An artist’s impression of the quasar 3C 279. Credit: ESO
APEX takes part in sharpest observation ever
The quasar observations made by connecting the APEX telescope to two others on different continents is a crucial step toward the goal of imaging supermassive black holes at the center of our galaxy and others. An international team of astronomers has observed the heart of a distant quasar with unprecedented sharpness, 2 million times finer than human vision. The observations, made by connecting the Atacama Pathfinder Experiment (APEX) telescope to two others on different continents for the first time, is a crucial step toward the dramatic scientific goal of the “Event Horizon Telescope” project: imaging the supermassive black holes at the center of our own galaxy and others.
Astronomers connected APEX in Chile to the Submillimeter Array (SMA) in Hawaii and the Submillimeter Telescope (SMT) in Arizona. They were able to make the sharpest direct observation ever of the center of a distant galaxy, the bright quasar 3C 279, which contains a supermassive black hole with a mass about 1 billion times that of the Sun and is so far from Earth that its light has taken more than 5 billion years to reach us.
The telescopes were linked using a technique known as Very Long Baseline Interferometry (VLBI). Larger telescopes can make sharper observations, and interferometry allows multiple telescopes to act like a single telescope as large as the separation — or “baseline” — between them. Using VLBI, the sharpest observations can be achieved by making the separation between telescopes as large as possible. For the quasar observations, the team used the three telescopes to create an interferometer with transcontinental baseline lengths of 5,900 miles (9,400 kilometers) from Chile to Hawaii; 4,500 miles (7,200km) from Chile to Arizona; and 2,900 miles (4,600km) from Arizona to Hawaii. Connecting APEX in Chile to the network was crucial, as it contributed the longest baselines.
The observations were made in radio waves with a wavelength of .05 inch (1.3 millimeters). This is the first time observations at a wavelength as short as this have been made using such long baselines. The observations achieved a sharpness, or angular resolution, of just 28 microarcseconds — about 8 billionths of a degree. This represents the ability to distinguish details an amazing 2 million times sharper than human vision. Observations this sharp can probe scales of less than a light-year across the quasar — a remarkable achievement for a target that is billions of light-years away.
The observations represent a new milestone toward imaging supermassive black holes and the regions around them. In the future, scientists plan to connect even more telescopes in this way to create the Event Horizon Telescope. This telescope will be able to image the shadow of the supermassive black hole in the center of our Milky Way Galaxy, as well as others in nearby galaxies. The shadow — a dark region seen against a brighter background — is caused by the bending of light by the black hole, and it would be the first direct observational evidence for the existence of a black hole’s event horizon — the boundary from which not even light can escape.
The experiment marks the first time that APEX has taken part in VLBI observations, and it is the culmination of three years of hard work at APEX’s high-altitude site on the 16,400-foot (5,000 meters) plateau of Chajnantor in the Chilean Andes, where the atmospheric pressure is only about half that at sea level. To make APEX ready for VLBI, scientists from Germany and Sweden installed new digital data acquisition systems, a very precise atomic clock, and pressurized data recorders capable of recording four gigabits per second for many hours under challenging environmental conditions. The data — four terabytes from each telescope — were shipped to Germany on hard drives and processed at the Max Planck Institute for Radio Astronomy in Bonn.
The successful addition of APEX is also important for another reason. It shares its location and many aspects of its technology with the new Atacama Large Millimeter/submillimeter Array (ALMA) telescope. ALMA is currently under construction and will finally consist of 54 dishes with the same 40-foot diameter (12m) as APEX, plus 12 smaller dishes with a diameter of 23 feet (7m). The possibility of connecting ALMA to the network is currently being studied. With the vastly increased collecting area of ALMA’s dishes, the observations could achieve 10 times better sensitivity than these initial tests. This would put the shadow of the Milky Way’s supermassive black hole within reach for future observations.
Cygnus X-1: Located in the constellation of Cygnus lies not only many beautiful nebulae and stars, but also contains a black hole that is considered to be part of an X-Ray Binary system. There currently is a large B-Type Blue supergiant star that is being ripped apart by “something” that we can’t visually see. It’s effects can be detected however. As the blue supergiant gets too close to the black hole, its gaseous surface becomes stripped away and an accretion disk is formed around the black hole. The temperature of this disk reaches millions of degrees fahrenheit which is hot enough for x-rays to be created. The black hole sometimes cannot handle all of the matter it takes in and releases the matter through jets perpendicular to the plane of the accretion disk. This extraordinary event has been witnessed many times and only further proves the existence of these mysterious objects that traverse the cosmos.
M83- Black hole outburst observed by Chandra
Scientists using the Chandra X-Ray Observatory have seen a remarkable outburst of X-rays from an old Black hole inside the M83 Spiral Galaxy.
The photo on the top is an optical image of spiral galaxy M83 from the Very Large Telescope in Chile, and the pinky cutout to the right is a composite of the optical and X-ray Photos. The data shows a massive increase in X-Ray output in a particular area. These outbursts are called ULXs (Ultraluminous X-Ray Sources) and this is one of the first times that a change of this magnitude has been observed in a binary system (companion star orbiting a neutron star, or black hole) The brightness of the ULX inside M83 increased by 3000%. This is evidence (along with a similar outburst inside M31) for lower-mass black holes which are more volatile than previously thought. The optical data shows a bright blue source (pictured bottom) which astronomers believe to be a disk of energetic material around the black hole which was picked up by its companion star.
Andromeda Galaxy- Our Milky Way galaxy will no longer take the shape of a barred, spiral galaxy when the enormous Andromeda Galaxy merges with us. Andromeda currently lies approximately 2.6 million light years away and is heading towards our galaxy at around 80 miles per second. I wouldn’t worry just yet as this collision will take place in 3.5 billion years; that’s how far away Andromeda is. It’s size is estimated to be around 200,000 light years in diameter and is measured to contain nearly one trillion stars. By comparison, our own galaxy probably has close to 400 billion stars. This picture beautifully shows the center of the Andromeda surrounded by hot blue stars, which are usually very massive and have short lives. Just like our own galaxy, it is believed that at the center of Andromeda lies a supermassive black hole. Imagine a region of space only 5 light years in diameter (Roughly the distance to the nearest star, Alpha Centauri), that contains the mass of 10 million stars. This enormous amount of mass can not be explained by what is seen visually through stars, gas and dust. Measuring stars near the core of active galaxies has proven that those stars nearest the core are orbiting “something” at speeds near 3,000 miles per second. For contrast, our sun orbits the center of the Milky Way at 135 miles per second. The numbers sort of speak for themselves and further proves the existence of supermassive black holes in the center of galaxies such as our Milky Way and the Andromeda galaxies.
The Death Of High-Mass Stars(15 Solar Masses and Above)
The previous lesson discussed fusion between hydrogen atoms into helium atoms(proton-proton chain), thus creating energy. A star of heavy mass also does this but produces energy in another way that smaller mass stars do not. This process is called the CNO Cycle. This is a six-step process that produces the same result as the proton-proton chain, which is four protons fusing, turning into a helium atom, and releasing energy. This cycle produces energy 1,000 times faster than the proton-proton chain does. The massive star needs to create a lot more energy to counter the immense force of gravity pushing down on it. It is important to recall that the more mass you have, the more gravity you have pushing down. On the moon you can float in mid air practically, on Earth, you fall back to the ground at the same speed no matter how heavy you are. (See Galileo’s Tower of Piza experiment). If you were on a neutron star, the weight of gravity pushing down is so strong that you would be flattened thinner than a piece of paper.
If you have a star that is 100 times the mass of our own sun for example, it is going to have 100 times the force of gravity trying to crush and destroy it. So in order to counter this immense force, the massive star has to produce A LOT more energy than a smaller star would. This causes massive stars to not live nearly as long as smaller stars because their fuel is exhausted much faster. The average lifetime for a massive star 15 solar masses or larger is in the millions of years, not billions of years.
The CNO cycle is only capable because massive stars contain large amounts of carbon, which was created from Helium atoms fusing with eachother. Whereas our small mass star no longer created a core of any elements higher than carbon because its mass was insufficient, the heavy mass star does not have this problem and will continue to create heavier and heavier elements in its core via fusion. When the core reaches 17 X 10 ^6 kelvin, or roughly 30,000,000 degrees Fahrenheit, the CNO cycle becomes the dominant force of energy production.
In sum, a Carbon atom captures one proton and becomes Nitrogen, emitting what is called a Gamma-ray(An electromagnetic particle of radiation). The nitrogen created is unstable and decays back to a carbon atom. The carbon atom has a slightly heavier mass and after capturing another proton, creates a slightly heavier Nitrogen atom once again, emitting another gamma-ray. This slightly heavier nitrogen atom then captures a proton and becomes Oxygen, emitting another gamma-ray. This oxygen atom decays into a slightly heavier nitrogen atom, and the last step of this stage involves the nitrogen atom capturing a proton and emitting an alpha-particle(consisting of two protons and two neutrons), which turns out to be the nucleus of a helium atom. This closes the cycle and with Helium being produced, energy is created. This part is a little overwhelming, but is important to understanding how massive stars create the energy needed to withstand the force of gravity.
The word Neutron has first been introduced here and it is important to remember this word as it has a lot to do with a massive star’s remnant once it dies.
Unlike small mass stars, when a massive star has a core of carbon, it does not stop there. It will use its outer shells to burn and create energy. The star seeks to burn its outer layers to create energy just as our smaller stars do. Yet, the more massive stars continue this chain down the periodic table until iron is reached. Pictured below is a diagram of a high mass star. You can see that there are many more layers than a smaller star has. Carbon fuses with carbon to create an oxygen core. Oxygen fuses with oxygen to create neon. Neon fuses and creates magnesium, magnesium fuses with itself and creates Silicon, and Silicon fuses with itself to create Iron. So what happens after Iron is reached is amazing, in my humble opinion. Iron actually cannot fuse with itself and instead causes the star to become “cooler” by absorbing energy instead of releasing any. Its inability to create energy from this fusion ends the star’s life, but not in a slow manner like low mass stars. This end of a star’s life creates an explosion that for a brief moment outshines an entire galaxy. The energy released from this explosion is equivalent to the amount of energy that star produced over its entire lifetime. That is just absolutely surreal. That is A LOT of energy released at once. This is what a supernova is. The extraordinary power released is equal to a trillion atomic bombs or more. Each element burned throughout the various shells provides the star with less and less time before it explodes via supernova. For example, Silicon is only burned for about 3 days in a high mass star and the fusion into iron destroys the star within seconds. Truly amazing considering this star has lived for millions of years. But in any event, once the iron in the core is attempted to fuse together and fails to do so, the core collapses in on itself, the weight of the massive star now entirely unstable. This type of supernova is called a, Core-Collapse supernova.
You might expect the entire star to blow up, but we know now that that is not the case. The overwhelming pressure of gravity pushing inwards on the star’s core actually squeezes together all the protons and electrons that make up the atoms in the core of the star. This creates a solid ball of neutrons, which has a density unlike anything in the universe. This density is one billion tons per cubic meter. In comparison, a tiny square cube of a neutron star weighs as much as an entire mountain. As I mentioned in the beginning, hypothetically, if you were to stand on a neutron star you would be flattened thinner than a piece of paper. Just as we have gravity here on earth, it takes a certain amount of power to leave Earth and travel into space.
Earth’s gravity has an effect on its “Escape velocity”, as first introduced by Sir Isaac Newton. By definition, escape velocity is, “the speed needed to ‘break free’ from a gravitational field without further propulsion.” For example, Earth’s escape speed is 11 kilometers/ second. If you are traveling any slower than that, you will not have the force needed to leave Earth. For Jupiter, the escape speed is 59.5 kilometers/ second, the largest and most dense of the eight planets. The sun has an escape speed of 617.5 kilometers/ second. The escape speed of a Neutron star depends solely on its mass. And considering a Neutron Star and a Black hole are almost the same thing, it can be inferred that the escape speed of a neutron star can span from thousands of kilometers per second up to the speed of light which is 299,792 kilometers per second or for the western folk, 186,000 miles per second. Think about that number for a second. If a neutron star has such incredible densities, then not even light, which is traveling at that unbelievable speed can escape the immense pull of gravity caused by the density of a neutron star.
This bit of information is so vital to our understanding of black holes. We can easily observe the gravitational influence that large objects have in space and infer the object’s density, mass, composition, etc. It explains why Jupiter, the planet with the heaviest mass has 64 moons!! Can you imagine? Its why we are orbiting the sun and it isn’t orbiting around us. It is why the sun in fact is orbiting around the center of the Milky Way Galaxy!! As you’ll see later, there is something lurking in the center of our galaxy that is the perfection of gravity’s immense effect on space.
Lighthouses In the Sky:
So, back to our now dead star…After our massive star has exploded, its remnant, a Neutron star is left behind and has some interesting characteristics. Its density has been discussed but what can we actually observe? Well what happens after this supernova is that the core is left but it is spinning at unbelievable rates. It is believed that the force of the star collapsing on top of this core is what gets the core spinning at such high rates. I would imagine that if one side of the star collapsed more than the other at just a slightly quicker rate, it would result in sending the star in an unbelievably fast spin.
Over 2000 neutron stars have been observed in 2011 and the observations we’ve made were more than just gravitational. Particular types of neutron stars are what you would call, “lighthouses” in space. What occurs as a result of their incredibly fast spin is that a beam of electromagnetic radiation from its poles is observed at rates measured in hundreds of times per second to as slow as one “pulse” every second. We can only observe these beams of radiation if it is aimed at Earth, however, which certainly limits the number of neutron stars we can observe that are pulsating. The name for these neutron stars is called, a Pulsar. It is also important to keep in mind that everything rotates. Earth rotates on its axis and is the reason we have days. There are planets that rotate so slow that it takes over one earth year just for that planet to revolve once on its axis. We observe this throughout our solar system. The pulsars created from these remnant supernova explosions are so regular that they are more accurate than the atomic clocks we use here on Earth. The pulsar is spinning at an incredibly fast and accurate rate. Something also to keep in mind is that with rotation, magnetic fields are created. Earth has its own magnetic field, which is why compasses point due North. It is how we are protected from the sun’s violent storms that reach us. But at our poles, there is a weakness in the gravitational field. We know this because of the Aurora Borealis, The Northern Lights. Particles from the sun interact with atmospheric particles on Earth and this combination creates the beautiful waves of colors we see across the sky. But you would not see this phenomenon at the equator. It will start at the poles and if the sun storm is strong enough, the Northern Lights can be seen further south. I mention this because our neutron star is no exception. And it is at its poles where radiation beams out. After millions of years, the rotation of these pulsars slows, and their magnetic field weakens ever so slightly. This enables Astronomers to calculate how old a neutron star is. If it is young, it will be spinning fast and will produce precise pulses of radiation from its poles. If it is an old neutron star, it will be doing neither.
The Crab Nebula:
One of the first observed and documented supernovas in history began in the year 185, but most are familiar with the beautiful image of the Crab Nebula, observed and documented by Chinese, Japanese, and Arab astronomers in the year 1054. This supernova occurred because a star, roughly 8-10 times the size of our sun reached the end of its life-cycle and created a core-collapse supernova. At the time this supernova occurred, it was described as being seen for over a month in the sky in broad daylight. Its remnants have been traveling through space at several thousand kilometers per second ever since then. I mention this because if you ever want to see exactly what I have written about, just look at the Crab Nebula. Its made of beautiful colors, particularly green, orange, and yellow. These colors, measured with a spectrometer tell Astronomers what elements this once massive star was made of. The heavy elements(> Carbon) we observe in space today were created only by supernova explosions. Gold and silver were created from supernovas. Remember that the next time you put on your jewelry :) At the center of the crab nebula, driving radiation outwards is a Pulsar with a spin rate of 30.2 times per second. This beautiful supernova remnant is pictured below.
The Grand Finale: Black Holes
The greatest mystery of them all. What happens when a star blows up and leaves behind nothing, but we know there is “something”? Strange question yes, but there is firm agreement amongst scientists that considering Einstein’s theory of general relativity has held up after all this time, it can be presupposed based on the predictions his theory makes that yes, there are black holes. Black holes are not black in the literal sense, but they are black because we cannot see this object in the night sky. It surely is there, however. As I’ve discussed, every object we observe is orbiting around something. A planet is orbiting around a star, a star is orbiting around the center of the galaxy…but what explains stars orbiting around nothing?
Black holes were the subject of great debate after pulsars were first detected. They too had been theorized based on the laws of gravity and mass as explained by Albert Einstein. But in 1978, the first major step in detecting black holes was taken; The launching of The Einstein X-Ray Observatory. Quite fitting given that he has had everything to do with the theory of black holes and our subsequent yearning for the discovery of one.
First to understand what an x-ray is, we must first recognize that any form of energy behaves in a wave-like manner. And depending on the frequency of these waves determines what kind of energy/information it carries. For example, on one end of the spectrum we have radio waves. Their frequencies are much longer. Along the spectrum there are microwaves, infrared waves, visible light(what you and I see), ultraviolet radiation, x-rays, and gamma rays. X-rays have incredibly short frequencies, thus therefore carrying a much higher energy than waves at the other end of the spectrum. We know also that when temperatures reach a certain degree, various electromagnetic waves are detected. It is known that at 10^6 kelvin, or roughly 1.8 million degrees, x-rays are created.
In 1964, a rocket flight into space detected at the time, one of the strongest sources of x-rays ever observed and it was coming from the direction in which the constellation Cygnus resides in the night sky.
Cygnus X-1 is named for the x-ray source that is coming from a “high-mass x-ray binary system” some 6,000 light years from Earth. Binary systems are actually quite common in the universe. As a matter of fact, the majority of stars form in pairs, or even comprise of 3 or more stars! In binary systems for example, it has been discovered that both stars do not form at the exact same time, nor do they acquire the exact same mass. It is when this occurs that scientists have a chance to observe something rather amazing. Imagine that both stars are massive giants, but one is more massive, say 40 solar masses, compared to its companion at 20 solar masses. We know from this entire lesson that the 40 solar mass star will die much quicker than its companion as it will exhaust its fuel faster. Our 40 mass star has just exploded in an unimaginably huge supernova, leaving behind a neutron star with a surface gravity stronger than the speed at which light or any radiation travels(299,792 kilometers/second). This by definition is a black hole. Now, what happens with our 20 solar mass star that once was orbiting around the 40 solar mass star?
The gravitational influence of the black hole and the proximity of the 20 solar mass star is not going to be good for that 20 solar mass star. The gravitational influence of the black hole is immense and unforgiving. It is so strong that the black hole literally pulls the companion star apart, creating what is called an Accretion Disk around the black hole as pictured below. This disk of gases from the companion star spiral inwards, feeding the black hole. Throughout this process, the black hole sometimes devours more than it can handle, and as a result, jets of excess material are launched out of the black hole at speeds half the speed of light, perpendicular to the accretion disk. The accretion disk becomes extremely hot because of friction between gas in the faster inner moving orbits combined with the slower orbits further away from the black hole. The temperatures of the gases in the innermost region of the accretion disk can reach 10^6 kelvin, our magic number for observing x-rays. Hence, the eventual confirmation that Cygnus X-1 was a source of x-ray emission produced from the energy released as a result of a black hole devouring a nearby star. The source of x-rays were detected from an incredibly small region with an estimated diameter of a mere 100,000 kilometers. The sun by comparison has a diameter of 1,000,000 kilometers, roughly. Pictured below also is Cygux X-1, an eerie looking region in space in which a black hole looms.
Singularities, Theories and the Conclusion of Black Holes
To summarize, a black hole is essentially, a supernova remnant with a core of ultra-dense neutrons that created a gravitational force so strong that not even light or radiation produced can escape. There are still many theories as to what else a black hole could be. Einstein’s theory of general relativity begs the question if there could be a high mass star collapse resulting in an object with infinite density, and therefore an infinite gravitational influence, resulting in what is called, a singularity. A singularity is basically the end or breakdown of logical explanation of certain laws of physics. The fact is, is that we really don’t know what a black hole leads to. Theories from Einstein suggest the presence of wormholes. We know that black holes create a massive indentation in space, a hole in space perhaps that can be traveled through? Highly doubtful. I think that if we were to see a black hole with our own two eyes, we would see chaos. A gravitational influence of this kind creates pressures and speeds of gases and particles that would destroy anything anywhere near it. Black holes are dangerous. They are rogue, meaning that they roam the universe with no restrictions or boundaries. Any star that is captured by its gravitation is doomed. It will lose all of its mass slowly but surely. Mass that will disappear once it makes it within the event horizon, the boundary surrounding the black hole which light can not escape…If our estimations are correct and there really are trillions of stars, then just how many of those stars attained a mass of 15 solar masses, large enough to one day explode in a supernova leaving behind a black hole? I think some basic mathematics would conclude that there is an eerily large amount of black holes in the universe. They would be hard to detect unless you know where you were looking. They don’t produce light and are incredibly small. However, the laws of gravity do give them away. Objects near a black hole spin very fast, objects too close get devoured, turned into an accretion disk, and are slowly digested by the black hole.
I would like to conclude by providing one last tantalizing detail of black holes; they get bigger. MUCH bigger. So big in fact that astronomers are in agreement that at the center of perhaps ALL galaxies lies a super-massive black hole. Its size may be 3 times the size of the sun, but its mass is equivalent to one billion suns!! The gravitational influence of an object like this can cause entire clusters of stars to orbit from millions of miles to many light years away. Our galaxy is 100,000 light years in diameter for example and everything is orbiting around the center in a spiral-like fashion. Studies are still underway to find more evidence for the super-massive black hole theory, but it sure would explain why we have measured millions of stars at the center of our galaxy, orbiting around “something” at unimaginable speeds. It is impossible to see the center of any of the galaxies we observe because there are so many stars at the center, obstructing our view of what may be within the orbits of those stars.
I devoted a lot of time to try to understand the process that stars undergo, from small stars like our sun, to large stars such as Betelguese, a Red Giant that will go “kaboom” one day, producing a spectacle unlike anything seen since the Crab Nebula supernova in 1054. Stars are what created you and I. From a scientific standpoint, we know this to be true. Our universe was once filled with an abundance of Hydrogen, the lightest element. Eventually, stars were created from condensed molecular clouds of Hydrogen and Helium, and through nuclear fusion, heavier elements were created because of the incredibly hot temperatures of the cores of these stars. When the large stars ran out of fuel, they exploded, releasing all of its mass into space at thousands of miles per hour. This mass, made of elements such as Carbon, Silicon, Magnesium, Iron…all make up the things here on Earth, our home planet. Our core of Earth is rich in Liquid iron. Our blood is made of iron! If stars never exploded into supernovas, none of us would be here because there would be nothing to make us up. That is a fact.
There is still much to learn about stars and the galaxies in which they are formed, and I feel it is a natural follow up subject to stellar evolution. I want to learn about the galaxies that create these stars in the first place. How are there so many of them? Why are some galaxies on a collision course with eachother and some are being driven away from one another, by a force yet to be completely identified (Dark energy). There are so many galaxies in the universe, but they are not orbiting around something like everything else seems to. The galaxies in the universe are spread out and most are flying away from our own galaxy at incredible speeds. What could have caused this? I look forward to addressing some of these important questions in the future…