83
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Is there a better explanation of this picture showing the very distant star "Earendel"?
I did the annotation of that figure for the press release, so let me start by apologizing for the poor explanation, and then try to dig deeper into what's going on :) (although you already seem to ...
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12
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Local neighbourhood and Superclusters
Structure formation
Structure in the Universe — galaxies, galaxy groups, clusters, and superclusters — forms from regions of the Universe which are denser than the average; dense enough the overcome ...
- 37.1k
10
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How do astronomers know that distant galaxies aren't actually nearby star clusters?
Other answers have provided general ideas about how to confirm that individual sources are distant galaxies and not clusters, so I'll focus on the question of how astronomers in the Dark Energy Survey ...
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10
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Why does the Bullet Cluster have many names?
Most astronomical sources don't have a poetic name such as the Bullet Cluster. Such names are usually coined for objects that may have a particular interest to the public (or the astronomical ...
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7
votes
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Is it possible for galaxy clusters to interact?
Yes.
Theoretically, structure is expected to form first on small scales (stars and stellar clusters), and later on increasingly larger scales — galaxies, groups, and eventually galaxy clusters (see e....
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7
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How do astronomers know that distant galaxies aren't actually nearby star clusters?
We measure the distance.
A cluster is a group of stars in close proximity to each other. For relatively near stars you can directly measure the distance via the parallax. That's what the Gaia ...
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6
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Does the Milky Way belong to a Galaxy cluster
The milky way is not part of a galaxy cluster. The local group is on a lobe of the Virgo supercluster.
Not all galaxies are members of large clusters, ours is in a small group. However the only ...
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Does the Milky Way belong to a Galaxy cluster
The Local Group contains 54 plus galaxies.
Don't know that that counts as much of a cluster.
Next up in scale, the Milky way is part of the Laniakea Supercluster
That contains about 100,000 galaxies, ...
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Would gravitational waves be subject to external gravitational perturbations?
Firstly, gravitational waves (GWs) are not an echo - we measure the direct signal.
The process you describe here is known as gravitational lensing, the deviation of (usually) light rays due to ...
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Why is this Einstein ring pink?
OK, guessing rather wildly in the absence of solid information....
The press-release page is here; that provides a bit more information
than the news article, and includes two images of (different ...
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6
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how to calculate distance between galaxies in the distant past
I'm assuming you're talking about physical distances (as opposed to any of the other distance measures in cosmology).
The comoving distance to a galaxy at redshift $z$ is
$$
d_C(z) = \frac{c}{H_0}\...
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5
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Fingers of God effect for galaxy clusters
I think the key point is how the velocity dispersion in a given structure compares with the velocity dispersion you would expect from the difference in the Hubble flow across the linear extent of the ...
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5
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Fingers of God effect for galaxy clusters
I'm going to break your question down into two sections.
Do galaxy clusters have measurable peculiar velocities?
The answer to this depends slightly on what is meant by "peculiar velocity". In the ...
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5
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Why does a right-handed circular polarized wave get lagged when going through ionized plasma?
What is the mathematical difference between their refraction indices?
The conventions on the signs of the direction of magnetic field vectors and of charges.
The tutorial specifies several things ...
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Why does the first measurements of the thermal Sunyaev-Zel’dovich effect from ALMA show a temperature decrease and not an increase at the cluster?
Calling it a "temperature decrease" is kind of misleading. (Possibly this is a side effect of the tendency to use "brightness temperature" in radio astronomy to mean measured ...
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5
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What is the distance of the closeset galaxy outside our local group and what is its name?
Your question can be interpreted in many ways.
Distance from Milky Way.
Distance from the geometric center of the Local Group.
Distance from the gravitational center of the Local Group
The galaxy ...
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What accounts into calculating the Hubble constant?
I think this might answer your question, I have quoted the important paragraph below.
If peculiar velocities could have any value, then this would make Hubble’s law useless.
However, peculiar ...
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4
votes
Why does the Bullet Cluster have many names?
Almost every object in space outside the solar system has multiple names (identifiers) because different astronomical surveys use different naming conventions. The Bullet Cluster has at least 25 ...
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4
votes
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Is there a consistent missing mass ratio for Galaxy Clusters?
Yes, all clusters, where sufficiently precise measurements available, require dark matter to explain their dynamics.
Yes, the dark matter should be concentrated around galaxies (though not as much as ...
- 146k
4
votes
3d distance between the Galaxies inside the galaxy cluster
You can't calculate the distances to galaxies in a cluster like that to any useful precision.
The mean redshift will give you an estimate of the mean distance of the cluster, but the individual ...
- 146k
3
votes
false to stable vacuum transition
The standard picture of vacuum decay events is very much like nucleation in a phase transition: it starts somewhere, and then expands at a constant speed - lightspeed in this case. So the future ...
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3
votes
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What distance is considered 'close' for the 9th nearest neighbor of a galaxy?
If galaxies were randomly distributed (a spatial Poisson process), then the probability of having $N$ galaxies inside a radius $r$ sphere is $\Pr[N]=\lambda^N e^{-\lambda} / N!$ where $\lambda = (4\pi ...
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3
votes
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What is the role of the random catalogue in calculating the two-point correlation function?
The point of the two-point correlation function (pun not intended) is to describe how clustered the galaxies in the universe are. Astronomers want to know if they're all bunched up in tight bundles ...
- 15k
3
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Centre (projected) of a galaxy cluster
Short answer, no, they don't.
Longer answer, it's complicated. There are, in essence, five different measures for the centre of a galaxy cluster, based on different physical properties of the cluster,...
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Is our supercluster part of a galaxy filament?
The Laniakea Supercluster contains several galaxy filaments, even just reading the wikipedia articles you provided you can see the difference in size of the two:
Galaxy Filament
They are massive, ...
- 1,481
3
votes
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Are 3D coordinate data from Sloan DSS-III available & easily accessible to non-pros?
BTW if anyone wants a quick and fast query to solution do the following:
Go to https://skyserver.sdss.org/dr12/en/tools/search/sql.aspx. Paste a query like this:
...
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Are 3D coordinate data from Sloan DSS-III available & easily accessible to non-pros?
SDSS DR12 Catalog Data
looks like a good starting point,
apparently pretty open to those willing and able to figure it out.
Their
SciServer Compute
site hosts Jupyter notebooks to query CasJobs in SQL....
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2
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How do I modify redshifts to gain corrected line of sight velocities?
You need a model for the motion of the Sun with respect to the Milky Way centre. You then have to subtract the component of this that is resolved towards the galaxy in question.
The solar motion ...
- 146k
2
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Initially non-flat space-time makes dark matter obsolete$\dots$
I think there a few problems with this idea.
First off, as Stan Liou indicates, the early universe expanded extremely rapidly, potentially through hyper-inflation during the inflationary epoch. While ...
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