Dark Matter Archives

November 1, 2016November 1, 2016 by Fraser Cain

How Many Galaxies Are There in the Universe?

The wonderful thing about science is that it’s constantly searching for new evidence, revising estimates, throwing out theories, and sometimes discovering aspects of the Universe that we never realized existed.

The best science is skeptical of itself, always examining its own theories to find out where they could be wrong, and seriously considering new ideas to see if they better explain the observations and data.

What this means is that whenever I state some conclusion that science has reached, you can’t come back a few years later and throw that answer in my face. Science changes, it’s not my fault.

I get it, VY Canis Majoris isn’t the biggest star any more, it’s whatever the biggest star is right now. UY Scuti? That what it is today, but I’m sure it’ll be a totally different star when you watch this in a few years.

What I’m saying is, the science changes, numbers update, and we don’t need to get concerned when it happens. Change is a good thing. And so, it’s with no big surprise that I need to update the estimate for the number of galaxies in the observable Universe. Until a couple of weeks ago, the established count for galaxies was about 200 billion galaxies.

Jacinta studies distant galaxies like those shown in this image from the Hubble Space Telescope, using the new 'stacking' technique to gather information only available through radio telescope observations. Credit: NASA, STScI, and ESA. — Jacinta studies distant galaxies like those shown in this image from the Hubble Space Telescope, using the new ‘stacking’ technique to gather information only available through radio telescope observations. Credit: NASA, STScI, and ESA.

But a new paper published in the Astrophysics Journal revised the estimate for the number of galaxies, by a factor of 10, from 200 billion to 2 trillion. 200 billion, I could wrap my head around, I say billion all the time. But 2 trillion? That’s just an incomprehensible number.

Does that throw all the previous estimates for the number of stars up as well? Actually, it doesn’t.

The observable Universe measures 13.8 billion light-years in all directions. What this means is that at the very edge of what we can see, is the light left that region 13.8 billion years ago. Furthermore, the expansion of the Universe has carried to those regions 46 billion light-years away.

Does that make sense? The light you’re seeing is 13.8 billion light-years old, but now it’s 46 billion light-years away. What this means is that the expansion of space has stretched out the light from all the photons trying to reach us.

What might have been visible or ultraviolet radiation in the past, has shifted into infrared, and even microwaves at the very edge of the observable Universe.

Since astronomers know the volume of the observable Universe, and they can calculate the density of the Universe, they know the mass of the entire Universe. 3.4 x 10^54 kilograms including regular matter and dark matter. They also know the ratio of regular matter to dark matter, so they can calculate the total amount of regular mass in the Universe.

In the past, astronomers divided that total mass by the number of galaxies they could see in the original Hubble data and determined there were about 200 billion galaxies.

Now, astronomers used a new technique to estimate the galaxies and it’s pretty cool. Astronomers used the Hubble Space Telescope to peer into a seemingly empty part of the sky and identified all the galaxies in it. This is the Hubble Ultra Deep Field, and it’s one of the most amazing pictures Hubble has ever captured.

The Hubble Ultra Deep Field seen in ultraviolet, visible, and infrared light. Image Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)

Astronomers painstakingly converted this image of galaxies into a 3-dimensional map of galaxy size and locations. Then, they used their knowledge of galaxy structure closer to home to provide a more accurate estimate of what the galaxies must look like, out there, at the very edge of our observational ability.

For example, the Milky Way is surrounded by about 50 satellite dwarf galaxies, each of which has a fraction of the mass of the Milky Way.

By recognizing which were the larger main galaxies, they could calculate the distribution of smaller, dimmer dwarf galaxies that weren’t visible in the Hubble images.

In other words, if the distant Universe is similar to the nearby Universe, and this is one of the principles of modern astronomy, then the distant galaxies have the same structure as nearby galaxies.

It doesn’t mean that the Universe is bigger than we thought, or that there are more stars, it just means that the Universe contains more galaxies, which have less stars in them. There are the big main galaxies, and then a smooth distribution curve of smaller and smaller galaxies down to the tiny dwarf galaxies. The total number of stars comes out to be the same number.

The Fornax dwarf galaxy is one of our Milky Way’s neighbouring dwarf galaxies. The Milky Way is, like all large galaxies, thought to have formed from smaller galaxies in the early days of the Universe. These small galaxies should also contain many very old stars, just as the Milky Way does, and a team of astronomers has now shown that this is indeed the case. This image was composed from data from the Digitized Sky Survey 2. Credit: ESO — The Fornax dwarf galaxy is one of our Milky Way’s neighbouring dwarf galaxies. Credit: ESO

The galaxies we can see are just the tip of the galactic iceberg. For every galaxy we can see, there are another 9, smaller fainter galaxies that we can’t see.

Of course, we’re just a few years away from being able to see these dimmer galaxies. When NASA’s James Webb Space Telescope launches in October, 2018, it’s going to be carrying a telescope mirror with 25 square meters of collecting surface, compared to Hubble’s 4.5 square meters.

Furthermore, James Webb is an infrared telescope, a specialized tool for looking at cooler objects, and galaxies which are billions of light-years away. The kinds of galaxies that Hubble can only hint at, James Webb will be able to see directly.

So, why don’t we see galaxies in all directions with our eyeballs? This is actually an old conundrum, proposed by Wilhelm Olbers in the 1700, appropriately named Olber’s Paradox. We did a whole article on it, but the basic idea is that if you look in any direction, you’ll eventually hit a star. It could be close, like the Sun, or very far away, but whatever the case, it should be stars in all directions. Which means that the entire night sky should be as bright as the surface of a star. Clearly it isn’t, but why isn’t it?

In fact, with 10 times the number of galaxies, you could restate the paradox and say that in every direction, you should be looking at a galaxy, but that’s not what you see.

A partial map of the distribution of galaxies in the SDSS, going out to a distance of 7 billion light years. The amount of galaxy clustering that we observe today is a signature of how gravity acted over cosmic time, and allows as to test whether general relativity holds over these scales. (M. Blanton, SDSS)

Except you are. Everywhere you look, in all directions, you’re seeing galaxies. It’s just that those galaxies are red-shifted from the visible spectrum into the infrared spectrum, so your eyeballs can’t perceive them. But they’re there.

When you see the sky in microwaves, it does indeed glow in all directions. That’s the Cosmic Microwave Background Radiation, shining behind all those galaxies.

It turns out the Universe has 10 times more galaxies than previously estimated – 2 trillion galaxies. Not 10 times the stars or mass, those numbers have stayed the same.

And, once James Webb launches, those numbers will be fine-tuned again to be even more precise. 1.5 trillion? 3.4 trillion? Stay tuned for the better number.

August 30, 2016February 8, 2023 by Matt Williams

Dark Matter: Hot Or Not?

Illustris simulation, showing the distribution of dark matter in 350 million by 300,000 light years. Galaxies are shown as high-density white dots (left) and as normal, baryonic matter (right). Credit: Markus Haider/Illustris

For almost a century, astronomers and cosmologists have postulated that space is filled with an invisible mass known as “dark matter”. Accounting for 27% of the mass and energy in the observable universe, the existence of this matter was intended to explain all the “missing” baryonic matter in cosmological models. Unfortunately, the concept of dark matter has solved one cosmological problem, only to create another.

If this matter does exist, what is it made of? So far, theories have ranged from saying that it is made up of cold, warm or hot matter, with the most widely-accepted theory being the Lambda Cold Dark Matter (Lambda-CDM) model. However, a new study produced by a team of European astronomer suggests that the Warm Dark Matter (WDM) model may be able to explain the latest observations made of the early Universe.

Continue reading “Dark Matter: Hot Or Not?”

August 17, 2016September 26, 2016 by Matt Williams

Physicists Maybe, Just Maybe, Confirm the Possible Discovery of 5th Force of Nature

The discovery of a possible fifth fundamental force could change our understanding of the universe. Credit: ESA/Hubble/NASA/Judy Schmidt

For some time, physicists have understood that all known phenomena in the Universe are governed by four fundamental forces. These include weak nuclear force, strong nuclear force, electromagnetism and gravity. Whereas the first three forces of are all part of the Standard Model of particle physics, and can be explained through quantum mechanics, our understanding of gravity is dependent upon Einstein’s Theory of Relativity.

Understanding how these four forces fit together has been the aim of theoretical physics for decades, which in turn has led to the development of multiple theories that attempt to reconcile them (i.e. Super String Theory, Quantum Gravity, Grand Unified Theory, etc). However, their efforts may be complicated (or helped) thanks to new research that suggests there might just be a fifth force at work.

In a paper that was recently published in the journal Physical Review Letters, a research team from the University of California, Irvine explain how recent particle physics experiments may have yielded evidence of a new type of boson. This boson apparently does not behave as other bosons do, and may be an indication that there is yet another force of nature out there governing fundamental interactions.

As Jonathan Feng, a professor of physics & astronomy at UCI and one of the lead authors on the paper, said:

“If true, it’s revolutionary. For decades, we’ve known of four fundamental forces: gravitation, electromagnetism, and the strong and weak nuclear forces. If confirmed by further experiments, this discovery of a possible fifth force would completely change our understanding of the universe, with consequences for the unification of forces and dark matter.”

The efforts that led to this potential discovery began back in 2015, when the UCI team came across a study from a group of experimental nuclear physicists from the Hungarian Academy of Sciences Institute for Nuclear Research. At the time, these physicists were looking into a radioactive decay anomaly that hinted at the existence of a light particle that was 30 times heavier than an electron.

In a paper describing their research, lead researcher Attila Krasznahorka and his colleagues claimed that what they were observing might be the creation of “dark photons”. In short, they believed that they might have at last found evidence of Dark Matter, the mysterious, invisible mass that makes up about 85% of the Universe’s mass.

This report was largely overlooked at the time, but gained widespread attention earlier this year when Prof. Feng and his research team found it and began assessing its conclusions. But after studying the Hungarian teams results and comparing them to previous experiments, they concluded that the experimental evidence did not support the existence of dark photons.

This is the signature of one of 100s of trillions of particle collisions detected at the Large Hadron Collider. The combined analysis lead to the discovery of the Higgs Boson. This article describes one team in dissension with the results. (Photo Credit: CERN) — *Signature of one of 100s of trillions of particle collisions detected by CERN’s Large Hadron Collider. Credit: CERN*

Instead, they proposed that the discovery could indicate the possible presence of a fifth fundamental force of nature. These findings were published in arXiv in April, which was followed-up by a paper titled “Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays“, which was published in PRL this past Friday.

Essentially, the UCI team argue that instead of a dark photon, what the Hungarian research team might have witnessed was the creation of a previously undiscovered boson – which they have named the “protophobic X boson”. Whereas other bosons interact with electrons and protons, this hypothetical boson interacts with only electrons and neutrons, and only at an extremely limited range.

This limited interaction is believed to be the reason why the particle has remained unknown until now, and why the adjectives “photobic” and “X” are added to the name. “There’s no other boson that we’ve observed that has this same characteristic,” said Timothy Tait, a professor of physics & astronomy at UCI and the co-author of the paper. “Sometimes we also just call it the ‘X boson,’ where ‘X’ means unknown.”

If such a particle does exist, the possibilities for research breakthroughs could be endless. Feng hopes it could be joined with the three other forces governing particle interactions (electromagnetic, strong and weak nuclear forces) as a larger, more fundamental force. Feng also speculated that this possible discovery could point to the existence of a “dark sector” of our universe, which is governed by its own matter and forces.

The Large Hadron Collider at CERN. Credit: CERN/LHC — *The existence of a fifth fundamental force could mean big things for the experiments being conducted with the Large Hadron Collider at CERN. Credit: CERN/LHC*

“It’s possible that these two sectors talk to each other and interact with one another through somewhat veiled but fundamental interactions,” he said. “This dark sector force may manifest itself as this protophopic force we’re seeing as a result of the Hungarian experiment. In a broader sense, it fits in with our original research to understand the nature of dark matter.”

If this should prove to be the case, then physicists may be closer to figuring out the existence of dark matter (and maybe even dark energy), two of the greatest mysteries in modern astrophysics. What’s more, it could aid researchers in the search for physics beyond the Standard Model – something the researchers at CERN have been preoccupied with since the discovery of the Higgs Boson in 2012.

But as Feng notes, we need to confirm the existence of this particle through further experiments before we get all excited by its implications:

“The particle is not very heavy, and laboratories have had the energies required to make it since the ’50s and ’60s. But the reason it’s been hard to find is that its interactions are very feeble. That said, because the new particle is so light, there are many experimental groups working in small labs around the world that can follow up the initial claims, now that they know where to look.”

As the recent case involving CERN – where LHC teams were forced to announce that they had not discovered two new particles – demonstrates, it is important not to count our chickens before they are roosted. As always, cautious optimism is the best approach to potential new findings.

Further Reading: University of California, Irvine

June 3, 2016June 13, 2016 by Evan Gough

The Hubble Constant Just Got Constantier

A team of astronomers using the Hubble Space Telescope have found that the current rate of expansion of the Universe could be almost 10 percent faster than previously thought. Image: NASA, ESA, A. Feild (STScI), and A. Riess (STScI/JHU)

Just when we think we understand the Universe pretty well, along come some astronomers to upend everything. In this case, something essential to everything we know and see has been turned on its head: the expansion rate of the Universe itself, aka the Hubble Constant.

A team of astronomers using the Hubble telescope has determined that the rate of expansion is between five and nine percent faster than previously measured. The Hubble Constant is not some curiousity that can be shelved until the next advances in measurement. It is part and parcel of the very nature of everything in existence.

“This surprising finding may be an important clue to understanding those mysterious parts of the universe that make up 95 percent of everything and don’t emit light, such as dark energy, dark matter, and dark radiation,” said study leader and Nobel Laureate Adam Riess of the Space Telescope Science Institute and The Johns Hopkins University, both in Baltimore, Maryland.

But before we get into the consequences of this study, let’s back up a bit and look at how the Hubble Constant is measured.

Measuring the expansion rate of the Universe is a tricky business. Using the image at the top, it works like this:

Within the Milky Way, the Hubble telescope is used to measure the distance to Cepheid variables, a type of pulsating star. Parallax is used to do this, and parallax is a basic tool of geometry, which is also used in surveying. Astronomers know what the true brightness of Cepheids are, so comparing that to their apparent brightness from Earth gives an accurate measurement of the distance between the star and us. Their rate of pulsation also fine tunes the distance calculation. Cepheid variables are sometimes called “cosmic yardsticks” for this reason.
Then astronomers turn their sights on other nearby galaxies which contain not only Cepheid variables, but also Type 1a supernova, another well-understood type of star. These supernovae, which are of course exploding stars, are another reliable yardstick for astronomers. The distance to these galaxies is obtained by using the Cepheids to measure the true brightness of the supernovae.
Next, astronomers point the Hubble at galaxies that are even further away. These ones are so distant, that any Cepheids in those galaxies cannot be seen. But Type 1a supernovae are so bright that they can be seen, even at these enormous distances. Then, astronomers compare the true and apparent brightnesses of the supernovae to measure out to the distance where the expansion of the Universe can be seen. The light from the distant supernovae is “red-shifted”, or stretched, by the expansion of space. When the measured distance is compared with the red-shift of the light, it yields a measurement of the rate of the expansion of the Universe.
Take a deep breath and read all that again.

The great part of all of this is that we have an even more accurate measurement of the rate of expansion of the Universe. The uncertainty in the measurement is down to 2.4%. The challenging part is that this rate of expansion of the modern Universe doesn’t jive with the measurement from the early Universe.

The rate of expansion of the early Universe is obtained from the left over radiation from the Big Bang. When that cosmic afterglow is measured by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) and the ESA’s Planck satellite, it yields a smaller rate of expansion. So the two don’t line up. It’s like building a bridge, where construction starts at both ends and should line up by the time you get to the middle. (Caveat: I have no idea if bridges are built like that.)

This Hubble Telescope image shows one of the galaxies used in the study. It contains two types of stars used to measure distances between galaxies. The red circles are pulsing Cepheid variable stars, and the blue X is a Type 1a supernova. Image: NASA, ESA, and A. Riess (STScI/JHU)

“You start at two ends, and you expect to meet in the middle if all of your drawings are right and your measurements are right,” Riess said. “But now the ends are not quite meeting in the middle and we want to know why.”

“If we know the initial amounts of stuff in the universe, such as dark energy and dark matter, and we have the physics correct, then you can go from a measurement at the time shortly after the big bang and use that understanding to predict how fast the universe should be expanding today,” said Riess. “However, if this discrepancy holds up, it appears we may not have the right understanding, and it changes how big the Hubble constant should be today.”

Why it doesn’t all add up is the fun, and maybe maddening, part of this.

What we call Dark Energy is the force that drives the expansion of the Universe. Is Dark Energy growing stronger? Or how about Dark Matter, which comprises most of the mass in the Universe. We know we don’t know much about it. Maybe we know even less than that, and its nature is changing over time.

“We know so little about the dark parts of the universe, it’s important to measure how they push and pull on space over cosmic history,” said Lucas Macri of Texas A&M University in College Station, a key collaborator on the study.

The team is still working with the Hubble to reduce the uncertainty in measurements of the rate of expansion. Instruments like the James Webb Space Telescope and the European Extremely Large Telescope might help to refine the measurement even more, and help address this compelling issue.

April 18, 2016April 8, 2018 by Evan Gough

Dwarf Dark Matter Galaxy Hides In Einstein Ring

The large blue light is a lensing galaxy in the foreground, called SDP81, and the red arcs are the distorted image of a more distant galaxy. By analyzing small distortions in the red, distant galaxy, astronomers have determined that a dwarf dark galaxy, represented by the white dot in the lower left, is companion to SDP81. The image is a composite from ALMA and the Hubble. Image: Y. Hezaveh, Stanford Univ./ALMA (NRAO/ESO/NAOJ)/NASA/ESA Hubble Space Telescope — The large blue light is a lensing galaxy in the foreground, called SDP81, about 4 billion light years away. The red arcs are the distorted image of a more distant galaxy, about 12 billion light years away. By analyzing small distortions in the red, distant galaxy, astronomers have determined that a dwarf dark galaxy, represented by the white dot in the lower left, is bound to SDP81. The image is a composite from ALMA and the Hubble. Image: Y. Hezaveh, Stanford Univ./ALMA (NRAO/ESO/NAOJ)/NASA/ESA Hubble Space Telescope

Everybody knows that galaxies are enormous collections of stars. A single galaxy can contain hundreds of billions of them. But there is a type of galaxy that has no stars. That’s right: zero stars.

These galaxies are called Dark Galaxies, or Dark Matter Galaxies. And rather than consisting of stars, they consist mostly of Dark Matter. Theory predicts that there should be many of these Dwarf Dark Galaxies in the halo around ‘regular’ galaxies, but finding them has been difficult.

Now, in a new paper to be published in the Astrophysical Journal, Yashar Hezaveh at Stanford University in California, and his team of colleagues, announce the discovery of one such object. The team used enhanced capabilities of the Atacamas Large Millimeter Array to examine an Einstein ring, so named because Einstein’s Theory of General Relativity predicted the phenomenon long before one was observed.

An Einstein Ring is when the massive gravity of a close object distorts the light from a much more distant object. They operate much like the lens in a telescope, or even a pair of eye-glasses. The mass of the glass in the lens directs incoming light in such a way that distant objects are enlarged.

Einstein Rings and gravitational lensing allow astronomers to study extremely distant objects, by looking at them through a lens of gravity. But they also allow astronomers to learn more about the galaxy that is acting as the lens, which is what happened in this case.

If a glass lens had tiny water spots on it, those spots would add a tiny amount of distortion to the image. That’s what happened in this case, except rather than microscopic water drops on a lens, the distortions were caused by tiny Dwarf Galaxies consisting of Dark Matter. “We can find these invisible objects in the same way that you can see rain droplets on a window. You know they are there because they distort the image of the background objects,” explained Hezaveh. The difference is that water distorts light by refraction, whereas matter distorts light by gravity.

As the ALMA facility increased its resolution, astronomers studied different astronomical objects to test its capabilities. One of these objects was SDP81, the gravitational lens in the above image. As they examined the more distant galaxy being lensed by SDP81, they discovered smaller distortions in the ring of the distant galaxy. Hezaveh and his team conclude that these distortions signal the presence of a Dwarf Dark Galaxy.

But why does this all matter? Because there is a problem in the Universe, or at least in our understanding of it; a problem of missing mass.

Our understanding of the formation of the structure of the Universe is pretty solid, at least in the larger scale. Predictions based on this model agree with observations of the Cosmic Microwave Background (CMB) and galaxy clustering. But our understanding breaks down somewhat when it comes to the smaller scale structure of the Universe.

One example of our lack of understanding in this area is what’s known as the Missing Satellite Problem. Theory predicts that there should be a large population of what are called sub-halo objects in the halo of dark matter surrounding galaxies. These objects can range from things as large as the Magellanic Clouds down to much smaller objects. In observations of the Local Group, there is a pronounced deficit of these objects, to the tune of a factor of 10, when compared to theoretical predictions.

Because we haven’t found them, one of two things needs to happen: either we get better at finding them, or we modify our theory. But it seems a little too soon to modify our theories of the structure of the Universe because we haven’t found something that, by its very nature, is hard to find. That’s why this announcement is so important.

The observation and identification of one of these Dwarf Dark Galaxies should open the door to more. Once more are found, we can start to build a model of their population and distribution. So if in the future more of these Dwarf Dark Galaxies are found, it will gradually confirm our over-arching understanding of the formation and structure of the Universe. And it’ll mean we’re on the right track when it comes to understanding Dark Matter’s role in the Universe. If we can’t find them, and the one bound to the halo of SDP81 turns out to be an anomaly, then it’s back to the drawing board, theoretically.

It took a lot of horsepower to detect the Dwarf Dark Galaxy bound to SDP81. Einstein Rings like SDP81 have to have enormous mass in order to exert a gravitational lensing effect, while Dwarf Dark Galaxies are tiny in comparison. It’s a classic ‘needle in a haystack’ problem, and Hezaveh and his team needed massive computing power to analyze the data from ALMA.

ALMA will consist of 66 individual antennae like these when it is complete. The facility is located in the Atacama Desert in Chile, at 5,000 meters above sea level. Credit: ALMA (ESO / NAOJ / NRAO)

ALMA, and the methodology developed by Hezaveh and team will hopefully shed more light on Dwarf Dark Galaxies in the future. The team thinks that ALMA has great potential to discover more of these halo objects, which should in turn improve our understanding of the structure of the Universe. As they say in the conclusion of their paper, “… ALMA observations have the potential to significantly advance our understanding of the abundance of dark matter substructure.”

April 15, 2016April 15, 2016 by Evan Gough

A Super-Fast Star System Shrugs Its Shoulders At Physics

This annotated artist's conception illustrates our current understanding of the structure of the Milky Way galaxy. Image Credit: NASA

Astronomers have found a pair of stellar oddballs out in the edges of our galaxy. The stars in question are a binary pair, and the two companions are moving much faster than anything should be in that part of the galaxy. The discovery was reported in a paper on April 11, 2016, in the Astrophysical Journal Letters.

The binary system is called PB3877, and at 18,000 light years away from us, it’s not exactly in our neighborhood. It’s out past the Scutum-Centaurus Arm, past the Perseus Arm, and even the Outer Arm, in an area called the galactic halo. This binary star also has the high metallicity of younger stars, rather than the low metallicity of the older stars that populate the outer reaches. So PB3877 is a puzzle, that’s for sure.

PB3877 is what’s called a Hyper-Velocity Star (HVS), or rogue star, and though astronomers have found other HVS’s, more than 20 of them in fact, this is the first binary one found. The pair consists of a hot sub-dwarf primary star that’s over five times hotter than the Sun, and a cooler companion star that’s about 1,000 degrees cooler than the Sun.

Hyper-Velocity stars are fast, and can reach speeds of up to 1,198 km. per second, (2.7 million miles per hour,) maybe faster. At that speed, they could cross the distance from the Earth to the Moon in about 5 minutes. But what’s puzzling about this binary star is not just its speed, and its binary nature, but its location.

Hyper-Velocity stars themselves are rare, but PB3877 is even more rare for its location. Typically, hyper velocity stars need to be near enough to the massive black hole at the center of a galaxy to reach their incredible speeds. A star can be drawn toward the black hole, accelerated by the unrelenting pull of the hole, then sling-shotted on its way out of the galaxy. This is the same action that spacecraft can use when they gain a gravity assist by travelling close to a planet.

This video shows how stars can accelerate when their orbit takes them close to the super-massive black holes at the center of the Milky Way.

But the trajectory of PB3877 shows astronomers that it could not have originated near the center of the galaxy. And if it had been ejected by a close encounter with the black hole, how could it have survived with its binary nature intact? Surely the massive pull of the black hole would have destroyed the binary relationship between the two stars in PB3877. Something else has accelerated it to such a high speed, and astronomers want to know what, exactly, did that, and how it kept its binary nature.

Barring a close encounter with the super-massive black hole at the center of the Milky Way, there are a couple other ways that PB3877 could have been accelerated to such a high velocity.

One such way is a stellar interaction or collision. If two stars were travelling at the right vectors, a collision between them could impart energy to one of them and propel it to hyper-velocity. Think of two pool balls on a pool table.

Another possibility is a supernova explosion. It’s possible for one of the stars in a binary pair to go supernova, and eject it’s companion at hyper-velocity speeds. But in these cases, either stellar collision or supernova, things would have to work out just right. And neither possibility explains how a wide-binary system like this could stay intact.

Fraser Cain sheds more light on Hyper-Velocity Stars, or Rogue Stars, in this video.

There is another possibility, and it involves Dark Matter. Dark Matter seems to lurk on the edge of any discussion around something unexplained, and this is a case in point. The researchers think that there could be a massive cocoon or halo of Dark Matter around the binary pair, which is keeping their binary relationship intact.

As for where the binary star PB3788 came from, as they say in the conclusion of their paper, “We conclude that the binary either formed in the halo or was accreted from the tidal debris of a dwarf galaxy by the Milky Way.” And though the source of this star’s formation is an intriguing question, and researchers plan follow up study to verify the supernova ejection possibility, its possible relationship with Dark Matter is also intriguing.

March 21, 2016April 12, 2016 by Matt Williams

Beyond WIMPs: Exploring Alternative Theories Of Dark Matter

The standard model of cosmology tells us that only 4.9% of the Universe is composed of ordinary matter (i.e. that which we can see), while the remainder consists of 26.8% dark matter and 68.3% dark energy. As the names would suggest, we cannot see them, so their existence has had to be inferred based on theoretical models, observations of the large-scale structure of the Universe, and its apparent gravitational effects on visible matter.

Since it was first proposed, there have been no shortages of suggestions as to what Dark Matter particles look like. Not long ago, many scientists proposed that Dark Matter consists of Weakly-Interacting Massive Particles (WIMPs), which are about 100 times the mass of a proton but interact like neutrinos. However, all attempts to find WIMPs using colliders experiments have come up empty. As such, scientists have been exploring the idea lately that dark matter may be composed of something else entirely. Continue reading “Beyond WIMPs: Exploring Alternative Theories Of Dark Matter”

March 14, 2016March 18, 2016 by Evan Gough

The Milky Way Galaxy’s Dark Halo Of Star Formation

Dark matter is invisible. Based on the effect of gravitational lensing, a ring of dark matter has been inferred in this image of a galaxy cluster (CL0024+17) and has been represented in blue. Image: NASA/ESA.

Dark Matter is rightly called one of the greatest mysteries in the Universe. In fact, so mysterious is it, that we here in the opulent sky-scraper offices of Universe Today often joke that it should be called “Dark Mystery.” But that sounds like a cheesy History Channel show, and here at Universe Today we don’t like cheesy, so Dark Matter it remains.

Though we still don’t know what exactly Dark Matter is, we keep learning more about how it interacts with the rest of the Universe, and nibbling around at the edges of what it might be. But before we get into the latest news about Dark Matter, it’s worth stepping back a bit to remind ourselves of what is known about Dark Matter.

Evidence from cosmology shows that about 25% of the mass of the Universe is Dark Matter, also known as non-baryonic matter. Baryonic matter is ‘normal’ matter, which we are all familiar with. It’s made up of protons and neutrons, and it’s the matter that we interact with every day.

Cosmologists can’t see the 25% of matter that is Dark Matter, because it doesn’t interact with light. But they can see the effect it has on the large scale structure of the Universe, on the cosmic microwave background, and in the phenomenon of gravitational lensing. So they know it’s there.

Large galaxies like our own Milky Way are surrounded by what is called a halo of Dark Matter. These huge haloes are in turn surrounded by smaller sub-haloes of Dark Matter. These sub-haloes have enough gravitational force to form dwarf galaxies, like the Milky Way’s own Sagittarius and Canis Major dwarf galaxies. Then, these dwarf galaxies themselves have their own Dark Matter haloes, which at this scale are now much too small to contain gas or stars. Called dark satellites, these smaller haloes are of course invisible to telescopes, but theory states they should be there.

But proving that these dark satellites are even there requires some evidence of the effect they have on their host galaxies.

Now, thanks to Laura Sales, who is an assistant professor at the University of California, Riverside’s, Department of Physics and Astronomy, and her collaborators at the Kapteyn Astronomical Institute in the Netherlands, Tjitske Starkenberg and Amina Helmi, there is more evidence that these dark satellites are indeed there.

In their paper “Dark influences II: gas and star formation in minor mergers of dwarf galaxies with dark satellites,” from November 2015, they provide an analysis of theory-based computer simulations of the interaction between a dwarf galaxy and a dark satellite.

Their paper shows that when a dark satellite is at its closest point to a dwarf galaxy, the satellite’s gravitational influence compresses the gas in the dwarf. This causes a sustained period of star formation, called a starburst, that can last for billions of years.

NGC 5253 is one of the nearest of the known Blue Compact Dwarf (BCD) galaxies, and is located at a distance of about 12 million light-years from Earth in the southern constellation of Centaurus. It is experiencing a starburst of hot, young stars, which could be caused by dark satellites. Image: NASA/ESA/Hubble.

Their modelling suggests that dwarf galaxies should be exhibiting a higher rate of star formation than would otherwise be expected. And observation of dwarf galaxies reveals that that is indeed the case. Their modelling also suggests that when a dark satellite and a dwarf galaxy interact, the shape of the dwarf galaxy should change. And again, this is born out by the observation of isolated spheroidal dwarf galaxies, whose origin has so far been a mystery.

The exact nature of Dark Matter is still a mystery, and will probably remain a mystery for quite some time. But studies like this keep shining more light on Dark Matter, and I encourage readers who want more detail to read it.

February 29, 2016August 21, 2016 by Matt Williams

Are Supermassive Black Holes Hiding Matter?

Mapping the Universe with satellites and ground-based observatories have not only provided scientists with a pretty good understanding of its structure, but also of its composition. And for some time now, they have been working with a model that states that the Universe consists of 4.9% “normal” matter (i.e. that which we can see), 26.8% “dark matter” (that which we can’t), and 68.3% “dark energy”.

From what they have observed, scientists have also concluded that the normal matter in the Universe is concentrated in web-like filaments, which make up about 20% of the Universe by volume. But a recent study performed by the Institute of Astro- and Particle Physics at the University of Innsbruck in Austria has found that a surprising amount of normal matter may live in the voids, and that black holes may have deposited it there.

In a paper submitted to the Royal Astronomical Society, Dr. Haider and his team described how they performed measurements of the mass and volume of the Universe’s filamentary structures to get a better idea of where the Universe’s mass is located. To do this, they used data from the Illustris project – a large computer simulation of the evolution and formation of galaxies.

As an ongoing research project run by an international collaboration of scientists (and using supercomputers from around the world), Illustris has created the most detailed simulations of our Universe to date. Beginning with conditions roughly 300,000 years after the Big Bang, these simulations track how gravity and the flow of matter changed the structure of the cosmos up to the present day, roughly 13.8 billion years later.

The process begins with the supercomputers simulating a cube of space in the universe, which measures some 350 million light years on each side. Both normal and dark matter are dealt with, particularly the gravitational effect that dark matter has on normal matter. Using this data, Haider and his team noticed something very interesting about the distribution of matter in the cosmos.

Essentially, they found that about 50% of the total mass of the Universe is compressed into a volume of 0.2%, consisting of the galaxies we see. A further 44% is located in the enveloping filaments, consisting of gas particles and dust. The remaining 6% is located in the empty spaces that fall between them (aka. the voids), which make up 80% of the Universe.

However, a surprising faction of this normal matter (20%) appears to have been transported there, apparently by the supermassive black holes located at the center of galaxies. The method for this delivery appears to be in how black holes convert some of the matter that regularly falls towards them into energy, which is then delivered to the sounding gas, leading to large outflows of matter.

This artist's concept illustrates a supermassive black hole with millions to billions times the mass of our sun. Supermassive black holes are enormously dense objects buried at the hearts of galaxies. Image credit: NASA/JPL-Caltech — *Artist’s impression of a supermassive black holes at the hearts of a galaxy. Credit: NASA/JPL-Caltech*

These outflows stretch for hundreds of thousands of lights years beyond the host galaxy, filling the void with invisible mass. As Dr. Haider explains, these conclusions supported by this data are rather startling. “This simulation,” he said, “one of the most sophisticated ever run, suggests that the black holes at the center of every galaxy are helping to send matter into the loneliest places in the universe. What we want to do now is refine our model, and confirm these initial findings.”

The findings are also significant because they just may offer an explanation to the so-called “missing baryon problem”. In short, this problem describes how there is an apparent discrepancy between our current cosmological models and the amount of normal matter we can see in the Universe. Even when dark matter and dark energy are factored in, half of the remaining 4.9% of the Universe’s normal matter still remains unaccounted for.

For decades, scientists have been working to find this “missing matter”, and several suggestions have been made as to where it might be hiding. For instance, in 2011, a team of students at the Monash School of Physics in Australia confirming that some of it was in the form of low-density, high energy matter that could only be observed in the x-ray wavelength.

In 2012, using data from the Chandra X-ray Observatory, a NASA research team reported that our galaxy, and the nearby Large and Small Magellanic Clouds, were surrounded by an enormous halo of hot gas that was invisible at normal wavelengths. These findings indicated that all galaxies may be surrounded by mass that, while not visible to the naked eye, is nevertheless detectable using current methods.

And just days ago, researchers from the Commonwealth Scientific and Industrial Research Organization (CSIRO) described how they had used fast radio bursts (FRBs) to measure the density of cosmic baryons in the intergalactic medium – which yielded results that seem to indicate that our current cosmological models are correct.

Factor in all the mass that is apparently being delivered to the void by supermassive black holes, and it could be that we finally have a complete inventory of all the normal matter of the Universe. This is certainly an exciting prospect, as it means that one of the greatest cosmological mysteries of our time could finally be solved.

Now if we could just account for the “abnormal” matter in the Universe, and all that dark energy, we’d be in business!

Further Reading: Royal Astronomical Society

December 17, 2015February 8, 2023 by Matt Williams

Big Bang Theory: Evolution of Our Universe

How was our Universe created? How did it come to be the seemingly infinite place we know of today? And what will become of it, ages from now? These are the questions that have been puzzling philosophers and scholars since the beginning the time, and led to some pretty wild and interesting theories. Today, the consensus among scientists, astronomers and cosmologists is that the Universe as we know it was created in a massive explosion that not only created the majority of matter, but the physical laws that govern our ever-expanding cosmos. This is known as The Big Bang Theory.

For almost a century, the term has been bandied about by scholars and non-scholars alike. This should come as no surprise, seeing as how it is the most accepted theory of our origins. But what exactly does it mean? How was our Universe conceived in a massive explosion, what proof is there of this, and what does the theory say about the long-term projections for our Universe?

The basics of the Big Bang theory are fairly simple. In short, the Big Bang hypothesis states that all of the current and past matter in the Universe came into existence at the same time, roughly 13.8 billion years ago. At this time, all matter was compacted into a very small ball with infinite density and intense heat called a Singularity. Suddenly, the Singularity began expanding, and the universe as we know it began.