Unanswered Questions
154 questions with no upvoted or accepted answers
4
votes
0
answers
269
views
Why the Hubble constant is so inconsistent?
Having a look on Wikipedia I noticed the following values (of the last 6 years) for the Hubble constant:
67.6±0.7 SDSS-III Baryon Oscillation Spectroscopic Survey
73.00±1.75 Hubble Space ...
- 316
3
votes
0
answers
41
views
Why MIT's Benjamin Rackham says "nearby ultracool dwarf SPECULOOS-3" would look "purplish-red, spotted, and flaring" from an airless orbiting planet?
May 15, 2024 MIT News article Newly discovered Earth-sized planet may lack an atmosphere includes the following:
“We can say from our spectra and other observations that the star has a temperature of ...
- 30.7k
3
votes
0
answers
107
views
Kepler to Cartesian and Cartesian to Kepler inaccuracies
I am programming a computer simulation set in a star system. I've used Rene Schwarz's wonderfully concise memorandi explaining converting from Kepler orbital elements into cartesian coordinates and ...
- 51
3
votes
0
answers
68
views
Gravitational recoil with stars/planets...?
When two black holes are merging, the resulting merge can be ejected if one of the black holes had less mass than the other one, so the gravitational waves emitted by both of them is unbalanced, and ...
- 1,017
3
votes
0
answers
56
views
Potential energy in an expanding universe
A question you wonderful geniuses can hopefully answer. Imagine a piece of string drawn between two galaxies. Space between the galaxies is expanding. What force is being applied to the string? Where ...
- 31
3
votes
0
answers
79
views
Deviations of conservation laws in the context of cosmological evolution?
If energy is "not conserved" in General Relativity (or at least, it is difficult to define it) in the context of an accelerating expanding spacetime (like it happens in our Universe), are ...
- 1,017
3
votes
0
answers
84
views
Cosmic microwave background the same as the first visible light at 379,000 yrs after the Big Bang? How do these measure the age of the universe?
Was the CMB emitted at the same time as visible light at 379,000 yrs after the BB ? Was this a one time event ? If headed away from us, how does it measure the age of the universe?
- 31
3
votes
0
answers
48
views
How can a busy high school student get into learning Astronomy?
I'm a high school student that has loved physics for quite some time, but have only started dabbling with the more complex things. I know a fair bit about quantum mechanics and such as I like it, but ...
- 39
3
votes
0
answers
77
views
What is the main difference between cyclotron, synchrotron, and gyrosynchrotron radiation?
How are these various types of radiation generated? What is the main difference between them? Can someone suggest a book related to these radiations?
- 15k
3
votes
0
answers
65
views
Why are CMB peak heights sensitive to the physical densities
A very simple question: why should it be that the CMB power spectrum allows constraints to be placed on the combination of parameters
$$\omega_c = \Omega_c h^2$$
$$\omega_b = \Omega_b h^2$$
as opposed ...
- 61
3
votes
0
answers
47
views
Heat map of portion of the sky visible for a given observatory on Earth?
Reading Calculating area of visible sky I started wondering which portion of the sky one could observe how long given the 3D coordinates of an observatory, and two points in time.
In other words, I ...
- 5,636
3
votes
0
answers
48
views
Classical Mechanics : Interaction Sun Radiation Pressure - Gravitation
I have a theoretical problem that merges the effects of a gravitational field and the Sun radiation pressure. The problem goes as follows:
A spacecraft orbits the Sun in absence of any other body ...
- 31
3
votes
0
answers
119
views
Gravity on Mercury's highest elevation?
This post answers what is Mars' gravity at its highest point (Olympus Mons) compared to the Earth's and Mars' standard, it's 0.3736 g (Mars standard is 0.3794 g). This also seems to be the lowest ...
- 30.7k
3
votes
0
answers
47
views
Superconducting space dust; what transient fields could induce persistent current loops?
Science Alert's Superconductivity Has Been Discovered in Meteorites For The First Time quotes from Superconductivity found in meteorites (Wampler et al. PNAS March 23, 2020)
The paper describes the ...
CommunityBot
- 1
3
votes
0
answers
122
views
Information on Planetary nebula formed from the death of our star the 'Sun'!
I want to know the expansion rate, composition, mass and density of hydrogen present of a Planetary nebula similar to that which will be formed after the death of our star the sun.
Knowing these ...
- 131