This artist's impression depicts a white dwarf star found in the closest known orbit around a black hole. As the circle around each other, the black hole's gravitational pull drags material from the white dwarf's outer layers toward it. Astronomers found that the white dwarf in X9 completes one orbit around the black hole in less than a half an hour. They estimate the white dwarf and black hole are separated by about 2.5 times the distance between the Earth and Moon — an extraordinarily small span in cosmic terms.
(Credit: NASA/CXC/M.Weiss)
Imagine being caught in the clutches of a black hole, being whirled around at dizzying speeds and having your mass slowly but continually sucked away. That’s the life of a white dwarf star that is doing an orbital dance with a black hole. And this dancing duo could be the first ultracompact black hole X-ray binary identified in our galaxy.
“This white dwarf is so close to the black hole that material is being pulled away from the star and dumped onto a disk of matter around the black hole before falling in,” said Arash Bahramian from the University of Alberta in Edmonton, Canada, and Michigan State University, first author of a new paper.
If you were the white dwarf in this predicament, you may wish for a quick end to it all. But somehow, the star does not appear to be in danger of falling in or being torn apart by the black hole.
“We don’t think it will follow a path into oblivion, but instead will stay in orbit,” Bahramian added.
Data from the Chandra X-ray Observatory, the NuSTAR mission and the Australian Telescope Compact Array (ATCA) shows evidence that this star whips around the black hole about twice an hour, and it may be the tightest orbital dance ever witnessed for a likely black hole and a companion star.
This seemingly unique binary system – with a great name, X9 — is located in the globular cluster 47 Tucanae, a dense cluster of stars in our galaxy about 14,800 light years from Earth.
Astronomers have been studying this system for a while.
“For a long time, it was thought that X9 is made up of a white dwarf pulling matter from a low mass Sun-like star,” Bahramian wrote in a blog post.
But 2015, radio observations with the ATCA showed the pair likely contains a black hole pulling material from a companion star called a white dwarf, a low-mass star that has exhausted most or all of its nuclear fuel.
“In 2015, Dr. Miller-Jones and collaborators observed strong radio emission from X9 indicating the presence of a black hole in this binary,” Bahramian continued. “They suggested that this might mean the system is made up of a black hole pulling matter from a white dwarf.”
Astronomers found an extraordinarily close stellar pairing in the globular cluster 47 Tucanae, a dense collection of stars located on the outskirts of the Milky Way galaxy, about 14,800 light years from Earth. Credit: X-ray: NASA/CXC/University of Alberta/A.Bahramian et al.
Looking at archived Chandra data, it showed changes in X-ray brightness in the same manner every 28 minutes, and Bahramian and his PhD supervisor Craig Heink think this is likely the length of time it takes the companion star to make one complete orbit around the black hole. Chandra data also shows evidence for large amounts of oxygen in the system, a characteristic feature of white dwarfs. They feel a strong case can be made that the companion star is a white dwarf. And this star would then be orbiting the black hole at just 2.5 times the distance between the Earth and the Moon.
“Eventually so much matter may be pulled away from the white dwarf that it ends up only having the mass of a planet,” said Heinke, also of the University of Alberta. “If it keeps losing mass, the white dwarf may completely evaporate.”
The researchers think this system would be a good candidate for future gravitational wave observatories to observe. It has to low of a frequency that is too low to be detected with Laser Interferometer Gravitational-Wave Observatory, LIGO, that made ground-breaking detections of gravitational waves last year. Systems like this could tell us more about gravitational waves, as well as providing more information about black hole binary systems.
“We’re going to watch this binary closely in the future, since we know little about how such an extreme system should behave”, said co-author Vlad Tudor of Curtin University and the International Centre for Radio Astronomy Research in Perth, Australia. “We’re also going to keep studying globular clusters in our galaxy to see if more evidence for very tight black hole binaries can be found.”
Artist’s impression of the VFTS 352 star system, the hottest and most massive double star system to date where the two components are in contact and sharing material. Credit: ESO/L. Calçada
Stellar collisions are an amazingly rare thing. According to our best estimates, such events only occur in our galaxy (within globular clusters) once every 10,000 years. It’s only been recently, thanks to ongoing improvements in instrumentation and technology, that astronomers have been able to observe such mergers taking place. As of yet, no one has ever witnessed this phenomena in action – but that may be about to change!
According to study from a team of researchers from Calvin College in Grand Rapids, Michigan, a binary star system that will likely merge and explode in 2022. This is an historic find, since it will allow astronomers to witness a stellar merger and explosion for the first time in history. What’s more, they claim, this explosion will be visible with the naked-eye to observers here on Earth.
Professor Lawrence Molnar of the Calvin College’s Dept. of Physics and Astronomy. He predicts KIC 9832227 will collide and explode in 2022. Credit: calvin.edu
This binary star system, which is known as KIC 9832227, is one that Prof. Molnar and his colleagues – which includes students from the Apache Point Observatory and the University of Wyoming – have been monitoring since 2013. His interest in the star was piqued during a conference in 2013 when Karen Kinemuchi (an astronomers with the Apache Point Observatory) presented findings about brightness changes in the star.
This led to questions about the nature of this star system – specifically, whether it was a pulsar or a binary pair. After conducting their own observations using the Calvin observatory, Prof. Molnar and his colleagues concluded that the star was a contact binary – a class of binary star where the two stars are close enough to share an atmosphere. This brought to mind similar research in the past about another binary star system known as V1309 Scorpii.
This binary pair also had a shared atmosphere; and over time, their orbital period kept decreasing until (in 2008) they unexpectedly collided and exploded. Believing that KIC 9832227 would undergo a similar fate, they began conducting tests to see if the star system was exhibiting the same behavior. The first step was to make spectroscopic observations to see if their observations could be explained by the presence of a companion star.
As Cara Alexander, a Calvin College student and one of the co-authors on the team’s research paper, explained in a college press release:
“We had to rule out the possibility of a third star. That would have been a pedestrian, boring explanation. I was processing data from two telescopes and obtained images that showed a signature of our star and no sign of a third star. Then we knew we were looking at the right thing. It took most of the summer to analyze the data, but it was so exciting. To be a part of this research, I don’t know any other place where I would get an opportunity like that; Calvin is an amazing place.”
Diagram showing the summer constellations of Cygnus and Lyra and the position of KIC 9832227 (shown with a red circle). Credit: calvin.edu
The next step was to measure the pair’s orbital period, to see it was in fact getting shorter over time – which would indicate that the stars were moving closer to each other. By 2015, Prof. Molnar and his team determined that the stars would eventually collide, resulting in a kind of stellar explosion known as a “Red Nova”. Initially, they estimated this would take place between 2018 and 2020, but have since placed the date at 2022.
In addition, they predict that the burst of light it will cause will be bright enough to be seen from Earth. The star will be visible as part of the constellation Cygnus, and it appear as an addition star in the familiar Northern Cross star pattern (see above). This is an historic case, since no astronomer has ever been able to accurately predict when and where a stellar collision would take place in the past.
What’s more, this discovery is immensely significant because it represents a break with the traditional discovery process. Not only have small research institutions and universities not been the ones to take the lead on these sorts of discoveries in the past, but student-and-teacher teams have also not been the ones who got to make them. As Molnar explained it:
“Most big scientific projects are done in enormous groups with thousands of people and billions of dollars. This project is just the opposite. It’s been done using a small telescope, with one professor and a few students looking for something that is not likely. Nobody has ever predicted a nova explosion before. Why pay someone to do something that almost certainly won’t succeed? It’s a high-risk proposal. But at Calvin it’s only my risk, and I can use my work on interesting, open-ended questions to bring extra excitement into my classroom. Some projects still have an advantage when you don’t have as much time or money.”
The model Prof. Molnar and his team constructed of the double star system KIC 9832227, which is a contact binary (i.e. two stars that are touching). Credit: calvin.edu.
Over the course of the next year, Molnar and his colleagues will be monitoring KIC 9832227 carefully, and in multiple wavelengths. This will be done with the help of the NROA’s Very Large Array (VLA), NASA’s Infrared Telescope Facility at Mauna Kea, and the ESA’s XMM-Newton spacecraft. These observatories will study the star’s radio, infrared and X-ray emissions, respectively.
Molnar also expects that amateur astronomers will be able to monitor the pair’s orbital timing and variations in brightness. And if he and his team’s predictions are correct, every student and stargazer in the northern hemisphere – not to mention people who just happen to be out for a walk – will be privy to the amazing light show. This is sure to be a once-in-a-lifetime event, so stay tuned for more information!
Interestingly enough, this historic discovery is also the subject of a documentary film. Titled “Luminous“, the documentary – which is directed by Sam Smartt, a Calvin professor of communication arts and sciences – chronicles the process that led Prof. Molnar and his team to make this unprecedented discovery. The documentary will also include footage of the Red Nova as it happens in 2022, and is expected to be released sometime in 2023.
The Sagittarius constellation, as imaged by the Hubble Space Telescope. Credit: IAU/NASA/ESA/HST
In May of 2016, the IAU Executive Committee approved of the creation of a special task force known as the Working Group on Star Names (WGSN). Composed of an international group of experts in astronomy, astronomical history, and cultural astronomy, the purpose of the WGSN is to formalize the names of stars that have been used colloquially for centuries.
This has involved sorting through the texts and traditions of many of the world’s cultures, seeking out unique names and standardizing their spelling. And after about six months, their labors have led to the creation of a new catalog of IAU star names, the first 227 of which were recently published on the IAU website.
This initiative grew out of the IAU’s Division C – Education, Outreach and Heritage group, which is responsible for engaging the public in all matters of astronomy. Their overall purpose is to establish IAU guidelines for the proposal and adoption of star names, to search historical and cultural literature for them, to adopt unique names that have scientific and historical value, and to publish and disseminate official IAU star name catalogs.
In this respect, the WGSN is breaking with standard astronomical practice. For many years, astronomers have named the stars they have been responsible for studying using an alphanumerical designation. These designations are seen as immensely practical, since star catalogs typically contain thousands, millions or even billions of objects. If there’s one thing the observable Universe has no shortage of, its stars!
However, many of these stars already have traditional names which may have fallen into disuse. The WGSN’s job, therefore, is to find commonly-used, traditional names of stars and determine which ones shall be officially used. In addition to preserving humanity’s astronomical heritage, this process is also intended to make sure that there is standardization in terms of naming and spelling, so as to prevent confusion.
What’s more, with the discovery of exoplanets becoming a regular thing nowadays, the IAU hopes to engage the international astronomical community in naming these planets according to their stars traditional name (if they have one). As Eric Mamajek, the chair and organiser of the WGSN, explained their purpose:
“Since the IAU is already adopting names for exoplanets and their host stars, it has been seen as necessary to catalogue the names for stars in common use from the past, and to clarify which ones will be official from now on.”
Artist’s impression of a system of exoplanets orbiting a low mass, red dwarf star. Credit: NASA/JPL
For instance, it can certainly be said that HD 40307 g – an exoplanet candidate that orbits within the habitable zone of its K-type star some 42 light years away – has a pretty clunky name. But what if, upon searching through various historical sources, the WGSN found that this star was traditionally known as “mikiya” (eagle) to the Hausa people of northern Nigeria? Then this super-Earth could be named Mikiya g (or Mikiya Prime). Doesn’t that sound cooler?
And this effort is hardly without precedent. As Mamajek explained, the IAU engaged in a very similar effort decades ago with respect to the constellations:
“A similar effort was conducted early in the history of the IAU, in the 1920s, when the 88 modern constellations were clarified from historical literature, and their boundaries, names, spellings, and abbreviations were delineated for common use in the international astronomical community. Many of these names are used today by astronomers for designations of variable stars, names for new dwarf galaxies and bright X-ray sources, and other astronomical objects.”
Much like the constellations, the new star names are largely rooted in astronomical and cultural traditions of the Ancient Near East and Greece. Their names are rendered in Greek, Latin or Aabic, and have likely undergone little change since the Renaissance, a time where the production of star catalogs, atlases and globes experienced an explosion in growth.
Others, however, are more recent in origin, having been discovered and named in the 19th or 20th centuries. The IAU is looking to locate as many ancient names as possible, then incorporate them into an official IAU-approved database with more modern stars. These databases will be made available for use by astronomers, navigators and the general public.
In accordance with WGSN guildines, shorter, one-word names are preferred, as are those that have their roots in astronomical, cultural or natural world heritage. The 227 names that have been released include 209 recently approved names by the WGSN, plus the 18 stars that the IAU Executive Committee Working Group for Public Naming of Planets and Planetary Satellites approved of in December 2015.
Among those names that were approved are Proxima Centauri (which is orbited by the closest exoplanet to Earth, Proxima b), as well as Rigil Kentaurus (the ancient name for Alpha Centauri), Algieba (Gamma-1 Leonis), Hamal (Alpha Arietis), and Muscida (Omicron Ursae Majoris).
This number is expected to grow, as the WGSN continues to revive ancient stellar names and add new ones that are suggested by the international astronomical community.
At one time, scientists believed that the Earth, the Moon, and all the other planets in our Solar System were perfect spheres. The same held true for the Sun, which they considered to be the heavenly orb that was the source of all our warmth and energy. But as time and research showed, the Sun is far from perfect. In addition to sunspots and solar flares, the Sun is not completely spherical.
For some time, astronomers believed this was the case with other stars as well. Owing to a number of factors, all stars previously studied by astronomers appeared to experience some bulging at the equator (i.e. oblateness). However, in a study published by a team of international astronomers, it now appears that a slowly rotating star located 5000 light years away is as close to spherical as we’ve ever seen!
Until now, observation of stars has been confined to only a few of the fastest-rotating nearby stars, and was only possible through interferometry. This technique, which is typically used by astronomers to obtain stellar size estimates, relies on multiple small telescopes obtaining electromagnetic readings on a star. This information is then combined to create a higher-resolution image that would be obtained by a large telescope.
Artist’s impression of a Sirius, an A-type Main Sequence White star. Credit: NASA, ESA and G. Bacon (STScI)
Laurent Gizon, a researcher with the Max Planck Institute, was the lead authjor on the paper. As he explained their research methodology to Universe Today via email:
“The new method that we propose in this paper to measure stellar shapes, asteroseismology, can be several orders of magnitude more precise than optical interferometry. It applies only to stars that oscillate in long-lived non-radial modes. The ultimate precision of the method is given by the precision on the measurement of the frequencies of the modes of oscillation. The longer the observation duration (four years in the case of Kepler), the better the precision on the mode frequencies. In the case of KIC 11145123 the most precise mode frequencies can be determined to one part in 10,000,000. Hence the astonishing precision of asteroseismology.”
Located 5000 light years away from Earth, KIC 11145123 was considered a perfect candidate for this method. For one, Kepler 11145123 is a hot and luminous, over twice the size of our Sun, and rotates with a period of 100 days. Its oscillations are also long-lived, and correspond directly to fluctuations in its brightness. Using data obtained by NASA’s Kepler mission over a more than four year period, the team was able to get very accurate shape estimates.
The variations in brightness can be interpreted as vibrations, or oscillations within the stars, using a technique called asteroseismology. Credit: Kepler Astroseismology team.
“We compared the frequencies of the modes of oscillation that are more sensitive to the low-latitude regions of the star to the frequencies of the modes that are more sensitive to higher latitudes,” said Gizon. “This comparison showed that the difference in radius between the equator and the poles is only 3 km with a precision of 1 km. This makes Kepler 11145123 the roundest natural object ever measured, it is even more round than the Sun.”
For comparison, our Sun has a rotational period of about 25 days, and the difference between its polar and equatorial radii is about 10 km. And on Earth, which has a rotational period of less than a day (23 hours 56 minutes and 4.1 seconds), there is a difference of over 23 km (14.3 miles) between its polar and equator. The reason for this considerable difference is something of a mystery.
In the past, astronomers have found that the shape of a star can come down to multiple factors – such as their rotational velocity, magnetic fields, thermal asphericities, large-scale flows, strong stellar winds, or the gravitational influence of stellar companions or giant planets. Ergo, measuring the “asphericity” (i.e. the degree to which a star is NOT a sphere) can tell astronomers much about the star structures and its system of planets.
Ordinarily, rotational velocity has been seen to have a direct bearing on the stars asphericity – i.e. the faster it rotates, the more oblate it is. However, when looking at data obtained by the Kepler probe over a period of four years, they noticed that its oblateness was only a third of what they expected, given its rotational velocity.
Laurent Gizon, the lead researcher of the study, pictured with asteroseismic readings of Kepler 11145123. Credit: Max Planck Institute for Solar System Research, Germany.
As such, they were forced to conclude that something else was responsible for the star’s highly spherical shape. “”We propose that the presence of a magnetic field at low latitudes could make the star look more spherical to the stellar oscillations,” said Gizon. “It is known in solar physics that acoustic waves propagate faster in magnetic regions.”
Looking to the future, Gizon and his colleagues hope to examine other stars like Kepler 11145123. In our Galaxy alone, there are many stars who’s oscillations can be accurately measured by observing changes in their brightness. As such, the international team hopes to apply their asteroseismology method to other stars observed by Kepler, as well as upcoming missions like TESS and PLATO.
“Just like helioseismology can be used to study the Sun’s magnetic field, asteroseismology can be used to study magnetism on distant stars,” Gizon added. “This is the main message of this study.”
The author enjoys a pretty display of the northern lights on October 23, 2016 under a starry sky. His new book, “Night Sky with the Naked Eye,” explores all the amazing things you can see in the sky without special equipment including satellites, planets, meteor showers and of course, the aurora.
My book Night Sky with the Naked Eye publishes today. It would have never seen the light of day much less ever been conceived were it not for Fraser Cain, publisher of Universe Today, and Nancy Atkinson, an editor and writer for the same. Several years ago, Nancy invited me to write for UT. I hopped at the chance. Before her contact, I’d been writing a daily blog on astronomy called Astro Bob (and still do).
Fast forward to last summer when I got an email from Nancy saying Page Street Publishing had contacted her about writing a book about space missions. The publisher also wanted a book about night sky observing without fancy equipment for which she recommended me. Me? I felt like the luckiest guy on the planet!
Book writing proceeds in many stages. First, the table of contents had to be prepared and approved. Then followed a sample chapter. The publisher chose the one on artificial satellites, which I wrote in about a week. The tone was right, but he asked for changes in the organization, which I dutifully made. By November, a contract followed and the project was underway with a first draft due to my editor in about 10 weeks.
Cover of my book that publishes today. Credit: Bob King
Writing is hard work. But it’s a special place all writers come back to again and again. We can’t help but keep trying to find just the right words to capture a concept or emotion. And when we do, a quiet pleasure flows down the spine like warmth creeping into cold fingers splayed in front of a fire. Not that these moments always come easily. Writer Colson Whitehead describes the experience of writing as “crawling through glass.” I would soon become well-acquainted with that feeling, too.
Nancy wrote her book Incredible Stories from Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos at nearly the same time. We were grateful for each other’s support, and it was a kick to follow her progress as well as bounce ideas around. With a tight deadline in front of me, I set to work immediately, taking more than two weeks of vacation from my regular job to make sure the draft was done on time. No way was I going to compromise an opportunity of a lifetime.
Maybe you’ve thought of writing a book, starting a blog or hope one day to write for Universe Today or another online astronomy site. There’s plenty of good advice for writers out there. I’ll share what worked for me.
#1:Put your butt in the chair and keep it in the chair. My wife reminded me of this often, adding that the book wasn’t going to write itself. Temptations are everywhere. Answering the phone, making another cup of tea, staring out the window and my favorite, shoveling the driveway. I had the cleanest driveway in the neighborhood. Even an inch of new snow was enough to grab the shovel and happily scrape down to the gravel. So yes, I did occasionally get out of the chair, but many times it did me good, freeing up the brain to see more clearly into a topic. Or dream up a fitting photo or illustration.
Creativity comes at odd little moments. It can flow while tapping away in front of a glowing screen or sneak into consciousness when you’re bending down to feed the dog. So a mix of activities seemed the best but with extra emphasis on staying put. I rarely hiked last winter and kept my walks in the neighborhood brief. Instead of observing at night, I wrote or gathered photos. By January, I joked to my friends that I’d voluntarily put myself under house arrest.
#2: Spill your guts, worry about the details later. It’s incredibly tempting when writing to continuously edit one’s work, going back over every sentence to make each “perfect”. This is a muse-killer. Though difficult to stick to, once you let your thoughts flow onto paper without worrying about spelling, clauses and the whole lot of burdensome rules, you’ll become a wild horse running free on the prairie. Let it out, let it out and worry about the commas later. I don’t play a musical instrument, but free-flow writing — just getting the ideas out — must feel something like riffing on a jazz melody.
#3: When stuck, move on to another topic, take a walk, listen to music. Struggling to describe an important concept or connecting your thoughts in a way that flows on the page can drive you nuts, even bring you to tears. Sure, you can keep beating on the idea like a madman hammering on a bent nail, but why why torture yourself? A little distraction can be good. Move on to another part of the story or a different chapter or get up and take a short walk. Defocusing allows the ideas you’re having a tug-of-war with to come of their own accord.
To keep track of ideas, topics and the photos I’d need for the book, I kept a notebook filled to the gills with lists. Checkmarks indicate tasks accomplished. Credit: Bob King
As the February 1 deadline approached, time took on a physical dimension under the intense pressure to get everything done. I cut time into little blocks that when added up would get me to the finish line on the first draft. I made it just in time, shipped off my copy via e-mail, got in the car to go to work and turn up the music really LOUD. For a fews days I was on top of the world. Invincible.
My editor, Elizabeth, contacted me later with positive comments and then returned the manuscript with “developmental edits” or questions about descriptions and organization. We pitched the ever-refined draft back and forth over the next few months. Each time I read through the ten chapters and made both suggested changes and other refinements. I also added photos during this stage and worked via e-mail with the layout staff to place the best images and graphics at the best places in the text. I shot more images and requested photos from talented astrophotographers, prepared the acknowledgments and sought our recommendations from respected scientists and writers.
This diagram from the book uses the human face to illustrate how changing lighting angles causes the phases of the moon. Credit: Bob King
The editors at Page Street were quite generous with photo usage, a joy for me because that’s what I do for a living. I’ve been a photographer and photo editor at the Duluth News Tribune in Duluth, Minn. for many years. My favorite subjects are people, but I slip in an aurora or eclipse now and again. And that’s the irony. I never saw myself as a writer.
Like many, I started by keeping a journal of my observations through the telescope and reflections about the night sky. The Astro Bob blog took that a step further and writing for Universe Today and Sky & Telescope let me find my voice. So I maybe I have a voice, and I like to think I can be a helpful guide at your side, but writer? That still seems too lofty a term to describe what I do. But here we are.
After several edits including the final one, when I was sent a thick stack of low-res black and white pages of the book to mark up and return, I rested briefly before beginning the final phase: publicity. This is the weird part, where you tell everyone what a nice book you’ve written and how it would make a great Christmas gift for that budding astronomer in the family. When I held the first copy in my hands I couldn’t believe that all those hours of work at the computer became a physical object, a beautiful one even.
This map from the book shows Saturn’s location around the time of opposition through 2021. Credit: Bob King, Source: Stellarium
I’m biased of course, but I think both beginning and amateur astronomers will find the book useful. It includes lots of suggested activities – set off in separate boxes – to encourage you to get out under the stars. I make regular mention of the Web and phone apps as ways to become more familiar with the constellations, learn of newly-discovered bright comets and even find a dark sky.
Besides the easy naked eye topics like how to find the brightest constellations or see the best meteor showers of the year, the book offers visual challenges. Have you ever seen craters on the Moon without optical aid or the midnight glow of the gegenschein? You’ll find out how in my book. As a photographer, I’ve included tips on how to focus a digital camera and use it to photograph the aurora or a space station pass.
I’d be willing to bet that most books aren’t as complete as their authors would hope. I had to cut precious photos, graphics, 3 years of a sky calendar and other bits and pieces from mine. Ouch! To this day, I’m still thinking of ways to improve it with a fresh photo, new diagram or change of wording. Now it’s your turn to be the judge.
The zodiacal light punctuated by the planet Jupiter towers over northern Wisconsin along Lake Superior near Duluth, Minn. this morning (Nov. 8). The book describes nighttime lights such as the zodiacal, gegenschein, airglow in addition to lunar halo and corona phenomena. Credit: Bob King
Throughout, Nancy and I rooted for one another and shared our ups and downs. Incredible Stories was to publish within a week of Night Sky, but a type corruption error discovered in several chapters put the book on hold. Her new publication date is December 20, and I encourage you to pre-order a copy, so it arrives in time for Christmas. Order a copy of my book also, and I promise the two of us will keep you company on those long winter nights ahead.
Can I share one final tip? Once you’ve found your passion, say ‘yes’ to every opportunity that furthers it. You’ll be amazed at the places that one word will take you to.
*** To order a copy of Night Sky with the Naked Eye just click an icon to go to the site of your choice — Amazon, Barnes & Noble or Indiebound. It’s currently available at the first two outlets for a very nice discount. It should also be at your local B&N bookstore. And don’t forget to vote today!
Artist’s impression of the exotic double object that consists of a tiny neutron star orbited every two and a half hours by a white dwarf star. Credit: ESO/L. Calçada
Searching the Universe for strange new star systems can lead to some pretty interesting finds. And sometimes, it can turn up phenomena that contradict everything we think we know about the formation and evolution of stars. Such finds are not only fascinating and exciting, they allow us the chance to expand and refine our models of how the Universe came to be.
For instance, a recent study conducted by an international team of scientists has shown how the recent discovery of binary system – a millisecond pulsar and a low-mass white dwarf (LMWD) – has defied conventional ideas of stellar evolution. Whereas such systems were believed to have circular orbits in the past, the white dwarf in this particular binary orbits the pulsar with extreme eccentricity!
To break it down, conventional wisdom states that LMWDs are the product of binary evolution. The reason for this is because that under normal circumstances, such a star – with low mass but incredible density – would only form after it has exhausted all its nuclear fuel and lost its outer layers as a planetary nebula. Given the mass of this star, this would take about 100 billion years to happen on its own – i.e. longer than the age of the Universe.
An artist’s impression of an accreting X-ray millisecond pulsar. The flowing material from the companion star forms a disk around the neutron star which is truncated at the edge of the pulsar magnetosphere. Credit: NASA/Goddard/Dana Berry
As such, they are generally believed to be the result of pairing with other stars – specifically, millisecond radio pulsars (MSPs). These are a distinct population of neutron stars that have fast spin periods and magnetic fields that are several orders of magnitude weaker than that of “normal” pulsars. These properties are thought to be the result of mass transfer with a companion star.
Basically, MSPs that are orbited by a star will slowly strip them of their mass, sucking off their outer layers and turning them into a white dwarf. The addition of this mass to the pulsar causes it to spin faster and buries its magnetic field, and also strips the companion star down to a white dwarf. In this scenario, the eccentricity of orbit of the LMWD around the pulsar is expected to be negligible.
However, when looking to the binary star system PSR J2234+0511, the international team noticed something entirely different. Here, they found a low-mass white dwarf paired with a millisecond pulsar which the white dwarf orbited with a period of 32 days and an extreme eccentricity (0.13). Since this defies current models of white dwarf stars, the team began looking for explanations.
“Millisecond pulsar-LMWD binaries are very common. According to the established formation scenario, these systems evolve from low-mass X-ray binaries in which a neutron star accretes matter from a giant star. Eventually, this star evolves into a white dwarf and the neutron star becomes a millisecond pulsar. Because of the strong tidal forces during the mass-transfer episode, the orbits of these systems are extremely circular, with eccentricities of ~0.000001 or so.”
An artist’s impression of a millisecond pulsar and its companion. The pulsar (blue) is accreting material from its bloated red companion star and increasing its rotation rate. Credit: ESA/Francesco Ferraro (Bologna Astronomical Observatory)
In addition, they consulted recent studies that looked at other binary star systems that show this same kind of eccentric relationship. “We now know [of] 5 systems which deviate from this picture in that they have eccentricities of ~0.1 i.e. several orders of magnitude larger that what is expected in the standard scenario,” said Antoniadis. “Interestingly, they all appear to have similar eccentricities and orbital periods.”
From this, they were able to infer the temperature (8600 ± 190 K) and velocity ( km/s) of the white dwarf companion in the binary star system. Combined with constraints placed on the two body’s masses – 0.28 Solar Masses for the white dwarf and 1.4 for the pulsar – as well as their radii and surface gravity, they then tested three possible explanations for how this system came to be.
These included the possibility that neutrons stars (such as the millsecond pulsar being observed here) form through an accretion-induced collapse of a massive white dwarf. Similarly, they considered whether neutron stars undergo a transformation as they accrete material, which results in them becoming quark stars. During this process, the release of gravitational energy would be responsible for inducing the observed eccentricity.
Artist’s illustration of a rotating neutron star, the remnants of a super nova explosion. Credit: NASA, Caltech-JPL
Second, they considered the possibility – consistent with current models of stellar evolution – that LMWDs within a certain mass range have strong stellar winds when they are very young (due to unstable hydrogen fusion). The team therefore looked at whether or not these strong stellar winds could have been what disrupted the orbit of the pulsar earlier in the system’s history.
Last, they considered the possibility that some of the material released from the white dwarf in the past (due to this same stellar wind) could have formed a short-lived circumbinary disk. This disk would then act like a third body, disturbing the system and increasing the eccentricity of the white dwarf’s orbit. In the end, they deemed that the first two scenarios were unlikely, since the mass inferred for the pulsar progenitor was not consistent with either model.
However, the third scenario, in which interaction with a circumbinary disk was responsible for the eccentricity, was consistent with their inferred parameters. What’s more, the third scenario predicts how (within a certain mass range) that there should be no circular binaries with similar orbital periods – which is consistent with all known examples of such systems. As Dr. Antoniadis explained:
“These observations show that the companion star in this system is indeed a low-mass white dwarf. In addition, the mass of the pulsar seems to be too low for #2 and a bit too high for #1. We also study the orbit of the binary in the Milky way, and it looks very similar to what we find for low-mass X-ray binaries. These pieces of evidence together favor the disk hypothesis.”
Cross-section of a neutron star. Credit: Wikipedia Commons/Robert Schulz
Of course, Dr. Antoniadis and his colleagues admit that more information is needed before their hypothesis can be deemed correct. However, should their results be borne out by future research, then they anticipate that it will be a valuable tool for future astronomers and astrophysicists looking to study the interaction between binary star systems and circumbinary disks.
In addition, the discovery of this high eccentricity binary system will make it easier to measure the masses of Low-Mass White Dwarfs with extreme precision in the coming years. This in turn should help astronomers to better understand the properties of these stars and what leads to their formation.
As history has taught us, understanding the Universe requires a serious commitment to the process of continuous discovery. And the more we discover, the stranger it seems to become, forcing us to reconsider what we think we know about it.
There’s a remote chance that inexplicable light variations in a star in the Northern Cross may be caused by the works of an alien civilization.
1,480 light years from Earth twinkles one of the greatest mysteries of recent times. There in the constellation Cygnus the Swan, you’ll find a dim, ordinary-looking point of light with an innocent sounding name — Tabby’s Star. Named for Louisiana State University astronomer Tabetha Boyajian, who was the lead author on a paper about its behavior, this star has so confounded astronomers with its unpredictable ups and downs in its brightness, they’ve gone to war on the object, drilling down on it with everything from the Hubble to the monster 393.7-inch (10-meter) Keck Telescope in Hawaii. Continue reading “The Search Is On For Alien Signals Around Tabby’s Star”
The Sloan Digital Sky Survey telescope stands out against the breaktaking backdrop of the Sacramento Mountains. 234 stars out of the Sloan's catalogue of over 2.5 million stars are producing an unexplained pulsed signal. Image: SDSS, Fermilab Visual Media Services
We all want there to be aliens. Green ones, pink ones, brown ones, Greys. Or maybe Vulcans, Klingons, even a being of pure energy. Any type will do.
That’s why whenever a mysterious signal or energetic fluctuation arrives from somewhere in the cosmos and hits one of our many telescopes, headlines erupt across the media: “Have We Finally Detected An Alien Signal?” or “Have Astronomers Discovered An Alien Megastructure?” But science-minded people know that we’re probably getting ahead of ourselves.
Skepticism still rules the day when it comes to these headlines, and the events that spawn them. That’s the way it should be, because we’ve always found a more prosaic reason for whatever signal from space we’re talking about. But, being skeptical is a balancing act; it doesn’t mean being dismissive.
What we’re talking about here is a new study from E.F. Borra and E. Trottier, two astronomers at Laval University in Canada. Their study, titled “Discovery of peculiar periodic spectral modulations in a small fraction of solar type stars” was just published at arXiv.org. ArXiv.org is a pre-print website, so the paper itself hasn’t been peer reviewed yet. But it is generating interest.
The two astronomers used data from the Sloan Digital Sky Survey, and analyzed the spectra of 2.5 million stars. Of all those stars, they found 234 stars that are producing a puzzling signal. That’s only a tiny percentage. And, they say, these signals “have exactly the shape of an ETI signal” that was predicted in a previous study by Borra.
A portion of the 234 stars that are sources of the pulsed ETI-like signal. Note that all the stars are in the narrow spectral range F2 to K1, very similar to our own Sun. Image: Ermanno F. Borra and Eric Trottier
Prediction is a key part of the scientific method. If you develop a theory, your theory looks better and better the more you can use it to correctly predict some future events based on it. Look how many times Einstein’s predictions based on Relativity have been proven correct.
The 234 stars in Borra and Trottier’s study aren’t random. They’re “overwhelmingly in the F2 to K1 spectral range” according to the abstract. That’s significant because this is a small range centred around the spectrum of our own Sun. And our own Sun is the only one we know of that has an intelligent species living near it. If ours does, maybe others do too?
The authors acknowledge five potential causes of their findings: instrumental and data reduction effects, rotational transitions in molecules, the Fourier transform of spectral lines, rapid pulsations, and finally the ETI signal predicted by Borra (2012). They dismiss molecules or pulsations as causes, and they deem it highly unlikely that the signals are caused by the Fourier analysis itself. This leaves two possible sources for the detected signals. Either they’re a result of the Sloan instrument itself and the data reduction, or they are in fact a signal from extra-terrestrial intelligences.
This graph shows the number of detected signals by Spectral Type of star. Image: Ermanno F. Borra and Eric Trottier
The detected signals are pulses of light separated by a constant time interval. These types of signals were predicted by Borra in his 2012 paper, and they are what he and Trottier set out to find in the Sloan data. It may be a bit of a red flag when scientist’s find the very thing they predicted they would find. But Trottier and Borra are circumspect about their own results.
As the authors say in their paper, “Although unlikely, there is also a possibility that the signals are due to highly peculiar chemical compositions in a small fraction of galactic halo stars.” It may be unlikely, but lots of discoveries seem unlikely at first. Maybe there is a tiny subset of stars with chemical peculiarities that make them act in this way.
To sum it all up, the two astronomers have found a tiny number of stars, very similar to our own Sun, that seem to be the source of pulsed signals. These signals are the same as predicted if a technological society was using powerful lasers to communicate with distant stars.
We all want there to be aliens, and maybe the first sign of them will be pulsed light signals from stars like our own Sun. But it’s all still very preliminary, and as the authors acknowledge, “…at this stage, this hypothesis needs to be confirmed with further work.”
The Breakthrough team don’t seem that excited about Borra’s findings. They’ve already poured cold water on it, trotting out the old axiom that “Extraordinary claims require extraordinary evidence” in a statement on Borra’s paper. They also give Borra’s findings a score of 0 to 1 on the Rio Scale. The Rio Scale is something used by the international SETI community to rank detections of phenomena that could indicate advanced life beyond Earth. A rating of 0 to 1 means its insignificant.
This is the cover of my new book “Night Sky with the Naked Eye”, a non-technical guide to all the great things visible with the naked eye at night. It’s published by Page Street Publishing and distributed by Macmillan and currently available for pre-order on Amazon and Barnes and Noble. Publication date is November 8. Look for it here on Universe Today soon!
If you’re like a lot of people, you don’t own a telescope but still have a passionate curiosity for what’s going on over your head. Good news! There’s lots to see up there without any equipment at all. This is the premise of my new book titled Night Sky with the Naked Eye, a guide to the wonders of the night sky that anyone can enjoy and understand whether you live in an apartment in the city or cabin 50 miles from nowhere.
This diagram from the book depicts why many satellites are visible during twilight before they’re eclipsed by Earth’s shadow. Credit: Gary Meader
I’ve always been amazed at how accessible the universe is. To make that personal connection to the cosmos we only need acquire the habit looking up. Total eclipses, monster auroras and rich meteor showers get a lot of coverage and rightly so, but there’s a lot of other stuff up there. Little things that stoke our sense of wonder happen all the time: Earth’s rising shadow at sunset, nightly satellite flyovers, the beauty of an earth-lit crescent moon or seeing your shadow by the light of Venus.
Skywatching not only informs and delights, it has the power to expand our perspective and sense of place in the scheme of things. Gazing up at the Milky Way on a dark summer night, we feel both humbled and fortunate to be alive. The night sky’s elixir of beauty, timelessness and possibility feeds an inner quietude that can be our strength in stressful times.
Night sky observing sometimes means pleasant surprises like seeing this rare Venus pillar and corona. The book explores both celestial and atmospheric phenomena. Credit: Bob King
While the book touches on the contemplative aspects of skywatching, the bulk of it is activity-oriented, intended to inspire you to get outside. I’ve got tips on weather-watching and making the most of online resources like Clear Dark Sky and satellite imagery to help you find clear skies for that must-see special event. And if light pollution is a problem where you live, we explore ways to make a difference in reducing it as well as using online atlases to find a dark observing site.
The book covers the basics of celestial and planetary motions, how to find the brighter constellations and naked-eye deep sky objects along with suggested night sky viewing activities to share with friends and family. There are 1o chapters in all:
Chapter 1: Wave “Hi!” to the Astronauts
Chapter 2: Anticipating the Night
Chapter 3: Rockin’ N’ Rollin’ Earth
Chapter 4: Dive Into the Dippers
Chapter 5: Four Seasons of Starlight
Chapter 6: Meet the Rabbit in the Moon
Chapter 7: Face to Face with the Planets
Chapter 8: Wish Upon a Shooting Star
Chapter 9: Awed by Aurora
Chapter 10: Curiosities of the Night
This is back of the Night Sky with the Naked Eye book jacket. My book will appear back to back with another space book, titled Incredible Stories from Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos, by Universe Today contributing editor Nancy Atkinson. Watch for her announcement shortly.
Not everything is a billion miles away. We also take time to examine and appreciate closer-to-home phenomena that are part of the nighttime experience like lunar halos, light pillars and the aurora borealis. No observers’ guide would be complete without challenges. How about seeing craters on the moon with no optical aid or spotting the gegenschein? It’s all here.
Because the Internet has become an integral part of our lives, the book includes numerous online resources as well as useful mobile phone apps related to constellation finding and aurora tracking and tips on night sky photography.
Whether for yourself or to give as a holiday gift for a budding skywatcher, I hope you check out my book, which will be featured in a special promotion here at Universe Today. It would be my privilege to serve as your night sky guide.
The possible nova in Lupus photographed on Sunday, Sept. 25 from Australia. The star is now bright enough to see in binoculars for observers in the far southern U.S. and points south. Credit: Joseph Brimacombe
On September 20, a particular spot in the constellation Lupus the Wolf was blank of any stars brighter than 17.5 magnitude. Four nights later, as if by some magic trick, a star bright enough to be seen in binoculars popped into view. While we await official confirmation, the star’s spectrum, its tattle-tale rainbow of light, indicates it’s a nova, a sun in the throes of a thermonuclear explosion.
The nova was discovered on Sept. 23 near the 3rd magnitude star Epsilon Lupi. It rose from fainter than magnitude +17.5 to its current magnitude +6.8 in just four nights … and it’s still rising. It’s visible low in the southwestern sky in late evening twilight low northern latitudes, the tropics and southern hemisphere. This map shows the sky facing southwest about an hour after sunset from Key West, Florida, latitude 24.5 degrees north. Source: Stellarium
The nova, dubbed ASASSN-16kt for now, was discovered during the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or “Assassin”), using data from the quadruple 14-cm “Cassius” telescope in CTIO, Chile. Krzysztof Stanek and team reported the new star in Astronomical Telegram #9538. By the evening of September 23 local time, the object had risen to magnitude +9.1, and it’s currently +6.8. So let’s see — that’s about an 11-magnitude jump or a 24,000-fold increase in brightness! And it’s still on the rise.
Use this chart with binoculars to help you find the likely nova. The field of view is about 5 degrees with north up. The “new star” lies between a bright triangle of stars to the east and the naked-eye star Epsilon Lupi to the west. Stars are labeled with magnitudes. Chart: Bob King, Source: Stellarium
The star is located at R.A. 15h 29?, –44° 49.7? in the southern constellation Lupus the Wolf. Even at this low declination, the star would clear the southern horizon from places like Chicago and further south, but in late September Lupus is low in the southwestern sky. To see the nova you’ll need a clear horizon in that direction and observe from the far southern U.S. and points south. If you’ve planned a trip to the Caribbean or Hawaii in the coming weeks, your timing couldn’t have been better!
Novae occur in close binary systems where one star is a tiny but extremely compact white dwarf star. The dwarf draws material into a disk around itself, some of which is funneled to the surface and ignites in a nova explosion. Credit: NASA
I’ve drawn the map for Key West, one of southernmost locations on the U.S. mainland, where the nova stands about 7-8° high in late twilight, but you might also see it from southern Texas and the bottom of Arizona if you stand on your tippytoes. Other locales include northern Africa, Finding a good horizon is key. Observers across Central and South America, Africa, India, s. Asia and Australia, where the star is higher up in the western sky at nightfall, are favored.
Nova means “new”, but a nova isn’t a brand new star coming to life but rather an explosion that occurs on the surface of an otherwise faint star no one’s taken notice of – until the blast causes it to brighten 50,000 to 100,000 times.
You can use this AAVSO chart to find the nova and track its changing brightness. Star magnitudes are shown to the tenth with the decimal omitted. Click to enlarge. Credit: AAVSO
A nova occurs in a close binary star system, where a small but extremely dense and massive (for its size) white dwarf siphons hydrogen gas from its closely-orbiting companion. After whirling around in a flattened accretion disk around the dwarf, the material gets funneled down to the star’s 150,000 F° surface where gravity compacts and heats the gas until it detonates in a titanic thermonuclear explosion. Suddenly, a faint star that wasn’t on anyone’s radar vaults a dozen magnitudes to become a standout “new star”.
Novae are relatively rare and almost always found in the plane of the Milky Way, where the stars are most concentrated. The more stars, the greater the chances of finding one in a nova outburst. Roughly a handful a year are discovered, many of those in Scorpius and Sagittarius, in the direction of the galactic bulge.
We’ll keep tabs on this new object and report back with more information and photos as they become available. You can follow the new celebrity as well as print out finder charts on the American Association of Variable Star Observers (AAVSO) website by typing ASASSN-16kt in the info boxes.
I sure wish I wasn’t stuck in Minnesota right now or I’d be staring down the wolf’s new star!
