On March 11, 2014, Dr. Marshall McCall published a paper, ‘A Council of Giants’, and released a video that put the findings of his research into perspective. As a student of astrophysics at York University, I was fortunate enough to have taken an astronomy course lectured by Dr. McCall. That very afternoon, Professor McCall presented us with his video, ‘Council of Giants’! I then took the opportunity to speak with him about his findings to get a better understanding of what they meant from Dr. McCall himself.
Dr. McCall attended The University of Texas in Austin for his graduate studies, where he was a grad student with Neil deGrasse Tyson, and went on to earn his PhD in astrophysics. He is currently the chair of Physics and Astronomy, and a professor at York University in Toronto, Canada. Dr. McCall specializes in the evolution of galaxies and galaxy aggregates. Also, he is a phenomenal professor and astrophysicist! Dr. McCall will be featured on tonight’s episode (April 14, 2014) of York Universe Radio to further discuss his findings in ‘A Council of Giants’ (information on how to tune in is provided below).
Galaxies exist in sheets, filaments, and voids, forming a cosmic web in the universe. A 3-dimensional view reveals formations resembling a sponge-like structure on the largest of scales. The Council of Giants consists of a local sheet of galaxies that encompasses our Local Group. Our Local Group of galaxies is 10 million light years in extent and is dominated by the Milky Way and Andromeda galaxies. The Milky Way and Andromeda cover an extent of about 3 million light years.
In this survey, galaxies were mapped out to within 20 million light years of the Milky Way. Dr. McCall included large galaxies only, placing the cutoff point at the brightness of the Large Magellanic Cloud (hence the galaxies being referred to as “Giants”). Thus, galaxies with a brightness of the LMC or less have been omitted from this survey. The reason Dr. McCall did this is because small galaxies like dwarf galaxies can be missed due to their low brightness. Also, the close proximity (on a cosmic scale) of the galaxies included in this survey eliminated the need to use redshift surveys which can introduce errors due to peculiar motion. (Peculiar motion is caused by gravitational forces between galaxies, groups, clusters, and superclusters that interfere with the redshift surveys of galaxies.)
This “Local Sheet of galaxies” includes 14 large galaxies, or “giants” (including the Milky Way and Andromeda), stretches out to about 40 million light-years in extent, and is remarkably thin at only 1.5 million light years thick. Looking down on the sheet, the largest galaxies “are arranged in a circle around us”, like a “Council”. Of the 14 galaxies, 12 are spirals, including the Milky Way and Andromeda. The remaining two are elliptical galaxies that interestingly lie on opposite ends of the Council. This indicates that during their earliest phases of development, these two elliptical galaxies may have assisted in forming the disk structures of the Milky Way and Andromeda by casting out winds that directed gas towards the Local Group. They also may have played a role in placing the Milky Way and Andromeda in orbit about each other.
Dr. McCall found that a balance point in the gravitational forces exists at distance of about 2.6 Mpc in radius from the Milky Way and Andromeda (or about 8.5 million light years, as 1 parsec = 3.26 light years). Here, the “gravitational tug of war” experienced by the galaxies in the Local Sheet balances out. What this suggests is that the stuff that the Milky Way is made of had to come from within that boundary and not from beyond, as material coming from beyond would have been absorbed by the surrounding galaxies.
According to Dr. McCall, a density enhancement of only 4% was required to produce the Local Group. What this means is that if you calculate the mass within this boundary, the result is an amount equal to within 4% of the masses of the Milky Way and Andromeda. Further, in order to have such a precise arrangement as that found in this Local Sheet, “nearby galaxies must have developed within a pre-existing sheet-like foundation comprised primarily of dark matter”, as stated in the press release.
The boundary formed by the Council of Giants has provided indications to the conditions under which the Milky Way may have formed. The two elliptical galaxies residing on opposite ends of the Council may have assisted in forming the disk structures of the Milky Way and Andromeda. This organization found by Dr. McCall in our “cosmic backyard”, which is but a tiny fraction of our universe, reflects on the organization of galaxies on the largest scales. Galaxies seem to come in sheets across the entire universe, coming together and forming web-like structures on the largest scales. Dr. McCall’s findings not only shed light on the formation of our galaxy, but also reflect galactic structure on largest scales in the universe. An astounding discovery, to find that we, the Milky Way and Andromeda, are surrounded by a circle of large galaxies, by a Council of Giants.
A special thank you to Dr. McCall for taking the time to discuss his findings in ‘A Council of Giants’ with me, and for being such an outstanding professor.
To listen to Dr. McCall on York Universe Radio tonight, tune in at 9 PM EDT
Watch the video: “Council of Giants”
Read the full paper: “A Council of Giants”
Andromeda is headed our way at about seventy five miles per second.
In about three or four billion years the Andromeda and Milky Way galaxies will collide. The result, if anybody is around to see it, will be beautiful. The two galaxies will pass through each other first. There is so much empty space, and the distance between stars so great, that it’s extremely unlikely that any stars will actually collide. But dust and gas clouds will, and that means that the rate of star creation will be greatly boosted.
Additionally, supernovae (which currently happen within either galaxy every 50 years or so) will likely start happening about once a year with some of them being close enough to outshine all the rest of the stars as seen from Earth.
Having passed through on a grazing course, Andromeda will retreat for a while, and then come back for a head-on collision. This time, the super-massive black holes at the centers of the galaxies will pass close enough together to pull each other in and merge. Gravitational waves will fling many stars out of the galaxies into intergalactic space, and will pull many others closer to the core. There’s a good chance that our sun (which will be a bit bigger, but still exist) along with its planets (Earth will still be there, but it will be parched and lifeless) will get pulled towards the center of the combined galaxies and then flung outward. (There’s a smaller chance that the flinging could send us right into one of the black holes.)
Our night sky right now is beautiful. But compared to what will be visible during these goings-on, it’s downright dull. The sky will be filled with so many stars that the night will no longer be dark. Gas clouds will glow brightly and in many colors. If we get close enough to the center, we’ll even be able to see massive gas jets shooting from the black holes in the core.
Shortly thereafter, the sun will finally expand to engulf the Earth bringing our planet to its final demise. But what an exit!!
(That article is about eight years old, but still accurate. The most substantive change to our knowledge since then is the confirmation in 2012 via Hubble data that the collision is, in fact, inevitable.)
Baby teeth appear around the ages of six months and three years and begin to be replaced at about six years of age.
Humans are born with the beginnings of permanent teeth under the gums below the baby teeth. Baby teeth guide the growth and development of the jawbones and of the permanent teeth. Losing baby teeth too early can result in jaw not developing correctly, and the permanent teeth coming in crooked or being overcrowded.
Different teeth handle food in different ways. Incisors (front teeth) are chisel-shaped, their sharp edges bite off relatively large pieces of food. The cuspids (canine teeth) are cone-shaped, and are used for grasping and tearing food. The bicuspids and molars have flattened surfaces and are used for grinding food.
photo credit: Stefan Schäfer
When it comes to protecting the Earth from potentially catastrophic asteroid collisions, NASA has finally offered a plan that doesn’t rely on getting additional budget: Prayer.
It may sound surprising to hear that kind of advice from an organization that many think of as a bastion of secular science, but it is actually a better plan than the next best which is to do nothing at all. With the tiny portion of our country’s budget that goes to NASA (half a penny from a tax dollar), it just isn’t realistic to do anything else. They keep looking and (depressingly) keep finding more and more rocks out there in this shooting gallery called home, but if they find one headed our way with enough mass and/or speed to kill us all, then there’s not a whole lot that they can do about it unless they catch it quite a lot earlier than they are likely to.
The only realistic solution is to fund NASA more robustly, and as much as we here at Science That (including most of our wonderful readers) support that idea, our lawmakers and many of their constituents don’t. So, if you don’t mind remaining helpless while the heavens throw rocks at you and try really hard to kill you, then feel free to just sit back and click the next link to some other thing on the internet and enjoy a day of surfing. On the other hand, if you’re the least bit irked that public safety takes such a backseat to so many other things, then write to your congresspeople and tell them that you’d like for them to please save the world. This is not a partisan issue – if an asteroid claims lives, it will not care who sits where. It will be an equal opportunity catastrophe.
One of my favorite sayings, which I heard from a very religious and very Irish aunt, was, “Pray for rain, but plant potatoes.” Whether prayer works or not, the time is here to plant potatoes by telling our leaders to stop waiting until it’s too late.
You know when you get that feeling in your knuckles, back, or neck and you just have to crack it? The action is often accompanied by a relatively loud popping sound that is sometimes met with awkward looks from passersby. Or, if you’re like me, it’s met with a scolding from your mother and a warning that you’ll cause damage to your bones by grinding them together.
It seems intuitive but what’s actually going on when you pop a joint? And is it dangerous? The short answer is we don’t know and… we don’t know. But we have some ideas.
The prevailing hypothesis involves something called synovial fluid and dissolved gases.
Synovial fluid exists within the joint capsule between two bones and acts as a lubricant. The fluid has within it dissolved gases, when you push a joint toward its limit the joint capsule is stretched and the dissolved gases are rapidly released from the synovial fluid causing a popping sound.
The joint can’t be popped again until the gasses are dissolved back into the synovial fluid, hence the delay in being able to pop a particular joint again.
While this is the leading explanation for most joint ‘cracking’ noises, popping noises can be generated via other means, if there is no delay in the ability to pop a joint it likely isn’t caused by the release of gas in the synovial fluid.
This leads us to our final question. Was Mom right about it being dangerous or harmful? The jury is still out on this one, results vary and are conflicting, some studies show no indication of harm or risk while others indicate that repetitive cracking may cause damage to surrounding tissues.
You’re probably in no real risk of severe damage. Know your body’s limits and when in doubt, consult a licensed physician.
P.S. I popped my knuckles about a dozen times while writing this. Am I alone? Did you crack your knuckles or neck while reading. Type up your thoughts with your newly limbered digits.
Everyone knows about the dazzling ring system of Saturn. The majestic gas giant’s elaborate system of rings makes Saturn a much loved target for observation through a telescope. What most people may not know is that Saturn has an even bigger, but very tenuous, ring—one that begins 6 million kilometers beyond the planet and extends outward another 12 million kilometers! Doing the math, we find that the diameter of this newly found ring is about 36 million kilometers. At a diameter of 116,464 kilometers, it would take 309 Saturns stacked across to fill the diameter of this ring. The ring is very thick as well—it would take about 20 Saturn diameters to match its thickness. If you could see it, the ring would span two full moons across the sky. The new ring is tilted at about 27° to the plane of the main ring system.
Another point of interest is that this ring orbits Saturn in a direction opposite that of the other rings and most of Saturn’s moons. This may explain why Saturn’s moon Iapetus has one dark side, as it is constantly slammed with dusty material from the ring. Orbiting in the direction of Saturn’s moon Phoebe and along the moon’s path, the origin of the gigantic ring may be from the moon itself due to collisions with other smaller bodies. Having a battered appearance, it is clear that Phoebe has lost a lot of its material. This material, along with debris from collisions with other objects, is likely what formed Saturn’s largest ring—the Phoebe ring.
The first time Saturn’s rings were discovered was in 1610 when Galileo Galilei pointed his telescope at the gas giant. Only back then, no one could conceive what planetary rings were, and he incorrectly guessed they were Saturn’s moons. In 1659, Christian Huygens solved the mystery—this was a ring system. Voyagers 1 and 2 provided a closer look at the rings in the 1980’s. The Cassini-Huygens spacecraft, launched in 1997 and arriving at the Saturn system in 2004, revealed the most detailed information about the system ever. But it was the Spitzer Space Telescope who discovered the new giant ring in 2009 with observations in the infrared.
Saturn’s main ring system is about one kilometer thick and 282,000 kilometers wide. The rings are relatively close together, except for the Cassini Division which spans about 4700 kilometers. Starting from the inner ring and working outwards, the main rings are known as C, B, and A, with the Cassini Division separating B and A. Within the A ring, there is yet another gap that is 325 kilometers wide—the Encke Gap. Less visible rings are the D ring (closest to the planet), and the F ring (beyond the A ring). Beyond the F ring are two even fainter rings called the G and E rings. The Roche Division, a 2600-kilometer-wide gap, separates rings A and F. There are several more gaps within the rings that are smaller, making this ring system very well defined and stunning to look at. Then, there is the Phoebe ring, visible in the infrared, inclined at 27° to the main ring system and circling in the opposite direction, far wider than the main ring system and lying far beyond it. While all the gas giants have rings, Saturn truly holds the most wondrous system of rings in the solar system.
Saturn’s Phoebe ring:
History of Saturn: http://huygensgcms.gsfc.nasa.gov/Shistory.htm
Saturn’s ring system:
Until recently, neurological studies involved implanting electrodes into specific regions of the brain. The activity of the neurons in contact with the electrodes was recorded, and correlated to the subject’s activity. Electrical stimulation can be used to fire neurons, but it covers a large area and can’t isolate specific neurons.
An ideal option is to have the ability to turn individual neurons on and off. To accomplish this, researchers turned to ion channels, which are specialized proteins, and depending on the type, either allow or block the movement of ions across a cell membrane (an example of an ion channel is rhodopsin, a light sensitive protein in the retina).
But how does one modify a neuron to include an ion channel? This requires engineering lentiviruses to carry the ion channel. The lentiviruses are inserted into specific neural regions, and the infection modifies the areas to include the ion channels.
Once the neurons include ion channels optical fibers are inserted into the modified neural regions. Specific light wave lengths are then can be used to turn the neurons on and off.
Although optogenetics is still in early stages, its potential has many exciting possibilities. Some applications include turning off compulsive behavior, restoring sight, curing Parkinson disease and epilepsy.
We have all heard the famous quotes “We are made of star stuff” from astronomer Carl Sagan and “We are not figuratively, but literally stardust” from astrophysicist Neil deGrasse Tyson. Now, let’s get into exactly what they mean, and how it is that we have come to be made from the stuff of stars.
Let’s begin with the two most common elements in the Universe: hydrogen, followed by helium. 13.8 billion years ago, the Big Bang gave rise to our Universe. The Big Bang created all the matter in the Universe after undergoing a series of events. The hydrogen nucleus is just a proton, so it was the first of the nuclei created, and the most abundant. Through nuclear reactions, hydrogen then formed helium nuclei. Very rarely, fusions led to the formation of lithium, and even less so, beryllium. This is pretty much all that was formed in the early Universe, because anything heavier requires more heat, and the Universe cooled quickly as it expanded with time. A point of interest is that all the hydrogen in the Universe today was formed when it was young—it is a relic of the Big Bang. Today, hydrogen and helium dominate the elements in the Universe at 98% by mass (about 73% hydrogen and 25% helium). The remaining 2% constitute the other elements.
The hydrogen produced in the early Universe then went into forming stars, stars that would fuse this hydrogen into heavier elements. Stars are like big nuclear fusion houses in which lighter elements are constantly being fused into heavier ones. A star begins by fusing hydrogen into helium. The lowest mass stars in the Universe run out to fuel once all their hydrogen has been fused into helium, leaving them with an inert helium white dwarf core. Medium sized stars like our Sun will fuse the helium into heavier elements like carbon and oxygen. Once all the helium is depleted, they are left with an inert carbon core and shed their layers in a planetary nebula, with a white dwarf remaining at the center.
Stars heavier than five solar masses are ones of particular interest—these are the stars that facilitate the formation of the heaviest atoms. Such stars will continue fusing carbon into even heavier elements. If a star is massive enough, it will go on fusing elements into nickel, which decays into iron, and become a red supergiant. Because it takes energy to fuse iron into heavier elements, iron is the end of the line for the star. At this point, the star will explode in a violent supernova that leaves behind either a neutron star or a black hole, depending on its mass. This explosion produces temperatures so high that it ignites nucleosynthesis again, producing elements as heavy as gold, platinum and silver, to name a few. Spewing elements the star once contained, and ones newly formed, the supernova essentially spreads out the necessary ingredients for life.
Elements spewed from supernovae enrich molecular clouds that condense under gravity, eventually forming stars, and possibly planets that orbit those stars. Such star systems will have all the ingredients required for life, thanks to stars fusing elements in their cores, and supernovae further fusing these elements into even heavier ones. On Earth, a few billion years combined with favorable conditions, the right distance from the Sun, and the required ingredients for life, resulted in a planet beaming with life. We can take “stardust” to be all atoms aside from hydrogen (which we know was exclusively formed during the Big Bang). Our bodies are composed of 60% water. Water is only about 11% hydrogen by mass. When looking at the rest of the stuff we are made of (which includes “stardust” and some hydrogen), we find that the human body is 93% stardust by mass—the remaining 7% is hydrogen, a relic of the big bang. In this way, we are all quite literally stardust, or star stuff (with a bit of Big Bang stuff).
Taking into account that this process is undergone everywhere in a universe as vast as the one in which we live, does it not follow that our universe may be beaming with life? The very stuff we are made of is spewed all over the universe, and becomes part of other molecular clouds that form star systems, systems that will be enriched will all the necessary ingredients for life… Life elsewhere seems almost inevitable, doesn’t it? I certainly think so.
When air moves against a boat’s sail, the momentum of the molecules in the air is imparted to the sail, causing the boat to move. Those molecules in the air have mass, and you multiply that mass by their velocity to determine how much momentum they possess.
That’s a simple example of classical Newtonian physics.
But we know that photons have no mass. If mass equals zero, then regardless of their velocity that multiplication works out to zero momentum. So how can a solar sail work?
If Isaac Newton’s classical model was entirely correct, then solar sails wouldn’t work. It’s Einstein’s relativity theories that fix it. As something accelerates (linearly for simplicity), it gains kinetic energy and its linear momentum increases. An actual particle of matter would have infinite mass and momentum if it got to light speed, which is why nothing with a rest mass can be accelerated to that speed.
Photons have no rest mass, though, and so don’t suffer from that problem.
The theory of relativity that people are most familiar with is E=mc², where E stands for Energy, m stands for mass, and c stands for the speed of light in a vacuum.
But that’s a simplified version that doesn’t take momentum into consideration.
The more correct (and slightly less able to fit on a postage stamp) formula is E²-p²c²=m²c⁴ where p is momentum.
With photons, m=0 since they have no mass. Since m=0, the equation reduces to E²-p²c²=0.
Solving for p, we get p=E/c.
Therefore, the momentum of a particle is equal to its energy (frequency) divided by the speed of light. Put simply, a photon of higher frequency has more momentum than one of low frequency.
When a photon hits a solar sail (or hits anything, really), it is absorbed and then re-emitted. Imagine standing on very slick ice when somebody throws a baseball to you. When you catch it (absorb the photon) you get pushed away from the person who threw it to you. When you throw it back (emit the photon), you get another equal push. That’s how reflection works, and is the key to solar sail propulsion.
The effect of a single photon is minuscule though, since the speed of light is a very big number to divide by, so it takes A LOT of them to push anything.
Thankfully, the sun puts out a mindbogglingly large number of photons. Let’s think about just how many.
The following is admittedly kind of an oddball way to calculate this, but it is more easily graspable than the more common method of using a calorimeter to measure a small patch and then multiplying it out.
To perceive a point of light the human eye needs about 7000 visible photons per second to pass through the pupil, which is about 6 square millimeters in size when dark-adapted. (Technically, it needs this many to hit the retina, but the pupil is smaller and it is the gatekeeper so the pupil is what counts when you’re talking about a point-source, which is what we’ll have here.)
Our sun is bright enough to be just barely perceptible from 55 light years away. So imagine a spherical surface 110 light years in diameter. Your pupil could anywhere on that surface and still get just enough photons to see the sun (assuming no obstructions).
The surface area of a sphere is 4πr². Let’s express it in square millimeters since that’s what we’re using for the pupil. That’s a surface area of 6.5 × 10²¹ square millimeters. The fully dark-adapted pupil is about 6 square millimeters, so divide by 6 to see how many places your pupil could be on that sphere, and we get about 10²¹ non-overlapping places. (Clearly, we’re rounding, but these are all estimates anyway.)
Since the sun is visible from all those places, that means that each of those places gets 7000 photons per second, so multiply by 7000. This tells us that the sun is pumping out 7 × 10²⁴ randomly distributed photons every second.
Seven septillion. Every second of every day. That’s obviously a rough estimate, but it’s reasonably close.
To show just how big that number is, think of it this way: If the sun were putting out one visible photon per second, it would take about six trillion times the current age of the universe for it to put out as many visible photons as it currently puts out every single second of every day. Just our sun, all by itself.
Mind blown yet? I hope not, because there’s something HUGE missing in all the above…
All that math only takes into account photons within the visual spectrum. There are a lot of photons being emitted by the sun outside the visible range as well.
As it turns out, as fun and interesting as that seven septillion visible photons per second is, the total number of photons emitted every second is actually 60,000,000,000,000,000,000 times greater!!!
Seven septillion TIMES sixty quintillion!
The actual number is approximately 4.2 × 10⁴⁴. Every second.
NOW your mind has permission to be blown.
How many of those photons hit your sail is a function of the sail’s surface area and shape, its distance from the sun, and its angle relative to the light coming from the sun.
But the point is, it’s a lot. Like, a WHOLE lot. And it’s a very good thing that the effect is so minuscule for each photon: If it was even just a little bigger for each photon, the entire solar system would be blown to smithereens.
Left- A modern lacewing larvae, bottom right- 110 million year old lacewing encased in amber, top right- artist rendering of the discovered specimen.
Lacewings are a group of insects with an interesting larval behavior; they have protrusions from their backs that they decorate with various objects they find in their environment as a form of camouflage.
They aren’t alone in this behavior; some types of crabs will also decorate themselves in order to better blend in with their surroundings. It is speculated that they may even be selective about what they choose, rather than just allowing any old thing to stick to their backsides. This is a relatively complex behavior that makes one question the intelligence required, especially in something like a larval insect.
It also causes one to wonder where along the evolutionary path this behavior first exhibited itself. Lacewing insect fossils previously found in the Dominican Republic are dated to 45 million years but a recent discovery pushes the date further still. Michael Engel a Paleontologist from the University of Kansas co-authored a paper about their discovery.
What they found was a 110 million year old larval lacewing encased in amber. The amber acting like a sepia colored time capsule preserved not only the insect but pieces of ancient fern tangled within the protrusions on its back. This pushes the date of camouflaging lacewings back 65 million years further, and according to Engel, “it’s also the earliest occurrence of this camouflaging behavior among insects as a whole.”
The fossil was discovered by a Ricardo Pérez-de La Fuente of the University of Barcelona, a doctoral student. They speculate that since the Lacewing lineage goes back to the Jurassic period, the behavior may go back as far as well.