Image from Dark Universe, showing the distribution of dark matter in the universe. Credit: AMNH
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”
The Aquila Constellation, aka "The Eagle". Credit: eaae-astronomy.org
Welcome to another edition of Constellation Friday! Today, we honor our dear friend and honored colleague, Tammy Plotner, by taking a look at the Aquila Constellation. Enjoy!
In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) released one of the most influential books in the history of astronomy. Known as the Almagest, this book included the 48 then-known constellation into a system of cosmology that would remain influential for over a thousand years. Among the 48 constellations listed in this book was Aquila, a constellation in the northern sky that extends across the celestial equator.
If you saw this, it would already be too late. Credit: NASA
You know that saying, “keep your friends close, but keep your enemies closer?” That advice needs to go right out the window when we’re talking black holes. They’re the worst enemies you could have and you want them as far away as possible.
We’re talking regions of space where matter is compressed so densely that the only way to escape is to be traveling faster than the speed of light. And as we know, you can’t go faster than the speed of light. So… there’s no escape.
Get too close to the black hole and you’ll be compressed beyond comprehension, perhaps into an infinitely small point.
But you can be reasonably distant from a black hole too, and still have your day ruined. A black hole reaches out through the light years with its gravity. And if one were to wander too close to our Solar System, it would wreak havoc on all our precious planets.
The planets and even the Sun would be gobbled up, or smashed together, or even thrown out of the Solar System entirely.
And as we learned in a previous episode, black holes are unkillable. Anything you might try to do to them just makes them bigger, stronger and angrier. Your only hope is to just wait them out over the eons it takes for them to evaporate.
It makes sense to keep track of all the black holes out there, just in case we might need to evacuate this Solar System in a hurry.
Where are the closest black holes?
There are two kinds of black holes out there: the supermassive black holes at the heart of every galaxy, and the stellar mass black holes formed when massive stars die in a supernova.
This artist’s impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783. Credit: ESO/M. Kornmesser
The supermassive ones are relatively straightforward. There’s one at the heart of pretty much every single galaxy in the Universe. One in the middle of the Milky Way, located about 27,000 light-years away. One in Andromeda 2.5 million light years away, and so on.
No problem, they supermassive ones are really far away, no threat to us.
The stellar mass ones might be more of a problem.
Here’s the problem. Black holes don’t emit any radiation, they’re completely invisible, so there’s no easy way to see them in the sky. The only you’d know there’s a black hole is if you were close enough to see the background starlight getting distorted. And if you’re close enough to see that, you’re already dead.
The closest black hole we know of is V616 Monocerotis, also known as V616 Mon. It’s located about 3,000 light years away, and has between 9-13 times the mass of the Sun. We know it’s there because it’s located in a binary system with a star with about half the mass of the Sun. Only a black hole could make its binary partner buzz around so quickly. Astronomers can’t see the black hole, they just know it’s there by the whirling gravity dance.
The next closest black hole is the classic Cygnus X-1, which is about 6,000 light-years away. It has about 15 times the mass of the Sun, and once again, it’s in a binary system.
The third closest black hole, is also in a binary system.
Artist’s illustration of Cygnus X-1, a stellar-mass black hole in a binary system. Credit: NASA/CXC/M.Weiss
See the problem here? The reality is that a fraction of black holes are in binary systems, but that’s our only way to detect them.
More likely there are more black holes much more close than the ones astronomers have been able to discover.
This all sounds terrifying, I’m sure, and now you’ve probably got one eye on the sky, watching for that telltale distortion of light from an approaching black hole. But these events are impossibly rare.
The Solar System has been around for more than 4.5 billion years, with all the planets going around and around without interruption. Even if a black hole passed the Solar System within a few dozen light years, it would have messed up the orbits significantly, and life probably wouldn’t be here to consider this fact.
We didn’t encounter a black hole in billions of years, and probably won’t encounter one for billions or trillions more years.
Sadly, the answer to this question is… we don’t know. We just don’t know if the closest black holes is a few light years away, or it’s actually V616 Mon. We’ll probably never know.
But that’s fine. They’re so rare it’s not worth worrying about.
Since the 1990s, scientists have been aware that for the past several billion years, the Universe has been expanding at an accelerated rate. They have further hypothesized that some form of invisible energy must be responsible for this, one which makes up 68.3% of the mass-energy of the observable Universe. While there is no direct evidence that this “Dark Energy” exists, plenty of indirect evidence has been obtained by observing the large-scale mass density of the Universe and the rate at which is expanding.
But in the coming years, scientists hope to develop technologies and methods that will allow them to see exactly how Dark Energy has influenced the development of the Universe. One such effort comes from the U.S. Department of Energy’s Lawrence Berkeley National Lab, where scientists are working to develop an instrument that will create a comprehensive 3D map of a third of the Universe so that its growth history can be tracked.
The million-year-old star HL Tau and its protoplanetary disk. Image: Carrasco-Gonzalez et. al.; Bill Saxton, NRAO/AUI/NSF
The currently accepted theory of planet formation goes like this: clouds of gas and dust are compressed or begin to draw together. When enough material clumps together, a star is formed and begins fusion. As the star, and its cloud of gas and dust rotate, other clumps of matter coagulate within the cloud, eventually forming planets. Voila, solar system.
There’s lots of evidence to support this, but getting a good look at the early stages of planetary formation has been difficult.
But now, an international team of astronomers using the Karl G. Jansky Very Large Array (VLA) have captured the earliest image yet of the process of planetary formation. “We believe this clump of dust represents the earliest stage in the formation of protoplanets, and this is the first time we’ve seen that stage,” said Thomas Henning, of the Max Planck Institute for Astronomy (MPIA).
This story actually started back in 2014, when astronomers studied the star HL Tau and its dusty disk with the Atacama Large Millimetre/sub-millimetre Array (ALMA.) That image, which showed gaps in HL Tau’s proto-planetary disk caused by proto-planets sweeping up dust in their orbits, was at the time the earliest image we had of planet formation. HL Tau is only about a million years old, so planet formation in HL Tau’s system was in its early days.
Now, astronomers have studied the same star, and its disk, with the VLA. The capabilities of the VLA allowed them do get an even better look at HL Tau and its disk, in particular the denser area closest to the star. What VLA revealed was a distinct clump of dust in the innermost region of the disk that contains between 3 to 8 times the mass of the Earth. That’s enough to form a few terrestrial planets of the type that inhabit our inner Solar System.
On the left is the ALMA image of HL Tau. On the right is the VLA image showing the clump of dust near the star. Image: Carrasco-Gonzalez et al,; Bill Saxton, NRAO/AUI/NSF
“This is an important discovery, because we have not yet been able to observe most stages in the process of planet formation,” said Carlos Carrasco-Gonzalez from the Institute of Radio Astronomy and Astrophysics (IRyA) of the National Autonomous University of Mexico (UNAM).
Of course the star in question, HL Tau, is interesting as well. But the formation and evolution of stars is much more easily studied. It’s our theory of planet formation which needed some observational confirmation. “This is quite different from the case of star formation, where, in different objects, we have seen stars in different stages of their life cycle. With planets, we haven’t been so fortunate, so getting a look at this very early stage in planet formation is extremely valuable,” said Carrasco-Gonzalez.
What is a treasure? A pirate’s hoard of gold coins safely locked up in a chest would certainly fit. But would you say that something is a treasure when it’s freely available to anyone who wants to take the time? Seems unlikely, doesn’t it. Yet you may change your mind once you take in André van der Hoeven’s book “Treasures of the Universe – Amateur and Professional Visions of the Cosmos”. Within it are striking images that display the natural wealth and beauty that constantly surrounds us and that no chest could ever lock up.
Astrophotography at its core is quite simple; at night, take a camera outside, point the lens up and snap the shutter release. Anyone can do it. However, putting reason to what one captures in the lens is quite a different story. And to add further complexity, consider combining your captured image with someone else’s who’s taken a picture while on another continent or while in space. Last, after taking thousands of images, identify those with artistic as well as scientific merit.
Yes, this is a more complete way of considering astrophotography. And many people are partaking in it. So here’s a book that’s selling its version of night sky images. For anyone who enjoys the night skies, there’s a lot to like. The contents are divided into four groups; galaxies, clusters, nebulae and our solar system. Most images from beyond our solar system are well known, whether of entries in the Messier catalogue or the New General Catalogue (NGC). A few are of farther afield, such as from the Hubble eXtreme Deep Field.
The image presentation is often on a double page spread and has complementary text adjoining. The text provides the scientific merit usually by identifying how the subject of the image fits into the scheme of things, such as the supernova SN2011fe in the Galactic Wheel. The text also provides the photographic particulars, such as that of the Andromeda galaxy that resulted from the compilation of 11 000 separate snapshots. The selection of images makes for a fairly well known set and won’t lead to surprises. Given this, van der Hoeven’s book is a comfortable, complete treatise of his astrophotography.
Now views of space are everywhere on the Internet and other publications so you’re probably wondering “What’s this book bring to the table?” so to speak. After all, a lot of its images come from other government sources like the Hubble space telescope. That’s data free for anyone to peruse. And, the subject of the images, the universe, remains in place for anyone else to capture if they so desire. Both of these are true, but what isn’t obvious is the time and effort to create the images as well as the talent to engender a sense of artistry. Can you imagine the time to compile 11,000 pictures into one? Or spending over 27 night-time hours to collect data for one image? That’s the sort of time and effort involved.
Measuring artistry is another skill altogether and one of which I lay no great claim. Yet, looking at the composition of the spread of the Wizard Nebula warmly shrouded by a complex hydrogen cloud makes me pause. Yes, I know I’m looking at the result of the random arrangement of matter and energy. But there’s something just so darn compelling about the shapes and textures that makes me wonder. And I realize my wonder comes from the skill of the author in composing the shape. I’m impressed. This doesn’t mean that the author has claimed any predominance. Rather, throughout the book he provides encouragement and incitements for bigger and better. Whether it calls for astrophotography from the next-generation telescopes or for beginner astrophotographers to develop their skill, it pushes for more and better imagery. Yes, this book is more than just pretty pictures. It’s also instructive and telling. Another unusual aspect is that the book was funded through a Kickstarter.
As with a few other marvelous books with vistas of the universe, this book’s pages are in in a wide format (almost landscape size). The pages have matte-black background with clear white font text. The text for each image is usually clear, except for some with underlying images of light colours. These are few. For the selection of images, I find ones of galaxies and nebulae most rewarding. Finding shapes and patterns from clusters is more challenging.
And, after seeing the depth and expanse of the universe, I find the images from our solar system almost ordinary, though I know I shouldn’t. I like the section at the book’s end that describes the image details including the telescope, the camera and the exposures for various filters. Perhaps I can use these to dabble at my own artistry. I also appreciate the credits that list all the data sources and perhaps the people who processed the data, though these aren’t always obvious. I don’t like that the book had to eventually come to an end. I could have kept looking at many more pages.
Treasures are a measure of worth. For those who like gold, a pirate’s chest may be the ultimate high. For those who are drawn to the night, to the limitlessness of space, then the jewels of the night sky are the only ones worth viewing. For you who like the night, let André van der Hoeven’s book “Treasures of the Universe – Amateur and Professional Visions of the Cosmos” spirit you away to a viewing pleasure. With it in your hands you will hold more than any pirate’s chest could ever contain.
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.
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.
Messier 7, open cluster in Scorpius. Image taken from Stellarium. Credit: Roberto Mura
Welcome to another Messier Monday. In our ongoing tribute to the great Tammy Plotner, we bring you another item from the Messier Catalog!
In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.
However, not all of the Messier Objects were first observed in the 18th century. Some, like Messier 7 cluster (aka. NGC 6475 or the Ptolemy Cluster) have been known about since classical antiquity. As the name would suggest, this open star cluster was first observed in the 2nd century CE by Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy), who described it as a nebula in 130 CE.
Small helium white dwarfs can be caused by a binary partner (NASA)
Scientists have understood for some time that the most abundant elements in the Universe are simple gases like hydrogen and helium. These make up the vast majority of its observable mass, dwarfing all the heavier elements combined (and by a wide margin). And between the two, helium is the second lightest and second most abundant element, being present in about 24% of observable Universe’s elemental mass.
Whereas we tend to think of Helium as the hilarious gas that does strange things to your voice and allows balloons to float, it is actually a crucial part of our existence. In addition to being a key component of stars, helium is also a major constituent in gas giants. This is due in part to its very high nuclear binding energy, plus the fact that is produced by both nuclear fusion and radioactive decay. And yet, scientists have only been aware of its existence since the late 19th century.
