Confusion re Laniakea Super Cluster

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In summary, the conversation discusses the confusion surrounding the calculation of the mass of the Laniakea supercluster, with information from three different sources. The Wikipedia page (b) uses the term "binding mass" while the news article (a) uses the more common term "mass". The link to (c) explains that gravitational binding energy is the energy needed for a system to become gravitationally bound. The conversation also mentions a method for calculating the mass of the supercluster using visible light, baryonic dark matter, and non-baryonic dark matter. The speaker has decided to edit the Wikipedia page to change "binding mass" to "mass" and is seeking help in finding a source for the calculation of Laniakea's
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Buzz Bloom
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I have been trying to understand some facts about the Laniakea supercluster. I found information at three sites which when compared with each other creates some confusion.

a. http://www.ifa.hawaii.edu/info/press-releases/Laniakea/
b. https://en.wikipedia.org/wiki/Laniakea_Supercluster
c. https://en.wikipedia.org/wiki/Gravitational_binding_energy

(a) says
The orange contour encloses the outer limits of these streams, a diameter of about 160 Mpc. This region contains the mass of about 1017 suns: 100 million billion suns.​

(b) says
The Laniakea Supercluster encompasses 100,000 galaxies stretched out over 160 megaparsecs (520 million light-years). It has the approximate binding mass of 1017 solar masses.​
(b) has a link for "binding mass" the leads to (c).

(c) says
A gravitational binding energy is the energy that must be exported from a system for the system to enter a gravitationally bound state at a negative level of energy.
. . .
For a spherical mass of uniform density, the gravitational binding energy U is given by the formula
BindingEnergy.png

It is clear that "mass" and "binding mass" are not the same thing. At first, it seemed likely that the news article (a) was careless and used the more common term "mass" while Wikipedia's (b) used a more accurate but less familiar term "binding mass". But, then again, maybe not.

From (b)'s link to (c), is seems that a calculated value for "binding mass" would be
Mbind = U/c2.​
Then the ratio
r = Mbind / M​
would be a dimensionless ratio for the fraction of the mass M that would have to be removed from the system (in the form of kinetic energy or lost mass, or what?) if the systerm was to be gravitationally bound together. This concept seems a bit strange.

So, based on the above, I conclude that (b) was wrong, and (a) was right.

Unfortunately neither (a) nor (b) nor any of their references discusses the method used to calculate the mass of the supercluster. The method I am familiar with first calculates the total star mass from the amount of visible light (corrected for redshift). This result is then multiplied by a "standard" ratio (which takes into account baryonic dark matter, e.g, unilluminated gas and dust, to get to get a value for the total baryonic mass. This result is then multiplied by another ratio to include the non-baryonic dark matter.

Can anyone help me find a source that shows the calulation of Laniakea's mass?
 
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  • #2
I have decided after much thought to edit the Wikipedia page about the Laniakea supercluster, changing "binding mass" to "mass". An explanation for making this change is on the Talk page.

I have also reached the conlcusion that after 61 views and no responses that no one is likely to help me find a source that shows the calculation of Laniakea's mass.

I have one further related question that I hope someone will respond to. I will soon create a new thread, "The Dark Sky Ahead", in which I will post this question.
 

1. What is the Laniakea Super Cluster?

The Laniakea Super Cluster is a massive and complex region of space that contains thousands of galaxies, including our own Milky Way. It is considered to be one of the largest known structures in the observable universe.

2. How was the Laniakea Super Cluster discovered?

The Laniakea Super Cluster was discovered in 2014 by a team of astronomers using data from the Cosmicflows-2 project. By mapping the motions and distributions of galaxies, they were able to identify the boundaries of this super cluster.

3. What does "Laniakea" mean?

Laniakea is a Hawaiian word that means "immeasurable heaven" or "unimaginably vast sky". It was chosen as the name for this super cluster to reflect its immense size and complexity.

4. How big is the Laniakea Super Cluster?

The Laniakea Super Cluster is estimated to be about 500 million light years in diameter. To put that into perspective, the distance from Earth to the nearest star is about 4 light years.

5. What is the significance of the Laniakea Super Cluster?

The Laniakea Super Cluster is significant because it challenges our previous understanding of the structure and organization of the universe. It also helps us better understand the role of gravity in the formation and evolution of large-scale structures in the universe.

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