A new way to interact and explore Cassiopeia A, the remains of an exploded star, has launched. The press release below outlines this novel initiative between the Smithsonian Center for Learning and Digital Access and the Chandra X-ray Center. Led by Chandra’s Kimberly Arcand, this project allows you to watch, interact, or learn about this supernova remnant while delving into astrophysics, computer science, and more.
A decade ago, a team of scientists and image processors came together and created the first-ever three-dimensional model of Cas A. Now, this 3D model enters a new phase with the launching of "Journey Through an Exploded Star"” We hope you will explore with us.
Smithsonian Press Release: Smithsonian Launches “Journey through an Exploded Star” 3D Interactive Experience
The Smithsonian today made available a new online interactive that allows users to explore a three-dimensional (3D) visualization of the remnants of a supernova, or exploded star.
Designed for use by both general audiences and high school science classrooms, the free materials, available at https://s.si.edu/supernova, include an interactive simulation, a 360° video, and a multimedia instructional package.
The project was created by the Smithsonian Center for Learning and Digital Access in conjunction with the Center for Astrophysics | Harvard & Smithsonian (CfA), a collaboration that includes the Smithsonian Astrophysical Observatory (SAO).
To create the visualizations, the project uses data from the Chandra X-ray Observatory and Spitzer Space Telescope, the National Optical Astronomy Observatory's Mayall Telescope, and the MIT/Michigan/Dartmouth Observatory’s Hiltner Telescope.
“Journey” features the data visualization work of Kimberly Arcand, visualization and emerging technology lead for Chandra, which is operated on behalf of NASA by SAO.
“All of that data has to be translated and processed in a way that humans can see, so it’s really important to be able to study our Universe using different kinds of light” said Arcand. “Each band of light gives you different information, so it’s like adding puzzle pieces to fit into the greater whole.”
“Journey through an Exploded Star” offers three ways to explore content:
An online interactive simulation in which users navigate the fiery remains of a supernova and manipulate the real data to make their own visualization of the cosmos. (Closed Captioned, works across desktop browsers, and requires no software downloads.)
A 360° video tour, narrated by Arcand, explains how and why scientists study supernovas such as Cassiopeia A to gain a comprehensive picture of these cosmic explosions. (Works on desktop, mobile, and Google Cardboard devices.)
A high school classroom multimedia instructional package begins with the fundamentals of the electromagnetic spectrum and illustrates the production of elements from the explosions of stars. (Aligned to Next Generation Science Standards (HS-ESS1-3 and HS-PS4).)
The director of the Smithsonian Center for Learning and Digital Access, Stephanie L. Norby, said, “Projects such as this one make science learning both exciting and relevant for students. Using media tools, they can make a personal connection to topics that may initially seem esoteric to discover that there are forces that connect everyone to the stars.”
The Smithsonian Center for Learning and Digital Access makes all of this content freely available in its Smithsonian Learning Lab.
About the Smithsonian Center for Learning and Digital Access
The Smithsonian established the Smithsonian Center for Learning and Digital Access in 1976 to serve public education by bringing Smithsonian collections and expertise into the nation’s classrooms. For more than 40 years, it has published educational materials and provided one access point to Smithsonian educational resources. To understand the needs of teachers, students, and museum educators, the Center spent more than a decade in active experimentation and research, culminating in the launch of a new online platform — the Smithsonian Learning Lab. Since its launch in 2016, museum and classroom educators have used the Lab’s tools to create thousands of new examples — ranging from experiments to models — for using Smithsonian resources for learning. The Center now studies how teachers and students use digital museum resources and broadly disseminates this knowledge through professional development to advance museum and digital learning.
About the Center for Astrophysics | Harvard & Smithsonian
Headquartered in Cambridge, Mass., the Center for Astrophysics | Harvard & Smithsonian (CfA) is a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.
About the Chandra X-ray Observatory:
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
Smithsonian Center for Learning and Digital Access, Washington, DC
(202) 633-5291 firstname.lastname@example.org
We are pleased to welcome Yongquan Xue, a professor at the Department of Astronomy, University of Science and Technology of China (USTC), as a guest blogger. He is an astrophysicist whose main research field is X-ray high-energy astrophysics, and has been significantly involved in the Chandra Deep Fields. Yongquan led the Nature paper that is the subject of our latest press release on the discovery of a magnetar-powered X-ray transient. Before joining USTC in 2012, he worked at Penn State University as a postdoc, after obtaining his astrophysics B.S. and M.S. degrees at Peking University, and Ph.D. degree at Purdue University, respectively.
A neutron star is the compact object formed after a supernova explosion occurring in the late evolutionary stage of a massive star, and it is one of the most mysterious objects in the universe. It is composed of almost all neutrons, and has some extreme physical properties such as ultra-high density and a super-strong magnetic field. It is an excellent natural laboratory for testing basic physical laws. However, up to now, our understanding about the basic properties of neutron stars (e.g., the equation of state, which describes the relation among pressure, density, etc.) is still relatively vague.
Whether the direct outcome of a binary neutron-star merger can be a neutron star, rather than the “favorite” product of a black hole, has not been determined for years. Some theoretical studies predict that if the neutron-star equation of state is sufficiently stiff, that is, if the pressure increases sharply with the increase of nuclear density towards the center of the star, there should be at least some binary neutron-star mergers that would leave behind supramassive millisecond magnetars (see Figure 1) or even stable neutron stars. A supramassive neutron star is more massive than a typical neutron star and a magnetar has a magnetic field strength over 1014-1015 Gauss.
Figure 1: Artist's impression of a magnetar as the aftermath of a binary neutron-star merger (courtesy of Guoyan Wang and Cong He).
Because the X-ray radiation powered by such a post-merger magnetar essentially radiates evenly in all directions, we would expect to see an X-ray transient (i.e., a source that appears only for a short duration) that has no corresponding gamma-ray burst and has a characteristic light curve, if our viewing angle is not looking down the axis of the magnetar jet. (A “light curve” is a plot that shows how light from an object varies over time.) However, such sources had never been found until now.
We have recently discovered a new X-ray transient (dubbed CDF-S XT2, or XT2 for short) in the 7-million-second Chandra Deep Field-South (7Ms CDF-S), the deepest and most sensitive X-ray survey so far. The X-ray emission from XT2 lasts only about 7 hours, and the redshift of its host galaxy is 0.738, corresponding to a distance of about 6.6 billion light years away from us.
The observational data and theoretical analyses show that: (1) XT2 has no gamma-ray detection. (2) XT2 has a characteristic light curve -- a plateau plus a sharp decrease (see Figure 2, Top left), which is in perfect agreement with the theoretical predictions of X-ray emission from post-merger supramassive millisecond magnetars. (3) XT2 is located at the outskirts of its host galaxy (see Figure 2, Top right), which is consistent with the scenario of binary neutron stars being "kicked out" to the galaxy outskirts by the asymmetric counterforce of supernova explosions; furthermore, the probability that XT2 originates from the merger of binary compact stars, based on the physical properties of its host galaxy, is very high. (4) When the estimated event occurrence rate density of XT2-like transients is revised to the value expected in the local universe, it agrees with the value robustly derived from the first gravitational-wave detection (i.e., GW170817) of a binary neutron-star merger, which further supports a binary neutron-star merger origin for XT2. All the above arguments indicate that XT2 is very likely the first detected X-ray transient that is powered by a magnetar as the aftermath of a binary neutron-star merger, with no corresponding short gamma-ray burst.
Figure 2: Some key properties of XT2, including X-ray light curve (Top left), X-ray images at different time frames (Bottom), and offset to the host-galaxy center (Top right).
The discovery of XT2 verifies the previous theoretical predictions that the direct product of a binary neutron-star merger can be a supramassive millisecond magnetar. It also places strong constraints upon the basic physics regarding neutron star equation of state (i.e., must be stiff enough) and ultra-high magnetic field strength (i.e., greater than 1014-1015 Gauss), by eliminating a number of soft equation-of-state models of nuclear matter. This deepens our understanding of the basic properties of neutron stars. Finally it provides a new perspective to study binary neutron-star mergers and neutron stars themselves.
CDF-S XT2 Credit: X-ray: NASA/CXC/Uni. of Science and Technology of China/Y. Xue et al; Optical: NASA/STScI
These images show the location of an event, discovered by NASA's Chandra X-ray Observatory, that likely signals the merger of two neutron stars. A bright burst of X-rays in this source, dubbed XT2, could give astronomers fresh insight into how neutron stars — dense stellar objects packed mainly with neutrons — are built.
XT2 is located in a galaxy about 6.6 billion light years from Earth. The source is located in the Chandra Deep Field South (CDF-S), a small patch of sky in the Fornax constellation. The CDF-S is the deepest X-ray image ever taken, containing almost 12 weeks of Chandra observing time. The wider field of view shows an optical image from the Hubble Space Telescope of a portion of the CDF-S field, while the inset shows a Chandra image focusing only on XT2. The location of XT2, which was not detected in optical images, is shown by the rectangle, and its host galaxy is the small, oval-shaped object located slightly to the upper left.
On March 22, 2015, astronomers saw XT2 suddenly appear in the Chandra data and then fade away after about seven hours. By combing through the Chandra archive, they were able to piece together the history of the source's behavior. The researchers compared the data from XT2 to theoretical predictions made in 2013 of what the X-ray signature from two colliding neutron stars without a corresponding gamma ray bursts would look like.
When two neutron stars merge they produce jets of high energy particles and radiation fired in opposite directions. If the jet is pointed along the line of sight to the Earth, a flash, or burst, of gamma rays can be detected. If the jet is not pointed in our direction, a different signal is needed to identify the merger. This result provides scientists with an opportunity to study just such a case.
X-rays from XT2 showed a characteristic signature that matched those predicted for a newly-formed magnetar, that is, a neutron star spinning around hundreds of times per second and possessing a tremendously strong magnetic field about a quadrillion times that of Earth's.
The team think that the magnetar lost energy in the form of an X-ray-emitting wind, slowing down its rate of spin as the source faded. The amount of X-ray emission stayed roughly constant in X-ray brightness for about 30 minutes, then decreased in brightness by more than a factor of 300 over 6.5 hours before becoming undetectable. This showed that the neutron star merger produced a new, larger neutron star and not a black hole.
XT2's bright flare of X-rays gives astronomers another signal — in addition to the detection of gravitational waves — to probe neutron star mergers.
A paper describing these results appeared in the April 11th issue of Nature, led by Yongquan Xue (University of Science and Technology in China). NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
There are a lot of clichés that get thrown around when talking about big scientific discoveries. Words like “breakthrough” or “game changing” are often used. They grab people’s attention, but it’s fairly rare that they apply.
Today’s announcement of the first image ever taken of a black hole (more precisely, of its shadow) truly rises up to that standard. By definition, nothing not even light, can escape the gravitational grasp of a black hole. This, however, is only true if you get too close, and the boundary between what can and cannot get away is called the event horizon.
This dark portrait of the event horizon was obtained of the supermassive black hole in the center of the galaxy Messier 87 (M87 for short) by the Event Horizon Telescope (EHT), an international collaboration whose support includes the National Science Foundation. This achievement is certainly a breakthrough, and we at NASA’s Chandra X-ray Observatory congratulate and applaud the hundreds of scientists, engineers, and others who worked on the Event Horizon Telescope to obtain this extraordinary result.
As is well documented in today’s announcement, it took a remarkable effort and coordination from scientists and organizations around the world to even have a chance to make this happen. The result being heralded stems from an observing campaign during April 2017, when this global network of radio dishes observed M87 together.
But Chandra was not just a bystander! Rather, thanks to heroic efforts by schedulers at Chandra, EHT, and NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) mission, as well as by the EHT’s Multiwavelength Working Group, Chandra was used to observe M87 and other targets during the EHT campaign. While Chandra can’t see the shadow itself, its field of view is much larger than the EHT’s, so Chandra can view the full length of the jet of high-energy particles launched by the intense gravitational and magnetic fields around the black hole. This jet extends more than 1,000 light years from the center of the galaxy.
To use an analogy, consider a trumpeter in a concert hall: the EHT data, taken from radio telescopes around the globe, provide a close-up view of the mouthpiece (the origin of the sound, like the “central engine” of M87). The Chandra data, by contrast, reveal the sound waves as they travel down the trumpet and reverberate around the concert hall. (As with many analogies, the scale is not exact.) We need both of these pieces in order to understand the sound completely. (For a music analogy for interferometry and the EHT from the CfA’s Katie Bouman, see https://youtu.be/t5cSBmGkW3E).
As for the investigation of the black hole in M87, Chandra has been on the case for quite some time. First off, let’s start with some basics. M87 is an elliptical galaxy in the Virgo galaxy cluster, about 60 million light years away from Earth. For years, scientists have known that a supermassive black hole weighing several billion times the mass of the Sun sits at the center of M87.
Surrounding the elliptical galaxy is a reservoir of multimillion-degree gas, which glows brightly in X-ray light. Chandra's studies of this hot gas have given astronomers insight into the behavior and properties of the giant black hole. For example, astronomers have used Chandra data to discover ripples in the hot gas, which provide evidence for repeated outbursts from the black hole roughly every 6 million years or so. (As an aside and extension to the music analogy, these ripples represent sound waves in the hot gas. Since they are uneven, the “note” would likely be unharmonious noise rather than a melodic tone, many octaves below the threshold of human hearing.)
Given that Chandra has been a black hole explorer since its launch in 1999, it’s no surprise that astronomers would use it to augment the spectacular and difficult feat of taking an image of a black hole’s event horizon.
On behalf of the EHT’s Multiwavelength Working Group, Dr. Joey Neilsen of Villanova University and his collaborators put in a request for so-called Director’s Discretionary Time to observe M87 simultaneously with the EHT. While most Chandra observations are decided upon during a proposal and peer-review process, some time is allocated for unexpected or timely observations.
Chandra Director Belinda Wilkes awarded Neilsen and his colleagues nearly 30,000 seconds of observing time on M87 during April 2017. The hope was that the Chandra data could reveal whether M87 had a flare, or outburst, in X-rays during that time. Any X-ray variations might link temporally to what the EHT was seeing spatially close to the event horizon (i.e., in its images). Was material actively falling onto the black hole while the EHT was getting its revolutionary image? What was happening to energetic particles near and far from the event horizon during this time?
“Chandra’s X-ray observations coordinated with EHT represent an exciting opportunity to connect the dots between high-energy emission and the physics of accretion and ejection at the event horizon,” said Neilsen.
Neilsen, Villanova undergraduate student Jadyn Anczarski, and their collaborators used Chandra and NuSTAR to measure the X-ray brightness of the jet, a data point that EHT scientists used to compare their models of the jet and disk with the EHT observations.. Future questions the Chandra data may help explore include: How do black holes accelerate some particles to the very high energies that scientists have seen? How does the black hole produce the spectacular jets that Chandra and Hubble have studied for many years? Can data from Chandra and NASA’s NuSTAR observatory help play a role in determining more about the physics in this environment?
Scientists will be poring over the new EHT image and the papers that are being published in connection with this result for weeks, months, and even years to come. As they do, they will continue to pull in every resource they can — including famed black hole hunter, the Chandra X-ray Observatory — to learn as much as they can about these exotic and fascinating objects.
Do you have questions about this new result? Visit NASA's Chandra X-ray Observatory on Twitter (@chandraxray) with #EHTBlackHoleQ&A after the press conference at 10:30 am Eastern on April 10th for a live Question & Answer session with Dr. Joey Neilsen.
Astronomers frequently talk about selection effects, where results can be biased because of the way that the objects in a sample are selected. For example, if distant galaxies above a certain X-ray flux – the amount of observed X-rays – are selected for a survey, the most distant objects will tend to be the brightest.
For doing Chandra publicity we also have a bias, as we are always on the lookout for results where NASA’s Chandra X-ray Observatory data play a starring role. However, there are many papers where Chandra has an important supporting role instead, and other observatories are the stars. Our colleagues at the European Space Agency (ESA) and the University of California, Los Angeles (UCLA), have put out press releases on just such a result.
A team led by Gabriele Ponti of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, are reporting that they have used ESA’s XMM-Newton observatory to discover “two colossal ‘chimneys’ funneling material from the vicinity of the Milky Way’s supermassive black hole into two huge cosmic bubbles.” With the detection of these X-ray chimneys – published in Nature – astronomers can connect, for the first time, the giant bubbles detected by NASA’s Fermi gamma ray telescope with regions much closer to the black hole that have previously shown evidence for outflows of matter. In 2003, we publicized one of these results from Chandra work, led by Mark Morris of UCLA. These outflows might be driven by material falling into the supermassive black hole, or by the explosions of massive stars nearby.
Copyright: ESA/XMM-Newton/G. Ponti et al. 2019; ESA/Gaia/DPAC (Milky Way map); CC BY-SA 3.0 IGO
A large mosaic of XMM-Newton images clearly shows the chimneys, but a smaller mosaic of Chandra images also provide strong evidence for these large structures. The Chandra data also allowed Ponti and his team to make cross-checks with their XMM-Newton data in other ways. They were able to show with both XMM-Newton and Chandra that the upper and lower chimneys have similar properties, such as the densities and temperatures of the hot gas in the chimneys. This implies that both chimneys have the same origin. Cross-checks like these are how solid science is done.
Results from multiple observatories are often used in papers, at varying levels, but it’s challenging to get all of them covered in publicity, and the same applies to the scientists involved in the study. In our public affairs roles we need to promote our institution and observatories and scientists, but we also want to succinctly describe the science, which is what a general audience cares about the most. The story here about huge chimneys venting X-rays from the center of the galaxy is easier to tell without trying to give quotes to all nine authors. Other papers can have much longer lists of authors, including LIGO papers, which have more than a thousand. Even for single-author papers, other astronomers will have played a role in refereeing the paper, and giving advice, and making important advances in previous work. All of this means that press releases and media reports can give an exciting but biased view about how science is done, with just one or two researchers using just one or two observatories. It’s important to remember that astronomy research is fundamentally a team effort.
Want to take a trip to the center of the Milky Way? Check out a new immersive, ultra-high-definition visualization. This 360-movie offers an unparalleled opportunity to look around the center of the galaxy, from the vantage point of the central supermassive black hole, in any direction the user chooses.
By combining NASA Ames supercomputer simulations with data from NASA's Chandra X-ray Observatory, this visualization provides a new perspective of what is happening in and around the center of the Milky Way. It shows the effects of dozens of massive stellar giants with fierce winds blowing off their surfaces in the region a few light years away from the supermassive black hole known as Sagittarius A* (Sgr A* for short).
These winds provide a buffet of material for the supermassive black hole to potentially feed upon. As in a previous visualization, the viewer can observe dense clumps of material streaming toward Sgr A*. These clumps formed when winds from the massive stars near Sgr A* collide. Along with watching the motion of these clumps, viewers can watch as relatively low-density gas falls toward Sgr A*. In this new visualization, the blue and cyan colors represent X-ray emission from hot gas, with temperatures of tens of millions of degrees; red shows moderately dense regions of cooler gas, with temperatures of tens of thousands of degrees; and yellow shows of the cooler gas with the highest densities.
A collection of X-ray-emitting gas is seen to move slowly when it is far away from Sgr A*, and then pick up speed and whip around the viewer as it comes inwards. Sometimes clumps of gas will collide with gas ejected by other stars, resulting in a flash of X-rays when the gas is heated up, and then it quickly cools down. Farther away from the viewer, the movie also shows collisions of fast stellar winds producing X-rays. These collisions are thought to provide the dominant source of hot gas that is seen by Chandra.
When an outburst occurs from gas very near the black hole, the ejected gas collides with material flowing away from the massive stars in winds, pushing this material backwards and causing it to glow in X-rays. When the outburst dies down the winds return to normal and the X-rays fade.
The 360-degree video of the Galactic Center is ideally viewed through virtual reality (VR) goggles, such as Samsung Gear VR or Google Cardboard. The video can also be viewed on smartphones using the YouTube app. Moving the phone around reveals a different portion of the movie, mimicking the effect in the VR goggles. Finally, most browsers on a computer also allow 360-degree videos to be shown on YouTube. To look around, either click and drag the video, or click the direction pad in the corner.
Dr. Christopher Russell of the Pontificia Universidad Católica de Chile (Pontifical Catholic University) presented the new visualization at the 17th meeting of the High-Energy Astrophysics (HEAD) of the American Astronomical Society held in Monterey, Calif. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
Fancy a cup of cosmic tea? This one isn't as calming as the ones on Earth. In a galaxy hosting a structure nicknamed the "Teacup," a galactic storm is raging.
The source of the cosmic squall is a supermassive black hole buried at the center of the galaxy, officially known as SDSS 1430+1339. As matter in the central regions of the galaxy is pulled toward the black hole, it is energized by the strong gravity and magnetic fields near the black hole. The infalling material produces more radiation than all the stars in the host galaxy. This kind of actively growing black hole is known as a quasar.
Located about 1.1 billion light years from Earth, the Teacup's host galaxy was originally discovered in visible light images by citizen scientists in 2007 as part of the Galaxy Zoo project, using data from the Sloan Digital Sky Survey. Since then, professional astronomers using space-based telescopes have gathered clues about the history of this galaxy with an eye toward forecasting how stormy it will be in the future. This new composite image contains X-ray data from Chandra (blue) along with an optical view from NASA's Hubble Space Telescope (red and green).
The "handle" of the Teacup is a ring of optical and X-ray light surrounding a giant bubble. This handle-shaped feature, which is located about 30,000 light-years from the supermassive black hole, was likely formed by one or more eruptions powered by the black hole. Radio emission — shown in a separate composite image with the optical data — also outlines this bubble, and a bubble about the same size on the other side of the black hole.
Previously, optical telescope observations showed that atoms in the handle of the Teacup were ionized, that is, these particles became charged when some of their electrons were stripped off, presumably by the quasar's strong radiation in the past. The amount of radiation required to ionize the atoms was compared with that inferred from optical observations of the quasar. This comparison suggested that the quasar's radiation production had diminished by a factor of somewhere between 50 and 600 over the last 40,000 to 100,000 years. This inferred sharp decline led researchers to conclude that the quasar in the Teacup was fading or dying.
New data from Chandra and ESA's XMM-Newton mission are giving astronomers an improved understanding of the history of this galactic storm. The X-ray spectra (that is, the amount of X-rays over a range of energies) show that the quasar is heavily obscured by gas. This implies that the quasar is producing much more ionizing radiation than indicated by the estimates based on the optical data alone, and that rumors of the quasar's death may have been exaggerated. Instead the quasar has dimmed by only a factor of 25 or less over the past 100,000 years.
The Chandra data also show evidence for hotter gas within the bubble, which may imply that a wind of material is blowing away from the black hole. Such a wind, which was driven by radiation from the quasar, may have created the bubbles found in the Teacup.
Astronomers have previously observed bubbles of various sizes in elliptical galaxies, galaxy groups and galaxy clusters that were generated by narrow jets containing particles traveling near the speed of light, that shoot away from the supermassive black holes. The energy of the jets dominates the power output of these black holes, rather than radiation.
In these jet-driven systems, astronomers have found that the power required to generate the bubbles is proportional to their X-ray brightness. Surprisingly, the radiation-driven Teacup quasar follows this pattern. This suggests radiation-dominated quasar systems and their jet-dominated cousins can have similar effects on their galactic surroundings.
A study describing these results was published in the March 20, 2018 issue of The Astrophysical Journal Letters and is available online. The authors are George Lansbury from the University of Cambridge in Cambridge, UK; Miranda E. Jarvis from the Max-Planck Institut für Astrophysik in Garching, Germany; Chris M. Harrison from the European Southern Observatory in Garching, Germany; David M. Alexander from Durham University in Durham, UK; Agnese Del Moro from the Max-Planck-Institut für Extraterrestrische Physik in Garching, Germany; Alastair Edge from Durham University in Durham, UK; James R. Mullaney from The University of Sheffield in Sheffield, UK and Alasdair Thomson from the University of Manchester, Manchester, UK.
NGC 3079 Credit: X-ray: NASA/CXC/University of Michigan/J-T Li et al.; Optical: NASA/STScI
We all know bubbles from soapy baths or sodas. These bubbles of everyday experience on Earth are only a few inches across, and consist of a thin film of liquid enclosing a small volume of air or other gas. In space, however, there are very different bubbles — composed of a lighter gas inside a heavier one — and they can be huge.
The galaxy NGC 3079, located about 67 million light years from Earth, contains two "superbubbles" unlike anything here on our planet. A pair of balloon-like regions stretch out on opposite sides of the center of the galaxy: one is 4,900 light years across and the other is only slightly smaller, with a diameter of about 3,600 light years. For context, one light year is about 6 trillion miles, or 9 trillion kilometers.
The superbubbles in NGC 3079 give off light in the form of X-ray, optical and radio emission, making them detectable by NASA telescopes. In this composite image, X-ray data from NASA's Chandra X-ray Observatory are shown in purple and optical data from NASA's Hubble Space Telescope are shown in orange and blue. A labeled version of the X-ray image shows that the upper superbubble is clearly visible, along with hints of fainter emission from the lower superbubble.
NGC 3079: X-ray image (labeled)
New observations from Chandra show that in NGC 3079 a cosmic particle accelerator is producing ultra-energetic particles in the rims of the superbubbles. These particles can be much more energetic than those created by Europe's Large Hadron Collider (LHC), the world's most powerful human-made particle accelerator.
The superbubbles in NGC 3079 provide evidence that they and structures like them may be the source of high-energy particles called "cosmic rays" that regularly bombard the Earth. Shock waves — akin to sonic booms caused by supersonic planes — associated with exploding stars can accelerate particles up to energies about 100 times larger than those generated in the LHC, but astronomers are uncertain about where even more energetic cosmic rays come from. This new result suggests superbubbles may be one source of these ultra-energetic cosmic rays.
The outer regions of the bubbles generate shock waves as they expand and collide with surrounding gas. Scientists think charged particles scatter or bounce off tangled magnetic fields in these shock waves, much like balls rebounding off bumpers in a pinball machine. When the particles cross the shock front they are accelerated, as if they received a kick from a pinball machine's flipper. These energetic particles can escape and some may eventually strike the Earth's atmosphere in the form of cosmic rays.
The amount of radio waves or X-rays at different wavelengths, or "spectra," of one of the bubbles suggest that the source of the emission is electrons spiraling around magnetic field lines, and radiating by a process called synchrotron radiation. This is the first direct evidence of synchrotron radiation in high energy X-rays from a galaxy-sized superbubble, and it tells scientists about the maximum energies that the electrons have attained. It is not understood why synchrotron emission is detected from only one of the bubbles.
The radio and X-ray spectra, along with the location of the X-ray emission along the rims of the bubbles, imply that the particles responsible for the X-ray emission must have been accelerated in the shock waves there, because they would have lost too much energy while being transported from the center of the galaxy.
NGC 3079's superbubbles are younger cousins of "Fermi bubbles," first located in the Milky Way galaxy in 2010. Astronomers think such superbubbles may form when processes associated with matter falling into a supermassive black hole in the center of galaxy, which leads to the release of enormous amounts of energy in the form of particles and magnetic fields. Superbubbles may also be sculpted by winds flowing from a large number of young, massive stars.
A paper describing these results was led by Jiangtao Li of the University of Michigan and appears in The Astrophysical Journal. It is also available online. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
We welcome Orsolya Kovács, a third-year PhD student at the Eötvös Loránd University, Hungary where she obtained her MSc degree in astronomy, as our guest blogger. Currently, she is a pre-doctoral fellow at the Smithsonian Astrophysical Observatory, and is the first author on a recent paper on the WHIM featured in our latest press release.
I was working on a totally different subject before I started the missing baryon project with a small group of scientists at the Smithsonian Astrophysical Observatory (SAO) about two years ago. Before I came to the United States as a Ph.D. student, I was involved in analyzing optical data of variable stars observed at the beautiful Piszkéstető Station in the Mátra Mountains, Hungary. In my master’s thesis, I focused on the variable stars of an extremely old open cluster in the Milky Way, and at that time, I also got the chance to gain some observing skills from my Hungarian supervisor.
So the very beginning of my astronomy career was all about optical astronomy. But before getting really into optical astronomy and mountain life, I decided to interrupt this idyllic period, and find some new challenges: I wanted to spend part of my Ph.D. years learning X-ray astrophysics. With this in my mind, I applied to the SAO’s pre-doctoral program, and a few months later I arrived in Massachusetts.
Shortly after introducing me to the basics of X-ray astronomy, Ákos Bogdán at SAO proposed a crazy idea about how to observe the ‘invisible’, i.e. the missing part of the ordinary (baryonic) matter that could possibly solve the long-standing missing baryon problem. The missing baryon problem is related to the mismatch between the observed and theoretically predicted amount of matter.
Since theoretical predictions come from observations of the high-redshift, or early Universe, we can simply state that in the past, a hundred percent of the matter was there, but now, part of it is hiding somewhere. There are over 10^12 galaxies in the Universe, but the stars and gas in all these galaxies only account for a small fraction of all the ordinary matter. Simulations predict that during the evolution of the Universe, one third of the baryons (the missing part) gathered into filamentary structures. These structures are one of the biggest building blocks of the Universe, connecting galaxies and even clusters of galaxies with each other. Because they fill a huge volume, their density is extremely low, and thus, they are also exceedingly dim. These properties make them the perfect hiding place for the missing matter.
We were aware that it was a high-risk, high-reward project, because these filaments and the missing baryons should definitely be visible with future X-ray missions, but may be at the edge of detectability with current telescopes. Many previous studies attempted to explore these invisible filaments, but they could not deliver definite detections. However, since astronomy is often about tricky solutions, we swung into action and found a tricky technique to implement. The basic idea of our method was to look for filaments along the path to a quasar, a bright source of X-rays powered by a rapidly growing supermassive black hole. Our chosen quasar, H1821+643, is located about 3.4 billion light years from Earth.
Light Path (Credit: NASA/CXC/K. Williamson, Springel et al.)
We then co-added a bunch of Chandra X-ray observations of H1821+643 in the hope that these invisible filaments would become visible. This way we can improve the detectability of filaments. At first glance, the technical part of our ‘stacking’ method seemed to be pretty straightforward and should have easily been accomplished. However, our path to success was paved with a number of exciting riddles that presented our entire team — which consisted of several seasoned astronomers — with new and unexpected challenges. Not to mention the selection of the X-ray observations containing the invisible filaments, or the interpretation of the stacked signal we’ve detected.
We spent almost a year with the fine-tuning of our analysis. When we looked at the results, we realized that we found a puzzle piece that fits into the big picture predicted by simulations. This was a great relief for the entire team and probably for the whole astronomy community. Now we are certain in two things: some fraction of the missing matter is in the filaments, and taking risks can be very rewarding. Thanks H1821+643 for being a good quasar and illuminating those shadowy filaments in your sightline!
WHIM Simulation Credit: Illustration: Springel et al. (2005); Spectrum: NASA/CXC/CfA/Kovács et al.
New results from NASA's Chandra X-ray Observatory may have helped solve the Universe's "missing mass" problem, as reported in our latest press release. Astronomers cannot account for about a third of the normal matter — that is, hydrogen, helium, and other elements — that were created in the first billion years or so after the Big Bang.
Scientists have proposed that the missing mass could be hidden in gigantic strands or filaments of warm (temperature less than 100,000 Kelvin) and hot (temperature greater than 100,000 K) gas in intergalactic space. These filaments are known by astronomers as the "warm-hot intergalactic medium" or WHIM. They are invisible to optical light telescopes, but some of the warm gas in filaments has been detected in ultraviolet light. The main part of this graphic is from the Millenium simulation, which uses supercomputers to formulate how the key components of the Universe, including the WHIM, would have evolved over cosmic time.
If these filaments exist, they could absorb certain types of light such as X-rays that pass through them. The inset in this graphic represents some of the X-ray data collected by Chandra from a distant, rapidly-growing supermassive black hole known as a quasar. The plot is a spectrum — the amount of X-rays over a range of wavelengths — from a new study of the quasar H1821+643 that is located about 3.4 billion light years from Earth.
The latest result uses a new technique that both hones the search for the WHIM carefully and boosts the relatively weak absorption signature by combining different parts of the spectrum to find a valid signal. With this technique, researchers identified 17 possible filaments lying between the quasar and Earth, and obtained their distances.
Light Path. (Credit: NASA/CXC/K. Williamson, Springel et al.)
For each filament the spectrum was shifted in wavelength to remove the effects of cosmic expansion, and then the spectra of all the filaments were added together so that the resulting spectrum has a much stronger signal from absorption by the WHIM than in the individual spectra.
Indeed, the team did not find absorption in the individual spectra. But by adding them together, they turned a 5.5-day-long observation into the equivalent of almost 100 days' worth (about 8 million seconds) of data. This revealed an absorption line from oxygen expected to be present in a gas with a temperature of about one million Kelvin.
By extrapolating from these observations of oxygen to the full set of elements, and from the observed region to the local Universe, the researchers report they can account for the complete amount of missing matter.
A paper describing these results was published in The Astrophysical Journal on February 13, 2019, and is available online at https://arxiv.org/abs/1812.04625. The authors of the paper are Orsolya Kovács, Akos Bogdan, Randall Smith, Ralph Kraft, and William Forman all from the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Mass.