All Questions
2,901 questions
1
vote
1
answer
35
views
What is the mass of the brown dwarf/red dwarf boundary in super metal-rich objects?
I am trying to make a red dwarf with twice the metallicity of the Sun. What could its theoretical minimum mass be in Jupiter masses?
- 13
2
votes
0
answers
37
views
Can the rotation of the liquid layer of the core around the solid core stop a planet's overall spin rotation?
In some planets like Earth or Jupiter there is an external liquid or molten layer of the core which rotates around a more deeper solid core (partly due to the planet's spin itself). This dynamo effect ...
- 2,878
0
votes
0
answers
19
views
Finding the Flux Ratios of Two Stars in the V-Band [closed]
I am hoping to verify my approach / answer as I study for a final exam! I am given the V magnitudes for star A = 7.0 and star B = 8.5.
$$ \frac{F_B}{F_A} = 10^{-0.4(V_B - V_A)} $$
$$ \frac{F_B}{F_A} = ...
0
votes
0
answers
21
views
Maintaining the magnetic field in gas giants in the future?
Let's set a planetary system similar to the Solar system in the far future, where the gas giants have cooled down significantly.
Eventually, would the fluid metallic hydrogen layer solidify?
And if it ...
- 2,878
3
votes
1
answer
140
views
What are these circular objects on the JWST image?
While admiring this beautiful image (Spiderweb protocluster field) https://esawebb.org/news/weic2428/ captured by the James Webb Space Telescope (JWST), I noticed several (more than five) circular ...
- 41
0
votes
0
answers
38
views
Are density perturbations possible in a globally homogeneous and isotropic universe such as ours...?
I would like to ask some questions about an interesting paper that was written back in the late 90's (https://arxiv.org/abs/astro-ph/9701131)
There, the authors propose how the universe may evolve ...
- 2,878
0
votes
0
answers
18
views
Question on the poloidal and toroidal Magnetic field lines close to a astrophysical black hole
I'm trying to fully understand the force-free region near a Kerr black hole. A common picture is depicted as Figure 1, 1.
In this context, a generic magnetic field is:
$$\vec{B} = (\vec{B}_{P})+\vec{...
- 3,159
0
votes
0
answers
69
views
I'm doing my project work on astrophysics. So what i want to find how much black hole grows over time
So problem in the code I have to find the velocity of gas that falling in the black hole at the point of event horizon,from this i can find the increasing $dm$ mass from Bondi equation over $dt$ time. ...
0
votes
1
answer
65
views
Why is it that galaxies tend to form large-scale "sheet" and "filament" structures?
I recently picked up a book on physical cosmology, and the first couple of chapters make frequent reference to the development of large-scale "sheet" and "filament" structure. ...
- 163
0
votes
0
answers
28
views
Relativistic time effects or gravitational lensing in solar observations made by observatories and satellites?
As mentioned, I was wondering about whether there are any phenomena affecting the measurement made in Earths time-scale after a physics seminar at IISERTVM. Any discussions and answers from specific ...
- 1
0
votes
0
answers
67
views
Existence of hollow planets
Recently I read a sci-fi describing a species living in a closed hollow space in a planet. An earlier answer suggested that such structures could exist but will not be stable, if only effected by self ...
- 251
1
vote
0
answers
52
views
How can I (mathematically) see that, as you fell into a black hole, you would not see infinite time passing? [duplicate]
I'm currently taking a GR course and, as we were studying the Schwarzchild solution, we discussed how someone entering a black hole (Alice) could pass through the event horizon in finite proper time, ...
- 11
1
vote
1
answer
44
views
When and why does a protostar start to radiate again?
I'm currently the formation processes of stars in Carroll's "An Introduction into Modern Astrophysics" and Bennett's "The Essential Cosmic Perspective" and I'm currently stumped ...
- 85
0
votes
0
answers
59
views
What is the "compression force" in spaghettification?
15.2 (a) $M=0.5M_{\odot}$, $a=0.49\times10^9\mathrm{ms^{-2}}\approx4\times10^7g$. (b) A standing astronaut will be subject to a stretching tidal force. The gravitational acceleration felt by the feet ...
- 1
1
vote
0
answers
73
views
Entropy production and anisotropies in compact Bianchi type VIIh "universes"...?
I had a couple of questions concerning this interesting paper where the authors hypothesize how could anisotropic "stresses" be exploited to produce entropy (they indicate that an example of ...
- 2,878
-7
votes
1
answer
118
views
Does matter-anti-matter burning happen in stars?
I asked ChatGPT at what temperature anti-matter can spontaneously be created and I was told that a billion kelvin would be enough, which puts it into the temperatures at the cores of stars.
That seems ...
- 474
0
votes
0
answers
43
views
Are there other ways we know of a massive star becoming a Black Hole other than the star going supernova? [duplicate]
Are Black Holes in the past, but also in the present, possibly formed by a process other than "very massive stars going supernova"?
- 4,376
-1
votes
2
answers
89
views
Would a star with the same mass as a Black Hole appear as a dark star?
In the case of the Black Hole (BH) the surface is a few Km from the center of mass whereas in the case of an active star with the same mass as the BH, the surface can be be many millions of Km distant ...
- 4,376
-4
votes
1
answer
60
views
Can a galaxy's rotational energy account for dark matter?
I have heard that a wound clock weighs more than an unwound clock, because the energy stored in the winding gives the clock more mass: $E=mc^2$.
ChatGPT calculates that the rotational energy of a ...
3
votes
1
answer
79
views
How can black hole mergers happen if we cannot see anything fall into a black hole? [duplicate]
If we cannot observe anything fall into a black hole as an external observer, how can we observe a black hole merger?
- 31
0
votes
0
answers
42
views
Where's the barycenter of a hydrogen or helium atom?
Where's a hydrogen atom's nucleus-electron barycenter with respect to the nucleus? How about helium's nucleus-electron barycenter?
- 11
2
votes
1
answer
96
views
Why take the derivative of variables such as area, mass, and radius?
I'm taking a module on stars and the solar system; I've attached notes from our first lecture- hydrostatic equilibrium. I'm confused about the notation $\mathrm{d}$ for $\mathrm{d}A, \, \mathrm{d}r$, ...
5
votes
1
answer
65
views
Equations of Motion for the $N$-body Problem in the Astrocentric Frame
I’ve been studying Tremaine's Dynamics of Planetary Systems and have hit a roadblock.
In Chapter 4, titled 'The $N$-body Problem,' there is a derivation of the $N$-body equations of motion, which can ...
- 1,327
4
votes
0
answers
72
views
What is the time-averaged gravitational wave power of the Milky Way
I would like to learn, if possible, an estimate of the total time-averaged power of gravitational wave emission at frequencies below GHz by the Milky Way. For example the value might be something like
...
- 61.8k
2
votes
1
answer
78
views
Can a brown dwarf be ignited?
So, people love to talk about that time on the Manhattan Project where they were worried about setting off runaway fusion in Earth's atmosphere. Obviously (and luckily) that didn't happen, but I am ...
- 21
0
votes
0
answers
59
views
What is the shape of neutron star?
What would be the shape of a fast spinning neutron star?
Can it be a disk?
Or just a Saturn-like ring?
Or would it take the shape of the sun?
- 31
5
votes
0
answers
57
views
Gravothermal catastrophe in 2+1 and 4+1 dimensions?
Before I go do a week of numerical simulations...
In our 3+1D spacetime, gravitationally-bound systems of large numbers of particles, like stars in globular clusters, can be stable for long periods, ...
- 2,286
1
vote
1
answer
79
views
How exactly do neutron star mergers create heavy elements?
This is a follow up question to this as suggested by ProfRob:
Do neutron stars fuse elements?
And this one where ProfRob talks about the beta decay process being repressed in single neutron stars, but ...
- 29.3k
4
votes
0
answers
130
views
On the physical effects and intuitive interpretation of the NUT parameter (as in the Taub-NUT or Kerr-Taub-NUT solutions)
Various papers¹ have been written about the Taub-NUT or Kerr-Taub-NUT exact solutions to Einstein's equations, but while they describe mathematically precise (local or global) properties of that ...
- 850
0
votes
1
answer
50
views
How do I get galactic disk thickness as a function of distance from the galactic core? Reading "Galactic Dynamics", Second Edition
I'm trying to ask a good question that other people might wonder about too.
I am looking to calculate the disk thickness as a function of distance. I have my copy of "Galactic Dynamics", ...
- 126
-1
votes
1
answer
134
views
Do neutron stars fuse elements?
I have read these questions:
In reality, they fuse the hydrogen nuclei (the cores of the atom) together into helium nuclei.
https://solarsystem.nasa.gov/genesismission/gm2/mission/pdf/NeutronStars....
- 29.3k
0
votes
2
answers
48
views
Origin of Angular Momentum in Accretion disk formation
I read this paper, Formation of the Asymmetric Accretion Disk from Stellar Wind Accretion in an S-type Symbiotic Star, I didn't quite understand where the angular momentum came from.
Where I'm ...
- 31
0
votes
1
answer
65
views
Determining the mass of a black hole using fourier transformation
As a part of my assessment in school, I will determine the mass of a black hole from the x-ray data (not necessarily but I think x-ray is preferred in astronomy as well, I am open to recommendations) ...
- 11
1
vote
2
answers
98
views
If I drop a rock on the Sun, does it fall right to the center? [duplicate]
Hydrostatic equilibrium is what determines the diameter of the Sun. The internal gas pressure inside the sun equalizes with the pressure from Gravity on the outside. This is what determines the size ...
- 4,857
0
votes
0
answers
40
views
How fast does a pulsar lose its mass?
I was reading about pulsars, and that they do lose mass over time. How fast do they lose their mass?
I have seen somewhere that our sun loses 4 million tons of mass every second. I imagine a pulsar ...
- 31
0
votes
2
answers
82
views
Does Black Hole Formation Require Only Mass Density or Also Event Horizon Contact?
Black holes are firstly a solution of classical general relativity, suggesting that when a sufficiently large mass is in a sufficiently small region, a black hole would appear. This is supported by ...
9
votes
2
answers
2k
views
Has any astronomer ever observed that after a specific star going supernova it became a Black Hole?
Do we have any observational direct verification and historic record of a star after going supernova was turned into a Black hole?
- 4,376
0
votes
1
answer
32
views
Axions stars mass and radii
Are there any stringent bounds on the possible mass and radii of axion stars?
Some theories do predict the existence of axions or axion-like particles (in the mood these days). Given the fact the ...
- 6,727
0
votes
1
answer
36
views
AStronomic nova or supernova (Ia), what peak intensity and wavelength to expect in the UV, extinction coefficient of ozone layer?
see https://www.nasa.gov/centers-and-facilities/marshall/nasa-global-astronomers-await-rare-nova-explosion/. T Coronae Borealis is expected to go nova. Distance 2630 light-years. Its magnitude is ...
- 243
0
votes
1
answer
82
views
Could dark matter be responsible for periodic comet impacts on Earth?
I've been reading a fascinating paper by Lisa Randall and Matthew Reece on the potential role of dark matter in triggering periodic comet impacts on Earth, possibly linked to mass extinctions. The ...
- 336
2
votes
2
answers
140
views
Can I turn a Schwarzschild black hole into a Kerr black hole by dropping a spinning particle into it?
Pardon any obvious oversight, I have rediscovered my love and curiosity for astrophysics after ages. Initially, the black hole would be described by a Schwarzschild Metric, and then a Kerr Metric ...
- 7,455
0
votes
2
answers
63
views
Would a star made out entirely of Helium-4 be a boson star?
Boson stars (https://en.wikipedia.org/wiki/Exotic_star) are hypothetical, exotic matter, models of stars. They usually rely on exotic particles like axions.
However, Helium-4 is considered to be a ...
- 2,878
1
vote
1
answer
56
views
Is there any way in which orbits emitting gravitational waves could avoid coalescence?
In the very far future, all orbits will eventually coalesce as they lose orbital energy through gravitational waves emission.
However, can there be 3-body or N-body interactions in which the members ...
- 2,878
-1
votes
1
answer
139
views
Can a system of non-black holes become a black hole? [closed]
As we know, the Schwarzschild radius and mass are proportional: $r_s=\frac{2GM}{c^2}$. If the density of a substance is constant, the mass and radius of an object made of that substance are ...
- 428
1
vote
0
answers
37
views
Do magnetar stars relatively produce stronger gravitational waves than neutron stars? [closed]
According to Reissner-Nordstrom solution to Einstein's gravitational field equations in astronomy the electric or magnetic or both, field of a charged body of mass generates its own gravitational ...
- 4,376
8
votes
2
answers
3k
views
A study on the speed of gravity
I have just come across a paper which involves a study about the speed of gravity. This has rocked me a bit, since I thought it was well known gravitational fields travel at the speed of light, in ...
- 1,880
0
votes
0
answers
49
views
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 ...
- 179
0
votes
1
answer
115
views
The exact formula on relativistic electron degenerate pressure
I am studying white dwarf and I need relativistic electron degenerate pressure to calculate some physical problems like Chandrasekhar limit.
I only know that $p \approx n_e^{4/3}$ but the internet ...
- 183
4
votes
1
answer
233
views
Is the universe accelerated expansion slowing down?
Some months ago there were several articles like this one (https://bigthink.com/starts-with-a-bang/physicists-question-fate-universe/) claiming that the universe's accelerated expansion was found to ...
- 2,878
3
votes
2
answers
79
views
Simulating nebulae
How can we simulate nebulae shapes computationally?
What are the governing equations or forces acting on nebulae? Is it suitable to just use Navier Stokes fluid dynamics and solar winds or is there ...
- 131