All Questions
534 questions
32
votes
5
answers
15k
views
Can there be Electron and/or Proton Stars?
What happens to all of the electrons and protons in the material of a neutron star?
Could there ever be an electron star or a proton star?
- 1,672
32
votes
4
answers
1k
views
Metal-rich star formation
While discussing star formation on cosmological scales with some classmates, we mentioned the breakdown between the different stellar populations via metallicity:
Population III: $Z = [{\rm Fe/H}] \...
- 28.8k
26
votes
2
answers
8k
views
What happens to Protons and Electrons when a Neutron star forms?
What happens to Protons and Electrons when a Neutron star forms? At some point gravity overcomes the Pauli Exclusion Principle ( I assume) and they are all forced together. What happens in the process?...
user56903
21
votes
2
answers
1k
views
How can a spiral galaxy exist?
A spiral arm orbiting a central mass should be dispersed quite quickly as the outer elements would move more slowly than the inner ones. The Milky Way, is about 59 Galactic Years old, which, one would ...
- 779
19
votes
4
answers
26k
views
Why can't Iron fusion occur in stars?
It is said that iron fusion is endothermic and star can't sustain this kind of fusion (not until it goes supernova). However star is constantly releasing energy from fusion of elements like Hydrogen ...
- 673
13
votes
5
answers
2k
views
Interstellar dust/matter distribution
It is known that one of the main problems of interstellar flight is a presence of matter between stars in form of very fine dust and huge asteroids. Which can slowly (or fast) destroy any ship.
What ...
- 665
12
votes
4
answers
3k
views
Shapes of galaxies
I've heard most of galaxies are spiral or ellipsoid shaped. Is it true?
If true, then why they form in such shapes?
How did arms of the spiral galaxies form?
- 657
11
votes
2
answers
343
views
Formation of supermassive black holes
Scientists have found very bright source of light which they call quasar and the are found to be supermassive black holes. So these black holes are so massive that they cannot be formed by a supernova....
- 111
10
votes
4
answers
1k
views
What is the origin of spin of celestial objects?
In an older question from June 2011, Why does each celestial object spin on its own axis?, apparently revived by the system, a user is
asking about the origin of the rotation of celestial bodies.
The ...
- 3,808
4
votes
5
answers
14k
views
How much iron would I have to shoot into the Sun to blow it up?
My understanding--though it's from a Science Channel show so I'm not sure if it is correct--is that there is a fusion reaction happening in the center of the sun. Atomic nuclei are being created and ...
- 181
2
votes
1
answer
455
views
In fusion inside stars (sun) or very hot gasses, how do the electrons get bound and what about tritons and $D$-$T$ vs $D$-$D$ fusion?
Most texts I've read focus on just the nuclei to begin with, but eventually start talking about Helium (or other) atoms and isotopes. A few aspects aren't clear to me and I'd be grateful for some ...
- 53
65
votes
3
answers
13k
views
Why is the Sun almost perfectly spherical?
Relatively recent measurements indicate that the Sun is nearly the roundest object ever measured. If scaled to the size of a beach ball, it would be so round that the difference between the widest ...
user81619
49
votes
5
answers
23k
views
Why aren't there spherical galaxies?
According to the Wikipedia page on Galaxy Types, there are four main kinds of galaxies:
Spirals - as the name implies, these look like huge spinning spirals with curved "arms" branching out
...
- 625
17
votes
3
answers
9k
views
Why does fusion stop at iron when nickel is most tightly bound?
My understanding is that stellar fusion naturally stops at iron because it is energetically unfavourable to grow the nucleus further.
But iron is only the third most tightly-bound nucleus, nickel is ...
- 5,188
15
votes
3
answers
12k
views
What would be the characteristics of Jupiter if it shrank?
So, I've heard from various works of science fiction about the prospect of turning Jupiter into a star. From what I know about the physics of such a task, it would require somehow condensing Jupiter ...
- 3,759
12
votes
1
answer
1k
views
Orange ring in a black hole image
What exactly is the origin of the orange ring around M$87$?
I understand that the image was not taken in the visible light range. The colors are therefore artificial.
I also read that the image ...
- 4,322
12
votes
4
answers
7k
views
What is the actual energy content of the Sun?
Beside the energy released by nuclear fusion in the core, the Sun is a hot plasma of hydrogen and helium ranging from thousands to million of degrees. So how does that translate into energy ?
I have ...
- 3,934
11
votes
2
answers
1k
views
Why are there spectral lines at all?
My somewhat basic understanding of the concept comes from lectures I've attended about the Bohr-model, which explains the phenomenon as arising from the fact that certain configurations of an atom can ...
- 556
11
votes
2
answers
3k
views
What happens when the black hole at a galactic core eats the galaxy? [duplicate]
I'm making several assumptions, not sure if any are correct:
there is a black hole at the center of a galaxy
the black hole is eating the galaxy
Eventually the galaxy will be gone, right?
Has this ...
anon
9
votes
4
answers
11k
views
Light formed by the sun?
This is an extract from the astrophysics chapter in my book:
Hydrogen atoms fuse to form helium. At the same time, lots of of gamma photons and neutrinos are produced. The photons take thousands ...
- 2,177
8
votes
2
answers
1k
views
How much faster is the fusion we make on Earth compared to the fusion that happens in the Sun?
I have come across many websites which state that proton-proton fusion, which is the dominant type of fusion that powers the Sun, is extremely slow; and that is why the Sun is still burning today. But ...
- 3,934
8
votes
3
answers
645
views
Jupiter radiation belt: where >MeV particles comes from?
When I read some discussion about exploration of Jupiter moons, or possibility of life there, a common argument is high dose of radiation in Jupiter's radiation belt (several orders of magnitude ...
- 987
7
votes
1
answer
661
views
Do gravitational waves impart linear momentum to objects? (e.g. Quasar 3C 186)
The Washington Post article This black hole is being pushed around its galaxy by gravitational waves also includes an excellent NASA Goddard video description (also in YouTube) of the proposed ...
- 6,111
7
votes
2
answers
802
views
Black hole collision and the event horizon
Will the event horizons of a two black holes be perturbed or bent before a collision? What will the shape of the event horizon appear to be immediately after first contact?
- 81
5
votes
2
answers
45k
views
Temperature on the surface of the sun calculated with the Stefan-Boltzmann-rule
In a German Wikipedia page, the following calculation for the temperature on the surface of the Sun is made:
$\sigma=5.67*10^{-8}\frac{W}{m^2K^4}$ (Stefan-Boltzmann constant)
$S = 1367\frac{W}{m^2}$ ...
- 345
5
votes
2
answers
284
views
How is angular momentum stored in the superfluid component of pulsars?
I am trying to understand current theories about why pulsars glitch. I have come across two explanations that I'm assuming are complementary, but which I am having trouble reconciling.
The inner ...
- 425
5
votes
1
answer
239
views
Temperature of a mixed plasma
I know the temperature, $T$, in $\mathrm{eV}$ and density, $n$, for the three ion components of a chosen plasma, say $\mathrm{O^+}$, $\mathrm{He^{++}}$, and $\mathrm{H^+}$. But I would like to know ...
- 51
4
votes
4
answers
937
views
A reference request for real world experimental data [closed]
I always use to wonder how the experimental physicists discover new particles every now and then whose dimensions/properties/mass/charge several order of magnitudes below that of anything that is ...
4
votes
1
answer
496
views
Why do galaxies "disappear?"
So, this bit of information confused me lately. Before, I figured galaxies were no longer visible by us because their luminosity decreased in an inverse square manner. However, while watching a movie ...
- 311
3
votes
2
answers
728
views
A question about the Fermi acceleration
In high school physics, we know that a charged particle cannot gain energy from a magnetic field. But, it seems that in the so-called Fermi acceleration, the particle is accelerated by the magnetic ...
- 1,075
3
votes
1
answer
381
views
Mach no. should be constant for existence of similarity solution
I am reading some research papers on Taylor-Sedov type self-similar solution to the blast wave problems...
It is written that for the existence of similarity solutions Mach number should be constant.....
- 83
0
votes
1
answer
202
views
Compressible gas dynamics in the context of astrophysics
I am looking for a resource that specializes and gives an emphasis on the dynamics of compressible fluids (gas dynamics) preferably in more than one dimensions, but one dimensional is also good, and ...
55
votes
5
answers
8k
views
What is happening when magnetic field lines snap or break?
In discussions of sun spots and auroras on Earth, magnetic field lines are often described as "snapping" or "breaking", with the result of releasing charged particles very ...
- 1,101
45
votes
4
answers
15k
views
What would happen if Jupiter collided with the Sun?
This question is inspired by a similar one asked on Quora. Let's say a wizard magicked Jupiter into the Sun, with or without high velocity. What happens?
The Quora question has two completely opposed ...
- 22.1k
39
votes
4
answers
6k
views
Are neutrino stars theoretically possible?
Since neutrinos
have a small mass and
are affected by gravity,
wouldn't it be theoretically possible to have such a large quantity of them so close to each other, that they would form a kind of a ...
- 775
34
votes
3
answers
5k
views
Do supernovae push neighboring stars outward?
I know that a supernova can mess up the heliosphere of nearby stars, but I'm wondering if it could physically push neighboring stars off their trajectories.
It's fun to imagine all the stars ...
- 1,053
32
votes
5
answers
3k
views
Why do we deal only with large scale magnetic fields in astrophysics, and not electric fields?
In astrophysics there is a lot going on about strong, large scale magnetic fields: in stars (prominences), magnetic dynamos, compact accretors collimating jets, etc. There's even a special ...
- 991
30
votes
6
answers
14k
views
Why are the orbits of planets in the Solar System nearly circular?
Except for Mercury, the planets in the Solar System have very small eccentricities.
Is this property special to the Solar System? Wikipedia states:
Most exoplanets with orbital periods of 20 days ...
- 53.7k
25
votes
4
answers
2k
views
Are Neutron stars transparent?
Neutrons have no charge so they would not, I think, interact with photons. Would a neutron star be transparent?
- 731
25
votes
1
answer
1k
views
Causes of hexagonal shape of Saturn's jet stream
NASA has just shown a more detailed picture of the hexagonal vortex/storm on Saturn:
http://www.ibtimes.com/nasa-releases-images-saturns-hexagon-mega-storm-may-have-been-swirling-centuries-1496218
...
- 181k
23
votes
1
answer
10k
views
How do we know Dark Matter is non-baryonic? [duplicate]
It seems widely stated, but not thoroughly explained, that Dark Matter is not normal matter as we understand it. Wikipedia states "Consistency with other observations indicates that the vast majority ...
- 3,271
21
votes
2
answers
5k
views
Are we living in a false vacuum? Is there any way to tell?
I was thinking of the noted 1980 paper by Sidney Coleman and Frank de Luccia--"Gravitational effects of and on vacuum decay"-- about metastable vacuum states that could tunnel to a lower energy "true ...
- 4,383
20
votes
2
answers
1k
views
Why don't stars in globular clusters all orbit in the same plane?
Globular clusters like Omega Centauri certainly don't seem to be very coplanar at all.
In other words, why doesn't the explanation at Why are our planets in the solar system all on the same disc/...
- 3,662
19
votes
4
answers
24k
views
Why are some galaxies flat?
What is the explanation for the flatness of some galaxies?
(If it's due to their rotation then why they are rotating, why some other galaxies are not flat etc., I would like to hear a nice and ...
- 2,176
19
votes
1
answer
1k
views
Why don't electrons and protons in a white dwarf combine before the electrons become ultrarelativistic?
I wanted to get a rough picture of how white dwarfs and the Chandrasekhar limit work. I wound up with an argument nearly identical to this one on Wikipedia up through the non-relativistic white dwarf. ...
- 53.7k
19
votes
5
answers
3k
views
How is hydrostatic pressure overcome when a star is formed?
If stars are formed by the collapse of dust clouds under gravity, how is the pressure of the dust cloud overcome?
As more material gathers together, gravity will increase, but pressure will also ...
- 952
19
votes
2
answers
2k
views
Is there evidence of dark matter in our galaxy?
Is there evidence of dark matter in our galaxy?
How can we measure this, say, how many percent of the center of our galaxy is dark matter?
I did not find the answer in the question What's dark ...
- 427
16
votes
5
answers
3k
views
How is it possible for astronomers to see something 13B light years away?
In a NPR News story from a few years back:
"A gamma-ray burst from about 13
billion light years away has become
the most distant object in the known
universe."
I'm a layman when it comes to ...
- 263
16
votes
3
answers
47k
views
What's the difference between gas and plasma?
A friend stated that stars are hot balls of gas, however we know that technically stars are plasma. Is his statement entirely incorrect? Can a plasma be considered a form of gas or should be referred ...
- 263
15
votes
2
answers
19k
views
How is the parallax angle actually measured?
I understand that parallax is used to measure distances to stars. But how is the parallax angle actually measured?
In the parallax diagram we have two similar triangles, but we don't know any values ...
- 385