APOD: Galaxy Cluster Abell 2666 (2017 Mar 10)

[APOD Robot]

Galaxy Cluster Abell 2666

Explanation: The galaxies of Abell 2666 lie far beyond the Milky Way, some 340 million light-years distant toward the high flying constellation Pegasus. Framed in this sharp telescopic image, the pretty cluster galaxies are gathered behind scattered, spiky, Milky Way stars. At cluster center is giant elliptical galaxy NGC 7768, the central dominant galaxy of the cluster. As the cluster forms, such massive galaxies are thought to grow by mergers of galaxies that fall through the center of the cluster's gravitational well. Typical of dominant cluster galaxies, NGC 7768 likely harbors a supermassive black hole. At the estimated distance of Abell 2666, this cosmic frame would span about 5 million light-years.

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[ta152h0]

do we live in a sphere 13.4 billion light years in radius or I am getting schooled again ?

[starsurfer]

I like the galaxy with the tidal tail near the top.

It's a wonderful coincidence that today's APOD is by Bernhard Hubl on the same day the CEDIC conference starts?

[sc02492]

Wolf, the age of the universe is estimated to be around 13.8 billion years based upon the latest assessment of the Hubble "constant". It is tempting to interpret this as meaning that the observable universe should be 13.8 billion light years in radius, but that would not be correct, because it doesn't take into account the continued expansion (and acceleration) of space. So a photon emitted by a galaxy just outside of 13.8 light years distance (for instance) will still reach us, eventually, because space is continuing to expand and will eventually encompass the space where that photon was originally emitted. Just as important, that photon continues to travel towards us, as space continues to expand away from us, again meaning that we will eventually detect that photon (which will be more and more red shifted since the space that contains it continues to accelerate faster and faster away from us due to dark energy). This is a long winded way of saying that the observable universe has a much larger radius than 13.8 light years (it's estimated to be more like 46 billion light years in radius), due to the continued (and accelerating) expansion of space. Actually, based upon this logic, there is an entire universe beyond a radius of 46 billion light years, that we cannot see because the light emitted by objects at that distance is too red shifted to be seen in visible light.

Steve Cannistra

[Brian Sherwood]

Steve,
If I understand you correctly, you are speaking about 'observable' space expanding? Else there couldn't be a photon origination outside of it?

Also, does anyone know how many galaxies are shown in today's picture of the Abell cluster? Not counting, but I estimate 50-100?

[rstevenson]

do we live in a sphere 13.4 billion light years in radius or I am getting schooled again ?

Wolf, I think the Wikipedia article on the Universe explains it well, in particular this section: Size and regions. For more info, there are links there which will lead you down the rabbit hole as far as you want to go. Here, for the impatient, are a few key sentences from that section...

... The spatial region that we can affect and be affected by is the observable universe. ...

The proper distance ... between Earth and the edge of the observable universe is 46 billion light-years ...

The distance the light from the edge of the observable universe has travelled is very close to the age of the Universe times the speed of light, 13.8 billion light-years, but this does not represent the distance at any given time because the edge of the observable universe and the Earth have since moved further apart. ...

So to summarise: the distance that light emitted very early in the life of the Universe has travelled to get to us is a little less than 13.8 bly, but the current distance from wherever that light originated to us 'now' is a little less than 46 bly.

It may be clear as mud, but it covers the ground.

Rob

[Chris Peterson]

do we live in a sphere 13.4 billion light years in radius or I am getting schooled again ?

Nobody knows the size of the Universe. It may or may not be infinite. Because of the finite speed of light and the expansion of the Universe, we can only observe part of it- cleverly called the observable universe. Beyond the edge of the observable universe things are moving away from us at faster than c, and are therefore forever beyond our ability to see. The edge of the observable universe is about 46 billion light years away- farther than the edge's light travel time of 13.8 billion years. The difference is because the entire time that light has been traveling towards us, the sources emitting it have been moving away from us (and it is precisely that expansion which has stretched out the wavelength of the light- cosmological redshift).

[Catalina]

So does acceleration result from the increase of the void to mass ratio (less gravitational effect) as the universe expands?

[sillyworm]

You can get a closer look at this Cluster & the surrounding area by searching NGC 7768(for example) and/or looking at the SIMBAD data here. http://spider.seds.org/ngc/ngc.cgi?7768

[ta152h0]

Well, time for an ice cold one and digest this thing, unencumbered by politics and religion.

[Ann]

So does acceleration result from the increase of the void to mass ratio (less gravitational effect) as the universe expands?

I think that no one really knows why the expansion of the universe is accelerating. But if we assume that matter is not currently being created in the universe - and currently we have no reason to believe that it is- but the "framework of the universe" (the void, if you will) is growing larger, then the role of matter in the universe is certainly decreasing. That could indeed conceivably affect the rate of the expansion of the universe.

But no one really knows what actually drives the acceleration of the universe.

Ann

[ta152h0]

I know why ! The Big Bang mechanism is still going. Time means nothing.

[DavidLeodis]

The montage of the enlargements of some of the galaxies brought up through the 'sharp telescopic image' link is very interesting http://astrophoton.com/abell2666.htm as also the annotated version of the image http://astrophoton.com/images/abell2666-1_id_full.jpg that can be found through the link.

[starsurfer]

The montage of the enlargements of some of the galaxies brought up through the 'sharp telescopic image' link is very interesting http://astrophoton.com/abell2666.htm as also the annotated version of the image http://astrophoton.com/images/abell2666-1_id_full.jpg that can be found through the link.

For anyone wondering, KUG stands for "Kiso Ultraviolet Galaxy".

[DavidLeodis]

The montage of the enlargements of some of the galaxies brought up through the 'sharp telescopic image' link is very interesting http://astrophoton.com/abell2666.htm as also the annotated version of the image http://astrophoton.com/images/abell2666-1_id_full.jpg that can be found through the link.

For anyone wondering, KUG stands for "Kiso Ultraviolet Galaxy".

Thanks starsurfer .

On seeing the acronyms I should have tried to find what CGCG, GIN, AGC, PGC 2MASX and KUG stand for, but I did not do so . From older APODs I did know that NGC is New General Catalog(Catalogue) or at least I hope so!