Research suggests our Galaxy’s brightest gamma-ray binary system may be powered by a magnetar star

An impression of the gamma-ray binary system LS 5039. A neutron star (left) and its massive, companion star (right). The research team suggests that the neutron star at the heart of LS 5039 has an ultra-strong magnetic field, and is arguably a magnetar. The field accelerates high-energy particles inside the bow-shaped region, thereby emitting gamma-rays that characterize the gamma-ray binary system. (Credit: Kavli IPMU)

A team of researchers led by members of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) has analyzed previously collected data to infer the true nature of a compact object—found to be a rotating magnetar, a type of neutron star with an extremely strong magnetic field—orbiting within LS 5039, the brightest gamma-ray binary system in the Galaxy. 

Including former graduate student Hiroki Yoneda, Senior Scientist Kazuo Makishima and Principal Investigator Tadayuki Takahashi at the Kavli IMPU, the team also suggest that the particle acceleration process known to occur within LS 5039 is caused by interactions between the dense stellar winds of its primary massive star, and ultra-strong magnetic fields of the rotating magnetar.

Gamma-ray binaries are a system of massive, high-energy stars and compact stars. They were discovered only recently, in 2004, when observations of very-high-energy gamma-rays in the teraelectronvolt (TeV) band from large enough regions of the sky became possible. When viewed with visible light, gamma-ray binaries appear as bright bluish-white stars, and are indistinguishable from any other binary system hosting a massive star. However, when observed with X-rays and gamma-rays, their properties are dramatically different from those of other binaries. In these energy bands, ordinary binary systems are completely invisible, but gamma-ray binaries produce intense non-thermal emission, and their intensity appears to increase and decrease according to their orbital periods of several days to several years.

Once the gamma-ray binaries were established as a new astrophysical class, it was quickly recognized that an extremely efficient acceleration mechanism should operate in them. While the acceleration of TeV particles requires tens of years in supernova remnants, which are renowned cosmic accelerators, gamma-ray binaries boost electron energy beyond 1 TeV in just tens of seconds. Gamma-ray binaries can thus be considered one of the most efficient particle accelerators in the Universe.

In addition, some gamma-ray binaries are known to emit strong gamma-rays with energies of several megaelectron volts (MeV). Gamma-rays in this band are currently difficult to observe; they were detected from only around 30 celestial bodies in the whole sky. But the fact that such binaries emit strong radiation even in this energy band greatly adds to the mystery surrounding them, and indicates an extremely effective particle acceleration process going on within them.

Around 10 gamma-ray binaries have been found in the Galaxy thus far—compared to more than 300 X-ray binaries that are known to exist. Why gamma-ray binaries are so rare is unknown, and, indeed, what the true nature of their acceleration mechanism is, has been a mystery—until now.

Through previous studies, it was already clear that a gamma-ray binary is  generally made of a massive primary star that weighs 20-30 times the mass of the Sun, and a companion star that must be a compact star, but it was not clear, in many cases, whether the compact star is a black hole or a neutron star. The research team started their attempt by figuring out which is generally the case.

One of the most direct pieces of evidence for the presence of a neutron star is the detection of periodic fast pulsations, which are related to the neutron star rotation. Detection of such pulsation from a gamma-ray binary almost undoubtedly discards the black hole scenario. 

In this project, the team focused on LS 5039, which was discovered in 2005, and still keep its position as the brightest gamma-ray binary in the X-rays and gamma-ray range. Indeed, this gamma-ray binary was thought to contain a neutron star because of its stable X-ray and TeV gamma-ray radiation. However, until now, attempts to detect such pulses had been conducted with radio waves and soft X-rays—and because radio waves and soft X-rays are affected by the primary star’s stellar winds, detection of such periodical pulses had not been successful.

This time, for the first time, the team focused on the hard X-ray band (>10 keV) and observation data from LS 5039 gathered by the hard X-ray detector (HXD) on board the space-based telescopes Suzaku (between September 9 and 15, 2007) and NuSTAR (between September 1 and 5, 2016)—indeed, the six-day Suzaku observation period was the longest yet using hard X-rays. 

Both observations, while separated by nine years, provided evidence of a neutron star at the core of LS 5039: the periodic signal from Suzaku with a period of about 9 seconds. The probability that this signal arises from statistical fluctuations is only 0.1 percent. NuSTAR also showed a very similar pulse signal, though the pulse significance was lower—the NuSTAR data, for instance, was only tentative. By combining these results, it was also inferred that the spin period is increasing by 0.001 s every year. 

Based on the derived spin period and the rate of its increase, the team ruled out the rotation-powered and accretion-powered scenarios, and found that the magnetic energy of the neutron star is the sole energy source that can power LS 5039.  The required magnetic field reaches 10¹¹ T, which is 3 orders of magnitude higher than those of typical neutron stars. This value is found among so-called magnetars, a subclass of neutron stars which have such an extremely strong magnetic field. The pulse period of 9 seconds is typical of magnetars, and this strong magnetic field prevents the stellar wind of the primary star from being captured by a neutron star, which can explain why LS 5039 does not exhibit properties similar to X-ray pulsars (X-ray pulsars usually occur in X-ray binary systems, where the stellar winds are captured by its companion star).

Interestingly, the 30 magnetars that have been found so far have all been found as isolated stars, so their existence in gamma-ray binaries was not considered a mainstream idea. Besides this new hypothesis, the team suggests a source that powers the non-thermal emission inside LS 5039—they propose that the emission is caused by an interaction between the magnetar’s magnetic fields and dense stellar winds. Indeed, their calculations suggest that gamma-rays with energies of several megaelectronvolts, which has been unclear, can be strongly emitted if they are produced in a region of an extremely strong magnetic field, close to a magnetar.

These results potentially settle the mystery as to the nature of the compact object within LS 5039, and the underlying mechanism powering the binary system. However, further observations and refining of their research is needed to shed new light on their findings. 

Paper details 

Journal: Physical Review Letter
Paper title: Sign of hard X-ray pulsation from the gamma-ray binary system LS 5039

Authors: Hiroki Yoneda (1,2,3), Kazuo Makishima (2,1), Teruaki Enoto (4), Dmitry Khangulyan (5), Takahiro Matsumoto (1), Tadayuki Takahashi (2,1)

Author affiliation:

1. Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan

2. Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa, Chiba 277-8583, Japan

3. RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
4. Extreme Natural Phenomena RIKEN Hakubi Research Team, Cluster for Pioneering Research, RIKEN, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
5. Department of Physics, Rikkyo University, 3-34-1 Nishi Ikebukuro, Toshima, Tokyo 171-8501, Japan

DOI: https://doi.org/10.1103/PhysRevLett.125.111103 (Posted on September 8, 2020)
Abstract of the dissertation
Preprint (arXiv.org page)
 

Media contact: 

John Amari
Press officer 
Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
E-mail: press@ipmu.jp
Tel: 080-4056-2767 

Source:  Kavli Institute for the Physics and Mathematics of the Universe

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Galaxy Survives Black Hole’s Feast – For Now

Illustration of the galaxy called CQ4479. The extremely active black hole at the galaxy’s center is consuming material so fast that the material is glowing as it spins into the black hole’s center, forming a luminous quasar. Quasars create intense energy that was thought to halt all star birth and drive a lethal blow to a galaxy’s growth. But SOFIA found that the galaxy CQ4479 is surviving these monstrous forces, holding on to enough cold gas, shown around the edges in brown, to birth about 100 Sun-sized stars a year, shown in blue. The discovery is causing scientists to re-think their theories of galactic evolution. Credits: NASA/ Daniel Rutter.Hi-res image

The hungriest of black holes are thought to gobble up so much surrounding material they put an end to the life of their host galaxy. This feasting process is so intense that it creates a highly energetic object called a quasar – one of the brightest objects in the universe – as the spinning matter is sucked into the black hole’s belly. Now, researchers have found a galaxy that is surviving the black hole’s ravenous forces by continuing to birth new stars – about 100 Sun-sized stars a year.   

The discovery from NASA’s telescope on an airplane, the Stratospheric Observatory for Infrared Astronomy, can help explain how massive galaxies came to be, even though the universe today is dominated by galaxies that no longer form stars. The results are published in the Astrophysical Journal. 

“This shows us that the growth of active black holes doesn’t stop star birth instantaneously, which goes against all the current scientific predictions,” said Allison Kirkpatrick, assistant professor at the University of Kansas in Lawrence Kansas and co-author on the study. “It’s causing us to re-think our theories on how galaxies evolve.” 

SOFIA, a joint project of NASA and the German Aerospace Center, DLR, studied an extremely distant galaxy, located more than 5.25 billion light years away called CQ4479. At its core is a special type of quasar that was recently discovered by Kirkpatrick called a “cold quasar.” In this kind of quasar, the active black hole is still feasting on material from its host galaxy, but the quasar’s intense energy has not ravaged all of the cold gas, so stars can keep forming and the galaxy lives on. This is the first time researchers have a detailed look at a cold quasar, directly measuring the black hole’s growth, star birth rate, and how much cold gas remains to fuel the galaxy. 

“We were surprised to see another oddball galaxy that defies current theories,” said Kevin Cooke, postdoctoral researcher at the University of Kansas in Lawrence, Kansas, and lead author of this study. “If this tandem growth continues both the black hole and the stars surrounding it would triple in mass before the galaxy reaches the end of its life.” 

As one of the brightest and most distant objects in the universe, quasars, or “quasi-stellar radio sources,” are notoriously difficult to observe because they often outshine everything around them. They form when an especially active black hole consumes huge amounts of material from its surrounding galaxy, creating strong gravitational forces. As more and more material spins faster and faster toward the center of the black hole, the material heats up and glows brightly. A quasar produces so much energy that it often outshines everything around it, blinding attempts to observe its host galaxy. Current theories predict that this energy heats up or expels the cold gas needed to create stars, stopping star birth and driving a lethal blow to a galaxy’s growth. But SOFIA reveals there is a relatively short period  when the galaxy’s star birth can continue while the black hole’s feast goes on powering the quasar’s powerful forces.  

Rather than directly observing the newborn stars, SOFIA used its 9-foot telescope to detect the infrared light radiating from the dust heated by the process of star formation.  Using data collected by SOFIA's High-resolution Airborne Wideband Camera-Plus, or HAWC+ instrument, scientists were able to estimate the amount of star formation over the past 100 million years. 

“SOFIA lets us see into this brief window of time where the two processes can co-exist,” said Cooke. “It’s the only telescope capable of studying star birth in this galaxy without being overwhelmed by the intensely luminous quasar.” 

The short window of joint black hole and star growth represents an early phase in the death of a galaxy, wherein the galaxy has not yet succumbed to the devastating effects of the quasar. Continued research with SOFIA is needed to learn if many other galaxies go through a similar stage with joint black hole and star growth before ultimately reaching the end of life. Future observations with the James Webb Space Telescope, which is scheduled to launch in 2021, could uncover how quasars affect the overall shape of their host galaxies. 

SOFIA is a joint project of NASA and the German Aerospace Center. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California. The HAWC+ instrument was developed and delivered to NASA by a multi-institution team led by NASA’s Jet Propulsion Laboratory (JPL). 

Members of the news media interested in covering this topic should reach out to the NASA Ames newsroom.

Felicia Chou
NASA Headquarters, Washington 
202-358-0257
felicia.chou@nasa.gov

Alison Hawkes 
Ames Research Center, Silicon Valley, Calif.
650-604-4789
alison.hawkes@nasa.gov

Editor: Kassandra Bell

 

Source: NASA/SOFIA

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Extreme-Horizon: Understanding the “Dark” Universe and Primordial Galaxy Formation

The RAMSES simulation code is a numerical code for astrophysics and cosmology. It is based on an adaptive mesh refinement computing technique. The figure illustrates the adaptive mesh configuration based on the density of matter. Credit: CAE

The Extreme-Horizon collaboration run by teams at the CEA, CNRS, Sorbonne Université and Université Paris-Saclay has produced a completely new simulation of the evolution of cosmic structures – galaxies, stars and supermassive black holes – which begins a few moments after the Big Bang and continues to the present day. It describes the intergalactic regions, which represent 90% of the Universe’s volume, in unprecedented resolution. The simulation, which leads to two surprising results at the galactic and cosmological scales, constitutes one of the main ‘grand challenges’ carried out on GENCI’s Joliot-Curie supercomputer, at the CEA’s Very Large Computing Centre (TGCC). The results were published on November 4, 2020, in MNRAS and A&A Letters.

Visible matter constitutes only 16% of the Universe’s total mass. Little is known about the nature of the rest of that mass, which referred to as dark matter. Even more surprising is the fact that the Universe’s total mass accounts for only 30% of its energy. The rest is dark energy, which is totally unknown but is responsible for the Universe’s accelerated expansion.

Figure 1. View of the Extreme-Horizon simulation. The red is hot gas, generally expelled from galaxies by supermassive black holes. The grey is primordial cold gas, which feeds the galaxies along the cosmic filaments. The green is gas enriched with heavy elements (metals) due to the effect of massive star explosions (supernovae). Credit: CAE

To find out more about dark matter and dark energy, astrophysicists use large-scale surveys of the Universe or detailed studies of the properties of galaxies. But they can only interpret their observations by comparing them to predictions by theoretical models of dark matter and dark energy. But these simulations take tens of millions of computing hours on supercomputers.

The Extreme-Horizon collaboration was able to run a simulation of the evolution of cosmic structures from the first few moments after the Big Bang to the present day, on the Joliot-Curie supercomputer, which offers computing power of 22 petaflops (22 x 10¹⁵ floating point operations per second). The volume of numerical data processed exceeded 3 TB (1012 bytes) at each step of the computation, justifying the use of new techniques for writing (RAMSES code with adaptive mesh refinement) and reading the simulation data.

Cosmology: correcting the data from the Lyman-α forest

The simulation’s first result concerns the interpretation of large structures of the distant Universe: intergalactic hydrogen clouds. Astrophysicists detect these by measuring the absorption of light from quasars, which are extremely luminous due to the presence of a supermassive black hole that attracts matter in its accretion disk. Each of the clouds along the line of sight produces an ‘absorption line’ (Lyman-α) with a specific redshift, due to the expansion of the Universe. All these lines form a dense ‘forest’, revealing the one-dimensional distribution of the hydrogen clouds, and therefore of matter, at distances between 10 and 12 billion light-years (ly).

Figure 2. View of the Extreme-Horizon simulation showing a region of 50 Mpc square. The gas temperature is shown here (violet ~10^4K – yellow ~10^7K). The main galaxies appear as cold spots within vast haloes of hot gas. Credit: CAE

However, many black holes between these quasars and us expel a considerable amount of energy into the intergalactic medium, changing its thermal state and the properties of the Lyman-α forest. The physical model used in the Extreme-Horizon simulation describes in detail this feedback, which biases estimates of cosmological parameters by several percent. The correction factor calculated will be vital, particularly for the DESI (Dark Energy Spectroscopic Instrument) experiment under construction in Arizona (USA), because the bias can exceed 5%, whereas the target accuracy is 1%.

Ultra-compact massive galaxies formed like a ‘beehive’

The Extreme-Horizon simulation’s high resolution in low density regions meant that it was able to describe ‘cold’ gas accretion by galaxies and the formation of ultra-compact massive galaxies when the Universe was only 2 to 3 billion years old. These atypical galaxies, recently observed with the Alma (Atacama Large Millimeter/Submillimeter Array) radio telescope in Chile, are formed by the rapid clustering of many very small galaxies. It was only possible to identify this ‘beehive’ method of growth because of Extreme-Horizon’s exceptional resolution.

Figure 3. Mass-to-size ratio of the galaxies in the Extreme-Horizon simulation (blue) compared to the ratio for the same region of the Universe re-simulated at the normal resolution of cosmological simulations (red). Extreme-Horizon reproduces the mass-to-size ratio of the galaxies observed (black curve) and explains the presence of ultra-compact galaxies (under the dashed curve) observed in the primordial Universe, through improved resolution in the diffuse medium that feeds galaxy formation. Credit: CAE

Grand challenge on the Joliot-Curie supercomputer 

Designed by the company Atos for GENCI (the French high-performance computing centre), the Joliot-Curie supercomputer, based on Atos’s BullSequana architecture, reached a peak computing power of 22 petaflops in 2020.

Grand challenges are exceptional simulations and computations carried out during the ‘Grand Challenge’ period which follows the installation of a new computer partition. This three-month period provides a unique opportunity for a small number of users to access a large share of the machine’s resources. They benefit from the support of the TGCC’s and the manufacturer’s teams, working together to optimize the computer’s operation during this ‘startup’ phase.

Extreme-Horizon was run on the new AMD ROME computation partition of GENCI’s Joliot-Curie supercomputer, operated by teams of computer scientists from the CEA’s Military Applications Division (DAM) at the Very Large Computing Centre (TGCC at Bruyères-Le-Châtel). The simulation took fifty million computing hours and used new data reading and writing techniques to reduce the disk space used and accelerate data access. The work was done with the support of several institutes and divisions within the CEA and of Université Paris-Saclay’s High-Performance Computing and Simulation Laboratory

The project was run as a collaboration between CEA-Irfu, AIM (CEA, CNRS, Université de Paris), IAP (CNRS, Sorbonne Université) and LIHPC (Université Paris-Saclay, CEA-DAM).

References:

“Formation of compact galaxies in the Extreme-Horizon simulation” by S. Chabanier, F. Bournaud, Y. Dubois, S. Codis, D. Chapon, D. Elbaz, C. Pichon, O. Bressand, J. Devriendt, R. Gavazzi, K. Kraljic, T. Kimm10, C. Laigle, J.-B. Lekien, G. Martin, N. Palanque-Delabrouille, S. Peirani, P.-F. Piserchia, A. Slyz, M. Trebitsch and C. Yèche, 4 November 2020, Astronomy & Astrophysics.

DOI: 10.1051/0004-6361/202038614

“The impact of AGN feedback on the 1D power spectra from the Ly α forest using the Horizon-AGN suite of simulations” by Solène Chabanier, Frédéric Bournaud, Yohan Dubois, Nathalie Palanque-Delabrouille, Christophe Yèche, Eric Armengaud, Sébastien Peirani and Ricarda Beckmann, 7 May 2020, Monthly Notices of the Royal Astronomical Society. 

DOI: 10.1093/mnras/staa1242

 Source: SciTechDaily

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Neil Gehrels Swift Observatory Gamma-Ray Burst associated with Kilonovae: ambushing the Standard Candle in its own nest

Illustration 1: NASA's Swift spacecraft spots its thousandth gamma-ray burst
Credit: MASA.

Gamma-Ray Bursts (GRBs) are the most luminous and explosive transient phenomena in the Universe after the Big Bang, but they are still puzzling phenomena regarding their emission mechanism even after more than 50 years from their discovery. A powerful tool for characterizing and classifying GRBs to allow them to be used as tracers of the expansion history of the Universe and to understand their mysterious and debated physical mechanisms has been recently presented by an international team of researchers led by Dr. hab. Maria Dainotti, Assistant Professor at Jagiellonian University, Poland and concurrently serving as Senior Research Scientist at RIKEN and affiliate Research Scientist at Space Science Institute, in Boulder, Colorado.

The new article, which has been accepted by the Astrophysical Journal, pays particular attention to the GRBs associated with Kilonovae, and to a sample called the Platinum sample for which the maximum redshift observed is 5, much more distant than the maximum redshift at which the SNe Ia have been observed.

Astronomers can only directly measure distances to objects that are close to Earth and can extrapolate the distances to objects farther out. All the objects that serve as rungs on the cosmological distance ladder have known luminosities and are referred to as "standard candles". Once the absolute luminosity of the standard candle is known, the distance to that object can be calculated based on its measured brightness. For example, the light of the same standard candle will appear dimmer when it is farther away. GRBs are so powerful that in a few seconds they emit the equivalent of the energy emitted by the Sun during its entire lifetime. Thus, it is possible to observe GRBs at incredibly large distances (a.k.a., high redshift), much further than standard candles like Ia-type supernovae (SNe Ia) that are observed at up to 11 billion light years. Using GRBs as a new type of standard candle will allow astronomers to study and comprehend cosmological issues that could change current models regarding the Universe's history and its evolution.

Despite decades of observations, a comprehensive model able to explain the underlying physical mechanisms and properties of these objects has not been reached yet. Many possible physical origins for GRBs have been proposed, like the explosion of an extremely massive star (the long duration GRBs) or the merging of two compact objects (the short duration GRBs). Many models about the progenitor responsible of powering GRBs have been proposed as well, such as a black hole, a neutron star (NS) or a rapidly rotating newly born NS with a high magnetific field (magnetar).

Kilonovae (in short: KNe) are astrophysical objects linked to short duration gamma-ray bursts, which are the result of explosions occuring after two very dense objects (for exampe, two neutron stars) merge together. The detection of X-ray emission at a location coincident with the given Kilonovae can also provide the missing observational link between short duration GRBs and gravitational wavesproduced by ssuch stellar mergers. The first detection of the Kilonovae associated with both gravitational waves emission and such a short GRB, namely GRB 170817, has opened a new era of observations and theoretical investigation. The missing piece to this long-standing story is the connection of KNe and the GRB observational correlations that Dainotti et al. now provide. 

Figure 2: The LX-T*X-Lpeak relation for the SGRB (short duration GRB) sample with separated KN-SGRB cases. We note here that all the KN-SGRBs (marked in yellow) fall below the best fitting plane. Credit: The Authors.

Even when all the GRBs are observed with the same satellite, in this case the NASA's Neil Gehrels Swift Observatory, the GRBs' features are seen to vary very widely over several orders of magnitude. This applies not only to the prompt emission (the main event in the gamma rays), but also to the extended afterglow phase (which follows the prompt emission and is seen over a wide range of wavelengths). Thus, the key point of the article by Dainotti et al., is the hunt for features which remain invariant according to peculiar classes of GRBs. 

Figure 3: Histograms of the distance from the Short Duration Plane for KN-SGRBs and SGRBs, considering the correction for selection biases and evolutionary effects. Credit: The Authors.

The team has found a 3-D correlation, i.e. a link between the following three variables that identifies a plane: duration of the X-ray plateau phase, its luminosity, and the luminosity of the peak prompt gamma ray feature. The distances of GRBs from a given class's plane allowed the authors to determine if GRBs belong to that particular class by showing different features related to this 3-D correlation. The Dainotti et al. study has also shown that although the GRBs-KNe events are a subsample of the larger class of short duration GRBs (red cuboids), they show some observational peculiarities: indeed, they all lie below the short fundamental plane as shown in Figure 2 (yellow truncated icosahedrons). In this analysis, selection biases and evolutionary effects (namely, how the variables change with distance or redshift) have been accounted for, and after correction for selection bias the 3D correlation for GRB-KNe is still tight together with the platinum sample, the tightest sample for the 3D correlation where only well-sampled determined features are taken into account. Thus, both the platinum and the GRBs-KNe plane seems to be the excellent tools for further cosmological studies.

In fact, the GRBs-KNe plane has the smallest observed distance from its plane, called the intrinsic scatter. Here this scatter is 29% smaller than a previous analysis, see Fig. 2, object of a NASA press in 2016, lead by Dr. Dainotti. We note that this finding has been reached in a natural way without assuming any observational criteria, as had been done in Dainotti et al. previous studies. This new result is thus a step much further ahead than previous analyses.

In addition, the separated KNe plane itself still has a very small distance from the 3D plane related to the KNe when evolution is accounted for, see Fig. 3. The smaller the distance is from the plane, the more useful the plane is to be used as a cosmological tool.

A great advantage of using the GRBs associated with Kilonovae is that the GRB-KNe events have a clearer physical emission process compared to other observational GRB classes. Thus, the leap forward in this study is that this sample has a physical grounding related to the fundamental plane relation regardless of the features of the plateau phase which can vary widely from one GRB to another.

Original publication: 

 

Prof. Maria Giovanna Dainotti, Aleksander Lenart, Giuseppe Sarracino, Shigehiro Nagataki, Salvatore Capozziello, Nissim Fraija; The X-ray fundamental plane of the Platinum Sample, the Kilonovae and the SNe Ib/c associated with GRBs, ApJ 2020 (DOI: 10.3847/1538-4357/abbe8a).

The research was conducted at the Department of High Energy Astrophysics of the Jagiellonian University’s Astronomical Observatory (OA UJ).

Contact:

Maria Giovanna Dainotti
Astronomical Observatory
Jagiellonian
M.Dainotti@oa.uj.edu.pl

 

Source: Astronomical Observatory of the Jagiellonian University

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A hint of new physics in polarized radiation from the early Universe

Figure: As the light of the cosmic microwave background emitted 13.8 billion years ago (left image) travels through the Universe until observed on Earth (right image), the direction in which the electromagnetic wave oscillates (orange line) is rotated by an angle β. The rotation could be caused by dark matter or dark energy interacting with the light of the cosmic microwave background, which changes the patterns of polarization (black lines inside the images). The red and blue regions in the images show hot and cold regions of the cosmic microwave background, respectively. (Credit: Y. Minami / KEK). Hi-res image

Using Planck data from the cosmic microwave background radiation, an international team of researchers has observed a hint of new physics. The team developed a new method to measure the polarization angle of the ancient light by calibrating it with dust emission from our own Milky Way. While the signal is not detected with enough precision to draw definite conclusions, it may suggest that dark matter or dark energy causes a violation of the so-called “parity symmetry.” 

The laws of physics governing the Universe are thought not to change when flipped around in a mirror. For example, electromagnetism works the same regardless of whether you are in the original system, or in a mirrored system in which all spatial coordinates have been flipped. If this symmetry, called “parity,” is violated, it may hold the key to understanding the elusive nature of dark matter and dark energy, which occupy 25 and 70 percent of the energy budget of the Universe today, respectively. While both dark, these two components have opposite effects on the evolution of the Universe: dark matter attracts, while dark energy causes the Universe to expand ever faster. 

A new study, including researchers from the Institute of Particle and Nuclear Studies (IPNS) at the High Energy Accelerator Research Organization (KEK), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) of the University of Tokyo, and the Max Planck Institute for Astrophysics (MPA), reports on a tantalizing hint of new physics—with 99.2 percent confidence level —which violates parity symmetry. Their findings were published in the journal Physical Review Letters on November 23, 2020; the paper was selected as the “Editors’ Suggestion,” judged by editors of the journal to be important, interesting, and well written.

The hint to a violation of parity symmetry was found in the cosmic microwave background radiation, the remnant light of the Big Bang. The key is the polarized light of the cosmic microwave background. Light is a propagating electromagnetic wave. When it consists of waves oscillating in a preferred direction, physicists call it “polarized.” The polarization arises when the light is scattered. Sunlight, for instance, consists of waves with all possible oscillating directions; thus, it is not polarized. The light of a rainbow, meanwhile, is polarized because the sunlight is scattered by water droplets in the atmosphere. Similarly, the light of the cosmic microwave background initially became polarized when scattered by electrons 400,000 years after the Big Bang. As this light traveled through the Universe for 13.8 billion years, the interaction of the cosmic microwave background with dark matter or dark energy could cause the plane of polarization to rotate by an angle β (Figure).

“If dark matter or dark energy interact with the light of the cosmic microwave background in a way that violates parity symmetry, we can find its signature in the polarization data,” points out Yuto Minami, a postdoctoral fellow at IPNS, KEK.

To measure the rotation angle β, the scientists needed polarization-sensitive detectors, such as those onboard the Planck satellite of the European Space Agency (ESA). And they needed to know how the polarization-sensitive detectors are oriented relative to the sky. If this information was not known with sufficient precision, the measured polarization plane would appear to be rotated artificially, creating a false signal. In the past, uncertainties over the artificial rotation introduced by the detectors themselves limited the measurement accuracy of the cosmic polarization angle β. 

“We developed a new method to determine the artificial rotation using the polarized light emitted by dust in our Milky Way,” said Minami. “With this method, we have achieved a precision that is twice that of the previous work, and are finally able to measure β.” The distance traveled by the light from dust within the Milky Way is much shorter than that of the cosmic microwave background. This means that the dust emission is not affected by dark matter or dark energy, i.e. β is present only in the light of the cosmic microwave background, while the artificial rotation affects both. The difference in the measured polarization angle between both sources of light can thus be used to measure β.

The research team applied the new method to measure β from the polarization data taken by the Planck satellite. They found a hint for violation of parity symmetry with 99.2 percent confidence level. To claim a discovery of new physics, much greater statistical significance, or a confidence level of 99.99995 percent, is required. Eiichiro Komatsu, director at the MPA and Principal Investigator at the Kavli IPMU, said: “It is clear that we have not found definitive evidence for new physics yet; higher statistical significance is needed to confirm this signal. But we are excited because our new method finally allowed us to make this ‘impossible’ measurement, which may point to new physics.”

To confirm this signal, the new method can be applied to any of the existing— and future—experiments measuring polarization of the cosmic microwave background, such as Simons Array and LiteBIRD, in which both KEK and the Kavli IPMU are involved.

Source: Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)

Paper details:

Journal: Physical Review Letters
Title: New extraction of the cosmic birefringence from the Planck 2018 polarization data

Authors: Yuto Minami (1), Eiichiro Komatsu (2,3)
Author affiliation:
1. High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan

2. Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), University of Tokyo, Chiba 277-8582, Japan

3. Max-Planck-Institut für Astrophysik, Karl-Schwarzschild Str. 1, 85741 Garching, Germany 

DOI: https://link.aps.org/doi/10.1103/PhysRevLett.125.221301 (November 23, 2020)
Abstract of the paper (Physical Review Letters page)

Research contact: 

Yuto Minami
Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK, Japan)
Postdoctoral Fellow
E-mail: yminami@post.kek.jp

Eiichiro Komatsu 
Kavli Institute for the Physics and Mathematics of the Universe,The University of Tokyo
Principal Investigator
Max Planck Institute for Astrophysics
Director of the Department of Physical Cosmology
E-mail: komatsu@mpa-garching.mpg.de
Tel: + 49-89-30000-2208

Media contact:

Hajime Hikino
PR office, High Energy Accelerator Research Organization (KEK, Japan)
E-mail: press@kek.jp
TEL: +81-29-879-6047

Hiroko Tada
PR office, Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK, Japan)
E-mail: htada@post.kek.jp
Tel: +81-29-864-5638

John Amari
Press officer 
Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
E-mail: press@ipmu.jp
Tel: 080-4056-2767 

Hannelore Hämmerle 
Press Officer 
Max Planck Institute for Astrophysics
E-mail: pr@mpa-garching.mpg.de 
Tel: +49-89-30000-3980

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VLA Sky Survey Reveals Newborn Jets in Distant Galaxies

Artist's conception of a galaxy with an active nucleus propelling jets of material outward from the galaxy's center.
Credit: Sophia Dagnello, NRAO/AUI/NSF.  Hi-Res File

VLA images of three galaxies in the new study, comparing what was seen in the earlier FIRST survey and the later VLASS. The newly-appearing bright radio emission indicates that the galaxies launched new jets of material sometime between the dates of the two observations. Credit: Nyland et al.; Sophia Dagnello, NRAO/AUI/NSF.Hi-Res File

Animation comparing images as seen by two VLA surveys, years apart. The newly-appearing radio emission indicates the galaxies launched new jets of material sometime between the two observations. Credit: Nyland et al.; Sophia Dagnello, NRAO/AUI/NSF.Hi-Res File

Astronomers using data from the ongoing VLA Sky Survey (VLASS) have found a number of distant galaxies with supermassive black holes at their cores that have launched powerful, radio-emitting jets of material within the past two decades or so. The scientists compared data from VLASS with data from an earlier survey that also used the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) to reach their conclusion.

“We found galaxies that showed no evidence of jets before but now show clear indications of having young, compact jets,” said Dr. Kristina Nyland, who is an NRC postdoctoral fellow in residence at the Naval Research Laboratory.

“Jets like these can strongly affect the growth and evolution of their galaxies, but we still don’t understand all of the details. Catching newborn jets with surveys like VLASS provides a measure of the role of powerful radio jets in shaping the lives of the galaxies over billions of years,” Nyland said.

VLASS is a project that will survey the sky visible from the VLA — about 80 percent of the entire sky — three times over seven years. The observations began in 2017 and the first of the three scans now is complete. Nyland and her colleagues compared data from this scan with data from the FIRST survey that used the VLA to observe a smaller portion of the sky between 1993 and 2011.

They found about 2,000 objects that appear in the VLASS images, but were not detected in the earlier FIRST survey. From these, they selected 26 objects that previously were categorized as galaxies with active nuclei — powered by supermassive black holes — by optical and infrared observations. The FIRST observations of the 26 objects had been made between 1994 and 2001. The VLASS observations were made in 2019. The intervals between observations of the objects thus ranged from 18 to 25 years.

They chose 14 of these galaxies for more detailed observations with the VLA. These observations provided higher-resolution images and also were done at multiple radio frequencies to get a more complete understanding of the objects’ characteristics.

“The data from these detailed observations tell us that the most likely cause of the difference in radio brightness between the FIRST and the VLASS observations is that the ‘engines’ at the cores of these galaxies have launched new jets since the FIRST observations were made,” explained Dillon Dong, from Caltech.

The black holes at the cores of galaxies are known to interact with the galaxies themselves, and the two evolve together. The jets launched from the regions near the black holes can affect the amount of star formation within the galaxy.

“Radio jets provide natural laboratories for learning about the extreme physics of supermassive black holes, whose formation and growth are believed to be intrinsically linked to that of the galaxy centers in which they reside,” said Pallavi Patil, of the University of Virginia.

“Jets as young as the ones discovered in our study can provide us with a rare opportunity to gain new insights on how these interactions between the jets and their surroundings work,” Nyland said.

“VLASS has proven to be a key tool for discovering such jets, and we eagerly await the results of its next two observing epochs,” said Mark Lacy, of the National Radio Astronomy Observatory.

Nyland and her colleagues plan further studies of the galaxies using the Very Long Baseline Array (VLBA), the Chandra X-Ray Observatory, and visible-light and infrared telescopes. They are reporting their results in the Astrophysical Journal.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Media Contact:

Dave Finley, Public Information Officer
(575) 835-7302
dfinley@nrao.edu

Source:  National Radio Astronomy Observatory (NRAO)/News

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A planet-forming disk still fed by the mother cloud

This false-colour image shows the filaments of accretion around the protostar [BHB2007] 1. The large structures are inflows of molecular gas (CO) nurturing the disk surrounding the protostar. The inset shows the dust emission from the disk, which is seen edge-on. The "holes" in the dust map represent an enormous ringed cavity seen (sideways) in the disk structure. © MPE 

Two different observations of the protoplanetary disk show signatures of the formation of a companion to the protostar . The grey scale represents the dust thermal emission from the disk, same as in the inset of Fig. 1. The red/blue contours show the molecular CO brightness emission levels from the northern/southern side of the dust cavity observed with ALMA. The brighter CO emission from the south indicates that the gas is hotter there. This location coincides with a zone of non-thermal emission tracing ionised gas (green contours) observed with the VLA (middle), which is observed in addition to the protostar (centre of the image). The team proposes that both the ionised gas and the hot molecular gas are due to the presence of a protoplanet or a brown dwarf in the cavity. The configuration of such a system is shown in the sketch on the right. © MPE; illustration: Gabriel A. P. Franco 

Stellar systems like our own form inside interstellar clouds of gas and dust that collapse producing young stars surrounded by protoplanetary disks. Planets form within these protoplanetary disks, leaving clear gaps, which have been recently observed in evolved systems, at the time when the mother cloud has been cleared out. ALMA has now revealed an evolved protoplanetary disk with a large gap still being fed by the surrounding cloud via large accretion filaments. This shows that accretion of material onto the protoplanetary disk is continuing for times longer than previously thought, affecting the evolution of the future planetary system.

A team of astronomers led by Dr. Felipe Alves from the Center for Astrochemical Studies (CAS) at the Max Planck Institute for Extraterrestrial Physics (MPE) used the Atacama Large Millimeter/submillimeter Array (ALMA) to study the accretion process in the stellar object [BHB2007] 1, a system located at the tip of the Pipe Molecular Cloud. The ALMA data reveal a disk of dust and gas around the protostar, and large filaments of gas around this disk. The scientists interpret these filaments as accretion streamers feeding the disk with material extracted from the ambient cloud. The disk reprocesses the accreted material, delivering it to the protostar. The structure observed is very unusual for stellar objects at this stage of evolution — with an estimated age of 1,000,000 years — when circumstellar disks are already formed and matured for planet formation. “We were quite surprised to observe such prominent accretion filaments falling into the disk”, said Alves. “The accretion filament activity demonstrates that the disk is still growing while simultaneously nurturing the protostar.”

The team also reports the presence of an enormous cavity within the disk. The cavity has a width of 70 astronomical units, and it encompasses a compact zone of hot molecular gas. In addition, supplementary data at radio frequencies by the Very Large Array (VLA) point to the existence of non-thermal emission in the same spot where the hot gas was detected. These two lines of evidence indicate that a substellar object — a young giant planet or brown dwarf — is present within the cavity. As this companion accretes material from the disk, it heats up the gas and possibly powers strong ionized winds and/or jets. The team estimates that an object with a mass between 4 and 70 Jupiter masses is needed to produce the observed gap in the disk.

“We present a new case of star and planet formation happening in tandem,” states Paola Caselli, director at MPE and head of the CAS group. “Our observations strongly indicate that protoplanetary disks keep accreting material also after planet formation has started. This is important because the fresh material falling onto the disk will affect both the chemical composition of the future planetary system and the dynamical evolution of the whole disk.” These observations also put new time constraints for planet formation and disk evolution, shedding light on how stellar systems like our own are sculpted from the original cloud.

 Source:  Max Planck Institute for Extraterrestrial Physics

Contacts

Dr. Felipe De Oliveira Alves
postdoc
+49 (0)89 30000-3897
0049(0)17637101004
+49 (0)89 30000-3950

Prof. Dr. Paola Caselli
acting director
+49 (0)89 30000-3400
+49 (0)89 30000-3399

Original publication

1. Felipe O. Alves, L. Ilsedore Cleeves, Josep M. Girart, Zhaohuan Zhu, Gabriel A. P. Franco, Alice Zurlo and Paola Caselli

A case of simultaneous star and planet formation
Astrophysical Journal Letters, 904 L6
DOI

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16-year-old Cosmic Mystery Solved, Revealing Stellar Missing Link

The blue ring nebula consists of two expanding cones of gas ejected into space by a stellar merger. as the gas cools, it forms hydrogen molecules that collide with particles in interstellar space, causing them to radiate far-ultraviolet light. invisible to the human eye, it is shown here as blue. Credit: NASA/JPL-Caltech/M. Seibert (Carnegie Institution for Science)/K. Hoadley (Caltech)/GALEX Team

The Blue Ring Nebula consists of two hollow, cone-shaped clouds of debris moving in opposite directions away from the central star. The base of one cone is traveling almost directly toward Earth. As a result, astronomers looking at the nebula see two circles that partially overlap. Credit: Mark Seibert

The Blue Ring Nebula, which perplexed scientists for over a decade, appears to be the youngest known example of two stars merged into one

Maunakea, Hawaii – In 2004, scientists with NASA’s space-based Galaxy Evolution Explorer (GALEX) spotted an object unlike any they’d seen before in our Milky Way galaxy: a large, faint blob of gas with a star at its center. Though it doesn’t actually emit light visible to the human eye, GALEX captured the blob in ultraviolet (UV) light and thus appeared blue in the images; subsequent observations also revealed a thick ring structure within it. So the team nicknamed it the Blue Ring Nebula. Over the next 16 years, they studied it with multiple Earth- and space-based telescopes, including W. M. Keck Observatory on Maunakea in Hawaii, but the more they learned, the more mysterious it seemed.

A new study published online on Nov. 18 in the journal Nature may have cracked the case. By applying cutting-edge theoretical models to the slew of data that has been collected on this object, the authors posit the nebula – a cloud of gas in space – is likely composed of debris from two stars that collided and merged into a single star.

While merged star systems are thought to be fairly common, they are nearly impossible to study immediately after they form because they’re obscured by debris kicked up by the collision. Once the debris has cleared – at least hundreds of thousands of years later – they’re challenging to identify because they resemble non-merged stars. The Blue Ring Nebula appears to be the missing link: astronomers are seeing the star system only a few thousand years after the merger, when evidence of the union is still plentiful. It appears to be the first known example of a merged star system at this stage.

Operated between 2003 and 2013 and managed by NASA’s Jet Propulsion Laboratory in Southern California, GALEX was designed to help study the history of star formation by observing young star populations in UV light. Most objects seen by GALEX radiated both near-UV (represented as yellow in GALEX images) and far-UV (represented as blue), but the Blue Ring Nebula stood out because it emitted only far-UV light.

The object’s size was similar to that of a supernova remnant, which forms when a massive star runs out of fuel and explodes, or a planetary nebula, the puffed-up remains of a star the size of our Sun. But the Blue Ring Nebula had a living star at its center. Furthermore, supernova remnants and planetary nebulas radiate in multiple light wavelengths outside the UV range, whereas the Blue Ring Nebula did not.

Phanton Planet

In 2006, the GALEX team looked at the nebula with the 5.1-meter Hale telescope at the Palomar Observatory in San Diego County, California, and then with the even more powerful 10-meter Keck Observatory telescopes. They found evidence of a shockwave in the nebula using Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS), suggesting the gas composing the Blue Ring Nebula had indeed been expelled by some kind of violent event around the central star.

“Keck’s LRIS spectra of the shock front was invaluable for nailing down how the Blue Ring Nebula came to be,” said Keri Hoadley, an astrophysicist at Caltech and lead author of the study. “Its velocity was moving too fast for a typical planetary nebula yet too slow to be a supernova. This unusual, in-between speed gave us a strong clue that something else must have happened to create the nebula.”

Data from Keck Observatory’s High-Resolution Echelle Spectrometer (HIRES) also suggested the star was pulling a large amount of material onto its surface. But where was the material coming from?

“The HIRES observations at Keck gave us the first evidence that the system was accreting material,” said co-author Mark Seibert, an astrophysicist with the Carnegie Institution for Science and a member of the GALEX team at Caltech, which manages JPL. “For quite a long time we thought that maybe there was a planet several times the mass of Jupiter being torn apart by the star, and that was throwing all that gas out of the system. Though the HIRES data appeared to support this theory, it also told us to be wary of that interpretation, suggesting the accretion may have something to do with motions in the atmosphere of the central star.”

To gather more data, in 2012, the GALEX team used NASA’s Wide-field Infrared Survey Explorer (WISE), a space telescope that studied the sky in infrared light, and identified a disk of dust orbiting closely around the star. Archival data from three other infrared observatories also spotted the disk. The finding didn’t rule out the possibility that a planet was also orbiting the star, but eventually the team would show that the disk and the material expelled into space came from something larger than even a giant planet. Then in 2017, the Hobby-Eberly Telescope in Texas confirmed there was no compact object orbiting the star.

More than a decade after discovering the Blue Ring Nebula, the team had gathered data on the system from four space telescopes, four ground-based telescopes, historical observations of the star going back to 1895 (in order to look for changes in its brightness over time), and the help of citizen scientists through the American Association of Variable Star Observers (AAVSO). But an explanation for what had created the nebula still eluded them.

Stellar Sleuthing

When Hoadley began working with the GALEX science team in 2017, “the group had kind of hit a wall” with the Blue Ring Nebula, she said. But Hoadley was fascinated by the thus-far unexplainable object and its bizarre features, so she accepted the challenge of trying to solve the mystery. It seemed likely that the solution would not come from more observations of the system, but from cutting-edge theories that could make sense of the existing data. So Chris Martin, principal investigator for GALEX at Caltech, reached out to Brian Metzger of Columbia University for help.

As a theoretical astrophysicist, Metzger makes mathematical and computational models of cosmic phenomena, which can be used to predict how those phenomena will look and behave. He specializes in cosmic mergers – collisions between a variety of objects, whether they be planets and stars or two black holes.

“It wasn’t just that Brian could explain the data we were seeing; he was essentially predicting what we had observed before he saw it,” said Hoadley. “He’d say, ‘If this is a stellar merger, then you should see X,’ and it was like, ‘Yes! We see that!'”

The team concluded the nebula was the product of a relatively fresh stellar merger that likely occurred between a star similar to our Sun and another only about one tenth that size (or about 100 times the mass of Jupiter). Nearing the end of its life, the Sun-like star began to swell, creeping closer to its companion. Eventually, the smaller star fell into a downward spiral toward its larger companion. Along the way, the larger star tore the smaller star apart, wrapping itself in a ring of debris before swallowing the smaller star entirely.

This was the violent event that led to the formation of the Blue Ring Nebula. The merger launched a cloud of hot debris into space that was sliced in two by the gas disk. This created two cone-shaped debris clouds, their bases moving away from the star in opposite directions and getting wider as they travel outward. The base of one cone is coming almost directly toward Earth and the other almost directly away. They are too faint to see alone, but the area where the cones overlap (as seen from Earth) forms the central blue ring GALEX observed.

Millennia passed, and the expanding debris cloud cooled and formed molecules and dust, including hydrogen molecules that collided with the interstellar medium, the sparse collection of atoms and energetic particles that fill the space between stars. The collisions excited the hydrogen molecules, causing them to radiate in a specific wavelength of far-UV light. Over time, the glow bec

Geometry of the Blue Ring Nebula (Animation) from Keck Observatory on Vimeo.

The Blue Ring Nebula consists of two expanding cones of debris. The base of one cone is moving toward Earth. Both bases are outlined in magenta, revealing shockwaves created as the debris races through space. Blue represents material behind the shockwave and is visible only where the cones overlap. Credit: NASA/JPL-Caltech/R. Hurt

 Source: W.M. Keck Observatory

 

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Stellar mergers may occur as often as once every 10 years in our Milky Way galaxy, meaning it’s possible that a sizeable population of the stars we see in the sky were once two.

“We see plenty of two-star systems that might merge someday, and we think we’ve identified stars that merged maybe millions of years ago. But we have almost no data on what happens in between,” said Metzger. “We think there are probably plenty of young remnants of stellar mergers in our galaxy, and the Blue Ring Nebula might show us what they look like so we can identify more of them.”

Though this is likely the conclusion of a 16-year-old mystery, it may also be the beginning of a new chapter in the study of stellar mergers.

“It’s amazing that GALEX was able to find this really faint object that we weren’t looking for but that turns out to be something really interesting to astronomers,” said Seibert. “It just reiterates that when you look at the universe in a new wavelength or in a new way, you find things you never imagined you would.”

We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research.

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About LRIS

The Low Resolution Imaging Spectrometer (LRIS) is a very versatile visible-wavelength imaging and spectroscopy instrument commissioned in 1993 and operating at the Cassegrain focus of Keck I. Since it has been commissioned it has seen two major upgrades to further enhance its capabilities: addition of a second, blue arm optimized for shorter wavelengths of light; and the installation of detectors that are much more sensitive at the longest (red)wavelengths. Each arm is optimized for the wavelengths it covers. This large range of wavelength coverage, combined with the instrument’s high sensitivity, allows the study of everything from comets (which have interesting features in the ultraviolet part of the spectrum), to the blue light from star formation, to the red light of very distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in2011 for research determining that the universe was speeding up in its expansion.

 

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About HIRES

The High-Resolution Echelle Spectrometer (HIRES) produces spectra of single objects at very high spectral resolution yet covering a wide wavelength range. It does this by separating the light into many “stripes” of spectra stacked across a mosaic of three large CCD detectors. HIRES is famous for finding exoplanets. Astronomers also use HIRES to study important astrophysical phenomena like distant galaxies and quasars and find cosmological clues about the structure of the early universe, just after the Big Bang.

 

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About W.M.Keck Observatori

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes near the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

 

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Cosmic Cinnamon Bun

UGC 12588
Credit: ESA/Hubble & NASA, R. Tully
Acknowledgement: Gagandeep Anand

Observed with the NASA/ESA Hubble Space Telescope, the faint galaxy featured in this image is known as UGC 12588. Unlike many spiral galaxies, UGC 12588 displays neither a bar of stars across its centre nor the classic prominent spiral arm pattern. Instead, to a viewer, its circular, white and mostly unstructured centre makes this galaxy more reminiscent of a cinnamon bun than a mega-structure of stars and gas in space.

Lying in the constellation of Andromeda in the Northern hemisphere, this galaxy is classified as a spiral galaxy. Unlike the classic image of a spiral galaxy, however, the huge arms of stars and gas in UGC 12588 are very faint, undistinguished, and tightly wound around its centre. The clearest view of the spiral arms comes from the bluer stars sprinkled around the edges of the galaxy that highlight the regions where new star formation is most likely taking place.

Source: ESA/Hubble/Potw

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Contorting Giants

SDSS J090122.37+181432.3
Credit: ESA/Hubble & NASA, S. Allam et al.

This NASA/ESA Hubble Space Telescope image features the galaxy LRG-3-817, also known as SDSS J090122.37+181432.3. The galaxy, its image distorted by the effects of gravitational lensing, appears as a long arc to the left of the central galaxy cluster.

Gravitational lensing occurs when a large distribution of matter, such as a galaxy cluster, sits between Earth and a distant light source. As space is warped by massive objects, the light from the distant object bends as it travels to us and we see a distorted image of it. This effect was first predicted by Einstein’s general theory of relativity.

Strong gravitational lenses provide an opportunity for studying properties of distant galaxies, since Hubble can resolve details within the multiple arcs that are one of the main results of gravitational lensing. An important consequence of lensing distortion is magnification, allowing us to observe objects that would otherwise be too far away and too faint to be seen. Hubble makes use of this magnification effect to study objects beyond the sensitivity of its 2.4-metre-diameter primary mirror, showing us the most distant galaxies humanity has ever encountered.

This lensed galaxy was found as part of the Sloan Bright Arcs Survey, which discovered some of the brightest gravitationally lensed high-redshift galaxies in the night sky. 

Source: ESA/Hubble/News/Potw

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Astronomers Discover New “Fossil Galaxy” Buried Deep Within the Milky Way

An artist’s impression of what the Milky Way might look like seen from above. The colored rings show the rough extent of the fossil galaxy known as Heracles. The yellow dot shows the position of the Sun. Image credit: Danny Horta-Darrington (Liverpool John Moores University), NASA/JPL-Caltech, and the SDSS 

An all-sky imageof the stars in the Milky Way as seen from Earth. The colored rings show the approximate extent of the stars that came from the fossil galaxy known as Heracles. The small objects to the lower right of the image are the Large and Small Magellanic Clouds, two small satellite galaxies of the Milky Way. Image credit: Danny Horta-Darrington (Liverpool John Moores University), ESA/Gaia, and the SDSS 

 

This movie shows a computer simulation of a galaxy like the Milky Way. The movie fast-forwards through simulated time from 13 billion years ago to today. The main galaxy grows as many small galaxies merge with it. Heracles resembles one of the smaller galaxies that merged with the Milky Way early in the process.  Credits: Video built by Ted Mackereth based on the EAGLE simulations. Download video (0:40, 25 MB)

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Scientists working with data from the Sloan Digital Sky Surveys’ Apache Point Observatory Galactic Evolution Experiment (APOGEE) have discovered a “fossil galaxy” hidden in the depths of our own Milky Way.

This result, published today in Monthly Notices of the Royal Astronomical Society, may shake up our understanding of how the Milky Way grew into the galaxy we see today.

The proposed fossil galaxy may have collided with the Milky Way ten billion years ago, when our galaxy was still in its infancy. Astronomers named it Heracles, after the ancient Greek hero who received the gift of immortality when the Milky Way was created.

The remnants of Heracles account for about one third of the Milky Way’s spherical halo. But if stars and gas from Heracles make up such a large percentage of the galactic halo, why didn’t we see it before? The answer lies in its location deep inside the Milky Way.

“To find a fossil galaxy like this one, we had to look at the detailed chemical makeup and motions of tens of thousands of stars,” says Ricardo Schiavon from Liverpool John Moores University (LJMU) in the UK, a key member of the research team. “That is especially hard to do for stars in the center of the Milky Way, because they are hidden from view by clouds of interstellar dust. APOGEE lets us pierce through that dust and see deeper into the heart of the Milky Way than ever before.”

APOGEE does this by taking spectra of stars in near-infrared light, instead of visible light, which gets obscured by dust. Over its ten-year observational life, APOGEE has measured spectra for more than half a million stars all across the Milky Way, including its previously dust-obscured core.

Graduate student Danny Horta from LJMU, the lead author of the paper announcing the result, explains, “examining such a large number of stars is necessary to find unusual stars in the densely-populated heart of the Milky Way, which is like finding needles in a haystack.”

To separate stars belonging to Heracles from those of the original Milky Way, the team made use of both chemical compositions and velocities of stars measured by the APOGEE instrument.

“Of the tens of thousands of stars we looked at, a few hundred had strikingly different chemical compositions and velocities,” Horta said. “These stars are so different that they could only have come from another galaxy. By studying them in detail, we could trace out the precise location and history of this fossil galaxy.”

Because galaxies are built through mergers of smaller galaxies across time, the remnants of older galaxies are often spotted in the outer halo of the Milky Way, a huge but very sparse cloud of stars enveloping the main galaxy. But since our Galaxy built up from the inside out, finding the earliest mergers requires looking at the most central parts of the Milky Way’s halo, which are buried deep within the disc and bulge.

Stars originally belonging to Heracles account for roughly one third of the mass of the entire Milky Way halo today – meaning that this newly-discovered ancient collision must have been a major event in the history of our Galaxy. That suggests that our Galaxy may be unusual, since most similar massive spiral galaxies had much calmer early lives.

“As our cosmic home, the Milky Way is already special to us, but this ancient galaxy buried within makes it even more special,” Schiavon says.

Karen Masters, the Spokesperson for SDSS-IV comments, “APOGEE is one of the flagship surveys of the fourth phase of SDSS, and this result is an example of the amazing science that anyone can do, now that we have almost completed our ten-year mission.”

And this new age of discovery will not end with the completion of APOGEE observations. The fifth phase of the SDSS has already begun taking data, and its “Milky Way Mapper” will build on the success of APOGEE to measure spectra for ten times as many stars in all parts of the Milky Way, using near-infrared light, visible light, and sometimes both.

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About the Sloan Digital Sky Survey

Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is www.sdss.org.

SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, Center for Astrophysics | Harvard & Smithsonian (CfA), the Chilean Participation Group, the French Participation Group, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU) / University of Tokyo, the Korean Participation Group, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatories of China, New Mexico State University, New York University, University of Notre Dame, Observatório Nacional / MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autónoma de México, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University.

Contacts:

Ricardo Schiavon

Liverpool John Moores University
R.P.Schiavon@ljmu.ac.uk
+44 (0)151 231 2945
 

Daniel Horta-Darrington

Liverpool John Moores University
D.HortaDarrington@2018.ljmu.ac.uk
+44 (0)151 231 2923
 

Karen Masters

SDSS Scientific Spokesperson, Haverford College
klmasters@haverford.edu
+1-610-795-6066
Twitter: @KarenLMasters / @SDSSurveys
 

Jordan Raddick

SDSS Public Information Officer

Johns Hopkins University

raddick@jhu.edu

+1-443-570-7105
Twitter: @raddick

 

Source:  Sloan Digital Sky Survey (SDSS)/Press Releases

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