Cosmological Constraints from the First-Year Hyper Suprime-Cam

Figure 1: (Left) The 3-dimensional dark matter map of the Universe inferred from one of the six HSC observation areas is shown in the background with various shades of blue (brighter areas have more dark matter). The map was inferred from the distortions of shapes of galaxies in the HSC data which are indicated by white sticks. The stick lengths represent the amount of distortion and the angle of the stick corresponds to the direction of the distortion. (Right) The measurements are enabled by the light from distant galaxies that travels through the Universe and gets deflected by matter at different epochs in the Universe, before reaching the Subaru Telescope.(Credit: HSC Project/UTokyo)

Using the Subaru Telescope, the Hyper Suprime-Cam (HSC) survey collaboration team has made and analyzed the deepest wide field map of the three-dimensional distribution of matter in the Universe. Led by Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Project Assistant Professor Chiaki Hikage, a team of scientists primarily from Japan including National Astronomical Observatory of Japan (NAOJ), Taiwan and Princeton University has used the gravitational distortion of images of about 10 million galaxies to make a precise measurement of the lumpiness of matter in the Universe. By combining this measurement with the European Space Agency Planck satellite's observations of the cosmic microwave background, and other cosmological experiments, the team has been able to further constrain the properties of the "dark energy" that dominates the energy density of the Universe.

Although dark matter cannot be directly seen, its gravitational effects, predicted by Albert Einstein's general theory of relativity, cause stretching and squeezing of the light from distant galaxies as they travel across the cosmos, to be detected by the Subaru Telescope. They are witness to the growth of cosmic structure (Figure 1, left) and can be used to unlock the mysteries of dark energy. The simplest model for dark energy was introduced by Einstein, termed the "Cosmological Constant." This model can explain all existing observations, including those of HSC.

The gravitational lensing effect from the distribution of dark matter in the Universe is quite weak, but results in small but measurable distortions in the images of the galaxies in the HSC images. Like a pointillist painting, the distorted images of millions of galaxies located at a range of distances paint a three-dimensional picture of the distribution of matter in the Universe (Figure 1, right). The HSC research team has precisely characterized the fluctuations or lumpiness of the distribution of dark matter, and the change in that lumpiness over billions of years - from its adolescence to adulthood. This lumpiness is a key parameter that describes how structure in the universe grew from its initial smooth beginnings after the Big Bang to the galaxies, stars and planets we see today. 

With the high-precision HSC data, the team measured the lumpiness with a precision of 3.6% (Figure 2), which is similar to the precision with which it has been measured by other lensing surveys. These other surveys, including the Dark Energy Survey (DES) carried out on the Victor Blanco Telescope in Chile, surveyed brighter and thus nearer-by galaxies than did the HSC; the consistency of results at different distances and thus cosmic epochs gives confidence in the robustness of the results.

Figure 2: The cosmological constraints on the clumpiness of the Universe today (S₈) predicted using observations at different times in the Universe. The HSC measurement of the clumpiness of the Universe is shown with the red symbol and are among the farthest measurements using weak gravitational lensing. These should be compared with the Planck results obtained from observations of the cosmic microwave background in the very early Universe and other contemporary weak lensing experiments the Kilo Degree Survey (KiDS) and DES. (Credit: HSC Project/UTokyo)

When compared to the fluctuations expected from those seen in the Universe's infancy by the Planck satellite, the HSC measurements offer a consistent picture of the cosmological model (Figure 3). The Universe today is dominated by dark matter and dark energy, and that dark energy behaves like Einstein's cosmological constant (Figure 4).

Figure 3: The cosmological constraints on the fractional contribution of matter to the energy budget of the Universe (rest of it corresponds to dark energy), and the clumpiness of the matter distribution today (S₈), as inferred from the analysis of the 3d dark matter map. The results of the clumpiness of the matter distribution from HSC observations of the distant Universe using weak gravitational lensing are consistent with results from other similar observations (DES and KiDS) of slightly nearby Universe. The results from the cosmic microwave background observations during the Universe's infancy obtained by the Planck satellite are shown in blue. (Credit: HSC Project)

Figure 4: Cosmological constraints on the dark energy equation of state (blue contours alone from HSC), red contours corresponds to constraints after combining with cosmological results from the Planck CMB satellite and other contemporary cosmological measurements using Supernovae and Baryon acoustic oscillations. (Credit: HSC Project)

However, taken together the results from weak lensing surveys prefer a slightly smaller value of fluctuations than that predicted by the Planck satellite (Figure 5). This could just be a statistical fluctuation due to the limited amount of data available, or might be a signature of the breakdown of the standard model of the Universe, based on General Relativity and the cosmological constant. 

Figure 5: The weak lensing surveys such as HSC prefer a slightly less clumpy Universe than that predicted by Planck. The pictures show the slight but noticeable difference as expected from large computer simulations. Is this difference a statistical fluctuation? Astronomers all around the world continue to collect more and more data to answer this question. (Credit: UTokyo, Image provided by Kavli IPMU Project Assistant Professor Takahiro Nishimichi)

The HSC team conducted the HSC survey using the Subaru Telescope on the summit of Maunakea, one of the best astronomical sites in the world. The combination of a large primary mirror with a diameter of 8.2 meters, a wide field camera that can observe the area of 9 full moons in a single shot, and superb image quality producing sharp images of each galaxy, makes the telescope well suited to conduct a wide yet deep imaging survey of the sky. The survey has covered about 140 square degrees of sky (the area of 3000 full moons) over 90 nights. 

The study required precise measurements of the shapes of galaxies. Since the weak lensing effect is quite small, the HSC team had to control various problems affecting the measurement of shapes, such as distortions due to the atmosphere and the instrument itself. The team overcame these difficulties by using detailed image simulations of the HSC survey based on images from the Hubble Space Telescope. 

When carrying out precise measurements of very small effects like weak lensing, it is known that people have a tendency to decide that their analysis is complete if their results confirm earlier results. The HSC team performed a so-called blind analysis of their data in order to avoid such 'confirmation bias." They carried out many tests of their catalogs for more than a year without ever seeing the actual values of cosmological parameters from their analysis or comparing with results from other experiments, waiting until they were completely satisfied with their results before allowing themselves to examine their cosmological implications. 

The HSC survey is on-going, the new HSC results come from a mere one tenth of the final survey. Upon completion, the survey will put considerably tighter constraints on cosmological parameters, deepening our understanding and further testing our understanding of both dark matter and dark energy. 

HSC lead developer, Dr. Satoshi Miyazaki, from NAOJ's Advanced Technology Center, commented on the new work based on the HSC data. "This paper is a very important milestone of the HSC project where we have peer reviews on the data analysis package to determine cosmological parameters. At the same time, it also demonstrates the quality of the HSC data compared with those of other projects. Scientifically, the result is very exciting because it is consistent with what we have shown in February 2018 suggesting that the number of dark matter halo is less than the expectation based on a standard cosmological model."

The research paper is available as a preprint (Chiaki Hikage, Masamune Oguri, Takashi Hamana, Surhud More, Rachel Mandelbaum, Masahiro Takada, et al., "Cosmology from cosmic shear power spectra with Subaru Hyper Suprime-Cam first-year data") on arxiv.org, and has now been submitted to the journal Publications of the Astronomical Society of Japan and will undergo rigorous peer review by the scientific community. This research is supported by KAKENHI (JP15H03654, JP16K17684, JP16H01089, JP17H06599, JP18H04348, JP18K03693, JP18H04350, JP15H05887, JP15H05892, JP15H05893, JP15K21733).

---

Links:

• Unprecedentedly Wide and Sharp Dark Matter Map (March 1, 2018 Subaru Telescope Press Release)
• Hyper Suprime-Cam Ushers in a New Era of Observational Astronomy (September 12, 2012 Subaru Telescope Press Release)
• Press release from Kavli Institute for the Physics and Mathematics of the Universe

Source: Subaru Telescope/Press Release

---

Making Head or Tail of a Galactic Landscape

Abell 2142

Credit X-ray: NASA/CXC/Univ. of Geneva, D. Eckert.

Optical: SDSS provided by CDS through Aladin. 

JPEG (214.4 kb) - Large JPEG (1.2 MB)  - Tiff (11.6 MB) - More Images

 

 Tour of Abell 2142 - More Animations

---

Astronomers have used data from NASA's Chandra X-ray Observatory to capture a dramatic image of an enormous tail of hot gas stretching for more than a million light years behind a group of galaxies that is falling into the depths of an even-larger cluster of galaxies. Discoveries like this help astronomers learn about the environment and conditions under which the Universe's biggest structures evolve.

Galaxy clusters are the largest structures in the Universe held together by gravity. While galaxy clusters can contain hundreds or even thousands of individual galaxies, the lion's share of mass in a galaxy cluster comes from hot gas, which gives off X-rays, and unseen dark matter. How did these cosmic giants get to be so big?

This new image shows one way: the capture of galaxies as they are drawn in by the extraordinarily powerful gravity of a galaxy cluster. In the left panel, a wide-field view of the cluster, called Abell 2142, is seen. Abell 2142 contains hundreds of galaxies embedded in multi-million-degree gas detected by Chandra (purple). The center of the galaxy cluster is located in the middle of the purple emission, in the lower part of the image. Only the densest hot gas is shown here, implying that less dense gas farther away from the middle of the cluster is not depicted in the purple emission. In this composite image, the Chandra data have been combined with optical data from the Sloan Digital Sky Survey in red, green, and blue.

Abell 2142

Credit X-ray: NASA/CXC/Univ. of Geneva, D. Eckert.

Optical: SDSS provided by CDS through Aladin. 

A bright X-ray tail located in the upper left of the image is aiming straight for Abell 2142. The right panel contains a closer view of this tail. A galaxy group containing four bright galaxies is near the "head" while the "tail" extends off to the upper left. (Galaxy groups, as defined by astronomers contain a handful to a few dozen galaxies, as opposed to much more populous galaxy clusters.) The direction of the tail and the sharp leading edge of the hot gas around the galaxy group, identified in the labeled version, shows that the group is falling almost directly towards the center of Abell 2142. A close-up view of the four bright galaxies (named G1, G3, G4 and G5) is shown as an optical and X-ray image. The galaxy G2 is a background object, rather than a member of the galaxy group.

Abell 2142

Credit X-ray: NASA/CXC/Univ. of Geneva, D. Eckert.

Optical: SDSS provided by CDS through Aladin. 

As the group of galaxies falls into Abell 2142, some of the hot gas is stripped off, much like leaves from a tree in the fall during a strong gust of wind. As the gas gets stripped off, it forms into a straight and relatively narrow tail that extends for some 800,000 light years. The shape of the tail suggests that magnetic fields draped around it are acting like a shield to contain the gas.Beyond about a million light years, the tail flares and becomes irregular. This may mean the turbulence in the galaxy cluster's hot gas is stronger in that area, helping to break down the effect of the magnetic shield. 

The lower side of the tail flares out more than the upper side. This may be caused by a previous asymmetry in the hot gas in the galaxy group. Such an asymmetry could result from an outburst generated by a supermassive black hole in one of the galaxies in the group, or from mergers between galaxies in the group. Such events could lead to some parts of the galaxy group's gas being stripped more easily than others.

The new Chandra data also confirm that two of four bright galaxies in the group, G3 and G4, contain rapidly growing, supermassive black holes. The two corresponding X-ray sources are closely overlapping in the Chandra image. 

A paper describing the results, led by Dominique Eckert of the University of Geneva in Switzerland, appeared in the Astronomy & Astrophysics journal and is 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.

A Quick Look at Abell 2142

---

Fast Facts for Abell 2142:

Scale: Image is about 33.5 arcmin across (about 11,550,000 light years); Inset: about 5.8 arcmin across (about 2,000,000 light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 15h 56m 15.89s | Dec 27° 22´ 31.5"
Constellation: Corona Borealis
Observation Date: August 20, 1999, October 4, 2014, December 1, 2014, December 3, 2014
Observation Time: 57 hours 14 minutes (2 days 9 hours 14 minutes)
Obs. ID: 1196, 1228, 17168, 17169, 17492
Instrument: ACIS
References: Eckert, D, et al., 2017, A&A, 605, A25. arXiv:1705.05844
Distance Estimate: About 1.2 billion light years (z=0.09)

Source: NASA’s Chandra X-ray Observatory

---

NASA Is Taking a New Look at Searching for Life Beyond Earth

A zoom into the Hubble Space Telescope photograph of an enormous, balloon-like bubble being blown into space by a super-hot, massive star. Astronomers trained the iconic telescope on this colorful feature, called the Bubble Nebula, or NGC 7635. Credits: NASA, ESA, and the Hubble Heritage Team (STScI/AURA), F. Summers, G. Bacon, Z. Levay, and L. Frattare (Viz 3D Team, STScI)

Since the beginning of civilization, humanity has wondered whether we are alone in the universe. As NASA has explored our solar system and beyond, it has developed increasingly sophisticated tools to address this fundamental question. Within our solar system, NASA’s missions have searched for signs of both ancient and current life, especially on Mars and soon, Jupiter’s moon Europa. Beyond our solar system, missions, such as Kepler and TESS, are revealing thousands of planets orbiting other stars. 

The explosion of knowledge of planets orbiting other stars, called exoplanets, and the results of decades of research on signatures of life - what scientists call biosignatures - have encouraged NASA to address, in a scientifically rigorous way, whether humanity is alone. Beyond searching for evidence of just microbial life, NASA now is exploring ways to search for life advanced enough to create technology.

Technosignatures are signs or signals, which if observed, would allow us to infer the existence of technological life elsewhere in the universe. The best known technosignature are radio signals, but there are many others that have not been explored fully. 

In April 2018, new interest arose in Congress for NASA to begin supporting the scientific search for technosignatures as part of the agency’s search for life. As part of that effort, the agency is hosting the NASA Technosignatures Workshop in Houston on Sept. 26-28, 2018, with the purpose of assessing the current state of the field, the most promising avenues of research in technosignatures and where investments could be made to advance the science. A major goal is to identify how NASA could best support this endeavor through partnerships with private and philanthropic organizations. 

To view the workshop online, visit: http://www.ustream.tv/channel/asteroid-initiative-idea-synthesis---3

On Thursday, Sept. 27 at 1 p.m. EDT, several of the workshop’s speakers will be answering questions in a Reddit AMA.

 What are Technosignatures? 

The term technosignatures has a broader meaning than the historically used “search for extraterrestrial intelligence,” or SETI, which has generally been limited to communication signals. Technosignatures like radio or laser emissions, signs of massive structures or an atmosphere full of pollutants could imply intelligence. 

In recent decades, the private and philanthropic sectors have carried out this research. They have used such methods as searching for patterns in low-band radio frequencies using radio telescopes. Indeed, humanity's own radio and television broadcasts have been drifting into space for a number of years. 

NASA’s SETI program was ended in 1993 after Congress, operating under a budget deficit and decreased political support, cancelled funding for a high-resolution microwave survey of the skies. Since then, NASA’s efforts have been directed towards furthering our fundamental understanding of life itself, its origins and the habitability of other bodies in our solar system and galaxy. 

History of the Search for Technological Life 

Efforts to detect technologically advanced life predates the space age as early 20th century radio pioneers first foresaw the possibility of interplanetary communication. Theoretical work postulating the possibility of carrying signals on radio and microwave bands across vast distances in the galaxy with little interference led to first “listening” experiments in the 1960s. 

Thanks to NASA’s Kepler mission’s discovery of thousands of planets beyond our solar system,including some with key similarities to Earth, it’s now possible to not just imagine the science fiction of finding life on other worlds, but to one day scientifically prove life exists beyond our solar system. 

As NASA's 2015 Astrobiology Strategy states: "Complex life may evolve into cognitive systems that can employ technology in ways that may be observable. Nobody knows the probability, but we know that it is not zero.” As we consider the environments of other planets, “technosignatures” could be included in the possible interpretations of data we get from other worlds. 

Debate about the probability of finding signals of advanced life varies widely. In 1961, astronomer Frank Drake created a formula estimating the number of potential intelligent civilizations in the galaxy, called the Drake equation, and calculated an answer of 10,000. Most of the variables in the equation continue to be rough estimates, subject to uncertainties. Another famous speculation on the subject called the Fermi paradox, posited by Italian physicist Enrico Fermi, asserted that if another intelligent life form was indeed out there, we would have met it by now. 

NASA’s SETI work began with a 1971 proposal by biomedical researcher John Billingham at NASA’s Ames Research Center for a 1,000-dish array of 100-meter telescopes that could pick up television and radio signals from other stars. “Project Cyclops” was not funded, but in 1976, Ames established a SETI branch to continue research in this area. NASA’s Jet Propulsion Laboratory (JPL) also began SETI work. 

In 1988, NASA Headquarters in Washington formally endorsed the SETI program leading to development of the High Resolution Microwave Survey. Announced on Columbus Day in 1992 - 500 years after Columbus landed in North America - this 10-year, $100 million project included a targeted search of stars led by Ames using the 300-meter radio telescope in Arecibo, Puerto Rico, and an all-sky survey led by JPL using its Deep Space Network dish. The program lasted only a year before political opposition eliminated the project and effectively ended NASA’s research efforts in SETI. 

Why Start Looking at Technosignatures Now?

Fueled by the discovery that our galaxy is teeming with planets, interest in detecting signs of technologically-advanced life is again bubbling up. Kepler’s discovery in 2015 of irregular fluctuations in brightness in what came to be known as Tabby’s Star led to speculation of an alien megastructure, though scientists have since concluded that a dust cloud is the likely cause. However, Tabby’s Star has demonstrated the potential usefulness of looking for anomalies in data collected from space, as signs of technologically-advanced life may appear as aberrations from the norm. 

Scientists caution that we will need more than an unexplained signal to definitively prove the existence of technological life. For example, there can be a lot of radio frequency interference from Earth-based sources.

NASA will continue assessing promising current efforts of research in technosignatures and investigating where investments could be made to advance the science. Although we have yet to find signs of extraterrestrial life, NASA is amplifying exploring the solar system and beyond to help humanity answer whether we are alone in the universe. 

From studying water on Mars, probing promising “oceans worlds” such as Europa or Saturn’s moon Enceladus, to looking for biosignatures in the atmospheres of exoplanets, NASA’s science missions are working together with a goal to find unmistakable signs of life beyond Earth. And perhaps that life could indeed be more technologically advanced than our own.

Fascinating.

Editor: Tricia Talbert

Source: NASA/Solar System and Beyond

---

Hubble’s Galaxies With Knots, Bursts

NGC 4858, NGC 4860

Credit: ESA/Hubble & NASA

In the northern constellation of Coma Berenices (Berenice's Hair) lies the impressive Coma Cluster —  a structure of over a thousand galaxies bound together by gravity. Many of these galaxies are elliptical types, as is the brighter of the two galaxies dominating this image: NGC 4860 (center).

 However, the outskirts of the cluster also host younger spiral galaxies that proudly display their swirling arms. Again, this image shows a wonderful example of such a galaxy in the shape of the beautiful NGC 4858, which can be seen to the left of its bright neighbor and which stands out on account of its unusual, tangled, fiery appearance.

NGC 4858 is special. Rather than being a simple spiral, it is something called a “galaxy aggregate,” which is as the name suggests a central galaxy surrounded by a handful of luminous knots of material that seem to stem from it, extending and tearing away and adding to or altering its overall structure. It is also experiencing an extremely high rate of star formation, possibly triggered by an earlier interaction with another galaxy. As we see it, NGC 4858 is forming stars so frantically that it will use up all of its gas long before it reaches the end of its life. The color of its bright knots indicates that they are formed of hydrogen, which glows in various shades of bright red as it is energized by the many young, hot stars lurking within.

This scene was captured by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3), a powerful camera designed to explore the evolution of stars and galaxies in the early universe.

Source: NASA/Hubble

---

Simulations uncover why supernova explosions of some white dwarfs produce so much manganese and nickel

Figure 1: An artist's conception of a single-degenerate Type Ia supernova scenario. Due to the stronger gravitational force from the white dwarf on the left, the outer material of the bigger, slightly evolving main-sequence star on the right is torn away and it flows onto the white dwarf, eventually increasing the mass of the white dwarf toward the Chandrasekhar mass. This carbon-oxygen white dwarf will later explode as a Type Ia supernova. (Credit: Kavli IPMU)

Figure 2: The colour plot of the temperature distribution of the benchmark Type Ia supernova model at about 1 second after explosion. The deflagration model with deflagration-detonation transition is used to produce this result. (Credit: Leung et al.) 

Figure 3: Distributions of representative elements ejecta velocity in the typical Type Ia supernova after all major nuclear reactions have ended. Colours represent the sites where the corresponding elements are produced. The arrow indicates the motion of ejecta’s. (Credit: Leung et al.)

Figure 4: The 57Ni against 56Ni for the models presented in this work. The observed data from Type Ia supernova SN 2012cg is also included. The data points along the line in the described direction stand for white dwarf models of masses from 1.30 to 1.38 solar mass respectively. (Credit: Leung et al.)

Figure 5: X-ray, optical & infrared composite image of 3C 397 (credit: X-ray: NASA/CXC/Univ of Manitoba/S.Safi-Harb et al, Optical: DSS, Infrared: NASA/JPL-Caltech)

Figure 6: Mass ratio Mn/Fe against Ni/Fe for the models presented in this work. The observed data from Type Ia supernova remnant 3C 397 is also included. The data points along the line in the described direction stand for white dwarf models of masses from 1.30 to 1.38 solar mass respectively. (Credit: Leung et al.)

Researchers have found white dwarf stars with masses close to the maximum stable mass (called the Chandrasekhar mass) are likely to produce large amounts of manganese, iron, and nickel after it orbits another star and explodes as Type Ia supernovae (figure 1).

A Type Ia supernova is a thermonuclear explosion (figure 2) of a carbon-oxygen white dwarf star with a companion star orbiting one another, also known as a binary system. In the Universe, Type Ia supernovae are the main production sites for iron-peak elements, including manganese, iron, and nickel, and some intermediate mass elements including silicon and sulfur (figure 3).

However, researchers today cannot agree on what kind of binary systems triggers a white dwarf to explode. Moreover, recent extensive observations have revealed a large diversity of nucleosynthesis products, the creation of new atomic nuclei from the existing nuclei in the star by nuclear fusion, of Type Ia supernovae and their remnants, in particular, the amount of manganese, stable nickel, and radioactive isotopes of 56-nickel and 57-nickel (figure 4).

To uncover the origin of such diversities, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Project Researcher Shing-Chi Leung and Senior Scientist Ken’ichi Nomoto carried out simulations using the most accurate scheme to date for multi-dimensional hydrodynamics of Type Ia supernova models. They examined how chemical abundance patterns and the creation of new atomic nuclei from existing nucleons depend on white dwarf properties and their progenitors.

“The most important and unique part of this study is that this is so far the largest parameter survey in the parameter space for the Type Ia supernova yield using the Chandrasekhar mass white dwarf,” said Leung.

A particularly interesting case was the supernova remnant 3C 397 (figure 5). 3C 397 is located in the Galaxy about 5.5 kpc from the center on the galactic disk. Its abundance ratios of stable manganese/iron and nickel/iron were found to be two and four times that of the Sun respectively. Leung and Nomoto found the abundance ratios among manganese, iron and nickel are sensitive to white dwarf mass and metallicity (how abundant it is in elements heavier than hydrogen and helium). The measured values of 3C 397 can be explained if the white dwarf has a mass as high as the Chandrasekhar mass and high metallicity (figure 6).

The results suggest remnant 3C 397 could not be the result of an explosion of a white dwarf with relatively low mass (a sub-Chandrasekhar mass). Moreover, the white dwarf should have a metallicity higher than the Sun’s metallicity, in contrast to the neighboring stars which have a typically lower metallicity.

It provides important clues to the controversial discussion of whether the mass of the white dwarf is close to the Chandrasekhar mass, or sub-Chandrasekhar mass, when it explodes as a Type Ia supernova.

The results will be useful in future studies of chemical evolution of galaxies for a wide range of metallicities, and encourage researchers to include super-solar metallicity models as a complete set of stellar models.

Leung says the next step of this study would involve further testing their model with more observational data, and to extend it to another subclass of Type Ia supernovae.

These results were published in the July 10 issue of The Astrophysical Journal.

---

Paper details

Journal: The Astrophysical Journal
Title: Explosive Nucleosynthesis in Near-Chandrasekhar Mass White Dwarf Models for Type Ia supernovae: Dependence on Model Parameters
Authors: Shing-Chi Leung (1), Ken’ichi Nomoto (1)

Author affiliations:

1. Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan

DOI: 10.3847/1538-4357/aac2df (Published 13 July, 2018)

---

Research contact

Shing Chi Leung
Project Researcher
Kavli Institute for the Physics and Mathematics of the Universe
University of Tokyo
E-mail: shingchi.leun@ipmu.jp

Ken'ichi Nomoto
Principal Investigator and Project Professor
Kavli Institute for the Physics and Mathematics of the Universe
University of Tokyo
TEL: +81-04-7136-6567
E-mail: nomoto@astron.s.u-tokyo.ac.jp

Media contact

Motoko Kakubayashi
Press officer
Kavli Institute for the Physics and Mathematics of the Universe
University of Tokyo
TEL：04-7136-5980
E-mail: press@ipmu.jp

Source: Kavli IPMU

---

Hubble Uncovers Never Before Seen Features Around a Neutron Star

Artist's Impression of Disk Around a Neutron Star

This illustration shows a neutron star (RX J0806.4-4123) with a disk of warm dust that produces an infrared signature as detected by NASA’s Hubble Space Telescope. The disk wasn’t directly photographed, but one way to explain the data is by hypothesizing a disk structure that could be 18 billion miles across. The disk would be made up of material falling back onto the neutron star after the supernova explosion that created the stellar remnant. Credits: NASA, ESA, and N. Tr’Ehnl (Pennsylvania State University).  Release Images

An unusual infrared light emission from a nearby neutron star detected by NASA’s Hubble Space Telescope, could indicate new features never before seen. One possibility is that there is a dusty disk surrounding the neutron star; another is that there is an energetic wind coming off the object and slamming into gas in interstellar space the neutron star is plowing through.

Although neutron stars are generally studied in radio and high-energy emissions, such as X-rays, this study demonstrates that new and interesting information about neutron stars can also be gained by studying them in infrared light, say researchers. 

The observation, by a team of researchers at Pennsylvania State University, University Park, Pennsylvania; Sabanci University, Istanbul, Turkey; and the University of Arizona, Tucson, Arizona could help astronomers better understand the evolution of neutron stars — the incredibly dense remnants after a massive star explodes as a supernova. Neutron stars are also called pulsars because their very fast rotation (typically fractions of a second, in this case 11 seconds) causes time-variable emission from light-emitting regions.

A paper describing the research and two possible explanations for the unusual finding appears Sept. 17, 2018 in the Astrophysical Journal.

“This particular neutron star belongs to a group of seven nearby X-ray pulsars — nicknamed ‘the Magnificent Seven’ — that are hotter than they ought to be considering their ages and available energy reservoir provided by the loss of rotation energy,” said Bettina Posselt, associate research professor of astronomy and astrophysics at Pennsylvania State and the lead author of the paper. “We observed an extended area of infrared emissions around this neutron star — named RX J0806.4-4123 — the total size of which translates into about 200 astronomical units (approximately 18 billion miles) at the assumed distance of the pulsar.”

This is the first neutron star in which an extended signal has been seen only in infrared light. The researchers suggest two possibilities that could explain the extended infrared signal seen by the Hubble. The first is that there is a disk of material — possibly mostly dust — surrounding the pulsar.

“One theory is that there could be what is known as a ‘fallback disk’ of material that coalesced around the neutron star after the supernova,” said Posselt. “Such a disk would be composed of matter from the progenitor massive star. Its subsequent interaction with the neutron star could have heated the pulsar and slowed its rotation. If confirmed as a supernova fallback disk, this result could change our general understanding of neutron star evolution.”

The second possible explanation for the extended infrared emission from this neutron star is a “pulsar wind nebula.”

“A pulsar wind nebula would require that the neutron star exhibits a pulsar wind,” said Posselt. “A pulsar wind can be produced when particles are accelerated in the electrical field that is produced by the fast rotation of a neutron star with a strong magnetic field. As the neutron star travels through the interstellar medium at greater than the speed of sound, a shock can form where the interstellar medium and the pulsar wind interact. The shocked particles would then emit synchrotron radiation, causing the extended infrared signal that we see. Typically, pulsar wind nebulae are seen in X-rays and an infrared-only pulsar wind nebula would be very unusual and exciting.”

Using NASA’s upcoming James Webb Space Telescope, astronomers will be able to further explore this newly opened discovery space in the infrared to better understand neutron star evolution.

In addition to Posselt, the research team included George Pavlov and Kevin Luhman at Pennsylvania State; Ünal Ertan and Sirin Çaliskan at Sabanci University; and Christina Williams at the University of Arizona. The research was supported by NASA, The Scientific and Technological Research Council of Turkey, the U.S. National Science Foundation, Pennsylvania State, the Penn State Eberly College of Science, and the Pennsylvania Space Grant Consortium.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

---

Related Links

This site is not responsible for content found on external links

• The science paper by B. Posselt et al.
• NASA's Hubble Portal
• Pennsylvania State University's Release

---

Contact

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu

Dr. Samuel J. Sholtis
Penn State Eberly College of Science, Office of Communications, University Park, Pennsylvania
814-865-1390
samsholtis@psu.edu

Source:  HubbleSite/News

---

Magnetic Waves Create Chaos in Star-Forming Clouds

Offner’s research will shed light on the processes inside star-forming regions such as 30 Doradus, seen in this view from Hubble Space Telescope. Credit: NASA/ESA/F. Paresce/R. O’Connell/WFC3 (Click image to access download options from hubblesite.org). Hi-res images

Cloud Models 

Models of two turbulent clouds without stars (left) and with stars launching winds (right). The colors show gas speed: grey (6-10 km/s), blue (12-25 km/s), and red (180-250 km/s). Credit: Stella Offner/UT Austin

Magnetic Waves from a Young Star

Gas density and velocity (top) and magnetic field strength and magnetic field lines (bottom) showing magnetic waves propagating ahead of the wind shell. The left and right panels show different models. The waves stand out when the surrounding gas is not turbulent. Credit: Stella Offner/UT Austin

---

New research by Stella Offner, assistant professor of astronomy at The University of Texas at Austin, finds that magnetic waves are an important factor driving the process of star formation within the enormous clouds that birth stars. Her research sheds light on the processes that are responsible for setting the properties of stars, which in turn affects the formation of planets orbiting them, and, ultimately, life on those planets. The research is published in the current issue of the journal Nature Astronomy.

Offner used a supercomputer to make models of the multitude of processes happening inside a cloud where stars are forming, in an effort to sort out which processes lead to which effects.

“These clouds are violent places,” Offner said. “It’s an extreme environment with all kinds of different physics happening at once,” including gravity and turbulence as well as radiation and winds from forming stars (called stellar feedback). The fundamental question, Offner said, is: “Why are the motions in these clouds so violent?”

Some astronomers attribute the observed motions to gravitational collapse, while others attribute it to turbulence and stellar feedback. Offner wanted to test these theories and study how stars shape their birth environment, but it’s virtually impossible to use telescope observations of these clouds to separate the influence of the various processes, she said.

“That’s why we need computer models,” Offner explained.

After comparing models of clouds with gravity, magnetic fields, and stars, Offner noticed extra motions.

 Her models showed that stellar winds interacting with the cloud magnetic field generated energy and influenced gas at far greater distances across the cloud than previously thought: These local magnetic fields caused action at a distance.

“Think of the magnetic fields like rubber bands that stretch across the cloud,” Offner said. “The winds push the field — it’s like rubber bands being plucked. The waves outrun the wind and cause distant motions.”

This research has implications for the tug-of-war between feedback — that is, the effect that the newly formed star has on its environment — and gravity on the scale of solar systems up to entire galaxies, Offner said.

As for the next step, Offner says she plans to study this process on larger scales, both in time and space. Her current study focused on one area within star-forming clouds; she said future studies will study the effects of magnetic fields and feedback on scales larger than a single cloud.

---

Media Contact:

Rebecca Johnson, Communications Mgr.
McDonald Observatory
The University of Texas at Austin
512-475-6763

Science Contact:

Dr. Stella Offner, Asst. Professor
Department of Astronomy
The University of Texas at Austin
512-471-3853

Source: McDonald Observatory/News

---

Astronomers Witness Birth of New Star from Stellar Explosion

These image from NASA's Hubble Space Telescope show SN 2012au, a supernova explosion that was the subject of a recent study that included researchers from the CfA. Credit: NASA/STScI.  High Resolution (jpg) - Low Resolution (jpg)

Cambridge, MA - The explosions of stars, known as supernovae, can be so bright they outshine their host galaxies. They take months or years to fade away, and sometimes, the gaseous remains of the explosion slam into hydrogen-rich gas and temporarily get bright again – but could they remain luminous without any outside interference?

That's what Dan Milisavljevic, an assistant professor of physics and astronomy at Purdue University, believes he saw six years after "SN 2012au" exploded. Until recently, Milisavlievic was at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass.

"We haven't seen an explosion of this type, at such a late timescale, remain visible unless it had some kind of interaction with hydrogen gas left behind by the star prior to explosion," he said. "But there's no spectral spike of hydrogen in the data – something else was energizing this thing."

As large stars explode, their interiors collapse down to a point at which all of their particles become neutrons. If the newly born star has a magnetic field and rotates fast enough, it can accelerate nearby charged particles and become what astronomers call a pulsar wind nebula. This is most likely what happened to SN 2012au, according to findings published in The Astrophysical Journal Letters. Other co-authors include Dan Patnaude and John Raymond, also from the CfA.

"We know that supernova explosions produce these types of rapidly rotating neutron stars, but we never saw direct evidence of it at this unique time frame," Milisavljevic said. "This a key moment when the pulsar wind nebula is bright enough to act like a lightbulb illuminating the explosion's outer ejecta."

SN 2012au was already known to be extraordinary – and strange – in many ways. Although the explosion wasn't bright enough to be termed a "superluminous" supernova, it was extremely energetic and long-lasting, and dimmed in a similarly slow light curve.

Milisavljevic predicts that if researchers continue to monitor the sites of extremely bright supernovae, they might see similar transformations.

"If there truly is a pulsar or magnetar wind nebula at the center of the exploded star, it could push from the inside out and even accelerate the gas," he said. "If we return to some of these events a few years later and take careful measurements, we might observe the oxygen-rich gas racing away from the explosion even faster."

Superluminous supernovae are a hot topic in transient astronomy. They're potential sources of gravitational waves and black holes, and astronomers think they might be related to other kinds of explosions, like gamma ray bursts and fast radio bursts. Researchers want to understand the fundamental physics behind them, but they’re difficult to observe because they’re relatively rare and happen so far from Earth.

Only the next generation of telescopes including the Giant Magellan Telescope, which astronomers have dubbed "Extremely Large Telescopes," will have the ability to observe these events in such detail.

"This is a fundamental process in the universe. We wouldn't be here unless this was happening," Milisavljevic said. "Many of the elements essential to life come from supernova explosions – calcium in our bones, oxygen we breathe, iron in our blood – I think it's crucial for us, as citizens of the universe, to understand this process."

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (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.

For more information, contact:

Megan Watzke
Harvard-Smithsonian Center for Astrophysics
+1 617-496-7998
mwatzke@cfa.harvard.edu

Peter Edmonds
Harvard-Smithsonian Center for Astrophysics
+1 617-571-7279
pedmonds@cfa.harvard.edu

Source: Harvard-Smithsonian Center for Astrophysics (CfA)

---

Awesome gravity

SDSS J1138+2754

Credit: ESA/Hubble & NASA

Acknowledgement: Judy Schmidt

Gravity is so much a part of our daily lives that it is all too easy to forget its awesome power — but on a galactic scale, its power becomes both strikingly clear and visually stunning.

This image was taken with the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) and shows an object named SDSS J1138+2754. It acts as a gravitational lens illustrates the true strength of gravity: A large mass — a galaxy cluster in this case — is creating such a strong gravitational field that it is bending the very fabric of its surroundings. This causes the billion-year-old light from galaxies sitting behind it to travel along distorted, curved paths, transforming the familiar shapes of spirals and ellipticals (visible in other parts of the image) into long, smudged arcs and scattered dashes.

Some distant galaxies even appear multiple times in this image. Since galaxies are wide objects, light from one side of the galaxy passes through the gravitational lens differently than light from the other side. When the galaxies’ light reaches Earth it can appear reflected, as seen with the galaxy on the lower left part of the lens, or distorted, as seen with the galaxy to the upper right.

This data were taken as part of a research project on star formation in the distant Universe, building on Hubble’s extensive legacy of deep-field images. Hubble observed 73 gravitationally-lensed galaxies for this project.

Source: ESA/Hubble/Potw

---

BUFFALO charges towards the earliest galaxies

PR Image heic1816a

BUFFALO’s view on Abell 370

PR Image heic1816b

The last of the Frontier Fields — Abell 370

PR Image heic1816c

Comparison between Frontier Fields and BUFFALO

PR Image heic1816d

Digitized sky survey image of Abell 370 (ground-based image)

---

Videos

PR Video heic1816a

Zooming onto the galaxy cluster Abell 370

PR Video heic1816b

Pan across Abell 370

---

New Hubble project provides wide-field view of the galaxy cluster Abell 370

The NASA/ESA Hubble Space Telescope has started a new mission to shed light on the evolution of the earliest galaxies in the Universe. The BUFFALO survey will observe six massive galaxy clusters and their surroundings. The first observations show the galaxy cluster Abell 370 and a host of magnified, gravitationally lensed galaxies around it.

Learning about the formation and evolution of the very first galaxies in the Universe is crucial for our understanding of the cosmos. While the NASA/ESA Hubble Space Telescope has already detected some of the most distant galaxies known, their numbers are small, making it hard for astronomers to determine if they represent the Universe at large.

Massive galaxy clusters like Abell 370, which is visible in this new image, can help astronomers find more of these distant objects. The immense masses of galaxy clusters make them act as cosmic magnifying glasses. A cluster’s mass bends and magnifies light from more distant objects behind it, uncovering objects otherwise too faint for even Hubble’s sensitive vision. Using this cosmological trick — known as strong gravitational lensing — Hubble is able to explore some of the earliest and most distant galaxies in the Universe.

Numerous galaxies are lensed by the mass of Abell 370. The most stunning demonstration of gravitational lensing can be seen just below the centre of the cluster. Nicknamed “the Dragon”, this extended feature is made up of a multitude of duplicated images of a spiral galaxy which lies beyond the cluster.

This image of Abell 370 and its surroundings was made as part of the new Beyond Ultra-deep Frontier Fields And Legacy Observations (BUFFALO) survey. This project, led by European astronomers from the Niels Bohr Institute (Denmark) and Durham University (UK), was designed to succeed the successful Frontier Fields project [1]. 101 Hubble orbits — corresponding to 160 hours of precious observation time — have been dedicated to exploring the six Frontier Field galaxy clusters. These additional observations focus on the regions surrounding the galaxy clusters, allowing for a larger field of view.

BUFFALO’s main mission, however, is to investigate how and when the most massive and luminous galaxies in the Universe formed and how early galaxy formation is linked to dark matter assembly. This will allow astronomers to determine how rapidly galaxies formed in the first 800 million years after the Big Bang — paving the way for observations with the upcoming NASA/ESA/CSA James Webb Space Telescope.

Driven by the Frontier Fields observations, BUFFALO will be able to detect the most distant galaxies approximately ten times more efficiently than its progenitor programme. The BUFFALO survey will also take advantage of other space telescopes which have already observed the regions around the clusters. These datasets will be included in the search for the first galaxies.

The extended fields of view will also allow better 3-dimensional mapping of the mass distribution — of both ordinary and dark matter — within each galaxy cluster. These maps help astronomers learn more about the evolution of the lensing galaxy clusters and about the nature of dark matter.

---

Notes

[1] Frontier Fields was a Hubble programme that ran from 2013 to 2017. Hubble spent 630 hours of observation time probing six notable galaxy clusters, all of which showed effects of strong gravitational lensing.

---

More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Image credit: NASA, ESA, A. Koekemoer, M. Jauzac, C. Steinhardt, and the BUFFALO team

---

Links

• BUFFALO project page
• Hubblesite release
• Press releases on the Frontier Fields

---

Contacts

Charles Steinhardt

Niels Bohr Institute

Copenhagen, Denmark

Tel: +45 35 33 50 10

Email: Steinhardt@nbi.ku.dk

Mathilde Jauzac

Durham University

Durham, UK

Tel: +44 7445218614

Email: mathilde.jauzac@durham.ac.uk

Mathias Jäger

ESA/Hubble, Public Information Officer

Garching, Germany

Tel: +49 176 62397500

Email: mjaeger@partner.eso.org

Source: ESA/Hubble/News

---

A Galactic Gem

PR Image eso1830a

A Galactic Gem

PR Image eso1830b

Digitized Sky Survey image around the spiral galaxy NGC 3981

PR Image eso1830c

NGC 3981 in the constellation of Crater

---

Videos

PR Video eso1830a

ESOCast 177 Light: A Galactic Gem (4K UHD)

PR Video eso1830b

Zooming into NGC 3981

PR Video eso1830c

Panning across NGC 3981

---

ESO’s FORS2 instrument captures stunning details of spiral galaxy NGC 3981

FORS2, an instrument mounted on ESO’s Very Large Telescope, has observed the spiral galaxy NGC 3981 in all its glory. The image was captured as part of the ESO Cosmic Gems Programme, which makes use of the rare occasions when observing conditions are not suitable for gathering scientific data. Instead of sitting idle, the ESO Cosmic Gems Programme allows ESO’s telescopes to be used to capture visually stunning images of the southern skies.

This wonderful image shows the resplendent spiral galaxy NGC 3981 suspended in the inky blackness of space. This galaxy, which lies in the constellation of Crater (the Cup), was imaged in May 2018 using the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument on ESO’s Very Large Telescope (VLT).

FORS2 is mounted on Unit Telescope 1 (Antu) of the VLT at ESO’s Paranal Observatory in Chile. Amongst the host of cutting-edge instruments mounted on the four Unit Telescopes of the VLT, FORS2 stands apart due to its extreme versatility. This ”Swiss Army knife” of an instrument is able to study a variety of astronomical objects in many different ways — as well as being capable of producing beautiful images like this one.

The sensitive gaze of FORS2 revealed NGC 3981’s spiral arms, strewn with vast streams of dust and star-forming regions, and a prominent disc of hot young stars. The galaxy is inclined towards Earth, allowing astronomers to peer right into the heart of this galaxy and observe its bright centre, a highly energetic region containing a supermassive black hole. Also shown is NGC 3981’s outlying spiral structure, some of which appears to have been stretched outwards from the galaxy, presumably due to the gravitational influence of a past galactic encounter.

NGC 3981 certainly has many galactic neighbours. Lying approximately 65 million light years from Earth, the galaxy is part of the NGC 4038 group, which also contains the well-known interacting Antennae Galaxies. This group is part of the larger Crater Cloud, which is itself a smaller component of the Virgo Supercluster, the titanic collection of galaxies that hosts our own Milky Way galaxy.

NGC 3981 is not the only interesting feature captured in this image. As well as several foreground stars from our own galaxy, the Milky Way, FORS2 also captured a rogue asteroid streaking across the sky, visible as the faint line towards the top of the image. This particular asteroid has unwittingly illustrated the process used to create astronomical images, with the three different exposures making up this image displayed in the blue, green and red sections of the asteroid’s path.

This image was taken as part of ESO’s Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. In case the data collected could be useful for future scientific purposes, these observations are saved and made available to astronomers through ESO’s science archive.

---

More Information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 15 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a strategic partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.

---

Links

• ESO’s Cosmic Gems programme
• Images of the VLT

---

Contacts

Calum Turner
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670
Email: pio@eso.org

Source: ESO/News

---