APOD: Galaxy Cluster Gas Creates Hole in... (2017 Apr 10)

[APOD Robot]

Galaxy Cluster Gas Creates Hole in Microwave Background

Explanation: Why would this cluster of galaxy punch a hole in the cosmic microwave background (CMB)? First, the famous CMB was created by cooling gas in the early universe and flies right through most gas and dust in the universe. It is all around us. Large clusters of galaxies have enough gravity to contain very hot gas -- gas hot enough to up-scatter microwave photons into light of significantly higher energy, thereby creating a hole in CMB maps. This Sunyaev�Zel'dovich (SZ) effect has been used for decades to reveal new information about hot gas in clusters and even to help discover galaxy clusters in a simple yet uniform way. Pictured is the most detailed image yet obtained of the SZ effect, now using both ALMA to measure the CMB and the Hubble Space Telescope to measure the galaxies in the massive galaxy cluster RX J1347.5-1145. False-color blue depicts light from the CMB, while almost every yellow object is a galaxy. The shape of the SZ hole indicates not only that hot gas is present in this galaxy cluster, but also that it is distributed in a surprisingly uneven manner.

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[Rocket Ron]

What is different about the 2 really bright objects/galaxies just to the right of centre/middle ?

[Boomer12k]

Interesting, I would not expect it to be uniform. The cluster is not that uniform... I wonder what OUR cluster looks like to them...

:---[===] *

[Ann]

What is different about the 2 really bright objects/galaxies just to the right of centre/middle ?

They are two really massive elliptical galaxies.

Click to view full size image

[c]Galaxy cluster RX J1347.5-1145.[/c]

Click to view full size image

The Virgo Cluster of galaxies.
Photo: Chris Mihos (Case Western Reserve University)/ESO

Distant galaxy cluster RX J1347.5-1145 is not necessarily so different from the nearby Virgo Cluster of galaxies, although RX J1347.5-1145 does seem to be more compact. Both clusters are dominated by massive elliptical galaxies.

But if the Virgo Cluster has blown a hole in the Cosmic Microwave Background, it isn't visible here!

We see many obvious lensed background galaxies in and around RX J1347.5-1145, but none in or around the Virgo Cluster. A possible reason for that might be that the Virgo Cluster is too nearby and seemingly large in the sky, with its mass distribution also "spread out all over". But I'll leave it to the math whizzes here at Starship Asterisk* to explain it much better than I could!

Ann

[DanielP]

It is NOT surprising that galaxy clusters are not very symmetrical, because the ratio of their age to dynamical timescale (about the time for a galaxy to cross the cluster) is small, of order 10 or less. Only when this ratio is large (>> 10), such as in globular clusters, initial irregularities can be smoothed out, symmetrizing the cluster.

[heehaw]

A wonderful image!

[BDanielMayfield]

How do we know for sure (or, are we in fact sure) that something similar, but on a smaller scale to the SZ effect is not the cause of the more general fluctuations in the CMB?

Bruce

[Tszabeau]

What would the hole look like if it was "uniform"?

[neufer]

How do we know for sure (or, are we in fact sure) that something similar, but on a smaller scale to the SZ effect is not the cause of the more general fluctuations in the CMB?

• Probably can't be entirely sure for the small scale CMB fluctuations.

<<To distinguish the SZ effect due to galaxy clusters from ordinary density perturbations, both the spectral dependence and the spatial dependence of fluctuations in the cosmic microwave background are used. Analysis of CMB data at higher angular resolution (high l values) requires taking into account the Sunyaev–Zel'dovich effect.>>

[BDanielMayfield]

What would the hole look like if it was "uniform"?

The edges of the hole would be more round or elliptical.

Bruce

[neufer]

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What would the hole look like if it was "uniform"?

The edges of the hole would be more round or elliptical.

Bruce

[BDanielMayfield]

How do we know for sure (or, are we in fact sure) that something similar, but on a smaller scale to the SZ effect is not the cause of the more general fluctuations in the CMB?

• Probably can't be entirely sure for the small scale CMB fluctuations.

<<To distinguish the SZ effect due to galaxy clusters from ordinary density perturbations, both the spectral dependence and the spatial dependence of fluctuations in the cosmic microwave background are used. Analysis of CMB data at higher angular resolution (high l values) requires taking into account the Sunyaev–Zel'dovich effect.>>

Very nice answer Art. Thanks.

Bruce

[sillyworm]

When observing the Galaxy clusters we are seeing them as they appeared many years ago.When observing the CMB ...does it appear to us in REAL time?

[BDanielMayfield]

When observing the Galaxy clusters we are seeing them as they appeared many years ago.When observing the CMB ...does it appear to us in REAL time?

Time is real in all epochs. We're seeing the galactic clusters as they were billions of years ago, the CMB is even older, the edge of the observable universe.

Bruce

[sillyworm]

I'm aware of the billions of year factor....I now see that the CMB is also a spectral light image(?) ...so..it appears to us NOW as it was at the beginning of the BIG BANG process?I'm pondering WHY the cluster(s) would be "punching" a hole in the CMB if the CMB came first? Or is the image of the CMB altered along with the changes that have occurred with all the Galaxies,etc?

[Chris Peterson]

I'm aware of the billions of year factor....I now see that the CMB is also a spectral light image(?) ...so..it appears to us NOW as it was at the beginning of the BIG BANG process?I'm pondering WHY the cluster(s) would be "punching" a hole in the CMB if the CMB came first? Or is the image of the CMB altered along with the changes that have occurred with all the Galaxies,etc?

The CMB represents photons that were released about 380,000 years after the Big Bang. They were produced by a 3000 K source, meaning that they peaked as yellow light (but having a wide spectral range). They've traveled for 13.7 billion years, during which time their point of origin has receded from us by some 46 billion light years. That expansion caused the photon wavelengths to be stretched out, from visible light to a few millimeter microwaves.

The clusters "punch holes" in the CMB in the sense that they alter its appearance by scattering CMB photons that pass through them.

[csw]

I've never understood how CMB can be "all around us" if it originated more or less from a single point, or at least a defined area. Shouldn't it be sort of like the sun's rays coming at us from only one direction -- from where the sun is? How can CMB bombard us from ALL angles?

If the answer pertains to general or special relativity, and space expanding, please don't bother trying to explain it. I won't get it.

Thanks!

Amateurishly,

Chris

[sillyworm]

Thank you Bruce & Chris.I guess what I was thinking was..Why...since the CMB photons were sent prior(?) to the formation of these galaxies...we don't see a background image unaltered by the Galaxies? Because the CMB is receding the photons are actually taking longer to get here because of this expansion? Thanks so much!!!!!!

[Chris Peterson]

I've never understood how CMB can be "all around us" if it originated more or less from a single point, or at least a defined area. Shouldn't it be sort of like the sun's rays coming at us from only one direction -- from where the sun is? How can CMB bombard us from ALL angles?

It didn't originate at a single point- not even close to it. It originated nearly uniformly throughout the volume of an already expanded Universe. The entire Universe was at about 3000 K, so it was glowing in visible light. The photons that still exist have been traveling through expanding space, so they are now microwave photons. The edge of the observable universe represents regions of space that were nearly adjacent to us after the Big Bang.

[Tszabeau]

The discussion makes it seem a bit more like a shadow than a hole.
If it's a hole, is it cylindrical and we are within the "cylinder"?

[neufer]

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[b][color=#0000FF]Schematic of the Sunyaev-Zeldovich effect that results in an increase in higher energy (blue shifted) photons of the CMR when seen through the hot gas present in cluster of galaxies. [size=85]http://astro.uchicago.edu/sza/primer.html (Adapted from L. Van Speybroeck)[/size][/color][/b]

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The discussion makes it seem a bit more like a shadow than a hole.

• You could call it a shadow.

[Fred the Cat]

Wonder if the earliest clusters would have produced a sour note in our universe? Maybe just a hiccup.

[sillyworm]

Thanks Chris You answered my question in your reply to CSW

[BDanielMayfield]

The up-scattering of photons was a new concept to me. I'm not questioning this process, but wouldn't the effect be the same if the CMB photons where merely deflected without altering their energies?

Bruce

[neufer]

[b][color=#0000FF]The dashed line represents the intensity of the cosmic microwave background with radio frequency. The solid line is the distortiong in the cosmic background intensity due to inverse-Compton scattering of photons through the gas presents in a cluster of galaxies. This is a schematic representation: the actual distortion is much smaller. (Credit: Carlstrom et al., Annual Reviews of Astronomy & Astrophysics vol 40, pg 643, 2002) [/color][/b]

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The up-scattering of photons was a new concept to me. I'm not questioning this process, but wouldn't the effect be the same if the CMB photons where merely deflected without altering their energies?

For every CMB photon deflected away from us there is a CMB photon deflected towards us (as in the cartoon above).

Blue shift is the only sure way to distinguish these features.