Unanswered Questions
170 questions with no upvoted or accepted answers
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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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7
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499
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Convert from Jy/beam km/s to W/m$^2$
I need to compare some ALMA observations of a protoplanetary disk to disk-integrated fluxes obtained from a model.
The ALMA observations are upper limits of non-detected spectral lines, where the RMS ...
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Get the expression of probed volume between 2 redshifts
1) I can't manage to find/justify the relation (1) below, from the common relation (2) of a volume.
2) It seems the variable r is actually the comoving distance and not comoving coordinates (with ...
CommunityBot
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6
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Radius of hydrogen cloud
I am using a 1.4 meter parabolic dish with HPBW of 10 degrees and a RTLSDR to study our milky way in hydrogen line. The structure of the galaxy is deduced as shown in the picture by plugging the ...
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BLC1 and Proxima Centauri's activity
From Wikipedia BLC1:
A paper by other astronomers released 10 days before the news report about BLC1 reports the detection of "a bright, long-duration optical flare, accompanied by a series of ...
6
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How far have stars been seen beyond the center of the Milky Way?
What lies near the center of the galaxy is of great interest and in recent times the motion of dozen(s) of stars at the center of our galaxy orbiting around Sgr A* have been measured in great detail. ...
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5
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Do all the accretion disks around a compact object (black hole or neutron star) emit astrophysical jet outflow?
Do all the accretion disks around a compact object (black hole or neutron star) emit astrophysical jet outflow? I mean is it mandatory for a jet to be emitted from an accretion disk?
If so, then why?
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What are some good books/online resources for astronomy problem sets?
I am currently studying for the international olympiad for astronomy and astrophysics (the syllabus can be found here: https://www.ioaastrophysics.org/syllabus/). I am currently using Carroll Ostlie's ...
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How to apply Fast Folding algorithm?
I have High Time Resolution Universe dataset. I have applied de-dispersion on this HTRU dataset, and thereafter I applied the folding function to fold the dataset.
How I can find that the periodicity ...
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Why isn't the relativistic jet visible in the image of the M87 black hole?
I'm referring to the infamous relativistic jet, which consists of matter being accelerated to near the speed of light, originating at the poles of the black hole:
But in the image of the black hole ...
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Estimate the number of pixels required to map the full primary beam of a Radio Telescope station
I am practising some exam questions for a radio interferometry exam, and I am struggling with this question:
The physical size of a single LOFAR station, operating at 150MHz is about 50m.
Estimate ...
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5
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Strength of core-envelope coupling in stars
For a star with a given Zero-Age Main Sequence (ZAMS) mass, as a function of metallicity how strongly is the star's core coupled to its envelope?
I understand that the core-envelope boundary is only (...
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DIY Radio Telescope (High School)
Background: I am attempting to build an RTL-SDR-based radio telescope for detecting hydrogen lines (21 cm) as a project with my HS Physics class. Several accounts are online, including parts lists ...
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Explanation for Planck 2018 temperature fluctuations strongest peaks
As it can be seen from Plank 2018 Cosmic Microwave Background temperature fluctuations data-
There are 3 sharp peaks at multipole expansions $\ell \approx 250, 550, 800 $. Also as multipole expansion ...
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How are shockwaves used to study magnetic fields of merging galaxy clusters?
Recently i read an article about how a shockwave 60 times larger than milky way galaxy is generated.When these shockwaves interacts with magnetic field, radio waves are emitted. I wanted to know how ...
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Why do the Centaurus A radio jets have two "arms" each? (Event Horizon Telescope image)
Fig. 2: Image analysis of the final model: a, Model image corresponding to the image from Fig. 1 with a pixel size of 2 μas. Here, the tentative position of the jet apex is indicated with a circle. ...
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4
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How much more mass would Mars need to currently have enough pressure for liquid water and oxygen?
My question is whether Mars just about failed to meet the threshold or missed it by a lot. It's been dry for 3 billion years. How much bigger would it have needed to be to buy it that extra time? Let'...
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How significant is the effect of galactic rotation on line broadening of carbon monoxide?
In class the other day, we were discussing observations of rotational transitions of carbon monoxide, namely, the $J=1\to0$ and $J=2\to1$ lines. We originally had assumed that both lines would have ...
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4
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Cosmology : Formula for the bias of galaxies
first I have posted originally on the physics stackexchange but I have not had answers about my question, so I try my luck on this specific forum (if forums leaders want to delete the original post on ...
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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 ...
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Will the SKA's total bandwidth still exceed the Earth's internet's bandwidth?
In the early 2010's there were many popular articles that said that the total bandwidth of the the Square Kilometer Array's optical fiber network for raw data from each dish would be larger than the ...
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3
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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 ...
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3
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Why are there red- and blue-shifted radio lobes on either side of the core for collimated bipolar outflows?
This is a velocity integrated picture of a molecular cloud, part of my homework. https://paste.c-net.org/AthenaMeasly
Question:
For collimated bipolar outflows, the general situation is that the red-...
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3
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68
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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
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What are radio frequencies sensitive to in galaxies?
Apart from 21cm line studies, radio emissions as well as signatures of different radio sources, do radio frequencies help in the identification of a particular physical structure or presence of some ...
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Questions about the Cocconi Morrison paper on interstellar communication
I have been reading the paper by Cocconi and Morrison on interstellar communication and I have trouble understanding their formulas.
The paper begins by stating, that a star similar to the quiet sun ...
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3
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104
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How will China's Xuntian space telescope use its Terahertz capability? THz Spectroscopy? Imaging? Something else?
An Update on the Chinese Space Station Telescope Project Hu Zhan, National Astronomical Observatories, CAS, KIAA, Peking University, On behalf of the CSST Team, ISSI-BJ Workshop: Weak gravitational ...
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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 ...
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Negative flux values in radio maps?
I am trying to understand some maps of radio emission in e.g the Milky Way. I continue to see in papers that these radio maps report negative values of the flux in Jansky units, although no ...
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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 ...
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