Herschel's look at the Southern Cross. Credits: ESA and the PACS consortium
[/caption]For the lucky residents of the Southern Hemisphere, or those fortunate enough to enjoy a vacation in Hawaii or Cancun, there’s a stellar delight that few Northerners know about. It’s called the Southern Cross, a small but beautiful constellation located in the southern sky, very close to the neighboring constellation of Centaurus. Originally known by the Latin name Crux, which is due to its cross shape, this constellation is one of the easiest to identify in the night sky. For centuries, it has served as a navigational beacon for sailors, an important symbol to the Egyptians, and played an important role in the spiritual beliefs of the Aborigines and many other cultures in the Southern Hemisphere.
The first recorded example of Crux’s discovery was around 1000 BC during the time of the Ancient Greeks. At the latitude of Athens, Crux was clearly visible, though low in the night sky. At the time, the Greeks identified it as being part of the constellation Centaurus. However, the precession of the equinoxes gradually lowered its stars below the European horizon, and they were eventually forgotten by the inhabitants of northern latitudes. Crux fell into anonymity for northerners until the Age of Discovery (from the early 15th to early 17th centuries) when it was rediscovered by Europeans. The first to do so were the Portuguese, who mapped it for navigation uses while rounding the southern tip of Africa. During this time, Crux was also separated from Centaurus, though it is not altogether clear who was responsible. Some attribute it to the French astronomer Augustin Royer who did it in 1679 while others believe it was Dutch astronomer PetrusPlancius who did the deed in 1613. Regardless, it is believed to have taken place in the 17th century, placing it within the context of European expansion and the revolution that was taking place in the sciences at the time.
In terms of cultural significance, the Crux, like all constellations, played an important role in the belief system of many cultures. In the ancient mountaintop village of Machu Picchu, a stone engraving exists which depicts the constellation. In addition, in Quechua (the language of the Incas) Crux is known as “Chakana”, which literally means “stair”, and holds deep symbolic value in Incan mysticism (the cross represented the three tiers of the world: the underworld, world of the living, and the heavens). To the Aborigines and the Maori, Crux is representative of animist spirits who play a central role in their ancestral beliefs. To the ancient Egyptians, Crux was the place where the Sun Goddess Horus was crucified, and marked the passage of the winter season. The Southern Cross is also featured prominently on the flags of several southern nations, including Australia, Brazil, New Zealand, Papua New Guinea, and Samoa.
We have written many articles about the Southern Cross constellation for Universe Today. Here’s an article about Crux, and here’s an article about constellations.
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It was just over a century ago that a little known French scientist named Henri Becquerel came across something new and immensely startling. At the time, while working with phosphorescent materials (i.e. materials that glow in the dark after being subjected to light), he discovered naturally occurring rays that he couldn’t account for. In time, these rays were discovered to be present in several naturally occurring elements, and were dubbed radioactivity. Those metals that exhibited them also came to be known as Radioactive Isotopes.
Radioisotopes, (also known as radioactive isotopes or radionuclides), are atoms with a different number of neutrons than a usual atom. Due to this imbalance, these isotopes have an unstable nucleus that decays, and in the process emitting alpha, beta and gamma rays until the isotope reaches stability. Once it’s stable, the isotope has transformed into another element entirely. Every chemical element has one or more radioisotopes, with over 1,000 isotopes accounted for in total. Approximately 50 of these are found in nature; the rest are produced artificially as the direct result of nuclear reactions or indirectly as the radioactive descendants of these products.
Of the naturally occurring radioisotopes, there are three categories that are used to group them. The first is primordial radionuclides, which originate mainly within the interior of stars and like uranium and thorium, are still present because their half-lives are so long that they have not yet completely decayed. The second group, secondary radionuclides, are radiogenic isotopes derived from the decay of primordial radionuclides and are characterized by their shorter half-lives. The third and final group is known cosmogenic radionuclides, which consists of isotopes like Carbon 14 which are constantly produced in the atmosphere due to cosmic rays. Artificially produced radionuclides, on the other hand, are produced by nuclear reactors, particle accelerators or by radionuclide generators (where a parent isotope, usually produced in a nuclear reactor, is allowed to decay to produce a radioisotope). In addition, nuclear explosions are known to produce artificial radioisotopes as well.
Radioisotopes are used today for a variety of purposes. When it comes to the field of nuclear medicine, radioactive isotopes are used in MRI’s and X-rays for diagnostic purposes, for targeted radiation therapy, and to sterilize medical equipment. In biochemistry and genetics, radionuclides are used in molecular and DNA research in order to “label” molecules and trace chemical and physiological processes. Carbon-14, a naturally occurring cosmogenic isotope, is used for carbon dating by archeologists, paleontologists, and geologists. In agriculture, radiation is used to stop the sprouting of root crops, kill parasites and pests, and in veterinary medicine. And when it comes to industry, radionuclides are used to study the rate of wear and corrosion of metals, to test for leaks and seams, analyze pollutants, study the movement of surface water, measure water runoffs from rain and snow, and the flow rates of streams and rivers.
We have written many articles about radioisotopes for Universe Today. Here’s an article about isotopes, and here’s an article about radioactive decay.
[/caption]In the world of physics, there are few people who have been more influential than Sir Isaac Newton. In addition to his contributions to astronomy, mathematics, and empirical philosophy, he is also the man who pioneered classical physics with his laws of motion. Of these, the first, otherwise known as the Law of Inertia, is the most famous and arguably the most important. In the language of science, this law states that: Every body remains in a state of constant velocity unless acted upon by an external unbalanced force. This means that in the absence of a non-zero net force, the center of mass of a body either remains at rest, or moves at a constant velocity. Put simply, it states that a body will remain at rest or in motion unless acted upon by an external and unbalanced force.
Prior to Aristotle’s theories on inertia, the most generally accepted theory of motion was based on Aristotelian philosophy. This ancient theory stated that, in the absence of an external motivating power, all objects on Earth would come to rest and that moving objects only continue to move so long as long there is a power inducing them to do so. In a void, no motion would be possible since Aristotle’s theory claimed that the motion of objects was dependent on the surrounding medium, that it was responsible for moving the object forward in some way. By the Renaissance, however, this theory was coming to be rejected as scientists began to postulate that both air resistance and the weight of an object would play a role in arresting the motion of that object.
Further advances in astronomy were another nail in this coffin. The Aristotelian division of motion into “mundane” and “celestial” became increasingly problematic in the face of Copernicus’ model in the 16th century, who argued that the earth (and everything on it) was in fact never “at rest”, but was actually in constant motion around the sun.Galileo, in his further development of the Copernican model, recognized these problems and would later go on to conclude that based on this initial premise of inertia, it is impossible to tell the difference between a moving object and a stationary one without some outside point of comparison.
Thus, though Newton was not the first to express the concept of inertia, he would later refine and codify them as the first law of motion in his seminal work PhilosophiaeNaturalis Principia Mathematica (Mathematical Principals of Natural Philosophy) in 1687, in which he stated that: unless acted upon by a net unbalanced force, an object will maintain a constant velocity. Interestingly enough, the term “interia” was not used in the study. It was in fact JohanneKepler who first used it in his Epitome AstronomiaeCopernicanae (Epitome of Copernican Astronomy) published from 1618–1621. Nevertheless, the term would later come to be used and Newton recognized as being the man most directly responsible for its articulation as a theory.
We have written many articles about the law of inertia for Universe Today. Here’s an article about Newton’s Laws of Motion, and here’s an article about Newton’s first law.
If you’d like more info on the law of inertia, check out these articles from How Stuff Works and NASA.
We’ve also recorded an entire episode of Astronomy Cast all about Gravity. Listen here, Episode 102: Gravity.
[/caption]In the last few centuries, in which time we have had several scientific revolutions, our understanding of heat, energy and the exchange thereof has grown exponentially. In particular has been the increasing ability to gauge the amounts of energy involved in particular processes and in turn create theoretical frameworks, units, and even tools with which to measure them. One such concept is the measurement known as Emissivity. Essentially, this is the relative ability of a material’s surface (usually written ? or e) to emit energy as radiation. It is expressed as the ratio of the emissivity of the material in question to the radiation emitted by a blackbody (an idealized physical body that absorbs all incident electromagnetic radiation) at the same temperature. This means that while a true black body would have an emissivity value of 1 (? = 1), any other object, known as a “grey body”, would have an emissivity value of less than 1 (? < 1).
In general, the duller and blacker a material is, the closer its emissivity is to 1. The more reflective a material is, the lower its emissivity. Emissivity also depends on such factors as temperature, emission angle, and wavelength of the radiation. At the opposite end of the spectrum is the material’s absorptivity (or absorptance), which is the measure of radiation absorbed by a material at a particular wavelength. When dealing with non-black surfaces, the relative emissivity follows Kirchhoff's law of thermal radiation which states that emissivity is equal to absorptivity. Essentially an object that does not absorb all incident light will also emit less radiation than an ideal black body.
An important function for emissivity has to do with the Earth’s atmosphere. Like all other “grey bodies”, the Earth’s atmosphere is able to absorb and emit radiation. The overall emissivity of Earth's atmosphere varies according to cloud cover and the concentration of gases that absorb and emit energy in the thermal infrared (i.e. heat energy). In this way, and by using the same criteria by which they are able to calculate the emissivity of “grey bodies”, scientists are able to calculate the amount of thermal radiation emitted by the atmosphere, thereby gaining a better understanding of the Greenhouse Effect.
Every known material has an emissivity coefficient. Those that have a higher coefficient tend to be polished metals, such as aluminum and anodized metals. However, certain materials that are not metals and are non-reflective, such as red bricks, asbestos, concrete and pressed carbon, have equally high coefficients. In addition, naturally occurring materials such as ice, marble, and lime also have high emissivity coefficients.
We have written many articles about emissivity of materials for Universe Today. Here's an article about heat rejection systems, and here's an article about absorptivity.
If you'd like more info on emissivity, check out these articles from Engineering Toolbox and Science World.
We’ve also recorded an entire episode of Astronomy Cast all about Electromagnetism. Listen here, Episode 103: Electromagnetism.
The Sun continues to be active! This movie from the Solar Dynamics Observatory starts at 11:35 UT on March 24, 2011 and goes through midnight. It shows the active area 1176 – and active it was. Several flares are visible — according to the SDO website, there are B, C and M class flares all seen in this 20 second video. See below for another movie from March 19 of a looping solar prominence eruption on the limb of the Sun. Continue reading “Fireworks on the Sun”
At 8:30 PM on Saturday 26th March 2011, lights will switch off around the globe for Earth Hour and people will commit to actions that go beyond the hour. We need you…
Earth Hour started in 2007 in Sydney, Australia when 2.2 million individuals and more than 2,000 businesses turned their lights off for one hour to take a stand against climate change. Only a year later and Earth Hour had become a global sustainability movement with more than 50 million people across 35 countries/territories participating. Global landmarks such as the Sydney Harbour Bridge, CN Tower in Toronto, Golden Gate Bridge in San Francisco, and Rome’s Colosseum, all stood in darkness, as symbols of hope for a cause that grows more urgent by the hour.
In March 2009, hundreds of millions of people took part in the third Earth Hour. Over 4000 cities in 88 countries/territories officially switched off to pledge their support for the planet, making Earth Hour 2009 the world’s largest global climate change initiative.
On Saturday, March 27th, Earth Hour 2010 became the biggest Earth Hour ever. A record 128 countries and territories joined the global display of climate action. Iconic buildings and landmarks from Asia Pacific to Europe and Africa to the Americas switched off. People across the world from all walks of life turned off their lights and came together in celebration and contemplation of the one thing we all have in common – our planet.
Earth Hour 2011 will take place on Saturday 26 March at 8.30PM (local time). This Earth Hour we want you to go beyond the hour, so after the lights go back on think about what else you can do to make a difference. Together our actions add up.
“All over the world individuals, communities, businesses and governments are creating new examples for our common future – new visions for sustainable living and new technologies to realize it,” said UN Secretary General Ban Ki-moon. “Tomorrow, let us join together to celebrate this shared quest to protect the planet and ensure human well-being. Let us use 60 minutes of darkness to help the world see the light.”
View from a helicopter of the summit of Mauna Kea in Hawaii. Image: Nancy Atkinson
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For about 300 nights out of the year, Mauna Kea on the Big Island of Hawaii is one of the best places in the world for ground-based astronomy. At an elevation of 4,205 meters (13,796 ft), the summit sits above a large portion of the Earth’s atmosphere, and usually, the sky is clear, calm and dry. Indeed, 13 giant telescopes sit Mauna Kea’s summit, and they have made some of the biggest discoveries in astronomy. But for the remaining nights of the year, a variety of weather-related issues can keep astronomers from observing, and visitors from climbing to the summit to see those pristine skies for themselves, as well as being able to watch some of our biggest eyes on the skies action. Sometimes clouds, high winds or humidity might keep the telescope domes closed, other times snow can close the roads. On a recent visit to Hawaii, heavy snow kept the roads closed for three days and my long-planned trip to the top of Mauna Kea was, disappointingly, scrubbed. But I did get a great behind the scenes tour of the W. M. Keck Observatory headquarters in Waimea.
The Keck Headquarters and visitor center in Waimea.
While the telescopes are up at at the top of the mountain, astronomers seldom actually work at the telescopes themselves. Instead they work out of remote operations offices at the headquarters in Waimea. There is an operations room for each of the twin 10-meter Keck telescopes: Remote Operations 1 works the Keck 1 telescope:
Remote Operations Room 1 for Keck 1. Image: Nancy Atkinson
And Remote Operations 2 works Keck 2:
Remote Operations Room 2 at the Keck Headquarters. Image: Nancy Atkinson
I arrived in the morning before any of the astronomers were there. “People who work for Keck help the visiting astronomers,” said Alexandra Starr, who works with the media and is a public information officer at the Keck headquarters. “Usually, the visiting astronomers start filtering in about 2 o’clock, and the people who work on the summit get things ready for what the astronomers want to observe. There is a camera for those down here to view how things are going for getting the telescope pointed exactly where they want it.”
But the domes on the telescope can’t be opened until the sun goes down.
“So, once they get everything set up, they go for an early dinner and then come back here and observe all night long,” said Starr. “We do have people working around the clock, however. For astronomers who have been here before, sometimes they don’t need a lot of assistance, but our support astronomers will help all the visiting astronomers get the best observing they can, and get the information they need while they are on the sky.”
About 125 people work full-time at Keck, of which two-thirds are local people from from Hawaii. With an annual operating budget of $11 million, the Observatory is one of the town’s largest employers.
At the headquarters, there are condos where the visiting astronomers can stay:
Facilities where visiting astronomers stay while at Keck. Image: Nancy Atkinson
Most astronomers have just two nights for observing, and Starr said it can be up to a year and a half from when astronomers submit a proposal to use the Keck telescopes to when they actually get to observe. But sometimes, depending on the astronomer and what they are observing, they’ll get to return again fairly quickly when the weather doesn’t allow for observing.
“The past 2 nights we haven’t been observing, and those people are in town ready to go,” Starr said.
The backside of facilities includes the observatory’s own mechanics shop. “We have eight 4-wheel drive automobiles to get to the summit, and our own mechanic shop to keep them all in top shape,” Starr said.
The Keck Observatory’s headquarters in Waimea is open to visitors, and volunteer guides are available Tuesday through Friday from 10 a.m. to 2 p.m. to share information about Keck and the other Mauna Kea observatories. The visitor’s center also has a conference room for public lectures from visiting astronomers.
Inside are models and images of the twin 10-meter Keck telescopes:
Models of the twin Keck telescopes inside the Keck visitor center. Image: Nancy Atkinson
The twin Keck telescopes are the world’s largest optical and infrared telescopes. Each telescope stands eight stories tall, weighs 300 tons and operates with nanometer precision. The telescopes’ primary mirrors are 10 meters in diameter and are each composed of 36 hexagonal segments that work in concert as a single piece of reflective glass.
Outside in the visitor center courtyard is a grassy area that represents the size of just one of the hexagonal segments, which are 1.8 meters (6 ft) in diameter.
The grassy area in the courtyard of the Keck Observatory visitor center is the same size as one of the 36 hexagonal glass segments that make up the 10-meter mirrors on the two Keck telescopes. Image: Nancy Atkinson
Each segment weighs .5 metric tons (880 pounds), and are three inches thick. They are made of a glass and ceramic composite called Zerodur. Zerodur itself is not reflective, so they are covered with a thin reflective layer of aluminum.
“While the telescope is actually working it is constantly fine tuning the position of the individual mirrors to make sure they are all in alignment,” said our tour guide Rosalind Redfield.
On the telescope, each segment’s figure is kept stable by a system of extremely rigid support structures and adjustable warping harnesses. During observing, a computer-controlled system of sensors and actuators adjusts the position of each segment – relative to the neighboring segment – to an accuracy of four nanometers, about the size of a few molecules, or about 1/25,000 the diameter of a human hair. This twice-per-second adjustment effectively counters the tug of gravity.
The twin Kecks, Subaru and IRTF seen from the eastern ridge at sunset. Credit: Pablo McLoud/Keck
Up at the summit, (which I can only share pictures provided by the Keck Observatory) Redfield said it is like the other side of the Moon. “Absolutely nothing grows up there, the elevation is so high it is completely barren,” she said. “There is fine, sandy type dirt, and they don’t like people driving up there as it stirs up dust. The paved road only goes so far, and anyone driving at the summit creates enough dust that it can cause a problem, and people are only allowed to drive up if you have a four-wheel drive.”
The sun sets on Mauna Kea as the twin Kecks prepare for observing. Credit: Laurie Hatch/ W. M. Keck Observatory
Mauna Kea summit as seen from the northeast. Credit: University of Hawaii.
The two Keck telescopes and the 8.3 meter Subaru telescopes take the very top of the mountain. They are joined by the 8.1 Gemini North Telescope , the 0.6-m educational telescope, from the University of Hawaii at Hilo, a 2.2-m telescope University of Hawaii Institute for Astronomy, the 3 meter NASA Infrared Telescope Facility, the 3.6 meter Canada-France-Hawaii Telescope, the 3.8 meter UKIRT (United Kingdom Infrared Telescope), the 10.4 Caltech Submillimeter Observatory, the 15 meter James Clerk Maxwell Telescope, the 8X6 meter Submillimeter Array and the 25 meter Very Long Baseline Array.
A map of the telescopes on Mauna Kea. Credit: University of Hawaii.
But, no climb to the summit for me — not this time anyway! I hope to return one day to Mauna Kea to see first-hand where science and nature come together to allow for continued discovery of our universe.
Clouds and snow obscure the summit of Mauna Kea as I drive away, after a climb to visit the Keck telescopes was nixed. Image: Nancy Atkinson.
For more information about the Keck Observatory, see their website, and if you are in Hawaii or going to be visiting the Big Island, find information here on how you can visit the Observatory headquarters, or go to the summit.
Stardust-NExT photographed jets of gas and particles streaming from Comet Tempel 1 during Feb 14, 2011 flyby. The raw image taken during closest approach has been extensively enhanced by outside analysts to visibly show the jets. Annotations show the location of the jets and the man-made crater created by a projectile hurled by NASA’s prior Deep Impact mission in 2005. Credit: NASA/JPL-Caltech/University of Maryland/Post process and annotations by Marco Di Lorenzo/Kenneth Kremer
[/caption]Farewell Stardust-NExT !
Today marks the end to the final chapter in the illustrious saga of NASA’s Stardust-NExT spacecraft, a groundbreaking mission of cometary exploration.
Mission controllers at NASA’s Jet Propulsion Laboratory commanded the probe to fire the main engines for the very last time today at about 7 p.m. EDT (March 24). The burn will continue until the spacecraft entirely depletes the tiny amount of residual fuel remaining in the propellant tanks. The Stardust probe is now being decommissioned and is about 312 million kilometers away from Earth.
This action will effectively end the life of the storied comet hunter, which has flown past an asteroid (Annefrank), two comets (Wild 2 and Tempel 1) and also returned the first ever pristine samples of a comet to Earth for high powered analysis by the most advanced science instruments available to researchers.
NASA’s Stardust space probe completed her amazing science journey on Feb. 14, 2011 by streaking past Comet Tempel 1 at 10.9 km/sec, or 24,000 MPH and successfully sending back 72 high resolution images of the comets nucleus and other valuable science data. Tempel 1 became the first comet to be visited twice by spacecraft from Earth.
During the Feb. 14, 2011 flyby of Comet Tempel 1, Stardust-NExT discovered the man-made crater created back in 2005 by NASA’s Deep Impact mission and also imaged gas jets eminating from the comet. My imaging partner Marco Di Lorenzo and myself prepared two posters illustrating the finding of the jets and the Deep Impact crater included in this article.
6 Views of Comet Tempel 1 and Deep Impact crater from Stardust-NExT spacecraft flyby on Feb. 14, 2011. Arrows show location of man-made crater created in 2005 by NASA’s prior Deep Impact comet smashing mission and newly imaged as Stardust-NExT zoomed past comet in 2011.
The images progress in time during closest approach to comet beginning at upper left and moving clockwise to lower left. Credit: NASA/JPL-Caltech/University of Maryland/Post process and annotations by Marco Di Lorenzo/Kenneth Kremer
The rocket burn will be the last of some 2 million rocket firings all told since the Stardust spacecraft was launched back in 1999. Over a dozen years, Stardust has executed 40 major flight path maneuvers and traveled nearly 6 billion kilometers.
The rocket firing also serves another purpose as a quite valuable final contribution to science. Since there is no fuel gauge on board or precise method for exactly determining the quantity of remaining fuel, the firing will tell the engineers how much fuel actually remains on board.
To date the team has relied on several analytical methods to estimate the residual fuel. Comparing the results of the actual firing experiment to the calculations derived from estimates will aid future missions in determining a more accurate estimation of fuel consumption and reserves.
“We call it a ‘burn to depletion,’ and that is pretty much what we’re doing – firing our rockets until there is nothing left in the tank,” said Stardust-NExT project manager Tim Larson of NASA’s Jet Propulsion Laboratory in Pasadena, Calif in a statement. “It’s a unique way for an interplanetary spacecraft to go out. Essentially, Stardust will be providing us useful information to the very end.”
Just prior to the burn, Stardust will turn its medium gain antenna towards Earth and transmit the final telemetry in real time. Stardust is being commanded to fire the thrusters for 45 minutes but the team expects that there is only enough fuel to actually fire for up to perhaps around ten minutes.
On March 24, at about 4 p.m. PDT, four rocket motors on NASA's Stardust spacecraft, illustrated in this artist's concept, are scheduled to fire until the spacecraft's fuel is depleted. Image credit: NASA/JPL-Caltech
As its final act, the transmitters will be turned off (to prevent accidental transmissions to other spacecraft), all communications will cease and that will be the end of Stardust’s life.
With no more fuel available, the probe cannot maintain attitude control, power its solar array or point its antenna. And its far enough away from any targets that there are no issues related to planetary protection requirements.
“I think this is a fitting end for Stardust. It’s going down swinging,” Larson stated in the press release.
Read more about the Stardust-NExT Flyby and mission in my earlier stories here, here, here, here, here, here and here
Relive the Feb. 14 Flyby of Comet Tempel 1 in this movie of NASA/JPL images
Stardust-NExT: 2 Comet Flybys with 1 Spacecraft.
Stardust-NExT made history on Valentine’s Day - February, 14, 2011 – Tempel 1 is the first comet to be visited twice by spacrecraft from Earth. Stardust has now successfully visited 2 comets and gathered science data: Comet Wild 2 in 2004 (left) and Comet Tempel 1 in 2011 (right).
Artist renderings Credit: NASA. Collage: Ken Kremer.Stardust-NExT location on March 11, 2011 just prior to farewell transmission. Credit: NASA/JPL
Many types of main sequence stars emit in the X-ray portion of the spectra. In massive stars, strong stellar winds ripping through the extended atmosphere of the star create X-ray photons. On lower mass stars, magnetic fields twisting through the photosphere heat it sufficiently to produce X-rays. But between these two mechanisms, in the late B to mid A classes of stars, neither of these mechanisms should be sufficient to produce X-rays. Yet when X-ray telescopes examined these stars, many were found to produce X-rays just the same.
The first exploration into the X-ray emission of this class of stars was the Einstein Observatory, launched in 1978 and deorbited in 1982. While the telescoped confirmed that these B and A stars had significantly less X-ray emission overall, seven of the 35 A type stars still had some emission. Four of these were confirmed as being in binary systems in which the secondary stars could be the source of the emission, leaving three of seven with unaccounted for X-rays.
The German ROSAT satellite found similar results, detecting 232 X-ray stars in this range. Studies explored connections with irregularities in the spectra of these stars and rotational velocities, but found no correlation with either. The suspicion was that these stars simply hid undetected, lower mass companions.
In recent years, some studies have begun exploring this, using telescopes equipped with adaptive optics to search for companions. In some cases, as with Alcor (member of the popular visual binary in the handle of the big dipper), companion stars have been detected, absolving the primary from the expectation of being the cause. However, in other cases, the X-rays still appear to be coming from the primary star when the resolution is sufficient to spatially resolve the system. The conclusion is that either the main star truly is the source, or there are even more elusive, sub-arcsecond binaries skewing the data.
Another new study has taken up the challenge of searching for hidden companions. The new study examined 63 known X-ray stars in the range not predicted to have X-ray emission to search for companions. As a control, they also searched 85 stars without the anomalous emission. This gave a total sample size of 148 target stars. When the images were taken and processed, it uncovered 68 candidate companions to 59 of the total objects. The number of companions was greater than the number of parent stars since some look to exist in trinary star systems or greater.
Comparing the percent of companions around X-ray stars to those that didn’t, 43% of the X-ray stars appeared to have companions, while only 12% of normal stars were discovered to have them. Some of the candidates may be the result of chance alignments and not actual binary systems giving an error of about ±5%.
While this study leaves some cases unresolved, the increased likelihood of X-ray stars to have companions suggests that the majority of cases are caused by companions. Further studies by X-ray telescopes like Chandra could provide the angular resolution necessary to ensure that the emissions are indeed coming from the partner objects as well as search for companions to even greater resolution.
X-ray Image of Tycho's Supernova Remnant. (NASA/CXC/Rutgers/K.Eriksen et al.)
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The Chandra X-Ray Observatory has taken a brand new, deep look inside the Tycho Supernova Remnant and found a pattern of X-ray “stripes.” The three-dimensional-like nature of this incredible image notwithstanding, nothing like these stripe-like features has ever been seen before inside the leftovers of an exploding star, but astronomers believe they could explain how some cosmic rays are created. Additionally, the stripes provide support for a theory about how magnetic fields can be dramatically amplified in supernova blast waves.
Cosmic rays are made up of electrons, positrons and atomic nuclei and they constantly bombard the Earth. In their near light-speed journey across the galaxy, the particles are deflected by magnetic fields, which scramble their paths and mask their origins. Supernova remnants have long been thought to be the source of cosmic rays, up to the “knee” of the cosmic ray spectrum at 10^15 eV, but so far, no specific sources have been located.
High Energy Stripes in the Tycho Supernova Remnant. Credit: NASA/CXC/Rutgers/K.Eriksen et al
But the stripes seen by Chandra, shown above in high-energy X-rays (blue), are thought to be regions where the turbulence is greater and the magnetic fields more tangled than surrounding areas. Electrons become trapped in these regions and emit X-rays as they spiral around the magnetic field lines. Regions with enhanced turbulence and magnetic fields were expected in supernova remnants, but the motion of the most energetic particles — mostly protons — was predicted to leave a messy network of holes and dense walls corresponding to weak and strong regions of magnetic fields, respectively.
Therefore, the detection of stripes was a surprise.
Schematic Illustration of the Tycho Stripes. Credit: NASA/CXC/M.Weiss.
The size of the holes was expected to correspond to the radius of the spiraling motion of the highest energy protons in the supernova remnant. These energies equal the highest energies of cosmic rays thought to be produced in our Galaxy. The spacing between the stripes corresponds to this size, providing evidence for the existence of these extremely energetic protons.
“We interpret the stripes as evidence for acceleration of particles to near the knee of the CR spectrum in regions of enhanced magnetic turbulence, while the observed highly ordered pattern of these features provides a new challenge to models of diffusive shock acceleration,” writes Kristoffer A. Eriksen and his team in their paper, “Evidence For Particle Acceleration to the Knee of the Cosmic Ray Spectrum in Tycho’s Supernova Remnant.”
