Tauris argues that a lopsided supernova explosion may be the source of certain hypervelocity stars (image credit: IsiacDaGraca).
Hypervelocity stars have been observed traversing the Galaxy at extreme velocities (700 km/s), but the mechanisms that give rise to such phenomena are still debated. Astronomer Thomas M. Tauris argues that lopsided supernova explosions can eject lower-mass Solar stars from the Galaxy at speeds up to 1280 km/s. “[This mechanism] can account for the majority (if not all) of the detected G/K-dwarf hypervelocity candidates,” he said.
Several mechanisms have been proposed as the source for hypervelocity stars, and the hypotheses can vary as a function of stellar type. A simplified summary of the hypothesis Tauris favors begins with a higher-mass star in a tight binary system, which finally undergoes a core-collapse supernova explosion. The close proximity of the stars in the system partly ensures that the orbital velocities are exceedingly large. The binary system is disrupted by the supernova explosion, which is lopsided (asymmetric) and imparts a significant kick to the emerging neutron star. The remnants of supernovae with massive progenitors are neutron stars or potentially a more exotic object (i.e., black hole).
Conversely, Tauris noted that the aforementioned binary origin cannot easily explain the observed velocities of all higher-mass hypervelocity stars, namely the B-stars, which are often linked to an ejection mechanism from a binary interaction with the supermassive black hole at the Milky Way’s center. Others have proposed that interactions between multiple stars near the centers of star clusters can give rise to certain hypervelocity candidates.
There are several potential compact objects (neutron stars) which feature extreme velocities, such as B2011+38, B2224+65, IGR J11014-6103, and B1508+55, with the latter possibly exhibiting a velocity of 1100 km/s. However, Tauris ends by noting that, “a firm identification of a hypervelocity star being ejected from a binary via a supernova is still missing, although a candidate exists (HD 271791) that’s being debated.”
The Milky Way is a spiral galaxy with several prominent arms containing stellar nurseries swathed in pink clouds of hydrogen gas. The sun is shown near the bottom in the Orion Spur. Credit: NASA
We live in a galaxy that is called the Milky Way. It’s called a barred spiral galaxy, which means that it has a spiral shape with a bar of stars across its middle. The galaxy is rather huge — at least 100,000 light-years in diameter, making it the second-biggest in our Local Group of galaxies.
More mind-blowing is that this mass of stars, gas, planets and other objects are all spinning. Just like a pinwheel. It’s spinning at 270 kilometers per second (168 miles per second) and takes about 200 million years to complete one rotation, according to the National Radio Astronomy Observatory. But why? More details below.
It’s worth taking a quick detour to talk about how long it takes the Solar System to move around the center of the galaxy. According to National Geographic, that’s about 225 million years. Dinosaurs were starting to arise the last time we were in the position we are today.
The rising Milky Way at Sentosa Island in Singapore. Credit and copyright: Justin Ng.
Scientists have mapped the spin using the Very Large Baseline Array, a set of radio telescopes. They examined spots where stars were forming and paid particular attention to those areas where gas molecules enhance radio emission, according to the National Radio Astronomy Observatory. Dubbed “cosmic masers”, these areas shine brightly in radio waves.
As Earth moves in its orbit, the shift of these molecules can be mapped against more distant objects. Measuring this shift shows how the entire galaxy rotates — and can even provide information about the mass of the Milky Way. So that’s all very neat, but why is it rotating in the first place?
If we think back to the early Universe, there are two big assumptions astronomers make, according to How Stuff Works: there was a lot of hydrogen and helium, with some parts denser than other areas. In the denser areas, gas clumped together in protogalactic clouds; the thickest areas collapsed into stars.
In this image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile young stars huddle together against a backdrop of clouds of glowing gas and lanes of dust. The star cluster, known as NGC 3293, would have been just a cloud of gas and dust itself about ten million years ago, but as stars began to form it became the bright group we see here. Clusters like this are celestial laboratories that allow astronomers to learn more about how stars evolve. Image Credit: ESO/G. Beccari
“These stars burned out quickly and became globular clusters, but gravity continued to collapse the clouds,” How Stuff Works wrote. “As the clouds collapsed, they formed rotating disks. The rotating disks attracted more gas and dust with gravity and formed galactic disks. Inside the galactic disk, new stars formed. What remained on the outskirts of the original cloud were globular clusters and the halo composed of gas, dust and dark matter.”
A simpler way to think about this is if you’re creating a pizza by tossing a ball of dough into the air. The spin of the dough creates a flat disc — just like what you observe in more complicated form in the Milky Way, not to mention other galaxies.
This artist’s impression shows the central part of the planetary nebula Henize 2-428. The core of this unique object consists of two white dwarf stars, each with a mass a little less than that of the Sun. They are expected to slowly draw closer to each other and merge in around 700 million years. This event will create a dazzling supernova of Type Ia and destroy both stars. Credit: ESO/L. Calçada
Two white dwarfs circle around one other, locked in a fatal tango. With an intimate orbit and a hefty combined mass, the pair is ultimately destined to collide, merge, and erupt in a titanic explosion: a Type Ia supernova.
Or so goes the theory behind the infamous “standard candles” of cosmology.
Now, in a paper published in today’s issue of Nature, a team of astronomers have announced observational support for such an arrangement – two massive white dwarf stars that appear to be on track for a very explosive demise.
The astronomers were originally studying variations in planetary nebulae, the glowing clouds of gas that red giant stars throw off as they fizzle into white dwarfs. One of their targets was the planetary nebula Henize 2-428, an oddly lopsided specimen that, the team believed, owed its shape to the existence of two central stars, rather than one. After observing the nebula with the ESO’s Very Large Telescope, the astronomers concluded that they were correct – Henize 2-428 did, in fact, have a binary star system at its heart.
This image of the unusual planetary nebula was obtained using ESO’s Very Large Telescope at the Paranal Observatory in Chile. In the heart of this colourful nebula lies a unique object consisting of two white dwarf stars, each with a mass a little less than that of the Sun. These stars are expected to slowly draw closer to each other and merge in around 700 million years. This event will create a dazzling supernova of Type Ia and destroy both stars. Credit: ESO
“Further observations made with telescopes in the Canary Islands allowed us to determine the orbit of the two stars and deduce both the masses of the two stars and their separation,” said Romano Corradi, a member of the team.
And that is where things get juicy.
In fact, the two stars are whipping around each other once every 4.2 hours, implying a narrow separation that is shrinking with each orbit. Moreover, the system has a combined heft of 1.76 solar masses – larger, by any count, than the restrictive Chandrasekhar limit, the maximum ~1.4 solar masses that a white dwarf can withstand before it detonates. Based on the team’s calculations, Henize 2-428 is likely to be the site of a type Ia supernova within the next 700 million years.
“Until now, the formation of supernovae Type Ia by the merging of two white dwarfs was purely theoretical,” explained David Jones, another of the paper’s coauthors. “The pair of stars in Henize 2-428 is the real thing!”
Check out this simulation, courtesy of the ESO, for a closer look at the fate of the dynamic duo:
Astronomers should be able to use the stars of Henize 2-428 to test and refine their models of type Ia supernovae – essential tools that, as lead author Miguel Santander-García emphasized, “are widely used to measure astronomical distances and were key to the discovery that the expansion of the Universe is accelerating due to dark energy.” This system may also enhance scientists’ understanding of the precursors of other irregular planetary nebulae and supernova remnants.
The team’s work was published in the February 9 issue of Nature. A copy of the paper is available here.
This artist’s impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus (The Centaur). Credit: ESO/M. Kornmesser
We’ve come a long way in 13.8 billion years; but despite our impressively extensive understanding of the Universe, there are still a few strings left untied. For one, there is the oft-cited disconnect between general relativity, the physics of the very large, and quantum mechanics, the physics of the very small. Then there is problematic fate of a particle’s intrinsic information after it falls into a black hole. Now, a new interpretation of fundamental physics attempts to solve both of these conundrums by making a daring claim: at certain scales, space and time simply do not exist.
Let’s start with something that is not in question. Thanks to Einstein’s theory of special relativity, we can all agree that the speed of light is constant for all observers. We can also agree that, if you’re not a photon, approaching light speed comes with some pretty funky rules – namely, anyone watching you will see your length compress and your watch slow down.
But the slowing of time also occurs near gravitationally potent objects, which are described by general relativity. So if you happen to be sight-seeing in the center of the Milky Way and you make the regrettable decision to get too close to our supermassive black hole’s event horizon (more sinisterly known as its point-of-no-return), anyone observing you will also see your watch slow down. In fact, he or she will witness your motion toward the event horizon slow dramatically over an infinite amount of time; that is, from your now-traumatized friend’s perspective, you never actually cross the event horizon. You, however, will feel no difference in the progression of time as you fall past this invisible barrier, soon to be spaghettified by the black hole’s immense gravity.
So, who is “correct”? Relativity dictates that each observer’s point of view is equally valid; but in this situation, you can’t both be right. Do you face your demise in the heart of a black hole, or don’t you? (Note: This isn’t strictly a paradox, but intuitively, it feels a little sticky.)
And there is an additional, bigger problem. A black hole’s event horizon is thought to give rise to Hawking radiation, a kind of escaping energy that will eventually lead to both the evaporation of the black hole and the destruction of all of the matter and energy that was once held inside of it. This concept has black hole physicists scratching their heads. Because according to the laws of physics, all of the intrinsic information about a particle or system (namely, the quantum wavefunction) must be conserved. It cannot just disappear.
Dr. Stephen Hawking of Cambridge University alongside illustrations of a black hole and an event horizon with Hawking Radiation. He continues to engage his grey matter to uncover the secrets of the Universe while others attempt to confirm his existing theories. (Photo: BBC, Illus.: T.Reyes)
Why all of these bizarre paradoxes? Because black holes exist in the nebulous space where a singularity meets general relativity – fertile, yet untapped ground for the elusive theory of everything.
Enter two interesting, yet controversial concepts: doubly special relativity and gravity’s rainbow.
Just as the speed of light is a universally agreed-upon constant in special relativity, so is the Planck energy in doubly special relativity (DSR). In DSR, this value (1.22 x 1019 GeV) is the maximum energy (and thus, the maximum mass) that a particle can have in our Universe.
Two important consequences of DSR’s maximum energy value are minimum units of time and space. That is, regardless of whether you are moving or stationary, in empty space or near a black hole, you will agree that classical space breaks down at distances shorter than the Planck length (1.6 x 10-35 m) and classical time breaks down at moments briefer than the Planck time (5.4 x 10-44 sec).
In other words, spacetime is discrete. It exists in indivisible (albeit vanishingly small) units. Quantum below, classical above. Add general relativity into the picture, and you get the theory of gravity’s rainbow.
Physicists Ahmed Farag Ali, Mir Faizal, and Barun Majumder believe that these theories can be used to explain away the aforementioned black hole conundrums – both your controversial spaghettification and the information paradox. How? According to DSR and gravity’s rainbow, in regions smaller than 1.6 x 10-35 m and at times shorter than 5.4 x 10-44 sec… the Universe as we know it simply does not exist.
“Say what??” -Albert Einstein
“In gravity’s rainbow, space does not exist below a certain minimum length, and time does not exist below a certain minimum time interval,” explained Ali, who, along with Faizal and Majumder, authored a paper on this topic that was published last month. “So, all objects existing in space and occurring at a time do not exist below that length and time interval [which are associated with the Planck scale].”
Luckily for us, every particle we know of, and thus every particle we are made of, is much larger than the Planck length and endures for much longer than the Planck time. So – phew! – you and I and everything we see and know can go on existing. (Just don’t probe too deeply.)
The event horizon of a black hole, however, is a different story. After all, the event horizon isn’t made of particles. It is pure spacetime. And according to Ali and his colleagues, if you could observe it on extremely short time or distance scales, it would cease to have meaning. It wouldn’t be a point-of-no-return at all. In their view, the paradox only arises when you treat spacetime as continuous – without minimum units of length and time.
“As the information paradox depends on the existence of the event horizon, and an event horizon like all objects does not exist below a certain length and time interval, then there is no absolute information paradox in gravity’s rainbow. The absence of an effective horizon means that there is nothing absolutely stopping information from going out of the black hole,” concluded Ali.
No absolute event horizon, no information paradox.
And what of your spaghettification within the black hole? Again, it depends on the scale at which you choose to analyze your situation. In gravity’s rainbow, spacetime is discrete; therefore, the mathematics reveal that both you (the doomed in-faller) and your observer will witness your demise within a finite length of time. But in the current formulation of general relativity, where spacetime is described as continuous, the paradox arises. The in-faller, well, falls in; meanwhile, the observer never sees the in-faller pass the event horizon.
“The most important lesson from this paper is that space and time exist only beyond a certain scale,” said Ali. “There is no space and time below that scale. Hence, it is meaningless to define particles, matter, or any object, including black holes, that exist in space and time below that scale. Thus, as long as we keep ourselves confined to the scales at which both space and time exist, we get sensible physical answers. However, when we try to ask questions at length and time intervals that are below the scales at which space and time exist, we end up getting paradoxes and problems.”
To recap: if spacetime continues on arbitrarily small scales, the paradoxes remain. If, however, gravity’s rainbow is correct and the Planck length and the Planck time are the smallest unit of space and time that fundamentally exist, we’re in the clear… at least, mathematically speaking. Unfortunately, the Planck scales are far too tiny for our measly modern particle colliders to probe. So, at least for now, this work provides yet another purely theoretical result.
The paper was published in the January 23 issue of Europhysics Letters. A pre-print of the paper is available here.
The Sun provides energy for life here on Earth through light and heat. Credit: NASA Goddard Space Flight Center
A quick think about optical astronomy would have you imagine that most of it takes place at night. Isn’t that when the stars and galaxies come out to play? Well, that assumption makes at least one glaring error: Earth happens to be close to a star that is worthy of study. It’s called the Sun, and it only appears during the day.
We love being close to the Sun because it gives energy that gives us light. But that same energy can also be damaging to eyes and to instruments. Below are how amateurs and professionals alike safely observe our closest stellar neighbor.
Amateur astronomy
The safest way to observe the Sun is by projecting it on to a surface. By doing this, you’ll be able to see huge sunspots and you can also watch as the star marches through a solar eclipse — if you’re lucky enough to be in the area.
This is how Sky & Telescope suggests you get it done: “Poke a small hole in an index card with a pencil point, face it toward the Sun, and hold a second card three or four feet behind it in its shadow. The hole will project a small image of the Sun’s disk onto the lower card.”
The partial solar eclipse on Nov. 2, 2013 at its peak over Israel. Credit and copyright: Gadi Eidelheit.
If you prefer to look at the Sun directly, you must protect your eyes and your equipment (binoculars/telescope/camera) from looking at it unexposed. We’ll refer you again to the Sky & Telescope article for the best expertise, but in general, understand that you will need special equipment to do it safely.
Professional astronomy
There are numerous larger telescopes that are used on the ground, which typically have special filters to block out the damaging parts of the Sun’s light. We have a few examples below, but we’re sure you’ll come up with more examples from your own neighborhoods!
Of note, professional astronomers use multiple tools to look at the Sun. They can examine the Sun in different wavelengths of light to see its surface and corona. They can use spectroscopy to see the elements produced in different parts of the Sun. They can study its radiation using radar, or its interior using techniques such as acoustic interferometry.
U.S. National Solar Observatory: The observatory has two major optical facilities, called the Dunn Solar Telescope (Sacramento Peak) and the McMath-Pierce Solar Telescope (Kitt Peak). Luckily for the public, both are open to visitors. The observatory also is part of the Global Oscillation Network Group, which looks at acoustic waves inside the Sun using six stations spaced around the world.
Big Bear Solar Observatory‘s New Solar Telescope can view features on the Sun that are as small as 50 miles (80 kilometers) across. It saw “first light” in 2010 and for now, is the largest aperture solar telescope at 1.6 meters across.
But that’s not all we’ve got. Here are a few examples of space telescopes in orbit:
The Sun as viewed by the Solar and Heliospheric Observatory (NASA/SOHO)
Solar and Heliospheric Observatory (SOHO): Launched in 1995, this NASA and European Space Agency is supposed to study the Sun’s interior, figure out more about the superheated solar corona or envelope that surrounds the Sun, and understand how the solar wind is created. It’s also a famous comet catcher and observer.
STEREO (Solar TErrestrial RElations Observatory):Launched in 2006, these twin spacecraft are in different parts of the Earth’s orbit: one ahead, and one behind. Their goal is to produce three-dimensional images of the Sun to improve space weather forecasting (specifically, when large eruptions on the Sun could disrupt Earth communications). As of early 2015, STEREO-B is not communicating with Earth.
Solar Dynamics Observatory: Launched in 2010, it aims to understand why the Sun has an 11-year solar cycle and to learn more about the Sun’s magnetic field and energy. The ultimate goal, again, is to improve space weather predictions.
We have written many articles about solar observatories, both ground and space-based, here on Universe Today. Here’s an article about the STEREO spacecraft seeing a tsunami on the Sun. We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.
Sometimes, it seems to be a cosmic misfortune that we only get to view the universe from a singular vantage point.
Take the example of our single natural satellite. As the Moon waxes and wanes through its cycle of phases, we see the familiar face of the lunar nearside. This holds true from the day we’re born until the day we die. The Romans and Paleolithic man saw that same face, and until less than a century ago, it was anyone’s guess as to just what was on the other side.
Enter the Space Age and the possibility to finally get a peek at the universe from different perspective via our robotic ambassadors. This week, the folks over at NASA’s Scientific Visualization Studio released a unique video simulation that utilized data from NASA’s Lunar Reconnaissance Orbiter to give us a view unseen from Earth. This perspective shows just what the phases of the Moon would look like from the vantage point of the lunar farside:
You can see the Moon going through the synodic 29.5 day period a familiar phases, albeit with an unfamiliar face. Note that the Sun zips by, as the lunar farside wanes towards New. And in the background, the Earth can be seen, presenting an identical phase and tracing out a lazy figure eight as it appears and disappears behind the lunar limb.
The lunar nearside: A familiar view. Credit: Stephen Rahn.
What’s with the lunar-planetary game of peek-a-boo? Well, the point of view for the video assumes that your looking at down at the lunar farside from a stationary point above the Moon. Note that the disk of the Moon stays fixed in place. The Moon actually ‘rocks’ or nods back and forth and side-to-side in motions referred to as libration and nutation, and you’re seeing these expressed via the motion of the Earth in the video. This assures that we actually get a peek over the lunar limb and see a foreshadowed extra bit of the lunar farside, with grand 59% of the lunar surface visible from the Earth. Such is the wacky motion of our Moon, which gave early astronomers an excellent crash course in celestial mechanics 101.
Now, to dispel some commonly overheard lunar myths:
Myth #1: The moon doesn’t rotate. Yes, it’s tidally locked from our perspective, meaning that it keeps one face turned Earthward. But it does turn on its axis in lockstep as it does so once every 27.3 days, known as a sidereal month.
Myth #2: The Farside vs. the Darkside. (Cue Pink Floyd) We do in fact see the dark or nighttime side of the Moon just as much as the daytime side. Despite popular culture, the farside is only synonymous with the darkside of the Moon during Full phase.
Humanity got its first glimpse of the lunar farside in 1959, when the Soviet Union’s Luna 3 spacecraft looked back as it flew past the Moon and beamed us the first blurry image. The Russians got there first, which is why the lunar farside now possesses names for features such as the “Mare Moscoviense”.
Our evolving view of the lunar farside over 60 years… Credit: NASA/LRO.
Think we’ve explored the Moon? Thus far, no mission – crewed or otherwise – has landed on the lunar farside. The Apollo missions were restricted to nearside landing sites at low latitudes with direct line of sight communication with the Earth. The same goes for the lunar poles: the Moon is still a place begging for further exploration.
China’s Chang’e 5 T1 pathfinder mission looks back at the Earth and the lunar farside. Credit: Xinhua/SASTIND.
Why go to the lunar farside? Well, it would be a great place to do some radio astronomy, as you have the bulk of the Moon behind you to shield your sensitive searches from the now radio noisy Earth. Sure, the dilemmas of living on the lunar farside might forever outweigh the benefits, and abrasive lunar dust will definitely be a challenge to lunar living… perhaps an orbiting radio astronomy observatory in a Lissajous orbit at the L2 point would be a better bet?
An artist’s conception of LRO in lunar orbit. Credit: NASA/LRO.
And exploration of the Moon continues. Earlier this week, the LRO team released a finding suggesting that surface hydrogen may be more abundant on the poleward facing slopes of craters that litter the lunar south pole region. Locating caches of lunar ice in permanently shadowed craters will be key to a ‘living off of the land’ approach for future lunar colonists… and then there’s the idea to harvest helium-3 for nuclear fusion (remember the movie Moon?) that’s still science fiction… for now.
Perhaps the Moonbase Alpha of Space: 1999 never came to pass… but there’s always 2029!
One several images NASA's Dawn spacecraft took on approach to Ceres on Feb. 4, 2015 at a distance of about 90,000 miles (145,000 kilometers) from the dwarf planet. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
NASA’s Dawn spacecraft has acquired its latest and closest-yet snapshot of the mysterious dwarf planet world Ceres. These latest images, taken on Feb. 4, from a distance of about 90,000 miles (145,000 km) clearly show craters – including a couple with central peaks – and a clearer though still ambiguous view of that wild white spot that has so many of us scratching our heads as to its nature.
Get ready to scratch some more. The mystery spot has plenty of company.
Take a look at some still images I grabbed from the video which NASA made available today. In several of the photos, the white spot clearly looks like a depression, possibly an impact site. In others, it appears more like a rise or mountaintop. But perhaps the most amazing thing is that there appear to be not one but many white dabs and splashes on Ceres’ 590-mile-wide globe. I’ve toned the images to bring out more details:
Here the spot appears more like a depression. Frost? Ice? Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDAHere the white spot is at the asteroid’s left limb. You can also see lots of additional smaller spots that remind me of rayed lunar craters. Of course, they may be something else entirely. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDALook down along the lower limb to spot a crater with a cool central peak. Note also how many white spots are now visible on Ceres. The mystery spot is a little right of center in this view. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDAOur mystery white spot is further right of center. Is it a rise or a hole?Are the streaks rays for fresh material from an impact the way the lunar crater Tycho appears from Earth? Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDAYet another view of the mystery spot. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Animation made from images taken by Dawn on Feb. 4. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Now let’s take a look at an additional NASA animation of Ceres made using processed images. As the spot first rounds the limb it looks like a depression. But just before it disappears around the backside a pointed peak seems to appear. Intriguing, isn’t it?
M1-67 is the youngest wind-nebula around a Wolf-Rayet star, called WR124, in our Galaxy. Credit: ESO
Wolf-Rayet stars represent a final burst of activity before a huge star begins to die. These stars, which are at least 20 times more massive than the Sun, “live fast and die hard”, according to NASA.
Their endstate is more famous; it’s when they explode as supernova and seed the universe with cosmic elements that they get the most attention. But looking at how the star gets to that explosive stage is also important.
When you look at a star like the Sun, what you are seeing is a delicate equilibrium of the star’s gravity pulling stuff in, and nuclear fusion inside pushing pressure out. When the forces are about equal, you get a stable mass of fusing elements. For planets like ours lucky enough to live near a stable star, this period can go on for billions upon billions of years.
Being near a massive star is like playing with fire, however. They grow up quickly and thus die earlier in their lives than the Sun. And in the case of a Wolf-Rayet star, it’s run out of lighter elements to fuse inside its core. The Sun is happily churning hydrogen into helium, but Wolf-Rayets are ploughing through elements such as oxygen to try to keep equilibrium.
The core of a red or blue supergiant moments before exploding as a supernova looks like an onion with multiple elements “burning” through the fusion process to create the heat to stay the force of gravity. Fusion stops at iron. With no energy pouring from the central core to keep the other elements cooking, the star collapses and the rebounding shock wave tears it apart. Credit: Wikimedia
Because these elements have more atoms per unit, this creates more energy — specifically, heat and radiation, NASA says. The star begins to blow out winds reaching 2.2 million to 5.4 million miles per hour (3.6 million to 9 million kilometers per hour). Over time, the winds strip away the outer layers of the Wolf-Rayet. This eliminates much of its mass, while at the same time freeing its elements to be used elsewhere in the Universe.
Eventually, the star runs out of elements to fuse (the process can go no further than iron). When the fusion stops, the pressure inside the star ceases and there’s nothing to stop gravity from pushing in. Big stars explode as supernova. Bigger ones see their gravity warped so much that not even light can escape, creating a black hole.
We still have a lot to learn about stellar evolution, but a few studies over the years have provided insights. In 2004, for example, NASA issued reassuring news saying these stars don’t “die alone.” Most of them have a stellar companion, according to Hubble Space Telescope observations.
A composite image with Chandra data (purple) showing a “point-like source” beside the remains of a supernova, suggesting a companion star may have survived the explosion. Hydrogen is shown in optical light (yellow and cyan) from the Magellanic Cloud Emission Line Survey and there is also optical data available from the Digitized Sky Survey (white). Credit: X-ray: NASA/CXC/SAO/F.Seward et al; Optical: NOAO/CTIO/MCELS, DSS
While at first glance this appears as just a simple observation, cosmologists said that it could help us figure out how these stars get so big and bright. For example: Maybe the bigger star (the one that turns into a Wolf-Rayet) feeds off its companion over time, gathering mass until it becomes stupendously big. With more fuel, the big stars burn out faster. Other things the smaller star could influence could be the bigger star’s rotation or orbit.
Here’s a few other facts about Wolf-Rayets, courtesy of astronomer David Darling:
Their names come from two French astronomers, Charles Wolf and Georges Rayet, who discovered the first known star of this kind in 1867.
Wolf-Rayets come in two flavours: WN (emission lines of helium and nitrogen) and WC (carbon, oxygen and hydrogen).
Stars like our Sun evolve into more massive red giants as they run out of hydrogen to burn in the core. When these stars begin to shed their outer layers, they behave somewhat similarly to Wolf-Rayets. So they’re called “Wolf-Rayet type stars”, although they’re not exactly the same thing.
Rosetta will dance close to 67P on Valentine's Day coming to within 3.7 miles of the comet. Credit: Bob King
Who doesn’t like to snuggle up with their Valentine on Valentine’s Day? Rosetta will practically whisper sweet nothings into 67P’s ear on February 14 when it swings just 3.7 miles (6 km) above its surface, its closest encounter yet.
Rosetta had been orbiting the comet at a distance of some 16 miles (26 km) but beginning yesterday, mission controllers used the spacecraft’s thrusters to change its orbit in preparation for the close flyby. First, Rosetta will move out to a distance of roughly 87 miles (140 km) from the comet this Saturday before swooping in for the close encounter at 6:41 a.m. CST on Feb. 14. Closest approach happens over the comet’s larger lobe, above the Imhotep region.
The relative position of Rosetta with Comet 67P/Churyumov–Gerasimenko at the moment of closest approach this Valentine’s Day when the spacecraft will pass just 3.7 miles (6 km) above the comet’s large lobe. Credit: ESA/C.Carreau with additions by the author
The close encounter will provide opportunities for Rosetta’s science instruments to photograph 67P’s surface at high resolution across a range of wavelengths as well as get a close sniff of what’s inside its innermost coma or developing atmosphere. Scientists will also be looking closely at the outflowing gas and dust to see how it evolves during transport from the comet’s interior to the coma and tail.
As Rosetta swoops by its view of the comet will continuously change. Instruments will collect data on how 67P’s dust grains reflect light across a variety of orbital perspectives – from shadowless lighting with the Sun at the orbiter’s back to slanted lighting angles – to learn more about its properties.
The Imhotep region of comet 67P features a large, relatively smooth region and a smattering of large boulders. Rosetta will make high resolutions of Imhotep during its close flyby. Credit: ESA/Rosetta/Navcam
“After this close flyby, a new phase will begin, when Rosetta will execute sets of flybys past the comet at a range of distances, between about 15 km (9 miles) and 100 km (62 miles),” said Sylvain Lodiot, ESA’s spacecraft operations manager.
During some of the close flybys, Rosetta trajectory will be almost in step with the comet’s rotation, allowing the instruments to monitor a single point on the surface in great detail as it passes by.
Helpful animation of how ESA mission controllers are changing Rosetta’s orbit to ready the probe for the Valentine’s Day flyby.
Perihelion, when the comet arcs closest to the Sun at a distance of 115.6 million miles (186 million km), occurs on August 13. Activity should be reaching its peak around that time. Beginning one month before, the Rosetta team will identify and closely examine one of the comet’s jets in wickedly rich detail.
“We hope to target one of these regions for a fly-through, to really get a taste of the outflow of the comet,” said Matt Taylor, ESA’s Rosetta project scientist.
This colorized image taken by the Cassini orbiter, shows Saturn's A and F rings, the small moon Epimetheus and Titan, the planet's largest moon.
Credit: NASA/JPL/Space Science Institute
Planetary rings are an interesting phenomena. The mere mention of these two words tends to conjure up images of Saturn, with its large and colorful system of rings that form an orbiting disk. But in fact, several other planets in our Solar System have rings. It’s just that, unlike Saturn, their systems are less visible, and perhaps less beautiful to behold.
Thanks to exploration efforts mounted in the past few decades, which have seen space probes dispatched to the outer Solar System, we have come to understand that all the gas giants – Jupiter, Saturn, Uranus and Neptune – all have their own ring systems. And that’s not all! In fact, ring systems may be more common than previously thought…
Jupiter’s Rings:
In was not until 1979 that the rings of Jupiter were discovered when the Voyager 1 space probe conducted a flyby of the planet. They were also thoroughly investigated in the 1990s by the Galileo orbiter. Because it is composed mainly of dust, the ring system is faint and can only be observed by the most powerful telescopes, or up-close by orbital spacecraft. However, during the past twenty-three years, it has been observed from Earth numerous times, as well as by the Hubble Space Telescope.
A schema of Jupiter’s ring system showing the four main components. Credit: NASA/JPL/Cornell University
The ring system has four main components: a thick inner torus of particles known as the “halo ring”; a relatively bright, but extremely thin “main ring”; and two wide, thick, and faint outer “gossamer rings”. These outer rings are composed of material from the moons Amalthea and Thebe and are named after these moons (i.e. the “Amalthea Ring” and “Thebe Ring”).
The main and halo rings consist of dust ejected from the moons Metis, Adrastea, and other unobserved parent bodies as the result of high-velocity impacts. Scientists believe that a ring could even exist around the moon of Himalia’s orbit, which could have been created when another small moon crashed into it and caused material to be ejected from the surface.
Saturn’s Rings:
The rings of Saturn, meanwhile, have been known for centuries. Although Galileo Galilei became the first person to observe the rings of Saturn in 1610, he did not have a powerful enough telescope to discern their true nature. It was not until 1655 that Christiaan Huygens, the Dutch mathematician and scientist, became the first person to describe them as a disk surrounding the planet.
Subsequent observations, which included spectroscopic studies by the late 19th century, confirmed that they are composed of smaller rings, each one made up of tiny particles orbiting Saturn. These particles range in size from micrometers to meters that form clumps orbiting the planet, and which are composed almost entirely of water ice contaminated with dust and chemicals.
Saturn and its rings, as seen from above the planet by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute/Gordan Ugarkovic
In total, Saturn has a system of 12 rings with 2 divisions. It has the most extensive ring system of any planet in our solar system. The rings have numerous gaps where particle density drops sharply. In some cases, this due to Saturn’s Moons being embedded within them, which causes destabilizing orbital resonances to occur.
However, within the Titan Ringlet and the G Ring, orbital resonance with Saturn’s moons has a stabilizing influence. Well beyond the main rings is the Phoebe ring, which is tilted at an angle of 27 degrees to the other rings and, like Phoebe, orbits in retrograde fashion.
Uranus’ Rings:
The rings of Uranus are thought to be relatively young, at not more than 600 million years old. They are believed to have originated from the collisional fragmentation of a number of moons that once existed around the planet. After colliding, the moons probably broke up into numerous particles, which survived as narrow and optically dense rings only in strictly confined zones of maximum stability.
Uranus has 13 rings that have been observed so far. They are all very faint, the majority being opaque and only a few kilometers wide. The ring system consists mostly of large bodies 0.2 to 20 m in diameter. A few rings are optically thin and are made of small dust particles which makes them difficult to observe using Earth-based telescopes.
The labeled ring arcs of Neptune as seen in newly processed data. Credit: M. Showalter/SETI Institute
Neptune’s Rings:
The rings of Neptune were not discovered until 1989 until the Voyager 2 space probe conducted a flyby of the planet. Six rings have been observed in the system, which are best described as faint and tenuous. The rings are very dark, and are likely composed by organic compounds processed by radiation, similar to that found in the rings of Uranus. Much like Uranus, and Saturn, four of Neptune’s moons orbit within the ring system.
Other Bodies:
Back in 2008, it was suggested that the magnetic effects around the Saturnian moon of Rhea may indicate that it has its own ring system. However, a subsequent study indicated that observations obtained the Cassini mission suggested that some other mechanism was responsible for the magnetic effects.
Years before the the New Horizons probe visited the system, astronomers speculated that Pluto might also have a ring system. However, after conducting its historic flyby of the system in July of 2015, the New Horizons probe did not find any evidence of a ring system. While the dwarf planet had many satellites aside from its largest (Charon), debris from around the planet has not coalesced into rings, as was theorized.
Artist’s impression of the New Horizons spacecraft in orbit around Pluto (Charon is seen in the background). Credit: NASA/JPL
The minor planet of Chariklo – an asteroid that orbits the Sun between Saturn and Uranus – also has two rings that orbit it. These are perhaps due to a collision that caused a chain of debris to form in orbit around it. The announcement of these rings was made on March 26th of 2014, and was based on observations made during a stellar occultation on June 3rd, 2013.
This was followed by findings made in 2015 that indicated that 2006 Chiron – another major Centaur – could have a ring of its own. This led to further speculation that there might be many minor planets in our Solar System that have a system of rings.
In short, four planets in our Solar System have intricate ring systems, as well as the minor planet Chariklo, and perhaps even many other smaller objects. In this sense, ring systems appear to be a lot more common in our Solar System than previously thought.
