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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50 views

What experiment does this “Tracing the History of Starlight” video try to explain?

The YouTube video Tracing the History of Starlight with NASA's Fermi Mission describes observation by the Fermi gamma ray telescope of EBL (extragalactic background light) gamma rays from 2,000 ...
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How to convert Log(g) vs T_eff to y vs (v-y)?

I have a plot in Log(g) vs T_eff coordinates from my stellar evolution model. The parameters of the model are M=0.8 M_solar, [Fe/H]=-1.19, Y=0.245. I want to convert it to the y vs (v-y) coordinates (...
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207 views

Calculating the sun’s position in ECI

I’m trying to calculate visible ISS passes and I need to calculate if the ISS is behind the earth by “drawing” a line between the ISS and the sun and seeing if it crosses earth. I have the ECI ...
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1answer
70 views

Distance to objects

When we read that, for instance, M31 is 2.54 ± 0.11 Mly (778 ± 33 kpc) away from us, does this distance estimate take into account the travel time of the light we observe? In other words, what is the "...
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1answer
62 views

Has “GHz-spinning dust” ever been demonstrated in the laboratory?

This excellent answer to the question What is the physics of the “spinning dust” contribution to Cosmic Microwave Background measurements? includes the figure below which helps show what it was the ...
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2answers
166 views

How would humans with appropriate equipment navigate the surface of Saturn's moon Titan on foot? [closed]

Taking into account the physical characteristics of Titan (e.g. surface gravity, atmospheric pressure), what would be the most efficient method of motion for an astronaut to navigate the surface of ...
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125 views

Total number density of galaxies and problematic expression in practise

This post comes from physics exchange forum, I have transfered it here, maybe I will be luckier since I have not received answers on the other forum. Here is the issue : I am asked to give the ...
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2answers
82 views

How to find the radius of a satellite not knowing the mass

If I know the semi-major axis, the density of the planet, and orbital period.. how can I find the radius of the satellite? I can't think of any formula to use.
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1answer
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What is the apparent magnitude of the weakest stars we can see in one telescope on the ground with a diameter of 2.4m? [duplicate]

All I know is its main mirror diameter; 2.40 m I also know that the eye, which its pupil is 5mm in diameter can see up to an apparent magnitude of 6. How can I calculate the apparent magnitude that ...
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626 views

How does gravity affect pressure under water?

How different would being under water in Europa differ from being under water on Earth? Would it be possible to dive deeper on Europa with a submarine than on Earth and by how much?
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397 views

What liquids can be found in the void space?

Is there any material natural or otherwise a free floating liquid that can exist in space? https://space.stackexchange.com/questions/32274/what-liquids-last-the-longest-in-space
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2answers
156 views

What is the minimum size to be a natural satellite?

Would a smaller satellite be more stable around a smaller planet where the same satellite would not be stable or last around a larger planet? I added the picture to show how moon size planets can ...
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1answer
101 views

How long will a ball of ice stay in orbit around Earth? [closed]

How big would a ball of frozen water need to be to last one orbit? How would atmospheric drag effect the ball of water? https://space.stackexchange.com/questions/32188/what-is-the-darkest-orbit-...
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117 views

How much of the Universe is subatomic? [closed]

How much does subatomic particles such as photons, tachyons, and electron being the biggest particles etc. occupy space? If put in a ball how big of a ball would that be?
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147 views

Estimates for “undetectable” planets in extra-solar systems

As far as I've been able to determine, it appears there are some significant limitations on our ability to detect exo-planets that are below certain sizes or beyond certain distances from their stars....
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1answer
106 views

What is the reason for magnetic braking?

What is the reason of Magnetic Braking in contact binary stars? Just dark spots? I mean hot spots can have this effect on binaries.
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27 views

How many fluorescent iron lines?

An iron atom has 26 electrons. Its 6.4 KeV line is a fluorescent line. There are 6.7 and 6.9 KeV lines also. How do they form? An electron from which energy level fills in which energy level? Is there ...
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49 views

A high-temperature isolated neutron star could be super-Eddington?

If the surface temperature of a young neutron star is hot enough, say, several KeV, its blackbody radiation could be super-Eddington? Did any paper discuss this scenario before?
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189 views

What was the length of the solar day 73 million years ago?

How could this be estimated, or how accurately could it be extrapolated from a present-day measurement of the Earth's spin-down rate?
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2answers
81 views

Is there a limit to how fast spacetime can bend/warp around an accelerating object?

If in the future a spaceship can accelerate to nearly the speed of light, will it encounter any kind of resistance/drag from the spacetime in front of it not being able to bend/warp fast enough around ...
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3answers
67 views

Hypothetically, if our sun was yellow would we still see “white” colours?

Hypothetically,if our sun was yellow would we still be able to see white colour on objects like snow,cotton etc.? Would we have the phenomenon of rainbow?
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1answer
76 views

Does time dilation increase within overlapping gravitational fields?

If a spaceship was to travel to the barycenter of a binary star (the stars having identical size and mass) and come to a stop there, would the people on board this spaceship find that time is moving ...
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1answer
98 views

Why does the adiabatic exponent decrease at the ionization zones?

The context is the ionization zones in stellar atmospheres or interiors, the Sun, for instance. The adiabatic exponent is the heat capacity ratio: $$\gamma = \frac{c_P}{c_V} = \frac{C_P}{C_V}$$ And,...
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1answer
123 views

Is it possible that the Universe is expanding due to additional Big Bang events?

Is it theoretically possible that the Universe is expanding due to additional Big Bang events that have occurred at the same location that the original Big Bang occurred at? Perhaps there has been an ...
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1answer
72 views

Is there a more modern/updated paper than Hurley's 2000 SSE?

I've implemented equations from Hurley's 2000 paper on Single Stellar Evolution (SSE) to model the stages of stellar evolution without having to use the full SSE code (or MESA for that matter). Is ...
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1answer
91 views

What is the difference between wind, jet and outflow?

For jets, I found a pdf file here Jet: collimated beam of matter of high velocity sources: young stars, active galactic nuclei, $\mu$-quasars, gamma­ ray bursts, planetary nebulae, pulsars ...
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1answer
120 views

What is Propeller Effect exactly?

I find the original reference seems to be here. I still do not understand the mechanism. It is necessarily occur in neutron binaries? Anyone can introduce it in detail? This paper is old.
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1answer
77 views

What irradiance does the Moon receive during a total lunar eclipse?

As we know, the total solar irradiance normally received by the Moon is about 1361 $W/m^2$ (the same as the top of the Earth's atmosphere). Of course, this changes during lunar eclipses, but the Moon ...
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1answer
156 views

Candidate major astronomical events circa 600-541 mya?

Are there any known major events around the 50-60 million years preceding the cambrian explosion that could explain the sudden increase in biodiversity? Specifically a supernova, or active galactic ...
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55 views

How to the find radius of a galaxy given its inclination? [closed]

If the semi major and semi minor axis of a galaxy are 3" and 1" respectively, how would you find the radius of the galaxy?
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0answers
51 views

What are the procedures and protocols to use with Gauss'method and personal observations?

I would like to use the Gauss' method to determine the orbit of planets of solar system. I would like to calculate their orbits with personal observations. What is the methodology/procedure/protocol ...
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1answer
68 views

Why are gravitational perturbations stronger at larger semi-major axes?

Why are mechanisms such as the Kozai-Lidov effect more prominent at at large semi-major axes? If we had a binary system of a primary and secondary body, with the third perturber as the Sun. Why is it ...
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57 views

Why does D4000 affect stellar age?

From my understanding D4000 is a ratio between the 'flux densities between 4050 and 4250 Angstroms and that between 3750 and 3950 Angstrom', from Poggianti et al (1997). However I do not understand ...
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1answer
79 views

What are the equations governing stellar evolution (Luminosity, Mass, Temperature, Radius)

I'm looking for ('simplified') equations governing stellar evolution. Especially how mass, luminosity, temperature and radius of a star change during it's lifetime. As well as equations which tell you ...
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1answer
77 views

Will all galaxies eventually become elliptical galaxies?

According to the Wikipedia article Elliptical galaxy, elliptical galaxies have a sparse interstellar medium. I know that probably sometimes two spiral galaxies collide then exponentially approach the ...
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1answer
62 views

Black Holes and Worm Holes [closed]

Can a Black Hole enter inside a Worm hole? If yes then what will a observer observe if it present at the another side of Worm hole?
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2answers
101 views

Detect Passage of Massive Relativistic Object

I came across an interesting article that speculates that we could detect an object of significant mass ("space-ship size") moving through our galactic neighborhood at a substantial fraction of the ...
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1answer
38 views

Secondary maximum in SNIa lightcurves for near infrared

Type Ia supernovae (SNIa) are thermonuclear supernovae that generates a lot of Nickel 56 which emits photons while disintegrating. How is the secondary maximum in lightcurves for reddish bands (see ...
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1answer
133 views

Black-hole becoming a star again - follow-up question [closed]

Some questions have been posed about black holes becoming stars again once they attract enough hydrogen/atomic matter from another star. Some answers were a forceful NO. Never. However - let's ponder ...
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2answers
194 views

What explains the existence of energy/matter if it cannot be created or destroyed?

If the energy/matter that was contained in the singularity before the Big Bang had always existed, and if it’s true that energy/matter cannot be created or destroyed, then what explains its existence?
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1answer
261 views

Is there any significant time dilation on other planets orbiting the sun?

Is there significant time dilation on the other planets orbiting the sun? Would an 'hour' experienced on earth actually be 59 or 61 minutes on other planets, depending on their distance to the sun? ...
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1answer
164 views

Effects of a rogue planet passing between the Earth and the Moon?

The plot of Thundarr the Barbarian got me thinking about the science behind the passage of a runaway planet between the Earth and the Moon and its effect on the Earth and Moon themselves, as well ...
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1answer
795 views

What is the actual black hole merger speed?

I have seen models of 2 black hole mergers. https://www.theverge.com/2017/11/16/16665132/gravitational-waves-ligo-virgo-black-holes-merger-multi-messenger-astronomy When we see a space ship appear ...
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2answers
295 views

What is the fastest a galaxy or other body has been measured to (or can) travel?

Our solar system travels at an average speed of 515,000 mph and our galaxy at 1.3 million mph through space. What is the fastest moving body in space recorded and the fastest can a black hole or ...
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1answer
68 views

Fundamental axioms in LCDM

What are the axioms (if any) behind the LCDM model of cosmology? NB: axioms, not postulates (e.g., inflation)
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3answers
208 views

Will the Sun's solar wind push a permanent magnet out of our solar system?

If you were place a strong permanent magnet into the solar wind, like a 1 inch cube neodymium magnet, would the charged particles of the solar wind colliding with the magnet's magnetic field push the ...
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1answer
121 views

Would the dynamic pressure of the Sun’s solar wind be strong enough to trap plasma ions within an open container?

If you were to place a long cylinder, open at one end and closed at the other end, and position this cylinder so that the open end is facing the Sun, and then you were to inject plasma ions, such as ...
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1answer
588 views

Angular Diameter Distance

The definition of the angular diameter distance is the ratio of an object's physical transverse size to its angular size. However when I was reading my textbook, Astrophysics in a Nutshell by Dan Maoz ...
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What's the profound reason(s) why the star formation rate drives the scatter of the mass-metallicity relation in galaxies?

Since decades it's well known that a correlation between stellar mass and metallicity (Z; both stellar and gas-phase Z, but here I focus on the gas-phase Z) exists (e.g., Tremonti+04; analysis of >...
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1answer
91 views

Are large body orbits self correcting?

If a rogue planet disrupts Earth's orbit slightly to cause a long winter or summer will the Earth's orbit normalize back close its original orbit over time? Could a Planet X or some other elliptical ...