APOD: The Perseus Cluster Waves (2017 May 04)

[neufer]

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so does anybody see the white nine (digit only, ie: [9]) in the centre of the image?

Is this someone labelling the picture.... or is it really there? There appear to be two letters partially obscured to the right of the nine, about eight point type as well.

I actually see a scribbled figure of a person singing, arms held out in front as if belting out opera....

[douglas]

It's not an either-or thing. It's both fact and artifact, and it takes a trained eye to interpret.

I wouldn't say the image as a whole could be classified as an artifact in any way. "Artifact" in imaging generally means some kind of structure which isn't related to the underlying data. Of course, there's noise in this image as there is in all images, and noise is often amplified by processing into artifacts. But the image as a whole is showing shock waves and other structure in the intracluster medium around NGC 1275 (the central galaxy in the Perseus Cluster) made apparent by removing the much more luminous glow of the galaxy itself. By flattening that, the otherwise obscured fine x-ray structure becomes visible.

A trained eye can always extract more information from an astronomical image. But this image does not require a trained eye in order to extract the most salient features that the processing was designed to reveal- the large scale wave pattern in the hot medium surrounding this galaxy.

Really, Chris? Is it .. Chandra strikes again? Recall Chandra imaged Orion's Trapezium where the purported IMBH was supposed to be, in effect "removing the much more luminous glow" of the Orion Nebula and no "shock waves" from your purported mobile IMBH were found. So by "flattening" the Trapezium nothing was found to indicate a BH, and by "simulating" as found in this video, Chandra would find nothing to indicate a Trapezium BH, either? Kind of like Chandra's "been there, done that"?

https://youtu.be/c_MfbxLhwEU

[xiox]

Here's a comparison of visible light with the X-ray emission: https://www.researchgate.net/figure/518 ... orth-Lower

The X-ray image is thermal emission from the hot plasma which fills up most of a galaxy cluster. It has temperatures of around 10 million K, heated as the material which formed the cluster collapsed. The energy source is the thermal energy (i.e. it cools in the absence of heat sources). The emission mechanism is thermal bremsstrahlung, if you're interested. Most of the baryonic matter (not dark matter, but normal electrons, protons, neutrons, etc), is in the form of this hot atmosphere. The atmosphere is supported by its pressure.

Oh, I should say that the hot plasma would rapidly cool. We think the black hole at the centre of NGC 1275, 3C84, is responsible for putting huge amounts of energy into the surrounding gas which prevents the rapid cooling. The black hole has jets which form bubbles of relativistic plasma in the hot gas, heating it. Despite this, there is still cooling and star formation in some locations (see picture of the filaments around NGC 1275).

[chadwick]

As often happens, the APOD explanations are ambiguous. Where is the "Perseus" cluster in relation to this "picture"? Is the center of this highly processed(?) image centered on a particular object?

[Guest]

Where else in the visible universe have we observed this? Is this a common phenomenon? That image is absolutely new to me.

[heehaw]

It's true it would be nice to be able to roll over the image and see a same-scale optical image of the cluster of galaxies. But I am hugely impressed with the image nonetheless. (With Herb Friedman and others at NRL I was the first to detect X-rays from any cluster of galaxies.)

[neufer]

I am hugely impressed with the image nonetheless. (With Herb Friedman and others at NRL
I was the first to detect X-rays from any cluster of galaxies.)

Are you Bowyer, Byram or Chubb

[MarkBour]

Sorry, I'm often stuck on the basics. What do the colors in this image represent? I see a progression from the center of the image which is an intense yellow-white to orange, and then darker as one moves out radially. But as a heat map, I'm not sure that matches the description; possibly if lighter colors are colder than darker colors. (Can someone help me out?)

There are multiple features that look interesting to me:

PerseusChandraA.jpg (108.68 KiB) Viewed 1332 times

• The first, the feature that has been mentioned, which looks like a wave (I prefer the term "wave" to "bay" -- quite apart from the simulation that suggests the feature is a Kelvin-Heimholtz wave -- it better helped me locate the feature in the image).
• Also at "7-o'clock" radially from the center, far closer to the center of the image than the wave, there is another interesting dark feature, perhaps about 40,000 ly in length.
• And another dark band, arc-shaped and centered at about 3 o'clock, which looks like it could be about 160,000 ly in length.

[tomatoherd]

Okay someone help me. Relieve my ignorance. This issue comes up a lot, and i puzzle every time.
If the intergalactic medium in this cluster has a temperature of "tens of millions of degrees", what does this mean? I realize that if the medium is extremely rarefied like such space, that the heat capacity can't be all that much. For illustration only, if one lone molecule in a cubic meter zipping around at relativistic speeds has a "temperature" of millions, would that essential vacuum feel cold or hot? With one molecule, that meter of space certainly couldn't cook my egg. (Related to this, if the ambient temperature of the whole cluster is "tens' of millions", how do all the physical processes work, and does that exclude possibility of life in those galaxies?) And if you answer that indeed, such a cubic meter would feel "cold", then what on earth is the purpose of talking about temperature? Wouldn't measures of energy be more helpful? What am i missing? I took 3 college physics courses, and got honors. Did I miss that week of class???

[Catalina]

So are the cluster waves generally in the shape of expanding concentric spheres or like a bowl or a cone or...? Also, like others reading the discussion, I would appreciate an image showing the cluster waves superimposed on a visible light image?

[geckzilla]

Okay someone help me. Relieve my ignorance. This issue comes up a lot, and i puzzle every time.
If the intergalactic medium in this cluster has a temperature of "tens of millions of degrees", what does this mean? I realize that if the medium is extremely rarefied like such space, that the heat capacity can't be all that much. For illustration only, if one lone molecule in a cubic meter zipping around at relativistic speeds has a "temperature" of millions, would that essential vacuum feel cold or hot? With one molecule, that meter of space certainly couldn't cook my egg. (Related to this, if the ambient temperature of the whole cluster is "tens' of millions", how do all the physical processes work, and does that exclude possibility of life in those galaxies?) And if you answer that indeed, such a cubic meter would feel "cold", then what on earth is the purpose of talking about temperature? Wouldn't measures of energy be more helpful? What am i missing? I took 3 college physics courses, and got honors. Did I miss that week of class???

I think a lot of people naturally wonder how it "feels" to the touch because that is what we are used to when thinking about temperature. But for astronomers it probably just means we get a lot of high energy wavelengths coming to us in the form of x-rays so an observatory like Chandra can take a look and produce an image out of it. If it wasn't "hot" enough, we'd only get lower energy wavelengths.

[bystander]

Click to play embedded YouTube video.

[Chris Peterson]

It's not an either-or thing. It's both fact and artifact, and it takes a trained eye to interpret.

I wouldn't say the image as a whole could be classified as an artifact in any way. "Artifact" in imaging generally means some kind of structure which isn't related to the underlying data. Of course, there's noise in this image as there is in all images, and noise is often amplified by processing into artifacts. But the image as a whole is showing shock waves and other structure in the intracluster medium around NGC 1275 (the central galaxy in the Perseus Cluster) made apparent by removing the much more luminous glow of the galaxy itself. By flattening that, the otherwise obscured fine x-ray structure becomes visible.

A trained eye can always extract more information from an astronomical image. But this image does not require a trained eye in order to extract the most salient features that the processing was designed to reveal- the large scale wave pattern in the hot medium surrounding this galaxy.

Really, Chris? Is it .. Chandra strikes again? Recall Chandra imaged Orion's Trapezium where the purported IMBH was supposed to be, in effect "removing the much more luminous glow" of the Orion Nebula and no "shock waves" from your purported mobile IMBH were found. So by "flattening" the Trapezium nothing was found to indicate a BH, and by "simulating" as found in this video, Chandra would find nothing to indicate a Trapezium BH, either? Kind of like Chandra's "been there, done that"?

Why would you necessarily expect a BH to show up? Most of the time, they are only visible because of their gravitational effect on their close surrounds... which is precisely the evidence used to infer the possibility of a BH near the Trapezium.

[Ann]

So are the cluster waves generally in the shape of expanding concentric spheres or like a bowl or a cone or...? Also, like others reading the discussion, I would appreciate an image showing the cluster waves superimposed on a visible light image?

Click to play embedded YouTube video.

Check out this video that bystander just posted. Towards the end of the video, you can see the cluster waves superimposed on the cluster itself. You can see that the waves are centered on the active galaxy Perseus A (NGC 1275), and you can see that the wave covers at least all of the central part of the cluster.

Ann

[Ann]

Sorry, I'm often stuck on the basics. What do the colors in this image represent? I see a progression from the center of the image which is an intense yellow-white to orange, and then darker as one moves out radially. But as a heat map, I'm not sure that matches the description; possibly if lighter colors are colder than darker colors. (Can someone help me out?)

As a color commentator, I feel obliged to offer an opinion.

I would guess that the image is originally black and white. Black and white astronomical images are typically colored white, yellow, orange, red/brown and black, particularly when the images are produced for educational purposes. Lighter colors normally represent higher temperatures, higher energies or greater concentrations.

An example of a false-color orange-looking originally black and white picture is this (ultraviolet?) ESA/NASA image of the Sun. As a color commentator, I hate the suggestion that the Sun is orange (it isn't!!!!), but it is made to look like that in very many "scientific" images.

Ann

[neufer]

If the intergalactic medium in this cluster has a temperature of "tens of millions of degrees", what does this mean? I realize that if the medium is extremely rarefied like such space, that the heat capacity can't be all that much. For illustration only, if one lone molecule in a cubic meter zipping around at relativistic speeds has a "temperature" of millions, would that essential vacuum feel cold or hot? With one molecule, that meter of space certainly couldn't cook my egg. (Related to this, if the ambient temperature of the whole cluster is "tens' of millions", how do all the physical processes work, and does that exclude possibility of life in those galaxies?) And if you answer that indeed, such a cubic meter would feel "cold", then what on earth is the purpose of talking about temperature? Wouldn't measures of energy be more helpful? What am i missing? I took 3 college physics courses, and got honors. Did I miss that week of class???

"Tens of millions of degrees" does, in fact, mean X-rays.

The Sun's 6,000K gives us visible light of energy ~2eV.

A 5,000 times hotter gas at 30,000,000K gives us X-ray light of energy ~10keV
...but that is not "zipping around at relativistic speeds" even for 510keV electrons.

If the gas was at densities of ~1/5000 atmospheric densities it might produce atmospheric pressures
...but the densities are many many orders of magnitude less than that!

Thus the gas would impart no pressure or heat and the non-relativistic particles are harmless.

The only danger might be the X-rays (depending upon their energy & intensity).

[Chris Peterson]

I would guess that the image is originally black and white. Black and white astronomical images are typically colored white, yellow, orange, red/brown and black, particularly when the images are produced for educational purposes. Lighter colors normally represent higher temperatures, higher energies or greater concentrations.

An example of a false-color orange-looking originally black and white picture is this (ultraviolet?) ESA/NASA image of the Sun. As a color commentator, I hate the suggestion that the Sun is orange (it isn't!!!!), but it is made to look like that in very many "scientific" images.

This false color palette (often called "heat") maps intensity to a color range- black to white, with intermediate grays ranging from reds to orange to yellow. This palette is popular because it maximizes the amount of range the eye can see while still maintaining what seems a natural sense of brightness. There are palettes that utilize the entire rainbow which let us see more intensity variation, but at the expense of losing the sense of actual intensity.

[MarkBour]

So, the X-ray intensity is mainly what is represented here. And the dark regions are interpreted as regions with less gas. Nothing in the image captures temperature variations. When galaxies pass by each other, many new stars can result. I wonder whether an encounter between to galaxy clusters can bring about the birth of a galaxy. I could almost imagine one arising in the region of the wave, if it could sweep up a lot of gas.

[neufer]

Click to play embedded YouTube video.

So, the X-ray intensity is mainly what is represented here. And the dark regions are interpreted as regions with less gas. Nothing in the image captures temperature variations.

Definitely density fluctuation...possibly adiabatic thermal fluctuations as well. If the fine structure involves the 9.6 million year sound waves mentioned earlier then the wavelengths are on the order of 10,000 light years.

When galaxies pass by each other, many new stars can result. I wonder whether an encounter between to galaxy clusters can bring about the birth of a galaxy.

[tomatoherd]

If the intergalactic medium in this cluster has a temperature of "tens of millions of degrees", what does this mean? I realize that if the medium is extremely rarefied like such space, that the heat capacity can't be all that much. For illustration only, if one lone molecule in a cubic meter zipping around at relativistic speeds has a "temperature" of millions, would that essential vacuum feel cold or hot? With one molecule, that meter of space certainly couldn't cook my egg. (Related to this, if the ambient temperature of the whole cluster is "tens' of millions", how do all the physical processes work, and does that exclude possibility of life in those galaxies?) And if you answer that indeed, such a cubic meter would feel "cold", then what on earth is the purpose of talking about temperature? Wouldn't measures of energy be more helpful? What am i missing? I took 3 college physics courses, and got honors. Did I miss that week of class???

"Tens of millions of degrees" does, in fact, mean X-rays.

The Sun's 6,000K gives us visible light of energy ~2eV.

A 5,000 times hotter gas at 30,000,000K gives us X-ray light of energy ~10keV
...but that is not "zipping around at relativistic speeds" even for 510keV electrons.

If the gas was at densities of ~1/5000 atmospheric densities it might produce atmospheric pressures
...but the densities are many many orders of magnitude less than that!

Thus the gas would impart no pressure or heat and the non-relativistic particles are harmless.

The only danger might be the X-rays (depending upon their energy & intensity).

Thanks Art.
But....I never said the intergalactic gases WERE zipping at relativistic speeds, i said 'for illustration only'.

But if this said gas at this vacuous density would not "feel" hot, and we'd only be in danger of x-ray damage (not thermal), if this space between galaxies wouldn't even warm up a cup of coffee, then what good does it do to speak of it in terms of 'millions of degrees"??? Why not speak of rads, or gauss, or whatever has some scientific use?
I'm still clueless, and I read most of the entire Wiki article on 'temperature'.

[neufer]

But if this said gas at this vacuous density would not "feel" hot, and we'd only be in danger of x-ray damage (not thermal), if this space between galaxies wouldn't even warm up a cup of coffee, then what good does it do to speak of it in terms of 'millions of degrees"??? Why not speak of rads, or gauss, or whatever has some scientific use?

• • We are talking about a gas here not a gauss.

  

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The temperature is directly related to the light radiated and the speed of sound producing the density structure.

[Chris Peterson]

But if this said gas at this vacuous density would not "feel" hot, and we'd only be in danger of x-ray damage (not thermal), if this space between galaxies wouldn't even warm up a cup of coffee, then what good does it do to speak of it in terms of 'millions of degrees"??? Why not speak of rads, or gauss, or whatever has some scientific use?

If Art's single example wasn't enough, there are many others. Almost every important formula that yields useful information about the properties of a gaseous region includes the temperature of the gas. It's a fundamental property.

[Ann]

Let's see if I got this correctly.

In a rarefied gas, whose temperature is millions of degrees, the typical atom (or ion, certainly?) will emit X-rays.

Human beings don't feel warmth when we are hit by X-rays at, say, the dentist's. Therefore we wouldn't feel warm if we were in space and were hit by X-rays emitted by extremely energetic ions, whose energy corresponds to a temperature of several million degrees.

If we get hit by a small amount of X-rays, that normally won't hurt us. But of course, floating around for long in space, unprotected by both the Earth's atmosphere and its magnetic field, and therefore getting exposed to more and more X-rays, wouldn't be good for us.

Then again, there are so many other reasons why it wouldn't be good for us to float around in space for very long.

Ann

[Chris Peterson]

Let's see if I got this correctly.

In a rarefied gas, whose temperature is millions of degrees, the typical atom (or ion, certainly?) will emit X-rays.

Temperature is a statistical property of the gas. In essence, it's a measure of the average kinetic energy of the particles. Individual atoms don't have a temperature (at least, not in any well defined sense). So in this very hot gas, what you have is very energetic atoms and ions and free electrons- typically moving at a high speed. Occasionally a free electron hits an ion, which produces bremsstrahlung, which is the primary source of x-rays in regions such as the one under discussion in this APOD.

Human beings don't feel warmth when we are hit by X-rays at, say, the dentist's. Therefore we wouldn't feel warm if we were in space and were hit by X-rays emitted by extremely energetic ions, whose energy corresponds to a temperature of several million degrees.

That's true, but a better way of thinking about it is how we would feel the gas itself, which the medium which is hot (not the x-rays). Because there are so few particles, the heat capacity is very low, and we wouldn't feel anything simply because our senses depend on detecting the energy transferred by millions or billions of particle collisions (with our skin), not the occasional single particle. The energies present in the rarefied gas are very high, but the energy density is low.

The ISS orbits in the thermosphere, where the atmospheric temperature is around 2000°C. But that air is so thin that there's very little energy transferred, which is why the ISS doesn't melt!

[neufer]

<<The ISS is partially protected from the space environment by Earth's magnetic field. From an average distance of about 70,000 km, depending on Solar activity, the magnetosphere begins to deflect solar wind around Earth and ISS. Solar flares are still a hazard to the crew, who may receive only a few minutes warning. In 2005, during the initial 'proton storm' of an X-3 class solar flare, the crew of Expedition 10 took shelter in a more heavily shielded part of the ROS designed for this purpose.

Subatomic charged particles, primarily protons from cosmic rays and solar wind, are normally absorbed by Earth's atmosphere. Outside Earth's atmosphere, crews are exposed to about 1 millisievert each day, which is about a year of natural exposure on Earth. This results in a higher risk of cancer for astronauts. Radiation can penetrate living tissue and damage the DNA and chromosomes of lymphocytes. These cells are central to the immune system, and so any damage to them could contribute to the lower immunity experienced by astronauts. Radiation has also been linked to a higher incidence of cataracts in astronauts. Protective shielding and drugs may lower risks to an acceptable level.

Radiation levels on the ISS are about five times greater than those experienced by airline passengers and crew. Earth's electromagnetic field provides almost the same level of protection against solar and other radiation in low Earth orbit as in the stratosphere. For example, on a 12-hour flight an airline passenger would experience 0.1 millisieverts of radiation, or a rate of 0.2 millisieverts per day; only 1/5 the rate experienced by an astronaut in LEO. Additionally, airline passengers experience this level of radiation for a few hours of flight, while ISS crew are exposed for their whole stay.>>

<<The sievert is of fundamental importance in dosimetry and radiation protection, and is named after Rolf Maximilian Sievert, a Swedish medical physicist renowned for work on radiation dosage measurement and research into the biological effects of radiation. One sievert carries with it a 5.5% chance of eventually developing cancer based on the linear no-threshold model. One sievert equals 100 rem (roentgen equivalent man).>>

<<Any vacuum tube operating at several thousand volts or more can produce X-rays as an unwanted byproduct, raising safety issues. The higher the voltage, the more penetrating the resulting radiation and the more the hazard. CRT displays, once common in color televisions and computer displays, operate at 3-40 kilovolts, making them the main concern among household appliances. Historically, concern has focused less on the cathode ray tube, since its thick glass envelope is impregnated with several pounds of lead for shielding, than on high voltage (HV) rectifier and voltage regulator tubes inside. The hazard associated with excessive voltages was eliminated with the advent of all solid state TVs, which have no tubes beside the CRT. Since 1969 the FDA has limited TV X-ray emission to 0.5 mR (milliroentgen) per hour. The flat screens used today do not have any vacuum tubes capable of emitting X-rays.>>