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  • richardmitnick 2:54 pm on September 5, 2017 Permalink | Reply
    Tags: ASAS-SN, ASASSN-16ma, , , , , , NASA Blueshift, Novas   

    From NASA blueshift: “Shock Waves Power an Exploding Star” 

    NASA Blueshift

    NASA Blueshift

    September 5, 2017
    Raleigh McElvery

    Roughly 50 times each year, a star nearing the end of its life accretes too much material from a close companion star and erupts in a violent display of light — shedding its outer surface and propelling shock waves into our galaxy — only to recover and smolder as it did before. This event is called a ‘nova.’

    This ability to “reprocess” sets novae apart from their rare supernovae counterparts, which occur only several times per century and self-destruct amid an even greater celestial outburst. And yet, it’s the more common novae that could hold the answers to essential questions regarding our universe.

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    As this nova illustration shows, when a white dwarf accretes too much material from its companion star, it ejects material in two district winds. Shock waves are created as the two winds collide, producing gamma rays (magenta). Research now suggests this may be the primary source of visible light as well. Credit: NASA’s Goddard Space Flight Center/S. Wiessinger

    Given that these events usually occur thousands of light years away, I went to discuss their significance with two more accessible sources: Laura Chomiuk and Kwan Lok Li of Michigan State University. Both scientists recently allied with Columbia University and the ASAS-SN project (of which Chomiuk is a key member) in hopes of untangling the fundamental processes underlying the lifecycle of stars.

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    ASAS-SN OSU

    3
    ASAS-SN Cerro Tololo

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    ASASSN-14li: Destroyed Star Rains onto Black Hole, Winds Blow it Back. NASA/Chandra

    They have turned their attention to one classical nova in particular, ASASSN-16ma, located within the “archer” constellation Sagittarius.

    Their paper, recently published in Nature Astronomy, suggests a novel source for the nova’s post-outburst glow — offering insight into other outer-space explosions.

    The authors explained that ASASSN-16ma is among the brightest novae ever detected by the Fermi Large Area Telescope — a satellite instrument built to observe cosmic events releasing a high-energy form of light called gamma rays. The Fermi Mission, spearheaded by NASA’s Goddard Space Flight Center, also discovered back in 2010 that novae generate these high-energy rays.

    Gamma rays are emitted as material is ejected from the star in two distinct winds or “outflows.” A slow burst is followed by a faster one, which then crashes into the first and creates a shock wave. Visible light also radiates from the same explosion, although until now most scientists believed it stemmed from nuclear reactions on the surface of the star.

    But something wasn’t right about the traditional explanation. Novae shouldn’t have enough power to produce gamma rays — nor release as much visible light as they do given their calculated luminosity limit.

    This inherent contradiction confounded astrophysicists and theorists alike, until last year when Chomiuk requested that Fermi focus on ASASSN-16ma for an extended duration to collect more sensitive data. As luck would have it, Fermi was already observing another nova in the same neighborhood, so Goddard’s team was more than happy to oblige, tilting their telescope slightly. When scientists began to sift through the data transmitted from the cosmos to Earth, one specific trend became abundantly clear.

    “Our results were telling us our previous assumption that all the luminosity comes from the surface of the star was flawed,” Chomiuk explained to me from her office in East Lansing. “A lot of it actually comes from the same place as the gamma rays,” she continued. That is, the colliding shock waves.

    Seeking an outsider’s perspective, I made my way to the second floor of Goddard’s astrophysics building to chat with one of the center’s Fermi aficionados, David Thompson. Eager to lend guidance, Thompson presented his miniature replica of the spacecraft, and indicated the boxy Large Area Telescope seated atop the winged satellite. “We’ve been seeing similar novae for years, but this was unexpected,” he said. “The authors have enough detail in their data to challenge the conventional wisdom about what makes novae bright.”

    But I soon learned these ideas weren’t entirely unprecedented. During every interview I conducted, one name kept coming up: collaborator and lead theorist, Brian Metzger of Columbia University. Metzger had been crunching the numbers on novae for several years, but lacked substantive data to bolster his hypotheses. That is, until now.

    “Novae have been observed by the naked eye since well before the modern era,” Metzger told me, “and yet our view of what is producing these bright outbursts continues to change.”

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    The Fermi LAT 60-month image, constructed from front-converting gamma rays with energies greater than 1 GeV. The most prominent feature is the bright band of diffuse glow along the map’s center, which marks the central plane of our Milky Way galaxy. Image credit: NASA/DOE/Fermi LAT Collaboration

    NASA/Fermi LAT


    NASA/Fermi Telescope

    Fermi’s Deputy Project Scientist, Elizabeth Hays, said Metzger’s paradigm had already garnered some buzz throughout the scientific community, although at the time the universe had yet to reveal an event that clearly reflected his calculations. Now, thanks to ASASSN-16ma, she affirmed his conjectures may expose what powers these nova outbursts — processes which might also extend to other kinds of stellar explosions, like dazzling supernovae as well as star mergers.

    “We’ve been ignoring this whole piece of the puzzle,” she said. “When we come across high-energy processes like these novae, it becomes clear just how much more work we have left to do.”

    Understanding novae shock and gamma ray production could also explain certain properties of accelerating particles traveling close to the speed of light, as well as the subsequent magnetic fields.

    When I asked Li what was next, he said he plans to continue using Fermi data to monitor nearby novae. Ultimately, he hopes to pinpoint similarly strong correlations between gamma ray and visible light emissions within additional novae. “We’re always looking for new sources to test our model, and ensure it truly and accurately describes gamma-ray phenomena in classical novae,” he added.

    Back at Goddard, Thompson repositioned his Fermi model on the shelf among his books, and agreed a single example alone does not constitute proof. But it’s certainly a good place to start. “These results prompt us to think about things in a new way,” he said, “and that’s what science is about.”

    See the full article here .

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  • richardmitnick 11:42 am on July 25, 2016 Permalink | Reply
    Tags: , NASA Blueshift,   

    From blueshift: “Thirty Years of Space VLBI” 

    NASA Blueshift

    NASA Blueshift

    July 25, 2016
    Koji Mukai

    As I write this in July 2016, it has been 30 years since the first successful space very long baseline interferometry (VLBI) observations were made. VLBI is the radio astronomy technique to use widely separated radio dishes to produce exquisite images of celestial radio sources – and space VLBI allows separation between dishes larger than the diameter of the earth, potentially producing higher resolution images.

    But astute readers might be questioning my sanity. Many sources, including a page on our Imagine the Universe site will tell you that the first space VLBI satellite was Japan’s HALCA, which was launched in 1997. And 1997 was less than 20 years ago. Both these statements cannot be true – can they? Actually, yes, they can be, and they are. The actual sentence on the linked page reads: “The first mission dedicated to space interferometry was the Japanese HALCA mission which ran from 1997 to 2005.” The key phrase is “dedicated to” – you see, we sometimes use somewhat awkward phrasing in communicating with the general public when we don’t want to bother you with all the details, at least not initially. The hidden detail behind the sentence above is that well before HALCA, there was an earlier satellite which was used to demonstrate that space VLBI is possible, even though it was not specially designed for that purpose.

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    Top: This radio image of the galaxy M87, taken with the Very Large Array (VLA) radio telescope in February 1989, shows giant bubble-like structures where radio emission is thought to be powered by the jets of subatomic particles coming from the the galaxy’s central black hole. The false color corresponds to the intensity of the radio energy being emitted by the jet. M87 is located 50 million light-years away in the constellation Virgo. Bottom: A Very Long Baseline Array (VLBA) radio image of the region close to the black hole, where an extragalactic jet is formed into a narrow beam by magnetic fields. The false color corresponds to the intensity of the radio energy being emitted by the jet. The red region is about 1/10 light-year across. The image was taken in March 1999. Credit: NASA, National Radio Astronomy Observatory/National Science Foundation, John Biretta (STScI/JHU), and Associated Universities, Inc.

    But let’s back up and start with a refresher on the basics. Professional astronomers and the general public alike like to have the sharpest, the most detailed images of astronomical objects. For UV and optical telescopes, we need bigger telescope mirrors for this, and to preferably launch them into space so the images are not blurred by the Earth’s atmosphere. With these telescopes, we can approach the diffraction limit – the fundamental limit on the sharpness of images set by the physics of light. You see, light is a wave, and there is an intrinsic fuzziness in how it goes through a slit, is reflected by a mirror, etc. The minimum angular size of an image – the diffraction limit – is proportional to the wavelength and inversely proportional to the diameter of the telescope mirror.

    Radio waves have wavelengths often measured in centimeters, much larger than the wavelength of visible light, by a factor of almost a million. While it is easier to build a bigger radio dish than a bigger optical telescope, there is a practical limit. The giant Arecibo radio telescope, famously featured in the film Contact, based on a book by Carl Sagan, used to be the biggest radio telescope in the world.

    NAIC/Arecibo Observatory, Puerto Rico, USA
    NAIC/Arecibo Observatory, Puerto Rico, USA

    Now China just completed what is considered to be the world’s biggest radio telescope.

    FAST Chinese Radio telescope under construction, Guizhou Province, China
    FAST Chinese Radio telescope

    Though the diameters of these big radio dishes are on the order of 100 times the diameters of the biggest visible light mirrors, the wavelengths of radio waves are still so large that the diffraction limited images from any of these single dish telescopes are not very sharp.

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    Primary mirror size comparisons. Note Arecibo is so big that it is only represented by a dark gray arc at the bottom of the image. [FAST is not represented at all.] Credit: Cmglee, creative commons.

    Interferometry to the rescue. If you have an array of radio dishes, they can be combined to increase the effective size of the telescope and obtain sharp images. In technical terms, a baseline is the separation between a pair of radio dishes; you want long (and short) baselines in a variety of directions to make a sharp image. For example, the Karl G. Jansky Very Large Array (VLA) has 27 movable dishes in a Y shaped configuration, each arm of which is 21 km (13 miles) long. Image-wise, its performance is similar to a single, 40 km diameter, telescope.

    NRAO/VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA
    NRAO/VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    VLBI is when you combine signal from multiple radio telescopes on Earth. Space VLBI allows you to have baselines that are longer than the diameter of the Earth. With VLBI (Earth-bound or including a satellite), you tend to have fewer participating telescopes, and you may have to rely on the rotation of the Earth or the orbital motion of the satellite to give you a variety of baselines. HALCA allowed baselines up to about 30,000 km (3 times the diameter of the Earth), and the Russian RadioAstron satellite has an orbit that takes it up to distances equivalent to halfway to the distance to the Moon.

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    Active galaxy (PKS 1519-273) as imaged with HALCA satellite, along with the National Science Foundation’s VLBA and VLA ground-based radio telescopes. This is the first VLBI image ever made using an orbiting radio-astronomy satellite. Credit: NRAO

    But space VLBI started 30 years ago, before these purposefully built satellites. What they used prior to them was the tracking and data relay satellite system (TDRSS), which NASA started in the 1980s for communication between the Space Shuttles and other satellites and ground stations. The communication is via radio waves in some of the same frequency bands used for astronomical radio observations. Back in July and August of 1986, astronomers and engineers used the TDRSS satellite (there was only one in orbit back then) together with the 64-m antenna of the NASA Deep Space Network at Tidbinbilla, Australia and the 64-m antenna of the Institute for Space and Astronautical Science in Usuda, Japan. They demonstrated space VLBI was possible, and that the three quasars they observed were very compact and beaming radio sources. This success opened the way for HALCA and RadioAstron.

    So, here’s to the 30th anniversary of the first successful space VLBI observations!

    See the full article here .

    [This article suffers from no mention of the Event Horizon Telescope (EHT), a new adventure in VLBI. Aimed specifically at exploration of supermassive black hole Sagittarius A*, at the center of the Milky Way, this new adventure will surely take on other projects in a life of its own. That is how science works.

    So, here is the EHT

    Event Horizon Telescope Array

    Event Horizon Telescope map
    Event Horizon Telescope map

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    Future Array/Telescopes

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL ]

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  • richardmitnick 4:11 pm on January 20, 2016 Permalink | Reply
    Tags: , , NASA Blueshift,   

    From NASA Blueshift: “A Conversation with John Mather” 

    NASA Blueshift
    NASA Blueshift

    January 20, 2016
    Maggie Masetti

    October 31st, 1995: The “Next Generation Space Telescope” (NGST) project, now known as “James Webb Space Telescope” (JWST) starts to become a reality. Twenty years later we’re sitting together with Dr. John Mather, Senior Project Scientist at Goddard and one of the Founders of JWST. Working at NASA for over 40 years provides a lot of experiences and stories.

    NASA James Webb Telescope
    NASA/Webb

    Daniela and Verena: How would you describe your areas of activity to a layperson?

    John Mather: Oh, to a layman it would look like I just sit and talk and write e-mails. But I guess, the more interesting thing is what the conversation is about. So the conversation is about ‘What do we need to do?’ so that the telescope will work. And so some days it’s about the engineers and technicians that found something that isn’t quite right, so ‘What are we going to do about it?’. Some days it is just making sure that the scientific world is ready. So we talk to our scientists around the world to say ‘This is how we’re going to operate the telescope. This is what you have to do to prepare a proposal.’ If you’re a scientist then you find your friends and you say ‘This is the topic I think we really should examine and then this is how much time we need from the telescope to answer our questions. This is why we’re the best team in the entire world to do this work.’ Afterwards, a committee will consider the proposals. We receive thousands of proposals – it’s a very popular telescope. So that’s what our conversations are about these days. A time ago, it was more about how could you possibly come up with a technology that would enable such a telescope. Because at the beginning none of this was possible – it was only an idea. So we needed mirrors and detectors and we needed to make an agreement amongst various space agencies about who was going to do what. All of those things were very tricky and they showed us what things to do.

    Temp 1
    Credit: NASA/Chris Gunn

    Daniela and Verena: What was your favorite moment at the JWST project so far?

    John Mather: It’s hard to say. I think my favorite moment will be when it goes up and successfully reaches orbit, unfolds in space and functions properly. That’s the thing everyone thinks about.

    Daniela and Verena: The JWST is a very complex construction project. In your eyes, what is its biggest challenge?

    John Mather: I think everyone believes that the biggest challenge is to make sure that it unfolds properly in space. Because this is new – that is not something we’ve done many times. Many observatories have things that unfold in space but ours is much more precise for the unfolding. So it’s complicated and has this big sunshield design – nobody ever needed a piece of plastic as big as a tennis court in space. It all has to be carefully designed, managed and tested. We also have to imagine every possible way to go wrong and then make sure that this does not happen. So it’s either by thinking about it or by designing something or by testing something that you have to succeed in making a good design. Then, at the very end, of course it’s the technicians, the people who actually touch the equipment, that have to do their job exactly right.

    Daniela and Verena: Winning the Nobel Prize is for sure an experience with far-reaching effects. Can you tell us if it resulted in any professional or private changes?

    John Mather: I think the main changes were getting far more invitations for traveling and speaking. I tried to make no other changes – I have the same job that I had beforehand. The prize came in 2006 and the telescope project was already eleven years old by then. So I’m still doing the same job and I just get more chances to talk to people.

    Daniela and Verena: We know that you’re a passionate traveler. What was your most impressive destination or trip?

    John Mather: I guess there are several. The most spectacular one was traveling to see the giant animals in Southern Africa – we went to Namibia and Botswana and we saw the lions and the elephants. Just thinking about the history where human beings come from and how we must have lived with lions everywhere back then – it sort of makes you think a lot. Because our history here on earth is so short as human beings, we’ve only been here for a very short time and those big animals also haven’t been here that long. Lions and elephants are also just a few million years old. Earth is like 4.6 billion years old – so what was going on between the beginning and now? That’s one of the things I love to think about. Another one is our cultural history. The first time I saw Italy and just see things written on the monuments in Latin and I thought ‘I really should have studied Latin in school so I would be able to read what they said.’ That only reaches back a few thousand years of history. So that seems to be the attraction that I feel. When traveling I’m thinking of history.

    Daniela and Verena: There are a lot of young people with brilliant ideas out there. Often they are not taken seriously and have struggles realizing their visions. Which advice would you give them?

    John Mather: Well, I don’t know if there’s any general advice but everything is about communication. And so sharing the ideas with other people, talking with your friends ‘I’ve got this idea, would you like to help me? Or can you make a better idea?’ – all of these things are part of the process that successful ideas have. I guess it’s always an interesting question because maybe the idea is bad. But how will you find out if you don’t try to push it forward? And maybe if you start pushing it then somebody will say ‘Oh, I have a better idea, let’s do that one instead.’ So I think it’s more like choosing the direction to go in than rather saying which exact tree you’re going to reach – it’s more direction-orientated than goal-orientated. People often talk about how goals are important to us. I think it’s less important than the direction along which the goals might be. Let’s say our direction is that we want to have civilization last for a billion years – what are the things that we have to do between now and a billion years?

    See the full article here .

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  • richardmitnick 3:19 pm on November 19, 2015 Permalink | Reply
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    From NASA Blueshift: “Doing Astronomy With Our Eyes Closed” 

    NASA Blueshift
    NASA Blueshift

    Dr. Ira Thorpe writes his first guest blog for Blueshift on gravitational waves. “What if I told you that there are waves that can travel through space itself and that physicists and astronomers are developing machines that will allow us to listen to them for the first time?”

    November 16, 2015
    Ira Thorpe

    In space, no one can hear you scream. Any sci-fi buff worth their dilithium crystals knows why: sound requires a medium such as air or water in which to propagate and empty space is well, empty. But what if I told you that there are waves that can travel through space itself and that physicists and astronomers are developing machines that will allow us to listen to them for the first time?

    They are called gravitational waves and they are a prediction of general relativity, Albert Einstein’s famous theory for understanding gravity which turns 100 years old this month. You may be familiar with explanations of the theory that describe spacetime as a “rubber” sheet that deforms when a massive object is placed on it. Well imagine that you were to press a finger down on such a sheet and release it. You’d get a wave that would travel outwards, somewhat like the waves in a pond when a stone is dropped in it.

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    In this artist’s conception, a binary black hole produces gravitational waves that travel outwards and carry energy away from the system. Image Credit: NASA

    With considerably more effort, it’s possible to crank through Einstein’s equations and show that there is indeed a mathematical solution that describes waves in spacetime and that these gravitational waves travel at the speed of light, come in two polarizations, and can carry energy, momentum, and information. You can also determine what it takes to generate these waves and where in the universe you might expect to find such systems.

    It turns out that the best sources typically involve exotic and extreme astrophysical objects such as white dwarfs, neutron stars, and black holes. One of the best sources is a tightly-bound binary system with two such objects orbiting around one another. The gravitational waves generated by such systems carry away energy and cause the objects to fall towards one another, which increases the amplitude of the gravitational waves and the rate at which they sap energy from the system. The result is a runaway collapse of the system that produces a cataclysmic merger of the objects and a burst of gravitational waves.

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    NASA scientists used supercomputers to solve Einstein’s equations for a merging black hole binary to predict the precise gravitational wave output. Image Credit: NASA

    Now if the objects in question happen to be made of matter, for example if they are neutron stars, the merger will produce a burst of electromagnetic energy that can be detected with today’s telescopes. In fact, this is a favored model for one type of gamma-ray burst. If on the other hand, the two objects are black holes, there may be no electromagnetic signal at all. In terms of energy released per unit time, what astronomers call luminosity, the final inspiral and merger of a binary black hole system is the most luminous event in the universe since the big bang and yet it is completely invisible to any instrument that observes in the electromagnetic spectrum.

    Physicists and astronomers have recognized the potential for building gravitational wave detectors for decades. They offer an opportunity to both understand the nature of gravity in its most extreme forms as well as an entirely new tool for doing astronomy. In many ways, a gravitational wave observatory is more like a listening device than a telescope. They tend to be sensitive to sources over a wide area of the sky, much like your ears can sense sounds coming from different directions. It’s also possible to observe multiple sources simultaneously, as the human ears (and brain) do when you talk on the phone with the TV on, the refrigerator humming, and a siren blaring in the distance.

    The problem is that detecting gravitational waves is hard. What you want to look for is the stretching of spacetime itself. This is done by placing two or more objects in near-perfect free-fall so that their motion will only be affected by gravity. You then closely monitor the distance between these objects and look for distortions caused by the passing gravitational waves. The size of these waves is measured with a dimensionless number called strain, which tells you the total displacement caused by the waves divided by the initial distance between the objects. For a typical astrophysical gravitational wave source, the strain at Earth is about one sextillionth. Don’t know your prefixes that far out? Neither did I. It’s one part in a billion trillion or 10^-21. This incredibly small number is sometimes wrongly interpreted as evidence that gravitational waves are weak. A better description is that spacetime is extremely stiff and it takes a tremendous amount of energy to make even a small distortion. That rubber sheet in the model should be more like a titanium sheet.

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    The LIGO observatory in Hanford, WA is one of several kilometer-scale interferometric gravitational wave detectors currently in operation. LIGO is sensitive to “high frequency” gravitational waves with with periods of seconds to milliseconds. Image credit: LIGO Laboratory

    You might think that measuring a number as small as 10^-21 would be in the realm of fantasy but it is in fact within the grasp of modern precision measurement techniques. Right now, several large collaborations of scientists are operating kilometer-scale detectors that can measure distance fluctuations on the order of 10^-19 m, more than a thousand times smaller than a proton. The most sensitive of these, known as LIGO, has just begun operating after a major upgrade and will likely make the historic first detection of a gravitational wave in the next few years. In fact there is a scandalous rumor circulating that they may have already detected one but are keeping it secret until they’ve checked and double-checked everything.

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    The ESA/NASA LISA mission is a concept for building a space-based gravitational wave observatory that spans millions of kilometers. Such an instrument would be sensitive to “mid-frequency” gravitational waves with with periods of hours to seconds. Image credit: NASA

    At the same time, others like myself are developing concepts for million-kilometer scale detectors in space. In fact, I’m part of an international effort led by the European Space Agency that will launch a satellite called LISA Pathfinder in December of this year. The purpose of this satellite is to demonstrate some of the novel technologies and measurement strategies that will be needed to realize a space-based gravitational wave observatory.

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    The ESA/NASA LISA Pathfinder mission is designed to demonstrate several of the key technologies that are needed to implement the LISA concept. Led by the European Space Agency with contributions from NASA and several European institutions, LISA Pathfinder will launch from French Guiana on Dec. 2nd, 2015. This image shows the spacecraft being fueled prior to being mated with the launch vehicle. Image credit: ESA-CNES-Arianespace / Optique Vidéo du CSG – P. Baudon

    ESA LISA Pathfinder
    ESA/NASA LISA Pathfinder soon to be satellite

    In the coming series of blog entries, I plan to introduce you to the LISA Pathfinder mission as well as talk more about gravitational waves and the technologies being developed to detect them. If you can’t wait for those entries, I encourage you to join me, Dr. Joey Shapiro-Key of the University of Texas Rio Grande Valley, and Dr. Shane Larson of the Adler Planetarium for a Google Hangout hosted by the American Astronomical and Astronautical Societies on November 20th at 3pm EST. You can follow along on Google+ or YouTube.

    See the full article here .

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  • richardmitnick 8:15 am on October 31, 2015 Permalink | Reply
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    From NASA Blueshift: “Back to School with GRB 101” 

    NASA Blueshift
    NASA Blueshift

    October 30, 2015
    Barb Mattson

    Up until a few years ago, gamma-ray bursts (or GRBs, for short) were arguably the biggest mystery in high-energy astronomy. Basically, gamma-ray bursts are brief, extremely bright bursts of gamma-rays (as the name implies). They appeared at random across the sky. But what are they? What causes that burst? And what can we learn from them?

    I find it hard to talk about gamma-ray bursts without going into the history, because it’s such a recently solved mystery. The mystery is so recent that I had a professor in grad school who mused that watching gamma-ray burst scientists was a bit like watching 6-year-olds play soccer. Just as the 6-year-olds run in a clump following the ball from one side of the field to another, the scientists would follow each new piece of evidence, which took them in a new direction.

    I’ll keep the history to a minimum, but you can read more on the Swift education site. Gamma-ray bursts were first discovered by the Vela satellites in the late 1960s. The primary job of the Vela satellites was to monitor the sky for gamma rays from Earth, which would be evidence of a nation testing nuclear weapons. The satellites started seeing bursts of gamma-rays, but they were instantly recognizable as coming from beyond Earth. Since those events weren’t Vela’s primary mission, the data for those bursts results sat in someone’s desk drawer for years until he had time to look back at them.

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    The Vela 5 satellites in the cleanroom. These were the first satellites to detect gamma-ray bursts. Image courtesy of Los Alamos National Laboratory.

    The biggest challenge of studying GRBs is that the burst of gamma-rays lasts for only a few seconds up to a couple minutes before disappearing completely. Early on, it was difficult to tell exactly where in the sky they were. In part, because they happened so quickly, but also because we needed better gamma-ray detectors. Before there was a single gamma-ray detector that could localize a GRB, astronomers used a variety of detectors with poor localization, but widely separated. Doing that, they could triangulate positions. The more detectors, the better they could localize the GRB.

    The next challenge was figuring out where the GRBs originated. Were they part of our galaxy? Or did they come from much further away? These were very bright bursts for a very short amount of time — putting out more energy than our entire sun will emit in its lifetime, but in just a few seconds! And at first, scientists couldn’t image that these powerful explosions could be from outside our galaxy. Such a bright burst would have to be come from extraordinary explosions to be seen that far away.

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    GRBs appear randomly across the sky as this all-sky map of the locations of over 2700 bursts detected by the BATSE instrument aboard the Compton Gamma Ray Observatory shows. Credit: NASA

    In 1997 when a satellite called BeppoSAX detected the first X-ray “afterglow” from a gamma-ray burst.

    BeppoSAX satellite
    BeppoSAX

    Afterglow is emission that lingers after the initial burst of gamma-rays. For the first time, astronomers were able to study a burst site after the GRB faded AND, even better, they could take a spectrum of the X-ray emission to find the distance. It turns out GRBs are distant. Very distant. Gamma-ray bursts are one of the most distant things we can detect.

    Since then, gamma-ray burst observations have focused on seeing the afterglow as soon as possible. It can be seen in X-ray, optical, ultraviolet, and radio wavelengths. Based on these observations, it started to become clear that most GRBs are associated with supernova explosions. Not all supernovae explosions create GRBs, and understanding the conditions that create a GRB are part of current research.

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    In the most common type of gamma-ray burst, illustrated here, a dying massive star forms a black hole (left), which drives a particle jet into space. Light across the spectrum arises from hot gas near the black hole, collisions within the jet, and from the jet’s interaction with its surroundings. Credit: NASA

    Our division at Goddard has two of the premiere satellites that are currently used for the study of GRBs – Swift and Fermi – so Blueshift has talked about GRBs a few times in the past.

    NASA SWIFT Telescope
    NASA/Swift

    NASA Fermi Telescope
    NASA/Fermi

    Blueshift interviewed the Principal Investigator of the Swift mission on the occasion of its 10th anniversary
    Blueshift talks about the other type of gamma-ray burst in their Awesomeness Round-up from April 11, 2011
    Listen to the podcast “We’re Back” to learn more about how Fermi studies GRBs
    Listen to the podcast “Life and Death” to hear about how Swift helped solve the mystery of GRBs

    See the full article here .

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  • richardmitnick 11:38 am on August 13, 2015 Permalink | Reply
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    From blueshift: “OSIRIS-REx” 

    NASA Blueshift
    NASA Blueshift

    August 13, 2015
    Jasmin Evans

    1
    Artist impression of the asteroid belt and Ceres. Credit: ESA/ATG media lab

    It is a hot topic of debate in the scientific and political communities as to the level of threat that these objects are to our planet. Every year, we are struck by hundreds of tons of debris from space, usually small rocks which land as meteorites or even smaller particles of dust which give us meteor showers. On top of this, we have many more close (in astronomical terms!) shaves, sometimes coming inside the orbital distance of the geostationary satellites which circle our globe. We only have to recall the 2013 even in Chelyabinsk, Russia, when a 50ft wide asteroid crashed in to the atmosphere and blew in windows and doors over a vast city populated by over 1 million people, to realise the vulnerability of our pale blue dot. It is with this in mind that the space agencies of the world are spearheading efforts to understand more about these objects, and get a closer look at what we are dealing with. NASA and the work at the Goddard Space Flight Center, are leading the charge with a mission that aims to do something as complex as any mission ever attempted.

    OSIRIS-REx is the name of the NASA mission, which will launch in October 2016 on a two year trip to Asteroid 101955, also known as Bennu.

    NASA OSIRIS-REx
    OSIRIS-REx

    On arrival, the spacecraft will spend a year in orbit, creating a very detailed shape and gravitational model of the asteroid through radar imaging and other remote sensing techniques, allowing scientists to use this data this to correct for any surprises that ground and space telescope based detailed observations did not pick up. It will also study the Yarkovsky effect, which is where the momentum of photons of light have a subtle yet measurable impact on the trajectory and rotation of an asteroid. There is a probability of Bennu colliding with Earth in 2182 due to the Yarkovsky effect and scientists want to work out as much as they can now, to mitigate against this becoming a reality.

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    Artist impression of OSIRIS-REx arriving at Bennu. Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab

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    Bennu

    After travelling to Bennu, the spacecraft will enter its orbital phase, the initial stage of studying the asteroid up close. Once this year long step is complete, the next is where the key goal of the mission takes place. The aim is to achieve a controlled touchdown on the surface, collect a sample and store it ready for the return to Earth. As there are many things that could go wrong with this part of the process, the spacecraft is equipped with three collection tubes so if the first attempt is unsuccessful they have another shot.

    So how do you collect samples from an asteroid? These are objects moving at huge velocities relative to the spacecraft, even after orbital insertion, with so little gravity, that it’s no easy ride. Therefore a controlled landing is critical. The extremely weak gravity of a body this size makes this part all the more complex. But, after what the team hopes is a successful touchdown, a robotic arm will extend out from the lander, allowing a sampling head to be lowered to the surface, and retain contact with it for just five seconds. During this time, Nitrogen gas is blasted on to the surface to loosen the surface regolith, permitting it to be collected by the sample head. With the opportunity for three attempts at collection, the spacecraft will, it is hoped, return with at least 60g and up to 2kg (around 4lbs) of material.

    As with the Apollo program, where Gene Cernan and Tom Stafford on Apollo 10, performed a dress rehearsal of the main event where they followed each procedure, bar landing, Osiris-Rex will do the same. Swooping down to within 25 metres of the surface before pulling up and doing everything except the sample collection.

    Once the sample is collected, the spacecraft will begin its return journey to Earth, and after around 2 years, if all goes according to plan, enter the atmosphere at a staggering 27,738 miles an hour, way faster than orbital entry interface for manned mission returns from the ISS and other low earth orbiting systems. The capsule has a heat shield, which will ablate away with temperatures around the 3000 degree centigrade mark, making the re-entry reminiscent again of the era of Apollo.

    The heat shield will take away 99% of the initial kinetic energy, until the spacecraft slows down enough at altitude for the parachutes to deploy, drifting slowly to the ground being tracked by NASA airborne groups before the ground based recovery teams to get the capsule, somewhere, hopefully in the deserts of Utah, after a gentle and soft landing.

    Then the science can really begin, with the most pristine example of an asteroid ever seen on Earth, uncontaminated, unlike the meteorites which bombard us, and hopefully the start of a detailed investigation in to how these mysterious bodies, remnants of the earliest formation of our solar system, really tick…and how we can avoid them.

    More information:

    http://www.asteroidmission.org/
    NASA.gov OSIRIS-REx website

    See the full article here.

    Please help promote STEM in your local schools.
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  • richardmitnick 3:04 pm on August 5, 2015 Permalink | Reply
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    From NASA Blueshift: “Black Hole Laboratories for Dark Matter” 

    NASA Blueshift
    NASA Blueshift

    August 5, 2015
    Maggie Masetti

    There is a lot we don’t know about dark matter – like what exactly it is. Because of this, we are always looking for ways to study it. It turns out that black holes might make the perfect laboratory environment for better understanding both black holes and the nature of dark matter.

    We talked to Dr. Jeremy Schnittman, the Goddard astrophysicist who has been working on computer simulations exploring the connections between black holes and dark matter. We had the opportunity to chat with him and had him give us the basics of his ideas.

    NASA Blueshift: What is dark matter? Why do we call it “dark”?

    Dr. Jeremy Schnittman: Dark matter is a hypothetical particle that pervades the entire universe, contributing more than five times more mass than normal matter like protons and electrons. While we have not yet actually seen dark matter directly (and thus, we call it “dark”), we see ample evidence for its existence through indirect means such as gravity.

    NASA Blueshift: What makes us think dark matter exists, if we can’t directly detect it?

    Dr. Jeremy Schnittman: The force of gravity is directly proportional to the total amount of mass present. So if you can measure how a star or galaxy is moving due to gravitational forces, it is straight-forward to measure how much mass is pulling on it. By looking at radiation like starlight and radio waves, we can measure how much of this mass is due to stars and gas, and in most cases, the answer is “not nearly enough mass!” The rest is attributed to dark matter.

    NASA Blueshift: Why would black holes be a good place to look for/at dark matter?

    Dr. Jeremy Schnittman: To better understand normal particles like protons and electrons, we typically accelerate them in a particle collider, smash them together, and look at the pieces that fly out. Since dark matter only interacts with gravity, we need a gravitational particle accelerator. Nothing does gravity better than a black hole! So not only does it attract a higher density of particles, but also increases the energy of their collisions.

    NASA Blueshift: Why do researchers use computer simulations? How do they differ from direct observations?

    Dr. Jeremy Schnittman: Before building a large, expensive space telescope, it is crucial to have a reliable prediction for what it will see. Computer simulations are much cheaper, and with increasing computer power, they are increasingly reliable. Yet experience teaches us to always expect the unexpected, and computer simulations almost by definition can ONLY predict things that are already expected. So it is always worth the time and money to go out and do real observations.

    2
    This visualization shows dark matter particles as gray spheres attached to shaded trails representing their motion. Redder trails indicate particles more strongly affected by the black hole’s gravitation and closer to its event horizon (black sphere at center, mostly hidden by trails). The ergosphere, where all matter and light must follow the black hole’s spin, is shown in teal. The black hole is viewed along its equator and rotates left to right. Credits: NASA Goddard’s Scientific Visualization Studio and NASA Goddard/Jeremy Schnittman

    2
    This image shows the gamma-ray signal produced in the computer simulation by annihilations of dark matter particles. Lighter colors indicate higher energies, with the highest-energy gamma rays originating from the center of the crescent-shaped region at left, closest to the black hole’s equator and event horizon. The gamma rays with the greatest chances of escape are produced on the side of the black hole that spins toward us. Such lopsided emission is typical for a rotating black hole. Credits: NASA Goddard/Jeremy Schnittman

    NASA Blueshift: What’s next for this research after this simulation?

    Dr. Jeremy Schnittman: Fortunately, we already have a space telescope in place for these observations: the Fermi Gamma-ray Observatory.

    NASA Fermi Telescope
    Fermi

    We plan to use existing data from Fermi to search for evidence of dark matter around known black holes. At the very least, we expect to be able to place new, more stringent limits on the properties of dark matter, such as the particle mass and cross section.

    NASA Blueshift: Thanks, Jeremy!

    You can read more about his computer simulations in this NASA feature article, and you can also watch the below video:

    See the full article here.

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  • richardmitnick 2:52 pm on July 22, 2015 Permalink | Reply
    Tags: , , NASA Blueshift   

    From NASA Blueshift: “How Many Stars in the Milky Way?” 

    NASA Blueshift
    NASA Blueshift

    July 22, 2015
    Maggie Masetti

    Recently I was asked to help someone answer the question of how many stars are in the Milky Way – that there were differing answers out there, and which was the right one?

    This question turns out to have a really interesting (and possibly frustrating?) answer. And the answer is that we really don’t know. We can make estimates, but there isn’t a firm, solid, 100% answer.

    1
    A gorgeous panorama of the Milky Way. Read more. Credit: ESO/S. Brunier

    Why is this? Well, first off, there isn’t a way to simply count the number of stars in the Milky Way individually – that’s where the estimates come in. To make an estimate, we have to calculate the mass of our galaxy, and then the percentage of that mass that is made up of stars.

    Then we have to decide what the mass of an average star is so we can calculate the number of stars in the galaxy. This is not trivial either – you could say our Sun is an average sized star, which would give you one estimate for the number of stars in the galaxy. But our Sun may not really be typical – there are a lot of much lower-mass stars out there. Using a low-mass red dwarf as an average-mass star will give you a totally different answer for the total number of stars in our galaxy.

    2
    This diagram shows a brown dwarf in relation to Earth, Jupiter, a low-mass star, and the sun. Credit: NASA

    It’s kind of like if you had a 10 pound bag. You can see in the top of the bag and can tell that there are coins there, mixed in with candy, dried beans, screws, rice, and other things you can’t see, but that must be heavy enough to make the bag weigh 10 pounds. Now try to calculate how many coins are in that bag – it’s hard to do because you can only really count the coins you can see – so you have to figure out if the contents of the bag that you can see is representative of the whole of the bag. Are coins evenly distributed throughout? Let’s say you can say with relative confidence that coins make up 10% of mass of the bag, or one pound. How many coins are there total? Well, you can see pennies and quarters and nickels, and each type of coin has a different mass and size. If you picked the quarter as being the average mass of a single coin, you might get one answer for the total number of coins. But if you picked the penny, which is lighter, you’d have a higher total number of coins because there are more pennies to the pound than quarters.

    3
    Image credit: theilr

    There are different models for estimating the number of stars in the Milky Way and the answers they give differ depending on what is used as the average mass of a star. The most common answer seems to be that there are 100 billion stars in the Milky Way on the low-end and 400 billion on the high end. But I’ve seen even higher numbers thrown around.

    3
    Credit: NASA, ESA, W. Clarkson (Indiana University and UCLA), and K. Sahu (STScl)

    See the full article here.

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  • richardmitnick 10:50 am on July 4, 2015 Permalink | Reply
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    From NASA Blueshift: 

    NASA Blueshift
    NASA Blueshift

    July 4, 2015
    Sara Mitchell

    Happy Fourth of July to those of you that celebrate it! We couldn’t let the date slip by without presenting a little display of cosmic fireworks. We think you’ll find they’re much quieter than the earthly kind.

    We start with this 3D visualization of the nebula Gum 29 with the star cluster Westerlund 2 at its core. Young stars light up the gas around them as we sail through:


    Credit: NASA, ESA, G. Bacon, L. Frattare, Z. Levay, and F. Summers (Viz3D Team, STScI), and J. Anderson (STScI)

    In 1901, GK Persei captivated skygazers as it briefly appeared as the brightest object in the night sky. Now, astronomers understand that this light show was caused by a thermonuclear explosion on the surface of a white dwarf star. This recent image of GK Persei contains X-rays from Chandra (blue), optical data from NASA’s Hubble Space Telescope (yellow), and radio data from the National Science Foundation’s Very Large Array (pink).

    2
    Image credit:
    X-ray: NASA/CXC/RIKEN/D.Takei et al; Optical: NASA/STScI; Radio: NRAO/VLA

    Supernova 1987A has put on a light show that has kept astronomers studying it for nearly 30 years. The vivid ring of material around the supernova, captured here by Hubble’s Advanced Camera for Surveys, was likely shed by the original star about 20,000 years before it exploded.

    4
    Image credit: NASA, ESA, P. Challis and R. Kirshner (Harvard-Smithsonian Center for Astrophysics)

    Astronomers have nicknamed this planetary nebula “Eskimo Nebula” because they see a head wearing a parka hood. The gas clouds around this object composed the outer layers of a Sun-like star thousands of years ago. Now, a strong wind of particles from the central star is ejecting the unusually long filaments seen around it.

    5
    Image credit: NASA/Andrew Fruchter (STScI)

    The Helix Nebula, another beautiful planetary nebula, has an eerie resemblance to a giant, all-seeing eye in this infrared image from the Spitzer Space Telescope. This object is what remains after the death of a small- to medium-sized star. The tiny white dot in the center is a white dwarf, the glowing red gas was blown out when the star died, and the outer gaseous layers are seen in brilliant blue and green.

    6
    Image credit: NASA/JPL-Caltech/Univ.of Ariz.

    A stellar nursery is a surprisingly violent and energetic place. Astronomers have a chance to peer inside NGC 3603, a starburst cluster in the constellation Carina, because ultraviolet radiation and stellar winds have blown a cavity in the gas and dust surrounding these huge young stars.

    7
    mage credit: NASA, ESA, R. O’Connell (University of Virginia), F. Paresce (National Institute for Astrophysics, Bologna, Italy), E. Young (Universities Space Research Association/Ames Research Center), the WFC3 Science Oversight Committee, and the Hubble Heritage Team (STScI/AURA)

    Enjoy and learn.

    See the full article here.

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  • richardmitnick 5:45 pm on December 9, 2014 Permalink | Reply
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    From blueshift: “Happy Birthday, Swift!” 

    NASA Blueshift
    NASA Blueshift

    December 9, 2014
    Maggie Masetti

    This is our third Happy Birthday post for a satellite in the last year or so – which is pretty cool actually, to have satellites that are hitting significant milestones and have had the longevity to still be doing great science. We had Fermi’s 5th birthday in August 2013, followed by Spitzer’s 10th in September 2013.

    NASA Fermi Telescope
    NASA/Fermi

    NASA Spitzer Telescope
    NASA/Spitzer

    And then we just recently hit Swift’s 10th birthday. What is Swift? Swift is an observatory that has been dedicated to studying gamma-ray bursts (GRBs) – and it can study GRBs and their afterglows at gamma ray, X-ray, ultraviolet, and optical wavelengths.

    NASA SWIFT Telescope
    NASA/Swift

    GRBs are short-lived bursts of gamma-ray light, which can last from few milliseconds to several minutes, and shine hundreds of times brighter than a typical supernova and about a million trillion times as bright as our Sun. Furthermore, when a GRB erupts, it is briefly the brightest source of cosmic gamma ray photons in the observable Universe. (Thanks to Imagine the Universe!, more info there.) What exactly was causing these incredibly energetic bursts was a big mystery. Enter Swift. Data from Swift (and also the gamma-ray Fermi observatory) have given us valuable clues that are helping us solve this mystery. (We got the scoop on the latest in the interview you’ll see below.

    We actually built Swift here at NASA Goddard. I was fortunate enough to get the chance to see the satellite before it launched. They displayed it in its cleanroom. Here is me 10 years ago with Brendan, Steve, and Meredith. (Meredith and Steve have been a huge help to Blueshift behind the scenes on the server side of things.)
    m

    s
    With Swift

    Sara and I talked to the Principal Investigator for the Swift mission, Neil Gehrels, to ask him 10 questions about Swift for its 10th Anniversary.

    Blueshift: What is your role with Swift? How long have you been involved with the project?

    Neil Gehrels: I am the lead scientist of Swift. In NASA jargon, my role is Principal Investigator. My involvement started at the very beginning in 1996 when Nick White and I conceived of the mission.

    Blueshift: How did Swift come to be?

    Neil Gehrels: NASA has competitions every other year for small to medium sized missions. Typically 40 teams put in proposals and one is chosen to fly through a rigorous and grueling peer review process. We proposed Swift in 1998 and were fortunate enough to have it selected. The observatory was constructed from 1999 to 2004 and then launched.

    Blueshift: Were you at the launch? What was it like to watch Swift head into space?

    Neil Gehrels: Yes, I was in the control center at the launch. It was one of the most exciting days of my life. Exhilaration mixed with fear of failure! Luckily everything went perfectly.

    Blueshift: Why gamma rays? What are they, and what do they tell us about the Universe?

    Neil Gehrels: Gamma rays are like really powerful X-rays. Just like the X-rays at the dentist office, they are very penetrating rays of light. The are produced in the hottest, most explosive events in the universe. We use them to study the death of stars and birth of black holes.

    Blueshift: What’s Swift’s role within the international fleet of astrophysics satellites?

    Neil Gehrels: Swift is the NASA’s premier satellite for observing the most explosive and dynamic sources in the universe. Objects such as gamma-ray bursts and supernovae. The observatory detects the transient sources and then repoints itself, without human intervention, at the source for detailed observations with the on-board telescopes

    Blueshift: What research have you personally done with Swift?

    Neil Gehrels: My personal research is studying gamma-ray bursts. Whenever one is detected by Swift, which occurs about twice per week, I receive a text message on my phone and run to the nearest computer to look at the new data.

    Blueshift: Did you expect to still be doing amazing science with Swift ten years later?

    Neil Gehrels: Swift was built to operate for 2 years, but hoped it would go much longer. It is such a joy to have it still working perfectly after ten years.

    Blueshift: Has Swift helped provide answers to major astronomical mysteries such as the cause of gamma-ray bursts?

    Neil Gehrels: Yes, Swift has made major discoveries every year. We found out that long and short gamma-ray bursts have very different origins. Long bursts are from exploding stars and short bursts are from the collision of compact neutron stars. Another big finding was the detection of 2 gamma-ray bursts from the very distant edges of the universe. They were produced in the explosions of very early stars.

    Blueshift: What do you think are the top discoveries made by Swift over the last decade?

    Neil Gehrels: In addition to the major discoveries about gamma-ray bursts, another biggie was detecting a the shredding of a star by a massive black hole. The star drifted too close to the black hole and was torn apart by the strong gravity of the black hole. Another fun discovery was a flash of X-rays from a new supernova explosion. We were lucky to be looking in the direction of a new supernova at the time the star first collapsed and discovered a brilliant pulse of X-rays. It was the long-predict “shock break-out” where a wave of heat zooms through the star at the moment of collapse and bursts out of the surface.

    Blueshift: What’s next for Swift?

    Neil Gehrels: Hopefully Swift will last another 10 years. We are using it in a new way lately, as a resource for astronomers. Our colleagues send an alert to us when they find something interesting going on in the universe and we point Swift at it.

    Blueshift:Thanks!

    And happy birthday to Swift, we hope you have many more!

    c
    The cake from Swift’s birthday party. Credit: Maggie Masetti

    See the full article, with animation, here.

    Please help promote STEM in your local schools.
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    Blueshift is produced by a team of contributors in the Astrophysics Science Division at Goddard. Started in 2007, Blueshift came from our desire to make the fascinating stuff going on here every day accessible to the outside world.

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