Failed dwarf galaxy survives galactic collision thanks to full dark-matter jacket

May 23, 2014
This is a false-color image of the Smith Cloud made with data from the Green Bank Telescope (GBT). Credit: NRAO/AUI/NSF

Like a bullet wrapped in a full metal jacket, a high-velocity hydrogen cloud hurtling toward the Milky Way appears to be encased in a shell of dark matter, according to a new analysis of data from the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT). Astronomers believe that without this protective shell, the high-velocity cloud (HVC) known as the Smith Cloud would have disintegrated long ago when it first collided with the disk of our Galaxy.

If confirmed by further observations, a halo of could mean that the Smith Cloud is actually a failed dwarf galaxy, an object that has all the right stuff to form a true galaxy, just not enough to produce stars.

"The Smith Cloud is really one of a kind. It's fast, quite extensive, and close enough to study in detail," said Matthew Nichols with the Sauverny Observatory in Switzerland and principal author on a paper accepted for publication in the Monthly Notices of the Royal Astronomical Society. "It's also a bit of a mystery; an object like this simply shouldn't survive a trip through the Milky Way, but all the evidence points to the fact that it did."

Previous studies of the Smith Cloud revealed that it first passed through our Galaxy many millions of years ago. By reexamining and carefully modeling the cloud, astronomers now believe that the Smith Cloud contains and is actually wrapped in a substantial "halo" of dark matter—the gravitationally significant yet invisible stuff that makes up roughly 80 percent of all the matter in the Universe.

"Based on the currently predicted orbit, we show that a dark matter free cloud would be unlikely to survive this disk crossing," observed Jay Lockman, an astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, and one of the coauthors on the paper. "While a cloud with dark matter easily survives the passage and produces an object that looks like the Smith Cloud today."

The Milky Way is swarmed by hundreds of high-velocity clouds, which are made up primarily of hydrogen gas that is too rarefied to form stars in any detectable amount. The only way to observe these objects, therefore, is with exquisitely sensitive radio telescopes like the GBT, which can detect the faint emission of neutral hydrogen. If it were visible with the naked eye, the Smith Cloud would cover almost as much sky as the constellation Orion.

Most high-velocity clouds share a common origin with the Milky Way, either as the leftover building blocks of galaxy formation or as clumps of material launched by supernovas in the disk of the Galaxy. A rare few, however, are interlopers from farther off in space with their own distinct pedigree. A halo of dark matter would strengthen the case for the Smith Cloud being one of these rare exceptions.

Currently, the Smith Cloud is about 8,000 light-years away from the disk of our Galaxy. It is moving toward the Milky Way at more than 150 miles per second and is predicted to impact again in approximately 30 million years.

"If confirmed to have dark matter this would in effect be a failed galaxy," said Nichols. "Such a discovery would begin to show the lower limit of how small a galaxy could be." The researchers believe this could also improve our understanding of the Milky Way's earliest star formation.

Explore further: Researchers suggest dark matter disk in Milky Way plane could signal rash of comet strikes on Earth

More information: Paper on Arxiv: arxiv.org/abs/1404.3209

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cantdrive85
2.6 / 5 (16) May 23, 2014
So prediction doesn't jive with observation and rather than consider the theory falsified, DM is the silver "bullet" to save the day. Pseudoscience at it best!
Dr_toad
May 23, 2014
This comment has been removed by a moderator.
yyz
4.5 / 5 (8) May 23, 2014
"I wish they'd given a bit more data."

DR, the study mentioned in this article looked at a couple of things. First, models of the Smith Cloud(SC), both with and w/o DM, were constructed and orbital passage through the galactic plane was examined. Those models without DM were found not to survive disk crossing while those with DM did, in agreement with an earlier study of the SC found here: http://arxiv.org/abs/0911.0684 . Several previous studies have found that the SC has made at least one crossing of the galactic plane already.

Secondly, data from the Fermi satellite was used in an unsuccessful attempt to detect gamma rays from DM annihilation in the SC, although upper limits were found. The MNRAS paper described in the article can be found here: http://arxiv.org/abs/1404.3209

Coincidentally, another recent search for gamma ray emission from the SC (also unsuccessful) has been submitted to ApJ is is available here: http://arxiv.org/abs/1405.1030
Captain Stumpy
4 / 5 (8) May 23, 2014
So prediction doesn't jive with observation and rather than consider the theory falsified, DM is the silver "bullet" to save the day
@cd
is this like your "prediction" of electrical discharge being the cause of Chelyabinsk detonation found here http://phys.org/n...oid.html where you said
Electric discharge can easily produce the heat and pressure required for the observation
you ignored empirical data
the Chelyabinsk asteroid had a well-recorded trajectory, and it left fragments on the Earth
Therefore, your assumption above clearly shows your lack of comprehension as well as ignorance of astrophysics. try reading the study and yyz's links
The current velocity of the Smith Cloud indicates that it has undergone at least one passage of the Galactic disc. Using hydrodynamic simulations we examine the present day structure of the Smith Cloud. We find that a dark matter supported cloud is able to reproduce the observed
Dr_toad
May 23, 2014
This comment has been removed by a moderator.
rah
3 / 5 (12) May 23, 2014
So this cloud of gas is wrapped by matter which cannot be seen or sensed or measured and has not been proven to even exist, but it's keeping this hydrogen cloud together? Couldn't it just as easily be magic or voodoo or its own gravity or God's will?
cantdrive85
2.1 / 5 (15) May 23, 2014
So this cloud of gas is wrapped by matter which cannot be seen or sensed or measured and has not been proven to even exist, but it's keeping this hydrogen cloud together? Couldn't it just as easily be magic or voodoo or its own gravity or God's will?

And now you understand the mechanics of mainstream astrophysics. Just believe and have faith because those who are studying this are far "smarter" than you are...
IMP-9
4.6 / 5 (9) May 23, 2014
Couldn't it just as easily be magic or voodoo or its own gravity or God's will?


And what do either of those things predict about the dynamics and observations of this structure? Absolutely nothing. You can make something up that can explain anything but it is completely useless because it is compatible with any observation. Dark matter is different, it's a physical model we can quantify. It makes predictions and is not comparable with every observation. This is the difference between science and guesswork. Science does Bayesian analysis and tells us models which are compatible with every observation hold no statistical weight.

Dark matter explains lensing, rotation, cluster dynamics, structure formation, it's far from perfect but it is the leading model. Science doesn't require faith like CD ignorantly claims, it's simply a matter of Bayes factors.
theon
2.7 / 5 (7) May 24, 2014
Don't bother to tell us how much normal matter and dark matter are expected. It's about the hype, not the content.
Pejico
May 24, 2014
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Gigel
4 / 5 (2) May 24, 2014
I wonder what could be the velocity spread of dark matter. A big enough clump of DM moving over yonder could easily perturb parts of galaxies.
Bob Osaka
2 / 5 (5) May 24, 2014
"Come over to the dark side, you don't know the power of the dark side, only together can we defeat the empirical evidence."
Human time scale is one of the biggest problems in cosmology. We could argue about the SC and its DM halo for the next eight million years. And then watch as it goes splat like a shell-less egg on a hot skillet.
The original mass of the SC may have been many times the mass observed today. How many times has it already passed through our galaxy?
It is holding its shape perhaps because we haven't observed it for that long and no outside force with enough strength is acting upon it to perturb its shape.
And here is the hard part: we're going to have to wait and see. Meanwhile you may pontificate DM all you like.
dogbert
May 24, 2014
This comment has been removed by a moderator.
philw1776
5 / 5 (1) May 24, 2014
A question. We know that DM interacts with ordinary baryonic matter only via gravitation. We see its effects in the rotational velocity of spiral galaxies, etc. Why doesn't the DM in this cloud for example settle into a smaller spherical space and attract the ordinary matter hydrogen to form stars? Is it so diffuse that even after 13+ gigayears, that attraction and condensation has not had enough time to happen? I think that is not so. Clues appreciated!
dogbert
May 24, 2014
This comment has been removed by a moderator.
IMP-9
5 / 5 (5) May 24, 2014
Why doesn't the DM in this cloud for example settle into a smaller spherical space and attract the ordinary matter hydrogen to form stars?


The leading model of dark matter says it's non-baryonic which means it has no friction and no static or ram pressure. As a result it is very difficult for it to collapse. In order to collapse a cloud must shed energy so it can take a lower orbit, it does this though collisions and friction. Without this collapse is very, very slow. This is why it is thought dark matter forms halos which extend far beyond the dense baryonic part of the galaxy.
pandora4real
1 / 5 (2) May 25, 2014
A question. We know that DM interacts with ordinary baryonic matter only via gravitation. We see its effects in the rotational velocity of spiral galaxies, etc. Why doesn't the DM in this cloud for example settle into a smaller spherical space and attract the ordinary matter hydrogen to form stars? Is it so diffuse that even after 13+ gigayears, that attraction and condensation has not had enough time to happen? I think that is not so. Clues appreciated!


Here's one. "All except gravity..." Personally I find gravity superfluous. Mass curves space-time. DM doesn't interact with anything. Another WAG. Singularities are pretty unscientific on a certain level. Rather than have the mass going into it disappear, why not postulate a multi-verse and that DM is pouring out of black holes? Baryons from another universe, they might be composed of quarks that don't work as matter in this universe. Hence they warp space-time but can't interact with anything.
Uncle Ira
2.3 / 5 (3) May 25, 2014
Here's one. "All except gravity..." Personally I find gravity superfluous. Mass curves space-time. DM doesn't interact with anything. Another WAG. Singularities are pretty unscientific on a certain level. Rather than have the mass going into it disappear, why not postulate a multi-verse and that DM is pouring out of black holes? Baryons from another universe, they might be composed of quarks that don't work as matter in this universe. Hence they warp space-time but can't interact with anything.


Yeah Skippy, that's one alright. Is that the serious idea? Or you just trying get somebody to talk with? But ol Ira suppose it is possible that you might be on to something, we'll wait for the smart peoples to weight in on it. But just between you Skippy and me Ira-Skippy, I don't think you are going to be proud of their report because I got no idea what you trying to say with that theory.
Pejico
May 25, 2014
This comment has been removed by a moderator.
iFujita
1 / 5 (3) May 26, 2014
I am not glad to change Newton's law for galaxies alone. But it is reasonable to consider the possibility of the universal gravity equation for the two dimensional space with certain depth like a pizza dough. Stars like the Sun are swaying up and down confined by the steep gradiant of the gravity field of the surfaces of the disk. Inside of this pizza dough, the space is ordinarily three dimensional while the distance of objects is relatively short, for example, within the solar system.
One trajectory of a matter has both the nearest and the furthest point from the center of the galaxy. And the circle tangent velocity against the center of the galaxy is to be constant. Then where has been the potential energy? We can find it in the vertical movement. When the trajectory comes the nearer to the center of the galaxy, it will sway up and down the more rapidly.
http://www.geocit...y01.html
Quantum Flux
1 / 5 (4) May 27, 2014
I predicted that the dust cloud would not be effected by Sgr A* because the law of thermodynamics is wrong where it claims energy cannot be created. If energy can not be created then the universe would not contain any energy. New energy entering the universe would be the equal opposite to the force of gravity and is the cause for the universe's expansion. I actually predicted that nothing would happen when this cloud got close. I was right. How could I make that prediction? Just like I predicted the stars nearest to the core of the galaxy would be young and the ones further away would be old. Just like my prediction, which science has not yet discovered, that the stars are born near the black hole and move away from it. This dust cloud most likely formed out of the energy Sgr A* once spewed. Accretion will most likely cause that material to accumulate & form a new star. Eventually we will see that black holes do not feed on gas and stars, they give birth to them.
no fate
2.3 / 5 (3) May 27, 2014
Eventually we will see that black holes do not feed on gas and stars, they give birth to them.


This is conceivable as long as we redifine the term "black hole". Currently it is a point of inifinite gravitational collapse which is physically impossible but mathematically worshipped...despite being indescribable mathematically...I have always loved that little bit of irony.
yyz
3.7 / 5 (3) May 27, 2014
Quantum Flux, I think you have your clouds mixed up. This article concerns the Smith Cloud, a High Velocity Cloud located 7600 pc from the galactic center and weighing in at over a million solar masses:

http://en.wikiped...7s_Cloud

http://arxiv.org/abs/0804.4155

Your post seems to be referring to the G2 cloud interacting with Sgr A*: http://en.wikiped...n_course

This tiny (~3 Earth mass) cloud is undergoing a close encounter with Sgr A*. While some astronomers predicted the cloud would be disrupted in the encounter, the cloud has managed to stay intact through its perigalactic passage (as predicted by other groups e.g. Geha). Contrary to your assertion, the cloud was greatly affected by the close passage and has now been stretched to many times its original length. Some parts of the cloud have yet to make their closest approach while other parts are streaming away. Fragmentation is observed.

yyz
5 / 5 (3) May 27, 2014
This series of images, taken with the Very Large Telescope in Chile, document changes in the shape of the G2 cloud during its encounter with Sgr A* over the past nine years:

http://www.mpe.mp..._new.png

Seems like it IS being affected by its close passage to the black hole.

supamark23
2.3 / 5 (3) May 27, 2014
So this cloud of gas is wrapped by matter which cannot be seen or sensed or measured and has not been proven to even exist, but it's keeping this hydrogen cloud together? Couldn't it just as easily be magic or voodoo or its own gravity or God's will?

And now you understand the mechanics of mainstream astrophysics. Just believe and have faith because those who are studying this are far "smarter" than you are...


One thing's for sure, they're a lot smarter than you...
Tuxford
1 / 5 (2) May 28, 2014
Ask the real question. Is it the chicken or the egg? Is the cloud a consequence of the dark matter halo, or is the dark matter halo a consequence of the massive cloud. I predict with sufficient observational power, we will find it to be the latter.

Quantum Flux
1 / 5 (1) Jun 12, 2014
Dark matter halo was only surmised after it did not become lunch for Sgr A*. Dark matter basically became an escape goat for failure to predict! Has an event horizon ever been observed? No, because they do not exist! Mark my word, if gravity from Sgr A* can hold onto stars some 50 thousand light years away then an equal opposite force has to be released from Sgr A* to causes the effect. Can't have one without the other else the galaxy would eventually shrink and disappear over time. Observations show the opposite, galaxies are expanding and growing, the oldest stars near the outside and the youngest ones near the core. Black holes create matter and energy they do not destroy!

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