An interesting multiple star discovery turned up in the ongoing hunt for exoplanetary systems.
The discovery was announced by Marcus Lohr of Open University early this month at the National Astronomy Meeting that was held at Venue Cymru in Llandudno, Wales.
The discovery involves as many as five stars in a single stellar system, orbiting in a complex configuration.
The name of the system, 1SWASP J093010.78+533859.5, is a phone number-style designation related to the SuperWASP exoplanet hunting transit survey involved with the discovery. The lengthy numerical designation denotes the system’s position in the sky in right ascension and declination in the constellation Ursa Major.
The SuperWASP-North array of cameras at La Palma in the Canary Islands. Image credit: The SuperWASP consortium
And what a bizarre system it is. The physical parameters of the group are simply amazing, though not as unique as some media outlets have led readers to believe. What is amazing is the fact that both pairs of binaries in the quadruple group are also eclipsing along our line of sight. Only five other quadruple eclipsing binary systems of this nature are known, to include BV/BW Draconis and V994 Herculis.
The very fact that the orbits of both pairs of stars are in similar inclinations will provide key insights for researchers as to just how this system formed.
The first pair in the system are contact binaries of 0.9 and 0.3 solar masses respectively in a tight embrace revolving about each other in just under six hours. Contact binaries consist of distorted stars whose photospheres are actually touching. A famous example is the eclipsing contact binary Beta Lyrae.
An animation of the orbits of the contact binary pair Beta Lyrae captured using the CHARA interferometer. Image credit: Ming Zhao et al. ApJ 684, L95
A closer analysis of the discovery revealed another pair of detached stars of 0.8 and 0.7 solar masses orbiting each other about 21 billion kilometres (140 AUs distant) from the first pair. You could plop the orbit of Pluto down between the two binary pairs, with room to spare.
But wait, there’s more. Astronomers use a technique known as spectroscopy to tease out the individual light spectra signatures of close binaries too distant to resolve individually. This method revealed the presence of a fifth star in orbit 2 billion kilometers (13.4 AUs, about 65% the average distance from Uranus to the Sun) around the detached pair.
“This is a truly exotic star system,” Lohr said in a Royal Society press release. “In principle, there’s no reason it couldn’t have planets in orbit around each of the pairs of stars.”
Indeed, ‘night’ would be a rare concept on any planet in a tight orbit around either binary pair. In order for darkness to occur, all five stellar components would have to appear near mutual conjunction, something that would only happen once every orbit for the hypothetical world.
Such a planet is a staple of science fiction, including Tatooine of Star Wars fame (which orbits a relatively boring binary pair), and the multiple star system of the Firefly series. Perhaps the best contender for a fictional quadruple star system is the 12 colonies of the re-imagined Battlestar Galactica series, which exist in a similar double-pair configuration.
How rare is this discovery, really? Multiple systems are more common than solitary stars such as our Sun by a ratio of about 2:1. In fact, it’s been suggested by rare Earth proponents that life arose here on Earth in part because we have a stable orbit around a relatively placid lone star. The solar system’s nearest stellar neighbor Alpha Centauri is a triple star system. The bright star Castor in the constellation of Gemini the Twins is a famous multiple heavyweight with six components in a similar configuration as this month’s discovery. Another familiar quadruple system to backyard observers is the ‘double-double’ Epsilon Lyrae, in which all four components can be split. Mizar and Alcor in the handle of the Big Dipper asterism is another triple-pair, six-star system. Another multiple, Gamma Velorum, may also possess as many as six stars. Nu Scorpii and AR Cassiopeiae are suspected septuple systems, each perhaps containing up to seven stars.
Fun fact: Gamma Velorum is also informally known as ‘Regor,’ a backwards anagram play on Apollo 1 astronaut ‘Roger’ Chaffee’s name. The crew secretly inserted their names into the Apollo star maps during training!
What is the record number of stars in one system? Hierarchy 3 systems such as Castor are contenders. A.A. Tokivinin’s Multiple Star Catalogue lists five components in a hierarchy 4 system in Ophiuchus named Gliese 644AB, with the potential for more.
How many stars are possible in one star system? Certainly, a hierarchy 4 type system could support up the eight stars, though to our knowledge, no example of such a multiple star system has yet been confirmed. Still, it’s a big universe out there, and the cosmos has lots of stars to play with.
A wide-field view of the constellation Ursa Major, with Theta Ursae Majoris selected (inset). Image credit; Stellarium
And you can see 1SWASP J093010.78+533859.5 for yourself. At 250 light years distant, the +9th magnitude binary is about 1.5 degrees north-northwest of the star Theta Ursa Majoris, and is an tough but not impossible split with a separation of 1.88” between the two primary pairs.
Finder chart for 1SWAP J093010.78+533859.5 with a five degree Telrad foV. Image credit: Stellarium
Congrats to the team on this amazing discovery… to paraphrase Haldane, the Universe is proving to be stranger than we can imagine!
The pentaquark, a novel arrangement of five elementary particles, has been detected at the Large Hadron Collider. This particle may hold the key to a better understanding of the Universe's strong nuclear force. [Image credit: CERN/LHCb experiment]
“Three quarks for Muster Mark!,” wrote James Joyce in his labyrinthine fable, Finnegan’s Wake. By now, you may have heard this quote – the short, nonsensical sentence that eventually gave the name “quark” to the Universe’s (as-yet-unsurpassed) most fundamental building blocks. Today’s physicists believe that they understand the basics of how quarks combine; three join up to form baryons (everyday particles like the proton and neutron), while two – a quark and an antiquark – stick together to form more exotic, less stable varieties called mesons. Rare four-quark partnerships are called tetraquarks. And five quarks bound in a delicate dance? Naturally, that would be a pentaquark. And the pentaquark, until recently a mere figment of physics lore, has now been detected at the LHC!
So what’s the big deal? Far from just being a fun word to say five-times-fast, the pentaquark may unlock vital new information about the strong nuclear force. These revelations could ultimately change the way we think about our superbly dense friend, the neutron star – and, indeed, the nature of familiar matter itself.
Physicists know of six types of quarks, which are ordered by weight. The lightest of the six are the up and down quarks, which make up the most familiar everyday baryons (two ups and a down in the proton, and two downs and an up in the neutron). The next heaviest are the charm and strange quarks, followed by the top and bottom quarks. And why stop there? In addition, each of the six quarks has a corresponding anti-particle, or antiquark.
Six types of quark, arranged from left to right by way of their mass, depicted along with the other elementary particles of the Standard Model. The Higgs boson was added to the right side of the menagerie in 2012. (Image Credit: Fermilab)
An important attribute of both quarks and their anti-particle counterparts is something called “color.” Of course, quarks do not have color in the same way that you might call an apple “red” or the ocean “blue”; rather, this property is a metaphorical way of communicating one of the essential laws of subatomic physics – that quark-containing particles (called hadrons) always carry a neutral color charge.
For instance, the three components of a proton must include one red quark, one green quark, and one blue quark. These three “colors” add up to a neutral particle in the same way that red, green, and blue light combine to create a white glow. Similar laws are in place for the quark and antiquark that make up a meson: their respective colors must be exactly opposite. A red quark will only combine with an anti-red (or cyan) antiquark, and so on.
The pentaquark, too, must have a neutral color charge. Imagine a proton and a meson (specifically, a type called a J/psi meson) bound together – a red, a blue, and a green quark in one corner, and a color-neutral quark-antiquark pair in the other – for a grand total of four quarks and one antiquark, all colors of which neatly cancel each other out.
Physicists are not sure whether the pentaquark is created by this type of segregated arrangement or whether all five quarks are bound together directly; either way, like all hadrons, the pentaquark is kept in check by that titan of fundamental dynamics, the strong nuclear force.
The strong nuclear force, as its name implies, is the unspeakably robust force that glues together the components of every atomic nucleus: protons and neutrons and, more crucially, their own constituent quarks. The strong force is so tenacious that “free quarks” have never been observed; they are all confined far too tightly within their parent baryons.
But there is one place in the Universe where quarks may exist in and of themselves, in a kind of meta-nuclear state: in an extraordinarily dense type of neutron star. In a typical neutron star, the gravitational pressure is so tremendous that protons and electrons cease to be. Their energies and charges melt together, leaving nothing but a snug mass of neutrons.
Physicists have conjectured that, at extreme densities, in the most compact of stars, adjacent neutrons within the core may even themselves disintegrate into a jumble of constituent parts.
The neutron star… would become a quark star.
The difference between a neutron star and a quark star. (Image Credit: Chandra)
Scientists believe that understanding the physics of the pentaquark may shed light on the way the strong nuclear force operates under such extreme conditions – not only in such overly dense neutron stars, but perhaps even in the first fractions of a second following the Big Bang. Further analysis should also help physicists refine their understanding of the ways that quarks can and cannot combine.
The data that gave rise to this discovery – a whopping 9-sigma result! – came out of the LHC’s first run (2010-2013). With the supercollider now operating at double its original energy capacity, physicists should have no problem unraveling the mysteries of the pentaquark even further.
A preprint of the pentaquark discovery, which has been submitted to the journal Physical Review Letters, can be found here.
The Milky Way glitters above the ALMA array in this image taken from a time lapse sequence during the ESO Ultra HD Expedition.
This article is a guest post by Anna Ho, who is currently doing research on stars in the Milky Way through a one-year Fulbright Scholarship at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany.
In the Milky Way, an average of seven new stars are born every year. In the distant galaxy GN20, an astonishing average of 1,850 new stars are born every year. “How,” you might ask, indignant on behalf of our galactic home, “does GN20 manage 1,850 new stars in the time it takes the Milky Way to pull off one?”
To answer this, we would ideally take a detailed look at the stellar nurseries in GN20, and a detailed look at the stellar nurseries in the Milky Way, and see what makes the former so much more productive than the latter.
But GN20 is simply too far away for a detailed look.
This galaxy is so distant that its light took twelve billion years to reach our telescopes. For reference, Earth itself is only 4.5 billion years old and the universe itself is thought to be about 14 billion years old. Since light takes time to travel, looking out across space means looking back across time, so GN20 is not only a distant, but also a very ancient, galaxy. And, until recently, astronomers’ vision of these distant, ancient galaxies has been blurry.
Consider what happens when you try to load a video with a slow Internet connection, or when you download a low-resolution picture and then stretch it. The image is pixelated. What was once a person’s face becomes a few squares: a couple of brown squares for hair, a couple of pink squares for the face. The low-definition picture makes it impossible to see details: the eyes, the nose, the facial expression.
A face has many details and a galaxy has many varied stellar nurseries. But poor resolution, a result simply of the fact that ancient galaxies like GN20 are separated from our telescopes by vast cosmic distances, has forced astronomers to blur together all of this rich information into a single point.
The situation is completely different here at home in the Milky Way. Astronomers have been able to peer deep into stellar nurseries and witness stellar birth in stunning detail. In 2006, the Hubble Space Telescope took this unprecedentedly detailed action shot of stellar birth at the heart of the Orion Nebula, one of the Milky Way’s most famous stellar nurseries:
A detailed close-up of stellar birth. Credit: NASA,ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team
There are over 3,000 stars in this image: The glowing dots are newborn stars that have recently emerged from their cocoons. Stellar cocoons are made of gas: thousands of these gas cocoons sit nestled in immense cosmic nurseries, which are rich with gas and dust. The central region of that Hubble image, encased by what looks like a bubble, is so clear and bright because the massive stars within have blown away the dust and gas they were forged from. Majestic stellar nurseries are scattered all over the Milky Way, and astronomers have been very successful at uncloaking them in order to understand how stars are made.
Observing nurseries both here at home and in relatively nearby galaxies has enabled astronomers to make great leaps in understanding stellar birth in general: and, in particular, what makes one nursery, or one star formation region, “better” at building stars than another. The answer seems to be: how much gas there is in a particular region. More gas, faster rate of star birth. This relationship between the density of gas and the rate of stellar birth is called the Kennicutt-Schmidt Law. In 1959, the Dutch astronomer Maarten Schmidt raised the question of how exactly increasing gas density influences star birth, and forty years later, in an illustration of how scientific dialogues can span decades, his American colleague Robert Kennicutt used data from 97 galaxies to answer him.
Understanding the Kennicutt-Schmidt Law is crucial for determining how stars form and even how galaxies evolve. One fundamental question is whether there is one rule that governs all galaxies, or whether one rule governs our galactic neighborhood, but a different rule governs distant galaxies. In particular, a family of distant galaxies known as “starburst galaxies” seems to contain particularly productive nurseries. Dissecting these distant, highly efficient stellar factories would mean probing galaxies as they used to be, back near the beginning of the universe.
Enter GN20. GN20 is one of the brightest, most productive of these starburst galaxies. Previously a pixelated dot in astronomers’ images, GN20 has become an example of a transformation in technological capability.
In December 2014, an international team of astronomers led by Dr. Jacqueline Hodge of the National Radio Astronomy Observatory in the USA, and comprising astronomers from Germany, the United Kingdom, France, and Austria, were able to construct an unprecedentedly detailed picture of the stellar nurseries in GN20. Their results were published earlier this year.
The key is a technique called interferometry: observing one object with many telescopes, and combining the information from all the telescopes to construct one detailed image. Dr. Hodge’s team used some of the most sophisticated interferometers in the world: the Karl G. Jansky Very Large Array (VLA) in the New Mexico desert, and the Plateau de Bure Interferometer (PdBI) at 2550 meters (8370 feet) above sea level in the French Alps.
With data from these interferometers as well as the Hubble Space Telescope, they turned what used to be one dot into the following composite image:
GN20 in unprecedented detail (false color image). The 10 kpc (10,000 parsec) scale corresponds to 32,600 light-years. Image credit: Jacqueline Hodge et al. 2015
This is a false color image, and each color stands for a different component of the galaxy. Blue is ultraviolet light, captured by the Hubble Space Telescope. Green is cold molecular gas, imaged by the VLA. And red is warm dust, heated by the star formation it is shrouding, detected by the PdBI.
Unbundling one pixel into many enabled the team to determine that the nurseries in a starburst galaxy like GN20 are fundamentally different from those in a “normal” galaxy like the Milky Way. Given the same amount of gas, GN20 can churn out orders of magnitude more stars than the Milky Way can. It doesn’t simply have more raw material: it is more efficient at fashioning stars out of it.
Some of the 66 radio antennas of ALMA, which can be linked to act like a much larger telescope. Image credit: ALMA (ESO/NAOJ/NRAO)/B. Tafreshi (twanight.org)
This kind of study is currently unique to the extreme case of GN20. However, it will be more common with the new generation of interferometers, such as the Atacama Large Millimeter/submillimeter Array (ALMA).
Located 5000 meters (16000 feet) high up in the Chilean Andes, ALMA is poised to transform astronomers’ understanding of stellar birth. State-of-the-art telescopes are enabling astronomers to do the kind of detailed science with distant galaxies – ancient galaxies from the early universe – that was once thought to be possible only for our local neighborhood. This is crucial in the scientific quest for universal physical laws, as astronomers are able to test their theories beyond our neighborhood, out across space and back through time.
This chart of the position of a nova (marked in red) that appeared in the year 1670 recorded by the astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions. Image credit: The Royal Society
It is a 17th century astronomical enigma that has persisted right up until modern times.
On June 20, 1670, a new star appeared in the evening sky that gave 17th century astronomers pause. Eventually peaking out at +3rd magnitude, the ruddy new star in the modern day constellation of Vulpecula the Fox was visible for almost two years before vanishing from sight.
The exact nature of Nova Vulpeculae 1670 has always remained a mystery. The event has often been described as a classic nova… but if it was indeed a garden variety recurrent nova in our own Milky Way galaxy, then why haven’t we seen further outbursts? And why did it stay so bright, for so long?
Now, recent findings from the European Southern Observatory announced in the journal Nature this past March reveal something even more profound: the Nova of 1670 may have actually been the result of a rare stellar collision.
The remnant of the nova of 1670 seen with modern instruments and created from a combination of visible-light images from the Gemini telescope (blue), a submillimetre map showing the dust from the SMA (yellow) and finally a map of the molecular emission from APEX and the SMA (red). Image credit: ESO/T. Kaminski
“For many years, this object was thought to be a nova,” said ESO researcher Tomasz Kaminski of the Max Planck Institute for Radio Astronomy in Bonn Germany in a recent press release. “But the more it was studied, the less it looked like an ordinary nova—or indeed any other kind of exploding star.”
A typical nova occurs when material being siphoned off a companion star onto a white dwarf star during a process known as accretion builds up to a point where a runaway fusion reaction occurs.
ESO researchers used an instrument known as the Atacama Pathfinder EXperiment telescope (APEX) based on the high Chajnantor plateau in Chile to probe the remnant nebula from the 1670 event at submillimeter wavelengths. They found that the mass and isotopic composition of the resulting nebula was very uncharacteristic of a standard nova event.
So what was it?
A best fit model for the 1670 event is a rare stellar merger, with two main sequence stars smashing together and exploding in a grand head on collision, leaving the resulting nebula we see today. This event also resulted in a newly recognized category of star known as a “red transient” or luminous red nova.
Universe Today caught up with Mr. Kaminski recently on the subject of red transients and the amazing find:
“In our galaxy we are quite confident that four other objects were observed in outburst owing to a stellar merger: V838 Mon (famous for its spectacular light echo, eruption 2002), V4332 Sgr (eruption 1994), V1309 Sco (observed as an eclipsing binary before its outburst in 2008), OGLE-2002-BLG-360 (recent, but most similar to CK Vul eruption, 2002).Red transients are bright enough to be observed in nearby galaxies. Among them are M31 RV (first recognized “red variable”, eruption 1989), M85 OT2006 (eruption 2006), NGC300 OT2008, etc. Very recently, a few months ago, another one went off in the Andromeda Galaxy. With the increasing number of sky surveys we surely will discover many more.”
Though astronomers such as Voituret Anthelme, Johannes Hevelius and Giovanni Cassini all noted the 1670 nova, the nebula and suspected progenitor star wasn’t successfully recovered until 1981. Often cited as the oldest and faintest observation of a nova, Hevelius referred to the 1670 apparition as ‘nova sub capite Cygni,’ or a new star located below the head of the Swan near the star Albireo the constellation of Cygnus. Astronomers of the day also noted the crimson color of the new star, also fitting with the modern red transient hypothesis of two main sequence stars merging.
This chart shows the small constellation of Vulpecula (The Fox), and the location of the exploding star Nova Vul 1670 (red circle). Image credit: ESO/IAU/Sky & Telescope
“We observed CK Vul with the hope to find some submillimeter emission, but were completely surprised by how intense the emission was and how abundant in molecules the gas surrounding CK Vul is,” Kaminski told Universe Today. “Also, we have ongoing observational programs to search for objects similar to CK Vul.”
Follow up observations of the region were also carried out by the Submillimeter Array (SMA) and the Effelsberg radio telescope in Germany. The Nova of 1670 occurred about 1,800 light years distant along the galactic plane in the Orion-Cygnus arm of our Milky Way galaxy, of which the Sun and our solar system is a member. We actually had a naked eye classical nova just last year in roughly the same direction, which was visible in the adjacent constellation of Delphinus the Dolphin.
Of course, these garden variety novae are in a distinctly different class of events from supernovae, the likes of which have not been seen in our galaxy with the unaided eye in modern times since Kepler’s supernova in 1604.
The Atacama Pathfinder Experiment (APEX) telescope on the hunt. Image credit: ESO/ Babak Tafreshi
How often do stars collide? While rogue collisions of passing stars are extremely rare—remember, space is mostly nothing—the odds go up for closely orbiting binary pairs. What would really be amazing is to witness a modern day nearby red transient in the act of formation, though for now, we’ll have to console ourselves with studying the aftermath of the 1670 event as the next best thing.
“Recent estimates give one (merger) event per 2 years in the Milky Way galaxy,” Kaminski told Universe Today. “But we currently know so little about violent merger events that this number is very uncertain.”
Previously cited as a recurrent nova, the story of the 1670 event is a wonderful example of how new methods, combined with old observations, can be utilized to solve some of the lingering mysteries of modern astronomy.
There is something about them that intrigues us all. These massive spheres of gas burning intensely from the energy of fusion buried many thousands of kilometers deep within their cores. The stars have been the object of humanity’s wonderment for as far back as we have records. Many of humanity’s religions can be tied to worshiping these celestial candles. For the Egyptians, the sun was representative of the God Ra, who each day vanquished the night and brought light and warmth to the lands. For the Greeks, it was Apollo who drove his flaming chariot across the sky, illuminating the world. Even in Christianity, Jesus can be said to be representative of the sun given the striking characteristics his story holds with ancient astrological beliefs and figures. In fact, many of the ancient beliefs follow a similar path, all of which tie their origins to that of the worship of the sun and stars.
Humanity thrived off of the stars in the night sky because they recognized a correlation in the pattern in which certain star formations (known as constellations) represented specific times in the yearly cycle. One of which meant that it was to become warmer soon, which led to planting food. The other constellations foretold the coming of a
The familiar constellation of Orion. Orion’s Belt can be clearly seen, as well as Betelgeuse (red star in the upper left corner) and Rigel (bright blue star in the lower right corner) Credit: NASA Astronomy Picture of the Day Collection NASA
colder period, so you were able to begin storing food and gathering firewood. Moving forward in humanity’s journey, the stars then became a way to navigate. Sailing by the stars was the way to get around, and we owe our early exploration to our understandings of the constellations. For many of the tens of thousands of years that human eyes have gazed upwards toward the heavens, it wasn’t until relatively recently that we fully began to understand what stars actually were, where they came from, and how they lived and died. This is what we shall discuss in this article. Come with me as we venture deep into the cosmos and witness physics writ large, as I cover how a star is born, lives, and eventually dies.
We begin our journey by traveling out into the universe in search of something special. We are looking for a unique structure where both the right circumstances and ingredients are present. We are looking for what astronomer’s call a Dark Nebula. I’m sure you’ve heard of nebulae before, and have no doubt seen them. Many of the amazing images that the Hubble Space Telescope has obtained are of beautiful gas clouds, glowing amidst the backdrop of billions of stars. Their colors range from deep reds, to vibrant blues, and even some eerie greens. This is not the type of nebula we are in search of though. The nebula we need is dark, opaque, and very, very cold.
You may by wondering to yourself, “Why are we looking for something dark and cold when stars are bright and hot?”
Image of a Dark Nebula Credit: ESO http://www.eso.org/public/images/eso1501a
Indeed, this is something that would appear puzzling at first. Why does something need to be cold first before it can become extremely hot? First, we must cover something elementary about what we call the Interstellar Medium (ISM), or the space between the stars. Space is not empty as its name would imply. Space contains both gas and dust. The gas we are mainly referring to is Hydrogen, the most abundant element in the universe. Since the universe is not uniform (the same density of gas and dust over every cubic meter), there are pockets of space that contain more gas and dust than others. This causes gravity to manipulate these pockets to come together and form what we see as nebulae. Many things go into the making of these different nebulae, but the one that we are looking for, a Dark Nebula, possesses very special properties. Now, let us dive into one of these Dark Nebulae and see what is going on.
As we descend through the outer layers of this nebula, we notice that the temperature of the gas and dust is very low. In some nebulae, the temperatures are very hot. The more particles bump into each other, excited by the absorption and emission of exterior and interior radiation, means higher temperatures. But in this Dark Nebula, the opposite is happening. The temperatures are decreasing the further into the cloud we get. The reason these Dark Nebulae have specific properties that work to create a great stellar nursery has to deal with the basic properties of the nebula and the region type that the cloud exists in, which has some difficult concepts associated with it that I will not fully illustrate here. They include the region where the molecular clouds form which are called Neutral Hydrogen Regions, and the properties of these regions have to deal with electron spin values, along with magnetic field interactions that effect said electrons. The traits that I will cover are what allows for this particular nebula to be ripe for star formation.
Excluding the complex science behind what helps form these nebulae, we can begin to address the first question of why must we get colder to get hotter. The answer comes down to gravity. When particles are heated, or excited, they move faster. A cloud with sufficient energy will contain far too much momentum among each of the dust and gas particles for any type of formations to occur. As in, if dust grains and gas atoms are moving too quickly, they will simply bounce off of one another or just shoot past each other, never achieving any type of bond. Without this interaction, you can never have a star. However, if the temperatures are cold enough, the particles of gas and dust are moving so slow that their mutual gravity will allow for them to start to “stick” together. It is this process that allows for a protostar to begin to form.
Generally what supplies energy to allow for the faster motion of the particles in these molecular clouds is radiation. Of course, there is radiation coming in from all directions at all times in the universe. As we see with other nebulae, they are glowing with energy and stars aren’t being born amid these hot gas clouds. They are being heated by external radiation from other stars and from its own internal heat. How does this Dark Nebula prevent external radiation from heating up the gas in the cloud and causing it to move too fast for gravity to take hold? This is where
Barnard 68 is a large molecular cloud that is so thick, it blocks out the light from stars that we normally would be able to see. Credit: ESO http://www.eso.org/public/images/eso0102a
the opaque nature of these Dark Nebulae comes into play. Opacity is the measure of how much light is able to move through an object. The more material in the object or the thicker the object is, the less light is able to penetrate it. The higher frequency light (Gamma Rays, X-Rays, and UV) and even the visible frequencies are affected more by thick pockets of gas and dust. Only the lower frequency types of light, including Infrared, Microwaves, and Radio Waves, has any success of penetrating gas clouds such as these, and even it is somewhat scattered so that generally they do not contain nearly enough energy to begin to disrupt this precarious process of star formation. Thus, the inner portions of the dark gas clouds are effectively “shielded” from the outside radiation that disrupts other, less opaque nebulae. The less radiation that makes it into the cloud, the lower the temperatures of the gas and dust within it. The colder temperatures means less particle motion within the cloud, which is key for what we will discuss next.
Indeed, as we descend towards the core of this dark molecular cloud, we notice that less and less visible light makes it to our eyes, and with special filters, we can see that this is true of other frequencies of light. As a result, the cloud’s temperature is very low. It is worth noting that the process of star formation takes a very long time, and in the interest of not keeping you reading for hundreds of thousands of years, we shall now fast forward time. In a few thousand years, gravity has pulled in a fair amount of gas and dust from the surrounding molecular cloud, causing it to clump together. Dust and gas particles, still shielded from outside radiation, are free to naturally come together and “stick” at these low temperatures. Eventually, something interesting begins to happen. The mutual gravity of this ever growing ball of gas and dust begins a snowball (or star-ball) effect. The more layers of gas and dust that are coagulated together, the denser the interior of this protostar becomes. This density increases the gravitational force near the protostar, thus pulling more material into it. With every dust grain and hydrogen atom that it accumulates, the pressure in the interior of this ball of gas increases.
If you remember anything from any chemistry class you’ve ever taken, you may recall a very special relationship between pressure and temperature when dealing with a gas. PV=nRT, the Ideal Gas Law, comes to mind. Excluding the constant scalar value ‘n’ and the gas constant R ({8.314 J/mol x K}), and solving for Temperature (T), we get T=PV, which means that the temperature of a gas cloud is directly proportional to pressure. If you increase the pressure, you increase the temperature. The core of this soon-to-be star residing in this Dark Nebula is becoming very dense, and the pressure is skyrocketing. According to what we just calculated, that means that the temperature is also increasing.
Artistic rendition of a star forming within a dark nebula. Credit: NASA/JPL-Caltech/R. Hurt (SSC)
We yet again consider this nebula for the next step. This nebula has a large amount of dust and gas (hence it being opaque), which means it has a lot of material to feed our protostar. It continues to pull in the gas and dust from its surrounding environment and begins heating up. The hydrogen particles in the core of this object are bouncing around so quick that they are releasing energy into the star. The protostar begins to get very hot and is now glowing with radiation (generally Infrared). At this point, gravity is still pulling in more gas and dust which is adding to the pressures exerted deep within the core of this protostar. The gas of the Dark Nebula will continue to collapse in on itself until something important happens. When there is little to nothing left near the star to fall onto its surface, it begins to lose energy (due to it radiating away as light). When this happens, that outward force lessens and gravity starts to contract the star faster. This greatly increases the pressure in the core of this protostar. As the pressure grows, the temperature in the core reaches a value that is crucial for the process that we are witnessing. The protostar’s core has become so dense and hot, that it reaches roughly 10 million Kelvin. To put that into perspective, this temperature is roughly 1700x hotter than the surface of our sun (at around 5800K). Why is 10 million Kelvin so important? Because at that temperature, the thermonuclear fusion of Hydrogen can occur, and once fusion starts, this newborn star “turns on” and bursts to life, sending out vast amounts of energy in all directions.
In the core, it is so hot that the electrons that zip around the hydrogen’s proton nuclei are stripped off (ionized), and all you have are free moving protons. If the temperature isn’t hot enough, these free flying protons (which have positive charges), will simply glance off one another. However, at 10 Million Kelvin, the protons are moving so fast that they can get close enough to allow for the Strong Nuclear Force to take over, and when it does the Hydrogen protons begin slamming into each other with enough force to fuse together, creating Helium atoms and releasing lots of energy in the form of radiation. It’s a chain reaction that can be summed up as 4 Protons yield 1 Helium atom + energy. This fusion is what ignites the star and causes it to “burn”. The energy liberated by this reaction goes into helping other Hydrogen protons fuse and also supplies the energy to keep the star from collapsing in on itself. The energy that is pumping out of this star in all directions all comes from the core, and the subsequent layers of this young star all transmit that heat in their own way (using radiation and convection methods depending upon what type of star has been born).
Newborn stars glow through their parent molecular cloud Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt
What we have witnessed now, from the start of our journey when we dove down into that cold Dark Nebula, is the birth of a young, hot star. The nebula protected this star from errant radiation that would have disrupted this process, as well as providing the frigid environment that was needed for gravity to take hold and work its magic. As we witnessed the protostar form, we may also have seen something incredible. If the contents of this nebula are right, such as having a high amount of heavy metals and silicates (left over from the supernovae of previous, more massive stars) what we could begin to see would be planetary formation taking place in the accretion disk of material around the protostar.
Remaining gas and dust in the vicinity of our new star would begin to form dense pockets by the same mechanism of
Artistic rendition of a protoplanet forming within the accretion disk of a protostar Credit: ESO/L. Calçada http://www.eso.org/public/images/eso1310a/
gravity, eventually being able to accrete into protoplanets that will be made up of gas or silicates and metal (or a combination of the two). That being said, planetary formation is still somewhat a mystery to us, as there seems to be things that we cannot explain yet at work. But this model of star system formation seems to work well.
The life of the star isn’t nearly as exciting as its birth or death. We will continue to fast forward the clock and watch this star system evolve. Over a few billion years, the remnants of the Dark Nebula have been blown apart and have also formed other stars like the one we witnessed, and it no longer exists. The planets we saw being formed as the protostar grew begin their billion year dance around their parent star. Maybe on one of these worlds, a world that sits at just the right distance away from the star, liquid water exists. Within that water contains the amino acids that are needed for proteins (all composed of the elements that were left over by previous stellar eruptions). These proteins are able to link together to start to form RNA chains, then DNA chains. Maybe at one point a few billion years after the star has been born, we see a space-faring species launch itself into the cosmos, or perhaps they never achieve this for various reasons and remain planet-bound. Of course this is just speculation for our amusement. However, now we come to the end of our journey that began billions of years ago. The star begins to die.
The Hydrogen in its core is being fused into Helium, which depletes the Hydrogen over time; the star is running out of gas. After many years, the hydrogen fusion process begins to stop, and the star puts out less and less energy. This lack of outward pressure from the fusion process upsets what we call the hydrostatic equilibrium, and allows gravity (which is always trying to crush the star) to win. The star begins to shrink rapidly under its own weight. But, just as we discussed earlier, as the pressure increases, so too does the temperature. All of that Helium that was left over
Inward force of gravity versus the outward pressure of fusion within a star (hydrostatic equilibrium) Credit: NASA
from the billions of years of hydrogen fusion now begins to heat up in the core. Helium fuses at a much hotter temperature than Hydrogen does, which means that the Helium rich core is able to be pressed inward by gravity without fusing (yet). Since fusion isn’t occurring in the Helium core, there is little to no outward force (given off by fusion) to prevent the core from collapsing. This matter becomes much denser, which we now label as degenerate, and is pushing out massive amounts of heat (gravitational energy becoming thermal energy). This causes the remaining Hydrogen that is in subsequent layers above the Helium core to fuse, which causes the star to expand greatly as this Hydrogen shell burns out of control. This makes the star “rebound” and it expands rapidly; the more energetic fusion from the Hydrogen shells outside of the core expanding the diameter of the star greatly. Our star is now a red giant. Some, if not all of the inner planets that we witnessed form will be incinerated and swallowed up by the star that first gave them life. If there happened to be any life on any of those planets that didn’t manage to leave their home world, they would certainly be erased from the universe, never to be known of.
This process of the star running out of fuel (first Hydrogen, then Helium, etc…) will continue for a while. Eventually, the Helium in the core will reach a certain temperature and begin to fuse into Carbon, which will put off the collapse (and death) of the star. The star we are currently watching live and die is an average-sized Main Sequence Star, so its life ends once it is finished fusing Helium into
Different planetary nebulae, all remnants of low mass stars ejecting their outer material as they die Credit: NASA
Carbon. If the star was much larger, this fusion process would proceed until we reached Iron. Iron is the element in which fusion does not take place spontaneously, meaning it requires more energy to fuse it than it gives off after fusion. However, our star will never make it to Iron in its core, and thus it has died after it exhausts its Helium reservoir. When the fusion process finally “turns off” (out of gas), the star slowly begins to cool and the outer layers of the star expand and are ejected into space. Subsequent ejections of stellar material proceed to create what we call a planetary nebula, and all that is left of the once brilliant star we watched spring into existence is now just a ball of dense carbon that will continue to cool for the rest of eternity, possibly crystallizing into diamond.
The death we witnessed just now isn’t the only way a star dies. If a star is sufficiently large enough, its death is much more violent. The star will erupt into the largest explosion in the universe, called a supernova. Depending on many variables, the remnant of the star could end up as a neutron star, or even a black hole. But for most of what we call the average sized Main Sequence Stars, the death that we witnessed will be their fate.
Artistic representation of the material around the supernova 1987A. Supernovae are among the most violent events in the universe Credit: ESO/L. Calçada
Our journey ends with us pondering what we have observed. Seeing just what nature can do given the right circumstances, and watching a cloud of very cold gas and dust turn into something that has the potential to breathe life into the cosmos. Our minds wander back to that species that could have evolved on one of those planets. You think about how they may have gone through phases similar to us. Possibly using the stars as supernatural deities that guided their beliefs for thousands of years, substituting answers in for where their ignorance reigned. These beliefs could possibly turn into religions, still grasping that notion of special selection and magnanimous thought. Would the stars fuel their desire to understand the universe as the stars did for us? Your mind then ponders what our fate will be if we do not attempt to take the next step into the universe. Are we to allow our species to be erased from the cosmos as our star expands in its death? This journey you just made into the heart of a Dark Nebula truly exemplifies what the human mind can do, and shows you just how far we have come even though we are still bound to our solar system. The things you have learned were found by others like you simply asking how things occur and then bringing the full weight of our knowledge of physics to bare. Imagine what we can accomplish if we continue this process; being able to fully achieve our place among the stars.
The vastness of the cosmos awaits us… Credit: NASA (Hubble Deep Field)
Short time exposure of the star Sirius with the camera attached to a small telescope. I tapped the tube to make the star bounce around, recording the star's rapid color changes as it twinkled. All photos by the author
We all have cameras, and the sky’s an easy target, so why not have a little fun? Ever since I got my first camera at age 12 I wanted to shoot time exposures of the night sky. That and a tripod are all you need. Presented here for your enjoyment are a few oddball and yet oddly informative images of stars and planets. Take the word “art” loosely!
Colorless mess. This is the companion to the Sirius image and shows Jupiter through the telescope. Notice how blandly white it appears. That’s because Jupiter’s disk is large enough to not show twinkling (and color changes) caused by atmospheric turbulence as in the case of point-like Sirius. Credit: Bob KingPleasing parallels. Orion’s Belt and Sword trail in this time exposure made with a 200mm lens. The fuzzy pink streak is the Orion Nebula. They’re trails are nearly parallel because the stars all lie close to the celestial equator and were crossing the meridian at the time. Credit: Bob KingStar Trek Effect. I centered Jupiter in the viewfinder, pressed the shutter button for a 20-second time exposure and slowly hand-zoomed the lens from 70mm to 200mm. It took a few tries because I was shooting blind, but even the rejects weren’t too bad. Credit: Bob KingColor by Fog. The colors of stars are accentuated when spread into a glowing disk by fog or light cloud. Orion is at right with the crescent moon at lower left. Credit: Bob KingSnow flies. During a time exposure taken on a snowy but partly cloudy night, snowflakes, illuminated by a yard light, streak about beneath a Full Moon earlier this winter. Credit: Bob KingStuttering Stars. For this image of the Big Dipper the camera was on a tracking mount. I left the shutter open for about 25 minutes with the tracking turned off so the stars would trail. Then the lens was covered with a black cloth for a few minutes to create a gap between this exposure and the next. After the cloth was removed, I started the tracking motor and kept the exposure running for a few minutes. A diffusion filter was used in front of the lens to soften and enlarge the brightest stars. Credit: Bob King
Hubble image of the Crab Nebula supernova remnant captured with the Wide Field and Planetary Camera 2. Credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)
“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars,” Carl Sagan famously said in his 1980 series Cosmos. “We are made of starstuff.”
And even today, observations with NASA’s airborne SOFIA observatory are supporting this statement. Measurements taken of the dusty leftovers from an ancient supernova located near the center our galaxy – aka SNR Sagittarius A East – show enough “starstuff” to build our entire planet many thousands of times over.
“Our observations reveal a particular cloud produced by a supernova explosion 10,000 years ago contains enough dust to make 7,000 Earths,” said research leader Ryan Lau of Cornell University in Ithaca, New York – the same school, by the way, where Carl Sagan taught astronomy and space science.
Composite image of SNR Sgr A East showing infrared SOFIA data outlined in white against X-ray and radio observations. (NASA/CXO/Herschel/VLA/Lau et al.)
While it’s long been known that supernovae expel enormous amounts of stellar material into space, it wasn’t understood if clouds of large-scale dust could withstand the immense shockwave forces of the explosion.
These observations, made with the joint NASA/DLR-developed Faint Object InfraRed Camera for the SOFIA Telescope (FORCAST) instrument, provide key “missing-link” evidence that dust clouds do in fact survive intact, spreading outward into interstellar space to seed the formation of new systems.
Interstellar dust plays a vital role in the evolution of galaxies and the formation of new stars and protoplanetary discs – the orbiting “pancakes” of material around stars from which planets (and eventually everything on them) form.
The findings may also answer the question of why young galaxies observed in the distant universe possess so much dust; it’s likely the result of frequent supernova explosions from massive early-generation stars.
“We have begun to contemplate our origins: starstuff pondering the stars; organized assemblages of ten billion billion billion atoms considering the evolution of atoms; tracing the long journey by which, here at least, consciousness arose.”
Nova Sagittarii 2015 No. 2 photographed this morning when it was easily visible to the naked eye at magnitude +4.4. The nova has been on the upswing since its discovered less than a week ago. Credit: Bob King
Great news about that new nova in Sagittarius. It’s still climbing in brightness and now ranks as the brightest nova seen from mid-northern latitudes in nearly two years. Even from the northern states, where Sagittarius hangs low in the sky before dawn, the “new star” was easy to spy this morning at magnitude +4.4.
While not as rare as hen’s teeth, novae aren’t common and those visible without optical aid even less so. The last naked eye nova seen from outside the tropics was V339 Del (Nova Delphini), which peaked at +4.3 in August 2013. The new kid on the block could soon outshine it if this happy trend continues.
This view shows the sky facing south-southeast shortly before the start of dawn in late March from the central U.S. The nova is centrally located within the Teapot. Source: Stellarium
Now bearing the official title of Nova Sagittarii 2015 No. 2, the nova was discovered on March 15 by amateur astronomer and nova hunter John Seach of Chatsworth Island, NSW, Australia. At the time it glowed at the naked eye limit of magnitude +6. Until this morning I wasn’t able to see it with the naked eye, but from a dark sky site, it’s there for the picking. So long as you know exactly where to look.
The chart and photo above will help guide you there. At the moment, the star’s about 15° high at dawn’s start, but it rises a little higher and becomes easier to see with each passing day. Find your sunrise time HERE and then subtract an hour and 45 minutes. That will bring you to the beginning of astronomical twilight, an ideal time to catch the nova at its highest in a dark sky.
Use this AAVSO chart to pinpoint the nova’s location and also to help you estimate its brightness. Numbers shown are star magnitudes with the decimal points omitted. Credit: AAVSO
To see it with the naked eye, identify the star with binoculars first and then aim your gaze there. I hope you’ll be as pleasantly surprised as I was to see it. To check on the nova’s ups and downs, drop by the American Association Variable Star Observers (AAVSO) list of recent observations.
Seeing the nova without optical aid took me back to the time before the telescope when a “new star” in the sky would have been met with great concern. Changes in the heavens in that pre-telescopic era were generally considered bad omens. They were also thought to occur either in Earth’s atmosphere or within the Solar System. The universe has grown by countless light years since then. Nowadays we sweat the small stuff – unseen asteroids – which were unknown in that time.
AAVSO light curve showing the nova’s brightening since discovery. Dates are along the bottom, magnitudes at left. If the trend continues, Nova Sgr #2 could outshine the 2013 nova in Delphinus very soon. Credit: AAVSO
Novae occur in binary star systems where a tiny but gravitationally powerful white dwarf star pulls gases from a close companion star. The material piles up in a thin layer on the dwarf’s hot surface, fuses and burns explosively to create the explosion we dub a nova. Spectra of the expanding debris envelope reveal the imprint of hydrogen gas and as well as ionized iron.
Artist’s view of a nova with an expanding cloud of debris surrounding the central fireball emitting red hydrogen-alpha light.
Shortly after discovery, the nova’s debris shell was expanding at the rate of ~1,740 miles per second (2,800 km/sec) or more than 6.2 million mph (10 million mph). It’s since slowed to about half that rate. Through a telescope the star glows pale yellow but watch for its color to deepen to yellow orange and even red. Right now, it’s still in the fireball phase, with the dwarf star hidden by an envelope of fiery hydrogen gas.
As novae evolve, they’ll often turn from white or yellow to red. Emission of deep red light from hydrogen atoms – called hydrogen alpha – gives them their warm, red color. Hydrogen, the most common element in stars, gets excited through intense radiation or collisions with atoms (heat) and re-emits a ruby red light when it returns to its rest state. Astronomers see the light as bright red emission line in the star’s spectrum. Spectra of the nova show additional emission lines of hydrogen beta or H-beta (blue light emitted by hydrogen) and iron.
There are actually several reasons why novae rouge up over time, according to former AAVSO director Arne Henden:
“Energy from the explosion gets absorbed by the surrounding material in a nova and re-emitted as H-alpha,” said Henden. Not only that but as the explosion expands over time, the same amount of energy is spread over a larger area.
“The temperature drops,” said Henden, “causing the fireball to cool and turn redder on its own.” As the eruption expands and cools, materials blasted into the surrounding space condense into a shell of soot that absorbs that reddens the nova much the same way dusty air reddens the Sun.
Nova Sagittarii’s current pale yellow color results from seeing a mix of light – blue from the explosion itself plus red from the expanding fireball. As for its distance from Earth, I haven’t heard, but given that the progenitor star was 15th magnitude or possibly fainter, we’re probably talking in the thousands of light years.
Wide view of the Sagittarius-Scorpius region with some of the brighter star clusters and nebulae labeled for binocular browsing. Credit: Bob King
In an earlier article on the nova’s discovery I mentioned taking a look at Saturn as long as you made the effort the get up early. Here’s a photo of the Sagittarius region you can use to help you further your dawn binocular explorations. The entire region is rich with star clusters and nebula, many of which were cataloged long ago by French astronomer Charles Messier, hence the “M” numbers.
Brightest star Sirius (lower center) rules the anthropocene night. Credit and copyright: Alan Dyer.
What’s the brightest star you can see in the sky tonight?
If you live below 83 degrees north latitude, the brightest star in the sky is Canis Alpha Majoris, or Sirius. Seriously, (bad pun intended) the -1st magnitude star is usually the fifth brightest natural object in the sky, and sits high to the south on February evenings… but has it always ruled the night? Continue reading “What is the Brightest Star in the Sky, Past and Future?”
A binary star system Credit: Michael Osadciw/University of Rochester
Astronomers have reported the discovery of a star that passed within the outer reaches of our Solar System just 70,000 years ago, when early humans were beginning to take a foothold here on Earth. The stellar flyby was likely close enough to have influenced the orbits of comets in the outer Oort Cloud, but Neandertals and Cro Magnons – our early ancestors – were not in danger. But now astronomers are ready to look for more stars like this one.
A comparison of the Solar System and its Oort Cloud. 70,000 years ago, Scholz’s Star and companion passed along the outer boundaries of our Solar System (Credit: NASA, Michael Osadciw/University of Rochester, Illustration-T.Reyes)
Lead author Eric Mamajek from the University of Rochester and collaborators report in The Closest Known Flyby Of A Star To The Solar System (published in Astrophysical Journal on February 12, 2015) that “the flyby of this system likely caused negligible impact on the flux of long-period comets, the recent discovery of this binary highlights that dynamically important Oort Cloud perturbers may be lurking among nearby stars.”
The star, named Scholz’s star, was just 8/10ths of a light year at closest approach to the Sun. In comparison, the nearest known star to the Sun is Proxima Centauri at 4.2 light years.
While the internet has been rife with threads and accusations of a Nemesis star that is approaching the inner Solar System and is somehow being “hidden” by NASA, this small red dwarf star with a companion represents the real thing.
In 1984, the paleontologists David Raup and Jack Sepkoski postulated that a dim dwarf star, now widely known on the internet as the Nemesis Star, was in a very long period Solar orbit. The elliptical orbit brought the proposed star into the inner Solar System every 26 million years, causing a rain of comets and mass extinctions on that time period. By no coincidence, because of the sheer numbers of red dwarfs throughout the galaxy, Scholz’s star nearly fits such a scenario. Nemesis was proposed to be in a orbit extending 95,000 A.U. compared to Scholz’s nearest flyby distance of 50,000 A.U. Recent studies of impact rates on Earth, the Moon and Mars have discounted the existence of a Nemesis star (see New Impact Rate Count Lays Nemesis Theory to Rest, Universe Today, 8/1/2011)
But Scholz’s star — a real-life Oort Cloud perturber — was a small red dwarf star star with a M9 spectral classification. M-class stars are the most common star in our galaxy and likely the whole Universe, as 75% of all stars are of this type. Scholz’s is just 15% of the mass of our Sun. Furthermore, Scholz’s is a binary star system with the secondary being a brown dwarf of class T5. Brown Dwarfs are believed to be plentiful in the Universe but due to their very low intrinsic brightness, they are very difficult to discover … except, as in this case, as companions to brighter stars.
The astronomers reported that their survey of new astrometric data of nearby stars identified Scholz’s as an object of interest. The star’s transverse velocity was very low, that is, the stars sideways motion. Additionally, they recognized that its radial velocity – motion towards or away from us, was quite high. For Scholz’s, the star was speeding directly away from our Solar System. How close could Scholz’s star have been to our system in the past? They needed more accurate data.
The collaborators turned to two large telescopes in the southern hemisphere. Spectrographs were employed on the Southern African Large Telescope (SALT) in South Africa and the Magellan telescope at Las Campanas Observatory, Chile. With more accurate trangental and radial velocities, the researchers were able to calculate the trajectory, accounting for the Sun’s and Scholz’s motion around the Milky Way galaxy.
Scholz’s star is an active star and the researchers added that while it was nearby, it shined at a dimly of about 11th magnitude but eruptions and flares on its surface could have raised its brightness to visible levels and could have been seen as a “new” star by primitive humans of the time.
The relative sizes of the inner Solar System, Kuiper Belt and the Oort Cloud. (Credit: NASA, William Crochot)
At present, Scholz’s star is 20 light years away, one of the 70 closest stars to our Solar System. However, the astronomers calculated, with a 98% certainty, that Scholz’s passed within 0.5 light years, approximately 50,000 Astronomical Units (A.U.) of the Sun.
An A.U. is the mean distance from the Earth to the Sun and 50,000 is an important mile marker in our Solar System. It is the outer reaches of the Oort Cloud where billions of comets reside in cold storage, in orbits that take hundreds of thousands of years to circle the Sun.
With this first extraordinary close encounter discovered, the collaborators of this paper as well as other researchers are planning new searches for “Nemesis” type stars. The Large Synoptic Survey Telescope (LSST) and other telescopes within the next decade will bring an incredible array of data sets that will uncover many more red dwarf, brown dwarf and possibly orphan planets roaming in nearby space. Some of these could likewise be traced to past or future near misses to the Sun and Earth system.
