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  • richardmitnick 12:27 pm on February 14, 2019 Permalink | Reply
    Tags: "Pulses from a Dead Star, , , , , , Little Green Men and a Historic Discovery", Pulsars- fast-spinning neutron stars, , UA's Mt. Lemmon Sky Center, UA's Steward Observatory, Walter Baade-discovered the Crab Nebula   

    From University of Arizona: “Pulses from a Dead Star, Little Green Men and a Historic Discovery” 

    U Arizona bloc

    From University of Arizona

    1
    John Cocke (Photo courtesy of Nathaniel Johnston/njohnstonphotography.com)

    Feb. 8, 2019
    Daniel Stolte

    In January 1969, only months before Neil Armstrong would step onto the moon, three UA scientists were the first to detect the optical flash from a pulsar — a stellar corpse thought to pack at least one-and-a-half times the mass of our sun into a city-sized, fast-spinning neutron star.

    Fifty years ago, a team of three undeterred University of Arizona astrophysicists huddled around a 36-inch telescope inside the dome of the UA’s observatory on top of Kitt Peak.

    U Arizona Steward Observatory at Kitt Peak, AZ, USA, altitude 2,096 m (6,877 ft)

    With cobbled-together electronic equipment, W. John Cocke, Mike Disney and Don Taylor and made a historic discovery: the first detection of light flashes coming from a pulsar, a fast-spinning neutron star.

    On Jan. 15, a public lecture at the UA’s Steward Observatory recounted the discovery. In the audience was none other than Cocke, a member of the original team and now professor emeritus. Cocke spoke to UANews about those few days in January 1969 that spawned a new field in astrophysics: the science of pulsars, ultra-dense corpses of formerly massive stars whose bizarre nature is only surpassed by black holes.

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    Located about 6,500 light-years from Earth in the constellation Taurus, the Crab Nebula is still expanding at a rate of more than 600 miles per second. (Image: Adam Block/UA Mt. Lemmon Sky Center)

    U Arizona Catalina Sky Survey, on Mount Lemmon, AR, USA, 9,171 ft (2,795 m)

    What are pulsars, and what can they tell us about the universe?
    Cocke: Pulsars are rotating neutron stars, which are the cores of exploded stars. A pulsar essentially is a rotating magnet, which generates an electric field, and these things are spinning so rapidly that the electric field is sucking material out from the surface of the star. That generates the high-intensity emission in radio, optical and ultraviolet wavelengths, even gamma rays. Out of each magnetic pole comes a continuous beam of electromagnetic emission as the thing rotates around. In order for us to see pulsars, their magnetic field axis has to be offset from the rotation axis, so their beam sweeps around like a lighthouse. As the beam sweeps past the Earth, we can see right down the pole just briefly as it flashes past, creating the sensation of seeing a pulse.

    In a way, pulsars teach us only about the very violent fates of the few stars that are massive enough to blow themselves completely to smithereens or collapse into a neutron star and finally a black hole. Most stars are going to die very, very slowly, and as the universe continues to expand, everything gets cooler and cooler, and the universe then dies, as T.S. Eliot would say, “not with a bang, but a whimper.”

    When your boss, Steward Observatory Director Bart Bok, learned about your observations and what you found, he was “horrified.” Why?
    Cocke: Because only one of us (Taylor) had experience with telescopes and instrumentation. Mike Disney and I were theorists, and the whole thing was so improbable, you see, that nobody, including us, thought that we would actually find something. A month before, I had asked a number of pundits at the American Astronomical Society Meeting whether it was a good idea or just a waste of time to look for this thing in the middle of the Crab Nebula, and they said, “Don’t bother, it won’t pan out.”

    2
    John Cocke next to the 21-inch telescope at Steward Observatory on the UA campus. (Photo courtesy of Nathaniel Johnston/njohnstonphotography.com)

    How did the project come about?
    Cocke: The first radio signals from what we now know are pulsars were detected by by Jocelyn Bell and Antony Hewish in the autumn of 1967.

    Women in STEM – Dame Susan Jocelyn Bell Burnell

    Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

    Dame Susan Jocelyn Bell Burnell 2009

    Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

    At that point, radio astronomers were really concerned how something as massive as a star could emit pulses that were only a second or a second and a half long. The first joke that came out was that these were radio signals from advanced civilizations, which became known as the LGM, the “Little Green Men” idea. Of course, nobody really believed that except people wearing tin foil helmets.

    At first the signals were believed to come from white dwarfs (burned-out stars similar to our sun) as they expanded and contracted. But then a very fast pulsating star was discovered in the Vela constellation in the Southern Hemisphere emitting pulses lasting one-tenth of a second, and that blew the white-dwarf theory right out of the water.

    In early November 1968, radio astronomers discovered this thing associated with the Crab Nebula that emitted about 30 pulses per second. At that point, everybody understood that they had to be neutron stars, and I had wondered about looking for optical counterparts of these things for a few months before. This pulsar, then, that was located rather near the Crab Nebula made me think of a very peculiar star in the middle of the Crab Nebula named for its discoverer, Swiss astronomer Walter Baade. He recognized that star was very peculiar and may be the collapsed remnant of the supernova explosion that had created the nebula itself. It is emitting a lot of light and even shows up on old photographic plates taken of the Crab Nebula. Mike Disney and I then teamed together, once we realized we were both theoreticians interested in gaining some experience doing observing. He suggested we cobble together some instrumentation that would allow us to do this.

    How did you go about making the first optical observations of a neutron star?
    Cocke: We were looking into a pretty broad spectrum in the visible light spectrum, and we knew that any optical signal coming through the 36-inch telescope from Baade’s star would be pretty faint. We weren’t really sure what was needed, except that we needed something that allowed us to build up signals in a computer synced to the pulsar itself, so we could gather up enough signal with overlapping pulses coming in that we could build up a detection out of the noise.

    Interestingly, there was a report in the 1950s about an experienced pilot who looked at Baade’s star during a public telescope viewing and remarked that it appeared to flash, but her observation was dismissed. However, we did not know this at the time. We knew there were other groups of astronomers looking at pulsars with slower signal frequency, and they were not having success. We attached a photometer to the telescope and connected that to an off-the-shelf device called CAT – computer of average transients – which had a total memory of 400 bytes and could build up a signal above the noise so you could actually see something interesting. All of this instrumentation was put together properly by Don Taylor, and he became the third member of the team.

    Can you tell us about the night of the discovery?
    Cocke: The first two nights were clear but wasted because I had made a mistake in calculating the Doppler shift due to Earth’s motion through space. A few cloudy nights followed, and we ran out of our allocated observing time. But it turned out that our colleague Bill Tifft was able to give us some of his observing nights because he had to take care of a family emergency. On January 15, within a few minutes of observing, we could see the pulse as it built up on the screen. We moved the telescope off Baade’s star to a nearby star or just a blank spot to see whether or not the signal would still come through like that, and it didn’t. Then we’d move it back on the pulsar but change the frequency setting so it was off, and we didn’t see that signal, so that was a good check. We then rechecked everything and did another round on the proper position and at the proper period, and the pulse would come up again. These were all checks we had to run to make sure this thing was real. On our screen, we saw a big main pulse and a smaller, secondary pulse – the exact pattern we expected from what the radio pulses look like. That was the final clincher.

    Are there any practical applications for pulsar science?
    Cocke: No. (pauses) Sorry about that.

    See the full article here .


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    Please help promote STEM in your local schools.

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    U Arizona campus

    The University of Arizona (UA) is a place without limits-where teaching, research, service and innovation merge to improve lives in Arizona and beyond. We aren’t afraid to ask big questions, and find even better answers.

    In 1885, establishing Arizona’s first university in the middle of the Sonoran Desert was a bold move. But our founders were fearless, and we have never lost that spirit. To this day, we’re revolutionizing the fields of space sciences, optics, biosciences, medicine, arts and humanities, business, technology transfer and many others. Since it was founded, the UA has grown to cover more than 380 acres in central Tucson, a rich breeding ground for discovery.

    Where else in the world can you find an astronomical observatory mirror lab under a football stadium?

    U Arizona mirror lab


    An entire ecosystem under a glass dome? Visit our campus, just once, and you’ll quickly understand why the UA is a university unlike any other.

     
  • richardmitnick 6:37 am on April 12, 2018 Permalink | Reply
    Tags: , , , Burçin Mutlu-Pakdil, Burçin’s Galaxy - PGC 1000174, Carnegie’s Las Campanas Observatory Chile over 2500 m (8200 ft) high, , , , UA's Steward Observatory,   

    From Science Node: Women in STEM – “Burçin’s galaxy” Burçin Mutlu-Pakdil 

    Science Node bloc
    Science Node

    30 Mar, 2018
    Ellen Glover

    1
    Burçin Mutlu-Pakdil

    As a little girl growing up in Turkey, Burçin Mutlu-Pakdil loved the stars.


    Burçin’s galaxy, AKA PGC 1000714, is a unique, double-ringed, Hoag-type galaxy exhibiting features never observed before. Courtesy North Carolina Museum of Natural Sciences.

    “How is it possible not to fall in love with stars?” wonders Mutlu-Pakdil. “I find it very difficult not to be curious about the Universe, about the Milky Way and how everything got together. I really want to learn more. I love my job because of that.”

    1
    Young or old? The object’s blue outer rings suggests it may have formed more recently than the center.

    Her job is at The University of Arizona’s Steward Observatory, one of the world’s premier astronomy facilities, where she works as a postdoctoral astrophysics research associate.

    U Arizona Steward Observatory at Kitt Peak, AZ, USA, altitude 2,096 m (6,877 ft)

    Just a few years ago, while earning her Ph.D. at the University of Minnesota, Mutlu-Pakdil and her colleagues discovered PGC 1000174, a galaxy with qualities so rare they’ve never been observed anywhere else. For now, it’s known as Burçin’s Galaxy.

    The object was originally detected by Patrick Treuthardt, who was observing a different galaxy when he spotted it in the background. It piqued the astronomers’ attention because of an initial resemblance to Hoag’s Object. This rare galaxy is known for its yellow-orange center surrounded by a detached outer ring.

    “Our object looks very similar to Hoag’s Object. It has a very symmetric central body with a very symmetric outer ring,” explains Mutlu-Pakdil. “But my work showed that there is actually a second ring on this object. This makes it much more complex.”

    Through extensive imaging and analysis, Mutlu-Pakdil found that, unlike Hoag’s Object, this new galaxy has two rings with no visible materials attaching them, a phenomenon not seen before. It offered the first-ever observation and description of a double-ringed elliptical galaxy.

    4
    Eye on the universe. Sophisticated instruments like the 8.2 meter optical-infrared Subaru Telescope on the summit of Mauna Kea in Hawaii allow astronomers to peer ever further into the stars–and into the origins of the universe.


    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

    Since spotting the intriguing galaxy, Mutlu-Pakdil and her team have evaluated it in several ways. They initially observed it via the Irénéé du Pont two-meter telescope at the Las Campanas observatory in Chile. And they recently captured infrared images with the Magellan 6.5-meter telescope also at Las Campanas.


    Carnegie Las Campanas Dupont telescope, Atacama Desert, over 2,500 m (8,200 ft) high approximately 100 kilometres (62 mi) northeast of the city of La Serena,Chile

    Carnegie 6.5 meter Magellan Baade and Clay Telescopes located at Carnegie’s Las Campanas Observatory, Chile. over 2,500 m (8,200 ft) high

    The optical images reveal that the components of Burçin’s Galaxy have different histories. Some parts of the galaxy are significantly older than others. The blue outer ring suggests a newer formation, while the red inner ring indicates the presence of older stars.

    Mutlu-Pakdil and her colleagues suspect that this galaxy was formed as some material accumulated into one massive object through gravitational attraction, AKA an accretion event.

    However, beyond that, PGC1000174’s unique qualities largely remain a mystery. There are about three trillion galaxies in our observable universe and more are being found all the time.

    “In such a vast universe, finding these rare objects is really important,” says Mutlu-Pakdil. “We are trying to create a complete picture of how the Universe works. These peculiar systems challenge our understanding. So far, we don’t have any theory that can explain the existence of this particular object, so we still have a lot to learn.”

    Challenging norms and changing lives

    In a way, Mutlu-Pakdil has been challenging the norms of science all her life.

    Though her parents weren’t educated beyond elementary school, they supported her desire to pursue her dreams of the stars.

    “When I was in college, I was the only female in my class, and I remember I felt so much like an outsider. I felt like I wasn’t fitting in,” she recalls of her time studying physics at Bilkent University in Ankara, Turkey.

    7
    Bilkent University

    8
    Astronomical ambassador. Mutlu-Pakdil believes in sharing her fascination for space and works to encourage students from all backgrounds to explore astronomy and other STEM fields.

    Throughout her education and career, Mutlu-Pakdil has experienced being a minority in an otherwise male-dominated field. It hasn’t slowed her down, but it has made her more passionate about promoting diversity in science and being a mentor to young people.

    “I realized, it is not about me, it is society that needs to change,” she says. “Now I really want to inspire people to do similar things. So kids from all backgrounds will be able to understand they can do science, too.”

    That’s why she serves as an ambassador for the American Astronomical Society and volunteers to mentor children in low-income neighborhoods to encourage them to pursue college and, hopefully, a career in STEM.

    She was also recently selected to be a 2018 TED Fellow and will present a TED talk about her discoveries and career on April 10.

    Through her work, Mutlu-Pakdil hopes to show people how important it is to learn about our universe. It behooves us all to take an interest in the night sky and the groundbreaking discoveries being made by astronomers like her around the world.

    “We are a part of this Universe, and we need to know what is going on in it. We have strong theories about how common galaxies form and evolve, but, for rare ones, we don’t have much information,” says Mutlu-Pakdil. “Those unique objects present the extreme cases, so they really give us a big picture for the Universe’s evolution — they stretch our understanding of everything.”

    See the full article here .

    Please help promote STEM in your local schools.
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    Science Node is an international weekly online publication that covers distributed computing and the research it enables.

    “We report on all aspects of distributed computing technology, such as grids and clouds. We also regularly feature articles on distributed computing-enabled research in a large variety of disciplines, including physics, biology, sociology, earth sciences, archaeology, medicine, disaster management, crime, and art. (Note that we do not cover stories that are purely about commercial technology.)

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  • richardmitnick 2:33 pm on March 2, 2018 Permalink | Reply
    Tags: , , , Bart Bok, , , KIC 08626021, UA's Bok Telescope, UA's Steward Observatory   

    From University of Arizona: “Bok to the Future: Sounding the Depths of a Dying Star” 

    U Arizona bloc

    University of Arizona

    March 1, 2018
    Daniel Stolte

    A small, aging telescope can still do mighty science, even helping astrophysicists undertake a virtual journey to the center of a dead star. What they discovered may change our knowledge of how stars — including our sun — evolve and age.

    1
    Vintage workhorse: Dedicated in 1969 and named after Bart Bok, who was director of the UA’s Steward Observatory at the time, the UA’s Bok Telescope has pointed its 90-inch primary mirror at the skies every night except Christmas Eve and a maintenance period during the summer rainy season. (Image courtesy of Steward Observatory)

    U Arizona Steward Observatory at Kitt Peak, AZ, USA, altitude 2,096 m (6,877 ft)

    There are times when having the latest and greatest in technology is not the only thing that counts, even in a field where success depends critically on technological advances, as it does in astronomy.

    This is the story of a telescope and instrument considered “vintage” by today’s standards, and how they allowed one group of researchers to succeed in making a discovery they wouldn’t otherwise have been able to make, had they relied exclusively on the advanced satellite instrument that collected the initial data.

    It all began when data taken by NASA’s Kepler spacecraft revealed that a white dwarf named KIC 08626021, the “corpse” of a star not unlike the sun, was pulsating. That in itself was not unusual. By the time a star becomes a white dwarf, it has burned all of its nuclear fuel and is cooling down for the last time. At several points during the cooling process, a white dwarf becomes unstable, causing it to pulsate simultaneously at multiple different frequencies. These deep vibrations are the key to unveiling the interior of the stellar remnant. The internal chemical stratification of the white dwarf star creates a unique signature in the modulation of the light coming out of the star, which, once deciphered, allows scientists to obtain a cartography of its internal structure.

    Astronomers who study how stars are born, how they age and how they die believe that white dwarfs, especially pulsators such as KIC 08626021, give us a preview of the afterlife of our sun, long after it has consumed our planet in its fiery throes of death. In fact, the vast majority of stars in the universe will end up as white dwarfs. These stellar relics retain the imprints of past physical processes such as nuclear burning and episodes of convective mixing — phenomena that are not all that well understood in the actual modeling of stellar evolution theory. To have a glimpse at the internal structure and composition of these stars allows scientists to better elucidate the physics at play during all phases of stellar evolution, including those occurring in our sun.

    But in the case of KIC 08626021, something was off. The pulsations that Kepler observed in this star were too rapid for the type of white dwarf that it was initially reported to be, based on the models astronomers commonly use to investigate these stars.

    “A light spectrum taken with the William Herschel Telescope on La Palma in the Canary Islands suggested that its atmosphere contained only helium and no hydrogen,” says Elizabeth Green, an associate astronomer at the University of Arizona’s Steward Observatory who helped decipher the star’s true nature.


    ING 4 meter William Herschel Telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, 2,396 m (7,861 ft)

    “This was a problem because a white dwarf of that type should have a cooler temperature and therefore slower oscillations than what Kepler saw.”

    Journey to the Center of a Star

    Green was part of an international team of astrophysicists from Toulouse, France; Montreal; Tucson; Liège, Belgium; and Beijing who set out to unravel the internal composition of KIC 08626021 by deciphering the brightness oscillations observed at its surface, using asteroseismology, a technique similar to methods that geophysicists use to study the structure of the Earth, analyzing the seismic waves caused by earthquakes. The researchers published their results in a recent article in the journal Nature.

    “In order to successfully model a star with asteroseismology, one needs to make the model as realistic as possible,” Green says. “This means that the values for a large number of different parameters must be specified: the total mass and radius of the star, the atmospheric temperature, the thickness and composition of the atmosphere and, in the case of a white dwarf like this one, whose interior is stratified in layers of different elements, the mass, thickness and composition of each interior layer.”

    In the process of modeling the interiors of stars, theoreticians first construct a range of theoretical stellar models covering all the possible values of every unknown parameter, and determine what pulsational frequencies would be excited in each one. Then they compare the resulting sets of model frequencies to the observed frequencies to see if there are any matches, and if so, which ones match the observations the best.

    “For stellar asteroseismology,” Green explains, “one of the best ways to prove that your models are realistic is to analyze a spectrum of the light from the star, determine its effective temperature and gravity, and show that these values agree with the temperature and gravity of the best asteroseismic model.”

    To do this, Green spent several nights pointing Steward’s Bok Telescope on Kitt Peak at the white dwarf KIC 08626021 — 1,376 light-years away in the constellation Cygnus. Using the telescope’s B&C spectrograph, she measured the amount of light that the star emits at different wavelengths, to obtain the so-called spectrum that her colleagues later analyzed to determine the actual atmospheric parameters of the dead star.

    Light Hits Arizona Mountaintop

    “Obtaining enough individual spectra to combine into a single useful spectrum was no small feat considering that this was a rather faint star for a telescope of this size,” Green says. “Nevertheless, we had enough time allocated to do the job properly. It would have been much more difficult to do with other, more powerful telescopes and instruments elsewhere, which have much more intense competition for observing time.”

    Green’s observations helped clear up a mystery that resulted in the proper classification of KIC 08626021. Her spectrum was the first to show convincingly that this white dwarf’s atmosphere was not composed entirely of helium, but contained significant traces of hydrogen as well. “Since hydrogen has a large effect on the opacity of the atmosphere, the slightly different atmospheric composition resulted in a higher calculated effective temperature for the star, consistent with its relatively rapid pulsations,” she says.

    The best-fitting asteroseismic solution not only matched the pulsational frequencies observed by the Kepler satellite “beautifully,” according to Green, “but now it also agreed extremely well with the temperature and gravity determined from the Bok Telescope spectrum.”

    Peeling back the different layers of the white dwarf revealed that the stellar core of these stars is bigger and richer in oxygen than predicted, and provided clues to all the main chemical elements present. In addition, a precise knowledge of the internal chemical composition of white dwarfs also is useful as a “cosmological chronometer” allowing astronomers to determine the ages of the various stellar populations of our galaxy.

    “To me, the most exciting part about this study is that we now have ‘observed’ values for things like the core size and oxygen abundance at the very center of a star that is nearing the end of its stellar life,” Green says. “It’s almost like real X-ray vision. These new results will be used to refine our knowledge of physical processes that take place in extreme conditions in the interiors of nearly all stars.”

    The study, “A large oxygen-dominated core from the seismic cartography of a pulsating white dwarf,” was led by Noemi Giammichele at the Institut de Recherche en Astrophysique et Planétologie (IRAP) of Toulouse, France.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    U Arizona campus

    The University of Arizona (UA) is a place without limits-where teaching, research, service and innovation merge to improve lives in Arizona and beyond. We aren’t afraid to ask big questions, and find even better answers.

    In 1885, establishing Arizona’s first university in the middle of the Sonoran Desert was a bold move. But our founders were fearless, and we have never lost that spirit. To this day, we’re revolutionizing the fields of space sciences, optics, biosciences, medicine, arts and humanities, business, technology transfer and many others. Since it was founded, the UA has grown to cover more than 380 acres in central Tucson, a rich breeding ground for discovery.

    Where else in the world can you find an astronomical observatory mirror lab under a football stadium? An entire ecosystem under a glass dome? Visit our campus, just once, and you’ll quickly understand why the UA is a university unlike any other.

     
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