SoylentNews is people
SoylentNews
from the noone-knows-how-the-cloud-works dept.
A nearly invisible dwarf galaxy is challenging the model of dark matter. An international team of astronomers, led by the Instituto de Astrofísica de Canarias (IAC) in collaboration with the University of La Laguna (ULL) and other institutions, discovered this fascinating galaxy dubbed "Nube."
Nube, which means "Cloud" in Spanish, was named by the 5-year-old daughter of one of the researchers, aptly reflecting the galaxy's ghostly and diffuse appearance. Its discovery is significant because its faint surface brightness allowed it to remain undetected in previous sky surveys, despite its considerable size.
"With our present knowledge we do not understand how a galaxy with such extreme characteristics can exist," says study first author Mireia Montes, researcher at the IAC and the ULL, in a media release.
Nube is unique in its properties, being ten times fainter yet ten times more extended than other dwarf galaxies with a similar number of stars. Its discovery is akin to finding a hidden treasure in a well-explored attic. Nube is large and yet faint, a ghostly apparition in the universe. To put it into perspective, it's about one-third the size of the Milky Way but has a mass comparable to the Small Magellanic Cloud.
What sets it apart is its significant amount of dark matter, an invisible substance that does not emit, absorb, or reflect light, making it undetectable by traditional telescopes.
Related: Bizarre Galaxy Discovered With Seemingly No Stars Whatsoever
(Score: 1) by khallow on Wednesday January 31 2024, @01:45PM (10 children)
Unless, of course, it does and this galaxy happens to have an unusually large amount of it relative to its visible matter. Remember we do have various sorts of dark matter presently (as you know, we ourselves are dark matter due to our low EM emissions per unit mass), we just don't yet know of enough of it to explain our observations.
I find it interesting, for example, how cold neutrinos (that is, neutrinos moving at slow interstellar speeds) still haven't been ruled out - aside from figuring how where they would come from. If there is a mechanism [sciencedirect.com] for creating enough of them, then that would explain things quite well. And they would be incredibly difficult to detect since they would have many orders of magnitude less energy than solar and human-generated neutrinos.
(Score: 4, Informative) by Immerman on Thursday February 01 2024, @05:22PM (9 children)
Again with this "we are made of dark matter" B.S.
The "Dark" in dark matter doesn't mean non-luminous, it means undiscovered. Like how Africa was once known as "The Dark Continent" - they never meant the sun didn't shine there.
Way back when it was first proposed, yes, dark matter could have just been undiscovered non-luminous matter like rocks, gas, etc. In fact that was the general assumption until we went to look for it.
Not anymore - we've searched for and ruled out almost all possible normal-matter candidates for dark matter - aside from being a huge number of black holes within an implausibly narrow range of sizes.
If it's not that, and it actually exists rather than just being an artifact of an imperfect understanding of gravity, then it's has to be something that not only doesn't emit light, but doesn't interact with it at all. Enough rocks, planets, etc. would obscure distant starlight, revealing its existence. We see no evidence of that. Enough gas would would absorb certain wavelengths of light passing through it, imprinting its absorption spectra over what was coming from the stars themselves. We see no evidence of that..
We're talking about the galaxy being embedded in a cloud of 5x more mass than all the stars combined. It could have hidden from the telescopes when the theory was first proposed, especially since nobody was looking for it. But our telescopes have gotten better, and we've been searching for any hint of evidence for anything that it could be. Whatever it is - light doesn't interact with it.
Which, yes, leaves cold neutrinos as a possibility, since light doesn't interact with them either. But you would have to explain both why none of our neutrino detectors are showing background neutrino levels levels radically higher than what we can detect coming from the sun, nuclear reactors, etc. As well as where they came from, since there's no known mechanism to explain how they could have cooled down rapidly enough from when they were in thermal equilibrium with the dense, hot, early universe, which would have required them to have relativistic velocities. And hot neutrinos couldn't have contributed to the early structure formation in the universe, which is one of the major arguments supporting the existence of dark matter.
So basically - if it is cold neutrinos, you've just replaced one mystery with an even bigger one. Which doesn't mean it's not true... but it's not super promising either.
What would be more promising is if we were to discover neutrinos actually do have radically more massive antiparticles that also don't interact with light. Those would be a prime Dark Matter candidate, as well as simultaneously solving the mystery of how neutrinos can have mass at all (and are thus able to oscillate between flavors) - since they need to have an antiparticle in order to couple with the Higgs Field and get mass the same way other fundamental particles do.
Science has a long history of big advances in our understanding answering multiple seemingly independent questions simultaneously. Like Relativity - which simultaneously fixed the problem of Maxwell's Equations predicting completely different electromagnetic forces based on your reference frame, explained the anomaly in Mercury's perihelion precession, and several others.
(Score: 1) by khallow on Thursday February 01 2024, @09:37PM (8 children)
Except it does mean non-luminous matter. Enough non-luminous matter of any sort moving at slow enough velocities in the places where it needs to be to explain observation.
Doubtful. We already have a huge unknown in the beginnings of the universe. This would illuminate that. At some point the universe would become transparent to neutrinos (possibly in a sufficiently gradual way that forces the neutrino fluid to match velocity), that's probably the earliest we can possibly observe via primordial subatomic particles unless there's something that interacts even less.
(Score: 2) by Immerman on Friday February 02 2024, @02:51PM (7 children)
Except we've looked where it needs to be, and can see nothing. And we've looked carefully enough that if it were gas, rocks, or almost anything else that interacted with photons, we'd have seen evidence of it. You'd basically need sufficiently small black holes, or maybe neutronium chunks, to get enough mass in the right places without the bits being large enough to be noticeable against the backlighting from other galaxies.
We also have a huge known in the moderately early universe, the CMBR, which tells us that the temperature was extremely hot and uniform ~13.5 billion years ago, which sets the temperature of the neutrinos as well - since even with their low interaction rate the preceding 370,000 years would have given them plenty of time to reach equilibrium with everything else. Which given their infinitesimal mass would mean relativistic velocities.
And the universe would always have been almost completely transparent to neutrinos, except maybe in the first few moments before quarks cooled enough to form protons and neutrons - assuming that actually happened (before the CMBR our knowledge gets increasingly uncertain). Only interacting via the weak force and gravity means that even stars and planets are almost completely transparent to neutrinos, they wouldn't really care about the plasma that made the early universe opaque to photons. Even a light year of solid lead would only stop about half of them.
(Score: 1) by khallow on Friday February 02 2024, @04:16PM (3 children)
Except? That would be non-luminous matter in a nutshell. You have to look indirectly. I understand gravitational lensing shows something is going on.
(Score: 2) by Immerman on Friday February 02 2024, @05:04PM (2 children)
Look at your hand - it's non-lumnous matter, yet you can still see it.
Pitch black night so you can't actually see your hand directly? Hold it up to the stars, and you can still see its outline by the stars that it obscures. And that's true of ALL luminous matter. Even glass is completely opaque across much of the EM spectrum.
And yet when we look at where we know dark matter must be, we see neither. So we know whatever is there (if there's really something there), it doesn't interact with light. Which rules out anything made of atoms.
(Score: 2) by Immerman on Friday February 02 2024, @05:17PM
Sorry, that should be:
And that's true of ALL normal matter.
not luminous
(Score: 1) by khallow on Saturday February 03 2024, @06:15AM
Only because it's near my face. If it were 50k light-years away at the edge of the Milky Way, I wouldn't see it that way, even if there were several million solar mass of them out there. At that point, you'd have to look for indirect effects like occultation or gravitational lensing.
The problem then is that a dense object like a hand doesn't occult much for its mass. Nebula are extremely puffy - Wikipedia states a typical nebula cloud the size of Earth would weigh a few kilograms. That's a few hands of mass. And illuminate that nebula with ionizing uv or x-rays and suddenly you have an object much brighter than its equivalent in hands would be.
We do see gravitational lensing.
(Score: 1) by khallow on Friday February 02 2024, @04:24PM (2 children)
This. Except in the first few moments. We don't have an understanding of the earliest moments of the universe, but it keeps getting hotter and denser.
(Score: 2) by Immerman on Friday February 02 2024, @05:07PM (1 child)
Right, so any neutrinos that existed at that time would be hot, and matter has been two diffuse since the CMBR for them to shed much of that heat.
(Score: 1) by khallow on Saturday February 03 2024, @06:29AM
Unless, of course, that velocity was shed. The paper I linked back some ways had a mechanism - interaction with strong magnetic fields.
And there would be additional velocity loss from red shift. For example, from the most distant galaxies, one gets red shifts of over 10. What that means is that light traveling from that galaxy loses a factor of ten or more energy in its travel to us. A typical near light-speed neutrino taking the same route would lose a similar amount of energy. Neutrinos from the initial moments of the Big Bang would lose much more energy due to much higher red shifts - we're talking orders of magnitude loss. If they start with initial extremely high energy, then they can stay hot and extremely fast even now. But if they don't, then they can well slow down enough by now that they can be caught by galaxies.
That's the theoretical mechanism for cold neutrino creation and capture.