Category: dark matter

Physicists Used Einstein’s Relativity To…

Physicists Used Einstein’s Relativity To Successfully Predict A Supernova Explosion

“When the lens and a background source align in a particular fashion, quadruple images will result. With slightly different light-travel paths, the brightness and arrival time of each image is unique. In November 2014, a quadruply-lensed supernova was observed, showcasing exactly this type of alignment. Although a single galaxy caused the quadruple image, that galaxy was part of a huge galaxy cluster, exhibiting its own strong lensing effects. Elsewhere in the cluster, two additional images of the same galaxy also appear.”

We normally think of light traveling in a straight line, but that’s only true if your space is flat. In the real Universe, mass and matter not only exist, but clump together into massive structures like galaxies, quasars, and galaxy clusters. When a background source of light passes through these foreground masses, the light can get bent and distorted into multiple images that are magnified and arrive at slightly different times. If an event occurs in one such image, we can predict, based on General Relativity, cluster dynamics, and dark matter, when that event will appear in the other images.

In November 2014, we discovered a multiply-lensed supernova, and predicted where and when it would appear in the other images. Einstein and dark matter both win again!

This Is The Real Reason We Haven’t Direc…

This Is The Real Reason We Haven’t Directly Detected Dark Matter

“So we keep looking, we keep thinking of new possibilities for what it could be, and we keep thinking of new ways to search for it. That’s what science at the frontiers is like. Personally, I don’t expect these direct detection attempts to be successful; we’re stabbing in the dark hoping we hit something, and there are little-to-no good reasons for dark matter to be in these ranges. But it’s what we could see, so we go for it. If we find it, Nobel Prizes and new physics discoveries for everyone, and if we don’t, we know a little more about where the new physics isn’t. But just as you shouldn’t fall for the hyper-sensationalized claims that dark matter has been directly detected, you shouldn’t fall for the ones that say “there’s no dark matter” because a direct detection experiment failed.”

At some point, when you’re looking for an unknown, you have to give up and declare it isn’t there. Sometimes you’re right, and other times, you discover that you either weren’t looking in the right place, or weren’t looking in the right way. It took over 25 years to find the neutrino from when Pauli first proposed it; over 50 years to find the Higgs boson from when it was first theorized; and over a century to find the first gravitational wave, first predicted by Einstein’s theory in 1915. So why, then, would we give up so quickly after not finding dark matter, after only a few decades of looking under a particular set of assumptions?

Dark matter isn’t easy to find, but it isn’t supposed to be. Absence of evidence is not evidence of absence. Learn the real reason we haven’t detected it, yet, today.

The Most Important X-Ray Image Ever Taken Prov…

The Most Important X-Ray Image Ever Taken Proved The Existence Of Dark Matter

“Yet the most important X-ray image of all time was an incredible surprise. This is the Bullet Cluster: a system of two galaxy clusters colliding at high speeds. As the gaseous matter inside collides, it slows, heats up, and lags behind, emitting X-rays. However, we can use gravitational lensing to learn where the mass is located in this system. he bending and shearing of light from background galaxies shows it’s separated from the matter’s and X-rays’ location. This separation is some of our strongest evidence for dark matter.”

There are many different lines of evidence for dark matter, but one of the biggest contentions of those who disbelieve it is that a direct empirical proof of its existence is needed. If it exists in a large, diffuse halo around every galaxy, cluster, and component of large-scale structure in the Universe, you should be able to prove it. Starting more than 10 years ago, astronomers have been able to do just that. When galaxy clusters collide, the overwhelming majority of normal matter, residing in the intracluster medium, should smash together, heat up, and emit X-rays. It does! But the biggest deal is that the gravitational mass, reconstructed through lensing, doesn’t coincide with the normal matter.

There must be some other type of matter from the normal, baryonic matter. Ergo, dark matter. Here’s (IMO) the most important X-ray story of all-time.

Ask Ethan: When Were Dark Matter And Dark Ener…

Ask Ethan: When Were Dark Matter And Dark Energy Created?

“Today [normal matter] is only 4.9% while Dark Matter and Dark Energy takes the rest. Where did they come from?”

The Universe, as we know it, got its start in earnest when the hot Big Bang began. Space was filled with all the particles and antiparticles of the Standard Model, up at tremendous energies, while the Universe then expanded, cooled, and gave rise to all we know. But when did dark matter and dark energy, which make up 95% of the Universe we know today, come into the picture? Was the Universe born with these components of energy? Or were they created at a later time? We have some inklings that dark matter was likely created in the extremely early stages, but may not have been present from the Universe’s birth. On the other hand, all theoretical signs point to dark energy always existing, but observationally, we have about 4 billion years where we cannot measure its presence at all.

Where do dark matter and dark energy come from? It’s a great cosmic mystery, but we do know something about it. Find out where we are today!

Modified Gravity Could Soon Be Ruled Out, Says…

Modified Gravity Could Soon Be Ruled Out, Says New Research On Dwarf Galaxies

“The fact that these two galaxies exhibit such different gravitational effects tell us that either something is very funny with one of them (something must be out-of-equilibrium), or that dark matter gets heated up by star formation and modified gravity cannot explain this. As always, more data, additional galaxies, and further research will be required to solve this mystery, but at long last, we’re looking at a viable way to prove modified gravity wrong on galaxy scales. Even without directly detecting a particle, dark matter might just achieve a knockout blow over its greatest competing alternative.”

If you have two galaxies in the Universe that look the same, you’d expect them to behave the same. After all, the laws that govern them ought to be identical, and so if their properties are identical, so should their behavior. The Draco and Carina dwarf galaxies are roughly the same mass, the same size, and have the same distribution of starlight. The only discernible difference is that one galaxy has only old stars, while the other has a mix of old and new stars. And yet, when we look at the gravitational effects of the mass on the stars, their behaviors are incredibly different. One seems to indicate a large unseen mass source in the center, and the other doesn’t.

In modified gravity, this makes no sense. But in dark matter theories, simple heating due to star formation could explain it all. Keep your ear to the ground, because this could lead to the death-knell for modified gravity!

How The Planck Satellite Forever Changed Our V…

How The Planck Satellite Forever Changed Our View Of The Universe

“Most importantly, a spectacular agreement to a never-before-achieved precision now exists between the CMB we observe and the theoretical predictions of a Universe with 5% normal matter, 27% dark matter, and 68% dark energy. There might be wiggle room of 1-2% in some of those numbers, but a Universe without dark matter and dark energy, both, in great abundance, is a no-go in the face of these observations. They’re real, they’re necessary, and their predictions match the full suite of data perfectly.

Inflation, neutrino physics, and the Big Bang have additional pieces confirming them, while alternatives and specific variants are better constrained. Most definitively, the Planck collaboration states, “We find no compelling evidence for extensions to the base-ΛCDM model.” At last, we can state, with extraordinary confidence, what the Universe is made of.”

For centuries, the question of what the Universe was made of was one of the most unknowable wonders of existence. This week, the Planck collaboration, whose team made the most accurate, precision measurements of the Big Bang’s leftover glow, released their final results, providing unprecedented answers to that question. We now know what the Universe is made of, how old it is, how fast it’s expanding, and a whole suite of other information about it, better than we’ve ever known before. The Planck satellite has revolutionized our view of the Universe, and we’re unlikely to ever do better using this line of inquiry.

How has our view of the Universe changed as a result of Planck? Come find out today!

This Is How Much Dark Matter Passes Through Yo…

This Is How Much Dark Matter Passes Through Your Body Every Second

“Dark matter, to the best of our knowledge, is out there in all directions. It may be invisible to our eyes, but we can feel its gravitational force. It passes through all the matter in the Universe, including human beings, as though it weren’t there at all. There are, to the best of our knowledge, no collisions or interactions other than its effects on curving spacetime. It doesn’t clump, cluster, or form structure like dark atoms or molecules.

And yet, if it has even the tiniest hint of an ability to collide with either normal matter or radiation, we’ll be able to detect it. Over the course of your life, about a milligram of dark matter will have passed through your body. If even one dark matter particle interacts with one proton or electron in your body, we’ll have a chance. When it comes to dark matter — one of the Universe’s deepest mysteries — it’s hard to ask for anything more.”

There’s a tremendous amount of astrophysical evidence that indicates the existence of dark matter. Grouped together in large, diffuse halos that surround every galaxy in the Universe, dark matter’s gravitational effects can be seen all across the Universe. This implies that there’s dark matter everywhere, including in the galaxy, in the Solar System, in the Earth, and even in your body. It’s not static, but simply passes right through you. If we can calculate and/or estimate how much dark matter there is and what it’s properties are, we can even come up with a figure for how much dark matter passes through you every second, and learn what that means for trying to directly detect it.

A human body might not be a great dark matter detector, but over your lifetime, a milligram of dark matter will have passed through your body. Come get the full story to learn more!

We Just Found The Missing Matter In The Univ…

We Just Found The Missing Matter In The Universe, And Still Need Dark Matter

“For over 40 years, scientists have argued over dark matter’s existence.

Big questions arose from the motions inside galaxies, clusters of galaxies, and along the cosmic web.

From their gravity, we can infer the total mass in the Universe.

Yet multiple sources indicate that only 15% of that mass can be baryonic: made of normal matter.”

Is dark matter truly necessary? Many argued that, until we found the entirety of the normal matter in the Universe, we couldn’t be sure. The motions of galaxies, clusters of galaxies, and the formation of large-scale structure and the cosmic web all indicate a certain amount of mass in the Universe, and many sources such as the CMB and big bang nucleosynthesis indicate that the “normal” matter can only be about 15% of the total, implying dark matter. But finding all the normal matter has proven elusive, with the theorized WHIM (warm-hot intergalactic medium) not showing up in sufficient abundance. In particular, the hot part just wasn’t there.

Until now. Observation made with XMM-Newton have at last revealed it, and it’s there in just the right, predicted amounts. And therefore, dark matter is still absolutely necessary.

How Does Our Earliest Picture Of The Universe …

How Does Our Earliest Picture Of The Universe Show Us Dark Matter?

“So all you need to do, to know whether your Universe has dark matter or not, is to measure these temperature fluctuations that appear in the CMB! The relative heights, locations, and numbers of the peaks that you see are caused by the relative abundances of dark matter, normal matter, and dark energy, as well as the expansion rate of the Universe. Quite importantly, if there is no dark matter, you only see half as many total peaks! When we compare the theoretical models with the observations, there’s an extremely compelling match to a Universe with dark matter, effectively ruling out a Universe without it.”

If your young Universe is full of matter and radiation, what happens? Gravitation works to pull matter into the overdense regions, but that means that the radiation pressure must rise in those regions, too, and that pushes back against the matter. On small scales, this pushback washes out the gravitational growth, but on large-enough scales, the finite speed that light can travel means that no wash-out can happen. Dark matter, however, doesn’t collide with radiation or normal matter, while normal matter collides with both radiation and itself. If we can calculate exactly how these three species interplay, we can calculate what types of patterns we expect to see in the Big Bang’s leftover glow, and then compare it with what we observe with satellites like WMAP and Planck. And what have we seen, exactly, when we’ve done that? 

We see that the Universe must contain dark matter to explain the observations. No alternative theory can match it.

Forget WIMPs, Axions And MACHOs: Could WIMPzil…

Forget WIMPs, Axions And MACHOs: Could WIMPzillas Solve The Dark Matter Problem?

“But what, exactly, is dark matter? And, moreover, can we be certain it exists? There are a huge suite of detectors and experiments out there searching for it, and yet no robust, verified, direct detection has ever been reported. There is no smoking gun we can point to and say, “this was an event caused by an interaction with dark matter.” The overwhelming majority of detectors out there are looking for WIMP-type dark matter, with a small contingent also looking for axions. (MACHOs, or other sources of “normal” dark matter, have been ruled out.) But all of this may be misguided. Dark matter might not be any of those things we’re looking for. In fact, it’s arguable that the candidate with the best motivations for it have no experiments to their name at all: WIMPzillas!”

Many detractors of dark matter point to the fact that we haven’t directly detected it yet as evidence that dark matter doesn’t exist. Yet practically every dark matter search that’s ever been performed has focused on just one particular class of dark matter: WIMPs. Well, WIMPs have been constrained very tightly, and we’re no closer to seeing WIMP dark matter than we were decades ago. But in that same time span, we’ve seen a number of exciting discoveries, including neutrino masses, come to fruition. Related to neutrino masses is the idea that there would be super-heavy right-handed neutrino counterparts to the light ones we see today. Could these “WIMPzillas” be the dark matter we’ve been looking for?

The theoretical motivation is compelling, and yet there are no detection experiments looking for one. Perhaps we need to fix that!