Chandra Shows Milky Way is Surrounded by Halo of Hot Gas

[CaptainPanic]

How can we be certain about the mass of the universe, when only recently the Chandra observatory found a halo of gas surrounding our own Milky way? Although the mass is unknown, it is huge: the estimates range between the mass of 10 and 60 billion suns (comparison: the milky way itself contains between 100 and 400 billion stars). That's a lot of mass we hadn't noticed until now.

 

And related, have we now found some of the missing dark matter? Why are we trying to invent new science to explain some missing mass in the universe, when it might just be thinly dispersed around the galaxies?

 

The estimated density of this halo is so low that similar halos around other galaxies would have escaped detection. (NASA)

 

I read this as: we just found out that our galaxy is perhaps up to 20% heavier than we originally thought, and we have no way to say whether other galaxies are also surrounded by such a gas cloud.

 

Also, wouldn't such a huge gas cloud interfere with all our measurements of other galaxies, just like the atmosphere interferes? Should any instuments be recalibrated and/or should results be recalculated?

[granpa]

the big halos surround superclusters

[alpha2cen]

Why the temperature is too high?

[Enthalpy]

If astronomers missed only 20% mass, they wouldn't bother about it!

They're looking for a factor of 20.

[Ophiolite]

Take care of the pennies and the pounds will take care of themselves.

[CaptainPanic]

In my opening post I expressed a second worry: what if our measurements are wrongly interpreted, because we don't correct for the interference of a gas cloud which surrounds us?

 

I'm no expert, but just interested, so some of my questions might be silly. Here is my worry, explained a little better:

 

We measure distances in the universe by the brightness of a type Ia supernova:

 

This category of supernovae produces consistent peak luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism. The stability of this value allows these explosions to be used as standard candles to measure the distance to their host galaxies because the visual magnitude of the supernovae depends primarily on the distance.(source: wikipedia)

 

If there is a halo surrounding us, don't we misjudge the distance, because part of the light is absorbed by that halo? Just like your visibility is reduced in fog? Which wavelengths are recorded from those supernovas? And can they be absorbed by a could of (very) hot basic gases such as hydrogen and oxygen?

[Spyman]

If there is a halo surrounding us, don't we misjudge the distance, because part of the light is absorbed by that halo? Just like your visibility is reduced in fog? Which wavelengths are recorded from those supernovas? And can they be absorbed by a could of (very) hot basic gases such as hydrogen and oxygen?

I am not an expert either but if our visibility is reduced due to a halo surrounding us then shouldn't scattering of light blur the images?

Edited September 27, 2012 by Spyman

[Enthalpy]

Supernovae brightness is just one part of the picture, the one that suggests an accelerating expansion and possibly dark energy widely taking the place of dark matter.

 

Dark matter is deduced from movements of globular clusters, galaxies clusters and superclusters, gravitational lensing.

 

As for light absorption, already the Herzsprung-Russel diagram compared between the Milky Way and the Magellanic clouds would have told it.

[CaptainPanic]

I am not an expert either but if our visibility is reduced due to a halo surrounding us then shouldn't scattering of light blur the images?

Judging by our own atmosphere, yes, there should be a little scattering. I would be surprised if there isn't any.

 

But absorption of certain wavelengths can be quite severe too. Here's a picture (wikipedia) about the difference in the intensity of the sun at the top of the atmosphere and at sea level.

I read (in the link in the 1st post) that the gas is probably mostly hydrogen and oxygen, but that they're not entirely sure. Those will be plasmas, I am assuming: single atoms and possibly free electrons. I don't know what those absorb. I am just wondering if it is relevant for our measurements.

 

Enthalpy, I don't understand your post. I am wondering whether there might be a chance that we got the luminosity of distant galaxies wrong, due to a halo. The Hertzsprung-Russell diagram deals with individual stars, not whole galaxies. If we use that diagram to conclude how far other galaxies are from us, that would mean they conclude a distance based on a measurement of luminosity. So, if the luminosity measurement is wrong due to a halo, the distance estimate is wrong too. But maybe your post implied a lot more - I am not too familiar with the Hertzsprung-Russell diagram, actually. (I just looked it up, to be honest).

[Spyman]

Judging by our own atmosphere, yes, there should be a little scattering. I would be surprised if there isn't any.

But can any relevant absorption still be large enough to make a difference when the blur is too small to be noticeable with our instruments?

[CaptainPanic]

It would be interesting to know how much matter we are actually talking about in comparison to our atmosphere.

 

I think it's not too hard to calculate (at least not an order-of-magnitude estimate), but I shouldn't be spending time on that today.

[Airbrush]

I read this as: we just found out that our galaxy is perhaps up to 20% heavier than we originally thought, and we have no way to say whether other galaxies are also surrounded by such a gas cloud.

 

I vaguely recall hearing that the amount of gas and dust in our galaxy, and perhaps all galaxies, is about the same mass as the mass of all visible stars in a galaxy.

 

Also dark matter is estimated to be over 5 times as massive as the ordinary matter.

[Spyman]

This discovery is not about dark matter and it is not some *new* matter suddenly discovered either, if confirmed they have found ordinary matter that we already knew should be here somewhere but previously couldn't find:

 

 

NASA's Chandra Shows Milky Way is Surrounded by Halo of Hot Gas

 

If the size and mass of this gas halo is confirmed, it also could be an explanation for what is known as the "missing baryon" problem for the galaxy.

 

Baryons are particles, such as protons and neutrons, that make up more than 99.9 percent of the mass of atoms found in the cosmos. Measurements of extremely distant gas halos and galaxies indicate the baryonic matter present when the universe was only a few billion years old represented about one-sixth the mass and density of the existing unobservable, or dark, matter. In the current epoch, about 10 billion years later, a census of the baryons present in stars and gas in our galaxy and nearby galaxies shows at least half the baryons are unaccounted for.

http://www.nasa.gov/mission_pages/chandra/news/H-12-331.html

 

 

Missing Baryons

 

Astronomers have known for some time that about half of all of the baryonic matter, a.k.a. protons and neutrons, in the recent, nearby Universe is unaccounted for. It's all there in the early Universe, so where did it go? One idea is that these missing baryons became part of an extremely diffuse weblike system of gas clouds from which galaxies and clusters of galaxies formed. One of the best ways to detect these missing baryons is through their faint, but observable, X-ray signatures.

http://chandra.si.edu/chronicle/0108/universe/

 

 

The Case of the "Missing Baryons

 

The best estimates are that all the stars, gas, and dust within galaxies constitute at most 40% of the baryons predicted by the Big Bang. Where are the rest?

 

The most likely place for the rest of the baryons to be hiding is in diffuse gas between the galaxies: the intergalactic medium. Astronomers can estimate the amount of gas in the intergalactic medium by essentially counting up the number of atoms that absorb the light from distant quasars. This number once again falls well short of that required by the Big Bang theory. If the gas is there, many of the atoms must be ionized, that is stripped of some of their electrons, so that they cannot absorb the radiation.

http://praxis.pha.jhu.edu/astro2/astro2_science/starburst.html

[Widdekind]

So, the new X-ray observations make "matter censuses" today tally with "matter census" tallies from billions of years ago...

 

but both tallies, even though they now (plausibly) match, are still insufficient to account for observed gravitational forces of attraction, which at all epochs imply ~6x more mass ("Dark Matter") to be "secretly associated" with the luminous, light-emitting-so-humans-can-see-it material ("Light Matter")?

 

The "missing baryons" problem notes that, over billions of years, ~half of the once-observed "Light Matter" has "faded into obscurity" ?? (But, according to the new X-ray observations, "fading away" may mean "thinning out so diffusely that only sensitive scans can catch the little light emitted"?) Meanwhile, separately, the observed gravity forces imply many times more unseen hidden "Dark Matter"?

 

Again, quoting from cited sources:

 

matter in "distant gas halos and galaxies" (seen from far far away, the way they were long long ago) --> galactic "gas halo" and possibly also "diffuse gas between the galaxies: the intergalactic medium"

So, ancient gas halos, around galaxies, have evidently heated up, puffed up, and thinned out, so that they have much lower surface brightness, and are effectively dimmer (for narrow-field observations?). Perhaps galaxy halo gas has heated up, over the aeons, due to progressive mergers, of proto-galaxies into ever larger (composite) galaxies ? Also, since the gravitational influences of "Dark Matter" have been observed "the entire time", from billions of years ago until today, so DM must be primordial, predating the earliest cited observations, from "10 billion years ago"? I.e. DM is older than even ancient "distant gas halos & galaxies"? The only things older than that are primordial (energy, H,He, first generation stars). DM already lurks hidden within the earliest proto-galactic clouds of dusty gas?

Edited September 29, 2012 by Widdekind

[Airbrush]

but both tallies, even though they now (plausibly) match, are still insufficient to account for observed gravitational forces of attraction, which at all epochs imply ~6x more mass ("Dark Matter") to be "secretly associated" with the luminous, light-emitting-so-humans-can-see-it material ("Light Matter")?

 

I like the questions you raise and good observations, but when you said 6x as much dark matter as light matter, that is a slight exaggeration. According to Wiki there is 5.25 times as much DM as LM.

 

 

"...its [DM] existence and properties are inferred from its gravitational effects on visible matter, radiation, and the large scale structure of the universe. Dark matter is estimated to constitute 84% of the matter in the universe and 23% of the mass-energy.[2]"

 

http://en.wikipedia.org/wiki/Dark_matter

 

84/23 = 5.25x

 

Does light matter (everything that is not dark matter) include all the invisible gas, dust, black holes, brown dwarfs, invisible planets and moons, and asteroids in the universe?

Edited September 30, 2012 by Airbrush

[imatfaal]

I like the questions you raise and good observations, but when you said 6x as much dark matter as light matter, that is a slight exaggeration. According to Wiki there is 5.25 times as much DM as LM.

 

 

"...its [DM] existence and properties are inferred from its gravitational effects on visible matter, radiation, and the large scale structure of the universe. Dark matter is estimated to constitute 84% of the matter in the universe and 23% of the mass-energy.[2]"

 

http://en.wikipedia....iki/Dark_matter

 

84/23 = 5.25x

 

Does light matter (everything that is not dark matter) include all the invisible gas, dust, black holes, brown dwarfs, invisible planets and moons, and asteroids in the universe?

 

Sorry Airbrush - you are doing your sums wrongly (although you have inserted the correct answer) .

 

"Dark matter is estimated to constitute 84% of the matter" - thus ~16% of the matter is luminous matter.

Thus the sum you want is 84/16 = 5.25

 

But you had 84/23 which in fact equals 3.65 The 23% in the wikiquote is the amount of dark matter compared to the the total mass-energy ie all the matter (dark and luminous) and all the energy (normal and dark)

[Widdekind]

I like the questions you raise and good observations, but when you said 6x as much dark matter as light matter, that is a slight exaggeration. According to Wiki there is 5.25 times as much DM as LM.

 

 

"...its [DM] existence and properties are inferred from its gravitational effects on visible matter, radiation, and the large scale structure of the universe. Dark matter is estimated to constitute 84% of the matter in the universe and 23% of the mass-energy.[2]"

 

http://en.wikipedia.org/wiki/Dark_matter

 

84/23 = 5.25x

 

Does light matter (everything that is not dark matter) include all the invisible gas, dust, black holes, brown dwarfs, invisible planets and moons, and asteroids in the universe?

Everything you suggested would currently be classified as "Dark" Matter.

 

Now, during star formation, the central stars capture >99% of the material. For example, in our solar system, the mass of all orbiting bodies (worlds, asteroids, comets) is perhaps [math]2 M_{Jupiter} \approx 0.002 M_{\odot}[/math]. So, to claim that the ~5x unseen DM is composed of those "world-like bodies" seems implausible. Conversely, uncritical extrapolation of the stellar initial-mass-function, estimated from astronomical observations, predicts an infinite number, of low-mass brown dwarves; uncritically accepted, DM could plausibly be composed, of dim faint brown dwarf "sub-stars", lurking out in space, not glowing (no core fusion), and so not telegraphing their existences, to humans on earth.

 

VETO

-- enter theoretical physicists, and theories of "Primordial Nucleosynthesis", derived from terrestrial labwork; and suddenly all the

non-glowing

DM "just must" be exotic particles of unspecified strangeness. That, however, is current mainstream.

[Spyman]

Also, since the gravitational influences of "Dark Matter" have been observed "the entire time", from billions of years ago until today, so DM must be primordial, predating the earliest cited observations, from "10 billion years ago"? I.e. DM is older than even ancient "distant gas halos & galaxies"? The only things older than that are primordial (energy, H,He, first generation stars). DM already lurks hidden within the earliest proto-galactic clouds of dusty gas?

Formation of the first galaxies

After the Big Bang, the universe, for a time, was remarkably homogeneous, as can be observed in the Cosmic Microwave Background or CMB (the fluctuations of which are less than one part in one hundred thousand). There was little-to-no structure in the universe, and thus no galaxies. Therefore we must ask how the smoothly distributed universe of the CMB became the clumpy universe we see today.

 

The most accepted theory of how these structures came to be is that all the large-scale structure of the cosmos we observe today was formed as a consequence of the growth of the primordial fluctuations, which are small changes in the density of the universe in a confined region. As the universe cooled clumps of dark matter began to condense, and within them gas began to condense. The primordial fluctuations gravitationally attracted gas and dark matter to the denser areas, and thus the seeds that would later become galaxies were formed. These structures constituted the first galaxies. At this point the universe was almost exclusively composed of hydrogen, helium, and dark matter. Soon after the first proto-galaxies formed, the hydrogen and helium gas within them began to condense and make the first stars.

http://en.wikipedia.org/wiki/Galaxy_formation_and_evolution#Formation_of_the_first_galaxies

 

 

Does light matter (everything that is not dark matter) include all the invisible gas, dust, black holes, brown dwarfs, invisible planets and moons, and asteroids in the universe?

Baryonic and nonbaryonic dark matter

Fermi observations of dwarf galaxies provide new insights on dark matter.A small proportion of dark matter may be baryonic dark matter: astronomical bodies, such as massive compact halo objects, that are composed of ordinary matter but which emit little or no electromagnetic radiation. Study of nucleosynthesis in the Big Bang produces an upper bound on the amount of baryonic matter in the universe, which indicates that the vast majority of dark matter in the universe cannot be baryons, and thus does not form atoms.

http://en.wikipedia.org/wiki/Dark_matter#Baryonic_and_nonbaryonic_dark_matter

[Airbrush]

Sorry Airbrush - you are doing your sums wrongly (although you have inserted the correct answer) .

 

"Dark matter is estimated to constitute 84% of the matter" - thus ~16% of the matter is luminous matter.

Thus the sum you want is 84/16 = 5.25

 

Thanks for the correction. I crunch numbers all day as a bookkeeper, and that error is an embarrassment.

Edited October 1, 2012 by Airbrush

[Widdekind]

i know of no cosmological computer simulations, that include the "small" astronomical star-scale effects, of turbulence. Perhaps primordial turbulence could have slammed streams of space-gas together, fast enough to overcome pressure, and so trigger bursts of primordial star formation??

[Enthalpy]

Hertzsprung-Russell diagram

The Hertzsprung-Russell diagram relates the absolute luminosity and the colour of a normal (main sequence) star. Individual stars are observed in remote galaxies, so if something absorbs their light, astronomers notice it, as they don't fit on the HR curve any more.

 

There are more tools. Except for some discrete lines, the spectrum of a star resembles the black body. If the continuous spectrum of a remote star differs too much from the black body, astronomers infer absorbing matter on the line of sight.

 

...dark matter could plausibly be composed, of dim faint brown dwarf "sub-stars"...

this is an abandoned explanation, because the micro-lensing effect of cold bodies that massive and abundent was searched and not observed.

[Widdekind]

http://phys.org/news/2011-09-cosmic-weight-reveals-black-hole-galaxy.html

 

The motions of gas around the cited galaxy look like they break down into an outer shell, spinning one way, and an oppositely spinning inner shell

 

this is an abandoned explanation

of course

 

because the micro-lensing effect of cold bodies that massive and abundent was searched and not observed.

no -- numerous lensings were observed, whose implications require... theories and models of the galactic halo... none based on... observations. To date, humans on earth have only weak relevant observing capability, and observing data

[EquisDeXD]

I am not an expert either but if our visibility is reduced due to a halo surrounding us then shouldn't scattering of light blur the images?

 

Not all substances "scatter" light, some allow it to pass through it bent or relatively unaltered. Concentrated gas if its not unionized doesn't change the frequency of light so often as it merely blocks light, like chalk in a glass of water. Not only that, but there are still "standard candles" or supernovae throughout different parts of the unvierse which have constant ranges of brightness per distance, and we can make inferences based on how the same magnitude of light from that distance acts when we observe it which means we can make inferences about its mass and of the objects around it, which tells us that the mass of not just our own, but of distant galaxies isn't accounted for by a very large factor. If the gas is only 20% of that, it's not enough.

Edited October 5, 2012 by EquisDeXD

[Spyman]

Not all substances "scatter" light, some allow it to pass through it bent or relatively unaltered. Concentrated gas if its not unionized doesn't change the frequency of light so often as it merely blocks light, like chalk in a glass of water. Not only that, but there are still "standard candles" or supernovae throughout different parts of the unvierse which have constant ranges of brightness per distance, and we can make inferences based on how the same magnitude of light from that distance acts when we observe it which means we can make inferences about its mass and of the objects around it, which tells us that the mass of not just our own, but of distant galaxies isn't accounted for by a very large factor. If the gas is only 20% of that, it's not enough.

I am sorry but I don't seem to be able to understand what points you are trying to make.

[Widdekind]

The famous Low-Surface Brightness (LSB) galaxy Malin 1 is not actually an LSB galaxy. Instead, a normal barred-spiral (SBa) galaxy about 60K ly across spins amidst an extended disk ten times larger. Now, Malin 1 has maintained its extended disk, as an isolated field galaxy, far from disturbing tidal interactions. Thus, the material comprising the extended disk has had cosmological aeons to "disk down". Whereas, our Milky Way's galactic disk was long long ago truncated by tidal interactions, with other galaxies & satellites. However, the material which would have comprised an isolated Milky Way's extended disk, would plausibly have been shock-heated, during those interactions, and so "puffed up" into a diffuse circum-galactic halo. Perhaps the Milky Way's hot halo (per OP) comprises the material which, in Malin 1, has remained cold and "disked down" ??

 

http://kencroswell.com/Malin1.html