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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Is it possible that a ultra-large portion of the space we live in is already inside a black hole? How could we refute this?
Trying to wrap my head around some concepts involving the very large gravitational fields of black holes, and what the gravitational gradients look like on a cosmic scale.
I'm familiar with the Great ...
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Is there another explanation, apart from the doppler effect, for the redshift observed in distant galaxies?
On episode 10 of the original Cosmos TV series, Carl Sagan mentions that some scientist don't agree that the redshift observed in distant galaxies is evidence of the big bang, stating that probably ...
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How fast is the universe expanding?
I've hear several theories stating that the universe is expanding faster than the speed of light, others claim that the universe expands faster the further away you measure it. Which of this is ...
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What happens to the 99.9 % of the sun-rays that do not fall on any planets or any other celestial body?
I assume that about 99.9% of the sun-rays that do not fall on any planet or any other celestial body keep on traveling farther and farther unto infinity. Apparently such rays get lost. Keeping in mind ...
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Why is there no concavity in the orbit of the moon around the Sun?
Such questions have been asked here and I have read the answers some of which are quite informative. However, I want an answer that's straightforward.
I have gone through the following paper by A B ...
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Relationship between absolute magnitude of a star and its luminosity?
Why does this relationship involves the absolute magnitude of the sun and its luminosity?
How to derive an expression relating the absolute magnitude of a star to its luminosity?
So according to the ...
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Why is the Moon's orbit so complicated?
I like to think I have a good enough understanding of astrophysics but there's still one thing that I just can't explain.
Why does the Moon orbit the Earth the way it does?
Many other moons in the ...
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Problem regarding the absorption lines of the Sun
Some of the wavelengths of light that are emitted from the Sun will be absorbed by atoms in the outer layer of the Sun and also the atmosphere of the Sun, and we see this as absorption lines in the ...
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Timescale of ignition of a protostar?
What is the timescale of start of nuclear fusion as T Tauri type star transforms into a Main Sequence star?
Wikipedia article on T Tauri type stars mentions:
Their central temperatures are too low ...
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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 have a chance of solving? Suppose the amateur has a PhD in some other field, owns a basic telescope, a set of filters, diffraction ...
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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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Universe and black holes
I know that the radius of the observable universe is about 46.6 billion light years and is expanding at every instant of time due to dark energy . So is it possible that we our entire universe could ...
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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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How does a neutron star collapse into a black hole?
We know the spectacular explosions of supernovae, that when massive enough, form black holes. The explosive emission of both electromagnetic radiation and massive amounts of matter is clearly ...
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Why don't (or can't) stars be more than 325 or so times the mass of the sun? What limits their size?
Is there a particular reason why stars cannot grow as massive as they want to?
And why doesn't this limit apply to supermassive black holes?
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How can astronomers pinpoint the location of the source of a neutrino?
In the popular press, in recent months, we have heard a lot about high-energy neutrinos from far outside our solar system reaching our detectors....
But I wonder...
If a single neutrino from a great ...
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How does a gravity slingshot actually work?
From what I know of elliptical orbits, an object speeds up near the periapsis and slows down at the apoapsis, much like we learned in high school physics how a sphere would roll down and back up a ...
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Is there a possibility that a white dwarf can turn into a neutron star or a black hole?
I know that a white dwarf is supported mainly by electron degeneracy pressure and that if it gains more than about 1.4 solar masses from any source (such as a companion star or a collision), it ...
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Why did astronomers believe most or all stellar black holes had masses no greater than 15 solar masses?
The so-called 'mass gaps' for black holes, according to theoretical models, are between 2-5 solar masses and 50 to 150 solar masses. (Actually, I have read that there is no good theoretical reason ...
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How can a black hole have a charge, or be charged?
So-called 'hairless' black holes (no-hair theory, or theorem?) , which is what real black holes are, can be described by just three characteristics: Mass, spin, and charge.
It is easy enough to ...
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Role of power laws in astronomy?
I often see astronomers fitting data to power laws. What about power laws makes them so useful in astronomy? Why are so many astronomical observations well-fit by power laws? I know it's a relation ...
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Have we discovered a Galaxy lacking in Dark matter?
This question is relevant but it was speaking about a specific discovery reported by pieter van Dokkum, and the answer then mentioned it was disputed whether the paper's conclusion is even correct.
I ...
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Assuming a sufficient amount of mass above the density threshold, does the actual concentration of the mass matter in creating a black hole?
I've heard that the actual density of a black hole (within the volume of the event horizon) is pretty low - does that mean that any sufficiently large volume of mass over that density is also a black ...
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Gravitational pull needed to keep a gas in atmosphere
How can you determine the gravitational force needed to keep a particular gas in the atmosphere of a planet (for example, carbon dioxide (CO2))?
I came across the following formula $\left(\frac{8RT}{...
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How does the gravitational wave strain from a rotating binary depend on the chirp mass, frequency and distance & what a short derivation looks like?
Our most familiar experience with wave propagation either from firsthand experience or in school comes from the phenomena of sound and light and radio electromagnetic propagation.
In air, we know that ...
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Explanation about the resonance, mean motion resonance and libration
I am studying for a project the dynamics of multi-planetary system in resonance. I have two questions about this domain.
In many articles they speak about 'mean motion resonance', what is the ...
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How long does lunar opposition surge last? Are there measurements of the full Moon getting suddenly brighter?
Wikipedia's opposition surge is a short article and forwards shadow hiding and coherent backscattering as proposed mechanisms, but it doesn't really explain how much the brightness of the Moon ...
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Satellite's orbit
What is the maximum distance for a satellite to orbit the earth? Does earth's gravity has the impact on satellite? I do know that earth's gravity will never be zero and it's gravity is inversely ...
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Can a neutron star ever be less than about 1.44 solar masses (the Chandrasekhar limit)? Why not?
I learned about the Chandrasekhar limit as being the UPPER limit, in terms of mass, for a white dwarf...
But, I have never heard of a neutron star being BELOW that mass, so I have wondered, recently, ...
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What is a good way to start learning Astrophysics [duplicate]
I am a junior in high school and throughout my life I have always had a fascination with space. I use to watch "Space's Deepest secrets" and stuff like that but after a while I stopped learning much ...
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Any ideas for an astronomy + ML project? [closed]
I wish to do an astronomy related project which incorporates machine learning.Do you have any suggestions?
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What should be the "poles" for irregular shaped bodies?
Continuation of: What is the definition of a "pole" of a celestial body?
uhoh's answer says that distinct bodies should have a center of mass. If the body is spherical, then the COM will be ...
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Why would a black hole's magnetic hair being short-lived not violate the no-hair conjecture, but long-lived hair would? How long is "long-lived"?
Phys.org's Magnetic 'balding' of black holes saves general relativity prediction says:
There is a potentially hairy threat to the conjecture, though. Black holes can be born with a strong magnetic ...
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Basic, learning examples of applications of CFD and MHD in astrophysics, and current research directions using these techniques?
I am an undergraduate in Physics, and I have an opportunity to work with a some of my seniors to learn Computational Fluid Dynamics (CFD) and Magnetohydrodynamics (MHD).
I would like to choose my ...
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Sudden Effects of Sun Disappearing [duplicate]
It takes 8 minutes for the sun's light to reach earth. If the sun were to instantly disappear, what would happen? I imagine that Earth would fly away on a path tangential to its orbit. What would ...
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Is a black hole made from a anti-matter star the same as a ordinary black hole?
Would a black hole from a star made of anti-matter be the same as a blackhole made of ordinary matter?.
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Fraction of initial mass lost (radiated) by neutron star mergers compared to black hole mergers?
GW190521 black hole merger total mass calculation and missing mass, how does this happen? notes that there are about 9 solar masses missing from the final black hole.
GW170817 is the first observed ...
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How to be an astrophysicist?
For a high-school students, what are the ways to become an astrophysicist?
What should he/she take in college?
What is the career path to become an astrophysicist?
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How is the Hubble constant determined from gravitational waves?
We know there is a discrepancy between measurements of the Hubble constant, $H_0$. On one side there is the method of the Planck mission, where they use the CMB and the $\Lambda$CDM model to determine ...
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How well conserved is etendue in extreme gravitational lensing scenarios?
This excellent answer to Could dark matter exist in the Universe in the form of sufficiently dense objects? includes the following image and description:
Light from the background galaxy circles a ...
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Is there anything currently 46 billion light years away from Earth that we can see?
If the oldest galaxy ever discovered, i.e GLASS-z13, is at a present proper distance of around 33 billion ly from Earth, why then do we define the observable universe to have a radius of around 46 ...
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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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Has the Penrose process ever been linked to an observed phenomenon in some way?
This answer to What defines the plane of an accretion disk around a black hole? mentions the Penrose process as a potential mechanism that could change the axis of the orbital angular momentum of an ...
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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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Why is molecular hydrogen (H2) so difficult for astronomers to detect?
I am reading a great deal about the various forms of hydrogen throughout the universe, and I keep reading that 'molecular hydrogen is notoriously difficult to detect', and other sentiments along those ...
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Is the age of the Universe really 13.8 billion years?
Ok, I know this has been asked by a lot of people, but my reason for asking this question is a bit different. Please read further.
I was watching a video by Fermilab (Start at 6:30, at 8:30 he ...
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What uncertainty does an error bar signify in astronomy?
When an astronomer talks about her/his topic and shows an X/Y-plot with error bars. What should one assume that those error bars represent?
1 standard deviation? Or 2? Or some specific significance ...
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The creation of comets
How are comet and meteors made, and what causes them to travel through space so fast? I have tried researching, but I decided this was the faster way.
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How do we know that comets definitely mase and not just fluoresce? What is it about 18-cm lines that indicates that is really masing per se?
Wikipedia's Astrophysical_maser#comets mentions some anecdotes of notable masers associated with comets, and Maser emissions from comets begins:
The 18-cm lines of the OH radical are the only well-...
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Discovery in Astronomy vs one in Physics - do they differ in required burden of evidence?
Discovery in Astronomy/Astrophysics (of astronomical objects) vs discovery of physical phenomena in experimental Physics (as such) - do they differ in required burden of evidence (with the notion, ...
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