the inverse Compton mechanism (in the most simple scenario ...
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Can there be free electrons in interstellar gas in the long term?

If I'm not mistaken, in interstellar gas, there can be clouds of free electrons (not "attached" to any atomic nucleus) But can they stay like that indefinetely? Or will they inevitably end ...
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How to change fits column format?

The response matrix column in my RMF fits file is in "PE" format. I want to change my matrix as 2D matrix. Is there any solution to this?
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What causes the Mikheyev-Smirnov-Wolfenstein (MSW) Effect? Virtual Z bosons?

What causes the neutrinos to oscillate more often or rapidly? Are they being “bounced around” by Z bosons in the intense furnace of the Sun? Is it due to an intense weak current?
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What are we misunderstanding about the scale factor-redshift relation? [closed]

If the scale factor as a function of time represents or is equal to the average distance between the galaxies, then it increases altogether with the CMB redshift $z$, but it also must be equal to the ...
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Fixing inconsistency between Velocity vs Redshift and Scale Factor vs Time plots to restore Doppler's validity for CMB redshift [closed]

Velocity vs Redshift on wikipedia I have a serious doubts about the above plot because it's inconsistent with the Scale Factor vs Time plot with the added Doppler line: $z=1100$ is the CMB redshift. ...
114 views

What exactly does $k\sigma$ mean in astrophysics and cosmology?

In statistics, $\sigma$ or $1\sigma$ is the standard deviation. For the normal distribution, approximately $68\%$ of the values lie within $1\sigma$ range, $95\%$ within $2\sigma$, and $99.7\%$ within ...
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Someone explain how a naked singularity is possible

I was reading this wiki article about naked singularities, however I don't really understand the how a gravitational singularity can simply exist without an event horizon. Can someone explain/...
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Mathematical modeling of the influence of components of the interstellar medium on the distortion of the wavefront of the observed object

Associated with: Flowchart of the pipeline of key processes for modeling wavefront distortion of astronomical objects: ground-based observation case Let's imagine for a moment that we are outside the ...
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1 vote
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Flowchart of the pipeline of key processes for modeling wavefront distortion of astronomical objects: ground-based observation case

Associated with: Mathematical modeling of the influence of components of the interstellar medium on the distortion of the wavefront of the observed object Being inspired by this article, as well as ...
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cross-matched SDSS-WISE catalog

Please where can I find cross-matched SDSS and WISE dataset for a machine learning project? (Galaxy-star-qso classification task)
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Do all photons coming out of the Sun go out radially?

I am trying to understand why we can assume that all light rays from the Sun are in parallel.
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Would we know if the universe was rotating?

I was wondering what we would observe if the universe had a small rotation. My conclusion was that galaxies on the equatorial plane of the universe would be slightly more redshifted than galaxies than ...
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Computing error bar for vertex of parabola-fit lightcurve

I have a long-term lightcurve for my source, to which I have used orthogonal distance regression to fit a quadratic model [expected flux]=a[year]²+b[year]+c. Part of our data analysis includes finding ...
596 views

References about neutrinos getting clumped in "structures" in the future?

I was wondering whether (standard model) neutrinos could form clumped structures (like halos perhaps). The problem with this is that neutrinos have a very light mass, have a great speed and do not ...
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python question-discrepancy between number of stars found

Ok, I get that this is a long question but it's ok if you don't know just thought I'd give this a try anyway. I get that it's a long shot. Basically I'm trying to replicate a methodology used in the ...
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Why MIT's Benjamin Rackham says "nearby ultracool dwarf SPECULOOS-3" would look "purplish-red, spotted, and flaring" from an airless orbiting planet?

May 15, 2024 MIT News article Newly discovered Earth-sized planet may lack an atmosphere includes the following: “We can say from our spectra and other observations that the star has a temperature of ...
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Project Analog Hypothetical Planet

For my story Project Analog, I was wondering if a hypothetical planet (Let's call it Suria). It has the same size and conditions as Earth with the same axis, tilt, and rotation, as well as one moon. ...
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What would the Big Crunch theoretically look/feel like?

In the Big Crunch theory, the expansion of the universe reverses, resulting in all matter contracting into a single point. Imagine you are alive at the time of this event. What would the sky look like?...
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How to estimate perturbations from other planets in Apsidal Precession

I am developing a fictional system which I want to calculate to as much detail as I can. Thus I have a question about astrophysics and astrophysical formulae. I know that Apsidal Precession is ...
233 views

Relative inclination with respect to line of sight

I'm encountering some difficulty understanding the concept of line of sight inclination. Typically, we assume that the observer is positioned perpendicular to the system being observed. Consequently, ...
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Can an astronomer fully work remotely? [closed]

My question today is addressed to those astronomers who have quite a lot of experience working remotely. In general terms, the answer to the question includes the following elements: the range of ...
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How long would a day be in an earth like - same size and all - planet but with double earth's orbit in time

I'm a writer, so I apologize in advance. On an earth like planet with and orbit double to ours in days, how long would days be? My planet would take aproximately 672 earth days to orbit around it's ...
2k views

Is the gravitational constant really constant over our Universe?

For instance, if objects are travelling at relatively high speed around 'c', is G the same value for them as for us on earth? I believe a lot of matter is travelling fast away from other matter, so is ...
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How to speed up REBOUND python simulations on a Jupyter notebook?

I'm running Python based computational astrophysics simulations on a Jupyter notebook, with the help of a library called REBOUND (also using REBOUNDx), to create a simulation containing the solar ...
172 views

Why does a white dwarf sometimes go 'nova' and sometimes supernova (type 1a)?

Obviously, when a white dwarf goes truly supernova, there is nothing left, not even, I have heard, a neutron star or black hole... But when certain white dwarf stars accrete certain amounts or types ...
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Local anisotropies in the expansion of the universe and tidal forces...?

In the context of the large-scale structure of the universe, there can be local anisotropies (https://www.aanda.org/articles/aa/full_html/2021/05/aa40296-21/aa40296-21.html). I understand from this ...
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Why do red dwarf (M-type) stars give off such violent flares and CMEs, out of proportion to their size and temperature?

Dr. Becky (Smethurst) just posted a new YouTube video mentioning, as I have heard many times, that it might not be possible for life to form on planets around Red Dwarf (M) stars because they would ...
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Expanding voids ending being collapsed?

According to some papers I've found 1, 2 expanding voids can be foun inside clouds of denser materials that can cause them to eventually collapse. I have two questions about this: Overdensities ...
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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 ...
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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 ...
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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 ...
1 vote
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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))...