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.

Filter by
Sorted by
Tagged with
3 votes
1 answer
626 views

When is it a good aproximation to consider a star to be an ideal gas?

I am currently taking a first course on stellar astrophysics, and I noticed that in some cases we use the ideal gas equation of state for stars, so we also use $\gamma =5/3$. Of course it can only be ...
Javier's user avatar
  • 408
3 votes
1 answer
2k views

How to calculate the mean molecular weight of the Sun

I have a homework question in which I need to estimate a parameter known as $\beta_{P}$ and also the core temperature, both for the Sun. However, prior to doing this I need to know the mean molecular ...
MichaelJRoberts's user avatar
1 vote
1 answer
527 views

Does this black hole magnetohydrodynamics equation even superficially make sense?

My question is about the journal paper mentioned in an Academia Stack Exchange post. Please understand that this paper has never been posted on arXiv, and I can provide only a link whose content is ...
arendellean's user avatar
1 vote
1 answer
227 views

How gravity works in a black hole? [closed]

In astronomy class, we have to state how gravity work in the black hole? I know for one fact is that black hole is strong enough to stretch you thin enough like a noodle. Any ideas?
Needtolearnmore's user avatar
1 vote
1 answer
60 views

In what units to quote the thermal Blackbody temperature

Just a quick question relating to the thermal Blackbody temperature of a celestial object. In the c.g.s regime of astrophysics, is it more 'sophisticated' to quote the thermal Blackbody temperature in ...
MichaelJRoberts's user avatar
10 votes
2 answers
997 views

Why are the magnetic poles of a pulsar so far off the rotational axis, yet stable?

My understanding is that a pulsar is a neutron star whose magnetic poles don't coincide with the rotational poles and whose magnetic poles sweep through Earth (allowing us to hear radio noise). If we ...
Bohemian's user avatar
  • 271
1 vote
1 answer
401 views

Spheres in space [duplicate]

I know that gravity will turn a mass into a sphere, which is why planets and stars are that shape. But then we have asteroids and small moons which are not spherical. Such as a couple of Pluto's moons....
Kilisi's user avatar
  • 111
12 votes
1 answer
330 views

Is any consensus forming on the solution to the "Lithium Problem"?

The "Lithium Problem" relates to the fact very-low-metallicity stars appear to have a Li/H ratio approximately one third of what would be expected. The ratio should be the same as the prediction from ...
Eubie Drew's user avatar
  • 1,070
-4 votes
1 answer
165 views

What if the earth stopped rotating and revolving at the same time? [closed]

What will happen to us are we going to move in a tangential direction with earth axis of rotation ?
Chloritone_360's user avatar
1 vote
1 answer
181 views

How is the heat production inside moons compliant with Conservation of Energy?

A Nova episode said that during stages of some moons' elliptical orbits, the moon is stretched, and friction causes the inside of the moon to heat up. I do not understand how this is compliant with ...
IOWF's user avatar
  • 25
0 votes
1 answer
91 views

Which force makes planets to continuously revolve around their parent star?

We know that planets revolve around their parent star (or specifically Barycenter), they maintain a specific speed of revolution so that they don't end up smashing into their planet star. Which force ...
Sirius's user avatar
  • 425
3 votes
1 answer
98 views

What is the accuracy of an artificial satellite at a certain magnitude?

When we say that 'accuracy of gaia satellite is 10 $\mu$as at $V = 10$ magnitude in position and annual proper motion'. What does this mean? Does it change over time?
user avatar
2 votes
2 answers
492 views

Calculating the mass of star

I am doing a project which requires that I have data for the mass of several stars. However, the data for mass of stars is obviously not readily available as it's really hard to calculate. In such a ...
pew31's user avatar
  • 117
4 votes
2 answers
769 views

Pulsars: How do astronomers measure minute changes in period (~picoseconds per year)?

I've been to some talks that mention how stable the period of a millisecond pulsar is over long periods of time. Recently, it was mentioned that astronomers have calculated the change in period over ...
Sam's user avatar
  • 489
6 votes
1 answer
154 views

What more could be learned from a rare astronomical event if we knew precisely when it would occur?

This is actually related to a question I recently asked on Worldbuilding, but seemed more appropriately asked here. To keep this from being too broad in scope, let's assume that someone figured out ...
IchabodE's user avatar
  • 526
9 votes
2 answers
871 views

Would a tablespoon of a neutron star remain intact?

I've heard people say that a tablespoon of neutron star would weigh over a billion tons. If we ever could take a tablespoon of one would it still remain intact with the same density?
matryoshka's user avatar
4 votes
2 answers
2k views

Circular formation around the moon

I have seen a large circular formation of cloud around the full moon sometimes. Have anyone seen the same? What is the reason behind this formation? Due to lunar attraction? Most of the sky is empty ...
Ganapathy C's user avatar
6 votes
1 answer
152 views

What happens to the Gas Pressure when working out the Eddington Luminosity?

I am looking at how the Eddington Luminosity is derived and I do no understand why we only care about $P_{rad}$? When working out $L_{Edd}$ you take the ratio between $dP_{rad}/dr$ and $dP_{...
turnip's user avatar
  • 161
2 votes
1 answer
232 views

Can you assume atmosphere height for the purpose of surface pressure calculation?

Given that by definition of scale height an atmosphere thins by a factor of 1/e^x where x is elevation in terms of scale height multiples (See the table here: Definition of Scale Height), can we ...
Marcin's user avatar
  • 296
16 votes
2 answers
954 views

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 ...
eclipse's user avatar
  • 161
6 votes
1 answer
402 views

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}{...
Marcin's user avatar
  • 296
3 votes
0 answers
323 views

Angular momentum in planetary disk formation

Reading about the formation of planetary disks, one of the major problems, it seems like, is the evacuation of angular momentum. Aparently planets can't form with the amount o angular momentum the ...
L.R.'s user avatar
  • 666
2 votes
1 answer
1k views

What happens to a white dwarf past the Chandrasekhar limit?

This is a multiple choice question I had trouble with on an exam. Will a white dwarf that has had too much mass piled on top of it a) undergo a thermonuclear flash and explode in a type IA supernova ...
Adelina's user avatar
  • 121
3 votes
2 answers
4k views

How would Jupiter's brightness relative to our sun seem to a remote observer (observing from a remote star)

Given that Jupiter is 5 AU from our sun and a remote observer viewing our solar system from some other part of our galaxy looks at it. We assume that Jupiter's radius is $11 \times 6700$ km. What ...
vondip's user avatar
  • 133
6 votes
2 answers
1k views

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 ...
LocalFluff's user avatar
  • 11.3k
1 vote
0 answers
105 views

Can an astronaut ever reach a Black Hole theoretically? [duplicate]

Ok, bear with me, while I try to explain the question I have. I read that time slows as we approach a black hole. So, suppose,theoretically, as astronaut is approaching a Black Hole. And he gets ...
user5496's user avatar
0 votes
1 answer
277 views

Collision of two Earths

Assume that two Earth-like planets orbited the same star, with elliptic orbits. Eventually, something occurs that caused the two planets to collide. What would be the outcome of such a catastrophe? ...
erdekhayser's user avatar
3 votes
1 answer
118 views

Exploiting symmetry in the axisymmetric Jeans equations

I'm solving the axisymmetric Jeans equations to determine the initial conditions for an exponential disk inside an NFW halo. The density profiles of the two components are \begin{equation} \rho_d(R,z)...
Robbie Fasano's user avatar
3 votes
1 answer
111 views

Where can I learn these Astrophysical techniques? [Read below]

Whenever I read any Astro papers in http://arxiv.org/ they usually talk about Data fitting or modelling or sentences like 'we fitted the spectral region by analytic functions i.e. by multi-component ...
Hari Seldon's user avatar
3 votes
1 answer
275 views

Is it accurate to say that we have a gravitational attraction towards all objects in the known universe?

Its probably small, but is there a theoretical gravitational attraction between all objects in the universe? Light can move pretty far, so does that mean gravity can as well, and is the gravity ...
bogen's user avatar
  • 2,342
14 votes
1 answer
2k views

What causes the dimensions of a star increase when its hydrogen fuel is exhausted?

What causes the dimensions of a star increase when its hydrogen fuel is exhausted? For example, the Sun is expected to increase its radius 250 times. What causes this if its temperature is expected to ...
Anixx's user avatar
  • 1,255
4 votes
2 answers
432 views

Is there a lower limit for the altitude of orbiting objects?

As I understand it, one object can orbit another at a variety of altitudes, and the stability of the orbit is determined by (among other things) the speed of the orbiting object. Go too slowly and ...
Nerrolken's user avatar
  • 637
0 votes
1 answer
136 views

Apocalypse on earth

What would it feel like on Earth if the Earth accelerated due to sudden changes in the solar system like ejection of another planet? Would there be giant tidal waves and other cataclysmic events?
Numberknot's user avatar
0 votes
2 answers
144 views

What is the size of the universe.is it infinite? [duplicate]

What is the exact size of the universe.is it infinite?
user2476's user avatar
2 votes
1 answer
714 views

Using Tully Fisher to measure Distance Problem

Can anyone explain by looking at the solution in the pic, how did the cos (i) came about? I guess they are getting this from the major-minor axis info in the question, but I am not sure about the ...
Hari Sheldon's user avatar
3 votes
1 answer
2k views

What is the Fundamental plane for Elliptical Galaxies?

An alternate explanation rather than from wikipedia is preferable.
Hari Sheldon's user avatar
7 votes
2 answers
333 views

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 ...
Ian Moriarty's user avatar
1 vote
1 answer
166 views

If the speed at which the universe contracts in reverse time decreases over time, then how did scientists arrive at a date for "The Big Bang"?

If the speed at which the universe expands is constantly increasing (just like a derivative), then the opposite must also be true: the speed at which the universe contracts in reverse time is ...
reuven's user avatar
  • 11
14 votes
2 answers
2k views

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 ...
Ian Moriarty's user avatar
6 votes
2 answers
619 views

Weight of a celestial body

How do astronomers find out the correct weight of a planet even though there isn't any direct means to weigh them? What technique do they use? Just curious!
Devgeet Patel's user avatar
3 votes
2 answers
15k views

Is a white dwarf hotter than a Red Giant?

From what I've read, white stars are hotter than red ones. But a white dwarf would have just heavy elements to fuse, so shouldn't it be less bright?
Yashbhatt's user avatar
  • 738
6 votes
2 answers
1k views

Observational evidence for the existence of black holes [duplicate]

What is the direct observational evidence that black holes exist? I have read that black holes have been detected through X-ray emission. What is some other observational evidence for black holes?
Frank's user avatar
  • 153
18 votes
3 answers
2k views

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 ...
Ky -'s user avatar
  • 766
1 vote
1 answer
3k views

Finding the radius of an eccentric orbit at any point

Knowing the apoapsis, periapsis and therefore period of an orbit, how can I find the radius of an object in an orbit at a given angle or time, whichever is needed. For example, if I have an object m ...
FaceySmile's user avatar
25 votes
3 answers
2k views

How does the evolution of a solar system not break the second law of thermodynamics?

Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck. As I understand it, the solar system evolved from a ...
user2346333's user avatar
1 vote
2 answers
486 views

How are the speed, distance and time of India's MOM and USA's Maven Mars missions calculated?

How do the scientists calculate the correct time to launch the Mars mission so that the satellite travel time is less? How they are synchronizing the speed of satellite with respect to earth and mars ?...
Santhosh's user avatar
  • 161
6 votes
2 answers
5k views

Our universe the surface of a 4-dimensional sphere?

The cosmic microwave background that we observe uniformly around us is usually explained by assuming that our universe is the surface of a four dimensional sphere. That way the uniformity makes sense ...
user3138766's user avatar
5 votes
2 answers
326 views

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 ...
Eduardo Serra's user avatar
1 vote
3 answers
1k views

Earth's gravitational pull on ISS

How do they make International space station to orbit the earth beyond Earth's gravity acting on it? We all know that ISS is rotating at an altitude of just 350km away. How could the ISS escape Earth'...
Praveen Kadambari's user avatar
4 votes
1 answer
280 views

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 ...
Praveen Kadambari's user avatar