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Astronomy Object of the Month

Astronomy Object of the Month: ROGUE I: a catalogue of Radio sources associated with Optical Galaxies and having Unresolved or Extended morphologies

The mosaic presenting examples of morphological types of radio sources highlighted in the Rouge I catalog. Credit: Kozieł-Wierzbowska i in. How small and young radio sources evolve into large structures? Do all of them grow to large sizes? How the apparence of the radio source depends on the power of central nucleus, environment, and projection? How is the radio activity of active galactic nuclei (AGN) related to activity in other ranges of the electromagnetic spectrum? To answer all these and many other questions large catalogues of properly identified and classified radio sources are needed. Such information is now provided by the ROGUE I catalogue, produced and published by female researchers from the Astronomical Observatory of the Jagiellonian University.

In the era of high-sensitivity and high-resolution radio surveys, the classification of radio emission from extragalactic sources is not always an easy task. In this regard, some radio sources can be real rogues.

 

Illustration 1: The mosaic presenting examples of morphological types of radio sources highlighted in the Rouge I catalog. Credit: Kozieł-Wierzbowska i in.

Radio emission from extragalactic radio sources can have many different shapes. In the map of a classical radio source a careful observer can distinguish a compact radio core, located at the position of the host galaxy, narrow jets terminating in hot spots and accompanied with the diffused radio lobes ( Faranoff-Riley type II), or spreading out in a form of plumes (Faranoff-Riley type I). However, radio sources with such classical morphologies represent only a fraction of the whole population. In some sources the jets start to bend at a small distance from the core forming a horseshoe-shape structure (wide-angle and narrow-angle tail sources). In others, we see two pairs of lobes inclined with respect to each other and forming an X-shaped structure. However, many times the radio structures have so complicated shapes that it is very difficult to say if they correspond to one source, or to two sources projected one on top of the other.

Nevertheless not only a classification of the radio structure is important, but also an identification with its host galaxy in optical/IR images. Such an identification allows one to determine the distance and measure basic astrophysical parameters like luminosity or size.

The first part of the ROGUE catalogue produced by a team of researchers from the Astronomical Observatory of the Jagiellonian University contains radio sources identified with galaxies that have high quality spectra in the Sloan Digital Sky Survey (SDSS). The search was conducted using 1.4 GHz radio data obtained with different resolutions and sensitivities (NVSS and FIRST radio surveys). This enabled the proper recognition of both extended radio lobes, as well as the compact cores. For the 32,616 ROGUE I radio sources positions, magnitudes, redshifts, and morphologies of the optical host, as well as the morphologies and luminosities of the radio structure have been listed. This makes the ROGUE I catalogue the largest of its kind.

The statistics of the sources in the ROGUE I catalogue show that the majority of the radio sources detected in large surveys have compact morphologies (90%) and only a small fraction develop large radio structures. Among extended radio sources, classical morphologies are the most numerous (~50%), and a significant number of giant (size larger than 0.7 Mpc), X-shaped, Z-shaped, and double-double radio sources were discovered. The majority of the radio sources in ROGUE I catalogue have early-type, mainly elliptical host galaxies. In the catalogue star-forming (SF) galaxies are also present, and a method how to distinguish radio AGN from a radio SF is proposed in a separate paper (Kozieł-Wierzbowska et al. 2021).

Manual identification and classification is very laborious and time-consuming. For future catalogues based on deeper surveys (like LOFAR or SKA) such a work will not be possible, unless it becomes a citizen science project where thousands of persons participate. The ROGUE catalogue can serve as a training set for a citizen science project or for an automatic classification.

Contact

Dr Dorota Kozieł-Wierzbowska

Astronomical Observatory
Jagiellonian University

Eddie [at] uj.edu.pl

Dr Natalia Żywucka-Hejzner

Centre for Space Research
North-West University

N.Zywucka [at] oa.uj.edu.pl

Original publication

Kozieł-Wierzbowska, D., Goyal, A. and Żywucka, N., Radio Sources Associated with Optical Galaxies and Having Unresolved or Extended Morphologies (ROGUE). I. A Catalog of SDSS Galaxies with FIRST Core Identifications, 2020, The Astrophysical Journal Supplement Series, 247, 28.

Project Website

The research was conducted at the Department of Stellar and Extragalactic Astronomy and Department of High Energy Astrophysics of the Jagiellonian University’s Astronomical Observatory (OAUJ). The work was financed by the NCN grants 2016/21/B/ST9/01620, 2018/29/B/ST9/02298 and DEC-2014/15/N/ST9/05171.

Astronomy Object of the Month: Ionized Iron Line in Radio Galaxy CGCG 292–057

Illustration: The 0.5–7.0 keV merged Chandra image of the entire structure of Pictor A, smoothed with 3σ Gaussian radius, with the 1.45 GHz VLA total and polarized intensity (3σ) contours superimposed (red and white, respectively). The two elongated yellow rectangles denote the areas across the high-polarization regions of the Eastern lobe, for which the team extracted the surface brightness profiles at X-ray and radio frequencies. Image credit: The Authors. Active Galactic Nuclei are Supermassive Black Holes residing in the centres of massive galaxies and accreting material at higher rates. Astronomers classify galaxies of three types: spirals, ellipticals and irregulars. If elliptical (early-type) galaxies and spiral or irregular (late-type) galaxies merge with one another, it may result in an X-shaped galaxy which is luminous in radio wavelengths.

There is presence of ionized atoms in the centre of CGCG 292-057. At the nucleus of the galaxy, there is a nuclear spectrum with atoms such as O+, N+,S+ – so-called Low-Ionization emission line-region (LINER). The morphology of CGCG292-057 has multiple components and plasma materials of various sizes. It has outer lobes extending up to ~230 kpc and inner lobes up to ~20 kpc. Active galaxies used to have two opposite jets emanating from the central engine, up to few millions years old, that are intermittent in nature. In the case of CGCG 292−057, one can potentially witness all the aforementioned processes at work, imprinted in the complex morphology of its radio jets and lobes, as well as in its host galaxy.

Illustration 1: The Chandra ACIS-S image of CGCG 292−057, with the superimposed 606 MHz radio contours from GMRT radio array. The white contours display the outer structure of the radio source, while the magenta ones map the inner radio structure. The Chandra image displays the 0.5–7.0 keV counts, smoothed with a 3 px radius Gaussian. Credit: The Authors.

Due to the presence of such peculiar characteristics, astronomers from Astronomical Observatory of the Jagiellonian University recently published a detailed analysis on the general spectral properties of the CGCG 292−057 nucleus, with those of other nearby LINERs studied in X-rays, using data collected by the Chandra X-ray observatory and making use of the unprecedented combination of the excellent angular resolution and high sensitivity of the Advanced Chandra Imaging Spectrometer instrument.

The active nucleus of the system has 393 net counts within the 0.5-7.0 keV range in the 2.5 arc sec radius, surrounded by a diffuse, low surface brightness emission. We carefully studied the Chandra Point spread function and the surface brightness profile, and in this way we found evidence for the presence of an excess X-ray emission component at kpc distances from the centre, which was quantified by Kolmogorov-Smirnov test. There is an excess emission from about 5 kpc from the centre, whose temperature is 0.8 keV. This is due to the result of compression and heating of the fraction of diffuse interstellar medium, heated due to expanding tiny jets emitting in the radio wavelengths.

The 0.5-7 keV spectrum of the CGCG 292−057 nucleus clearly displays an ionized iron line at ∼6.7 keV, with no accompanying neutral feature at 6.4 keV. We modelled the spectrum assuming various emission models, and concluded that a simple power-law or either thermal fits imply unphysical photon indices or equivalently very high and unconstrained plasma temperatures. The best fit is obtained assuming a phenomenological model consisting of a relatively steep-spectrum with a slope ~1.8. The X-ray continuum emission was absorbed by a relatively large amount of cold material with hydrogen atoms of the order 1023 cm-2 which was partially scattered by a cloud of ionized gas. The X-ray luminosity of the direct nuclear continuum at this phenomenological model is of the order ~1041 erg s-1. Photoionized gaseous material is located at ~0.02 light-years of the Broad-Line Region of the source. The spectrum has an observed equivalent width of the Fe XXV Kα line, which is of the order of 0.3 keV.

We compare the general spectral properties of the CGCG 292−057 nucleus with those of other nearby LINERs studied in X-rays, and argue that the system appears under-luminous in X-rays for its bolometric disk luminosity, and at the same time over-luminous in radio – In fact, on the radio-loudness vs. accretion rate plane. CGCG 292−057 is located almost exactly in between the populations of Seyferts+LINERs. This may be also hosted by disk galaxies and radio galaxies, which are typically of the elliptical shape.

 

Contact

Dr Karthik Balasubramaniam

Astronomical Observatory
Jagiellonian University

K.Balasubramaniam [at] uj.edu.pl

Original publication

K. Balasubramaniam, Ł. Stawarz, V. Marchenko, M. Sobolewska, C. C. Cheung, R. Thimmappa, and E.Kosmaczewski, Chandra View of the LINER-type Nucleus in the Radio-Loud Galaxy CGCG 292057: Ionized Iron Line and Jet-ISM Interactions, 2020, The Astrophysical Journal, 905, 148.

The research was conducted at the Department of High Energy Astrophysics of the Jagiellonian University’s Astronomical Observatory (OAUJ). The research used data obtained from the Chandra Data Archive. The work was partially financed by the NCN grant 2016/22/E/ST9/00061.

Astronomy Object of the Month: Complex Structure of the Eastern Lobe of the Pictor A Radio Galaxy

Illustration: The 0.5–7.0 keV merged Chandra image of the entire structure of Pictor A, smoothed with 3σ Gaussian radius, with the 1.45 GHz VLA total and polarized intensity (3σ) contours superimposed (red and white, respectively). The two elongated yellow rectangles denote the areas across the high-polarization regions of the Eastern lobe, for which the team extracted the surface brightness profiles at X-ray and radio frequencies. Image credit: The Authors. Pictor A, classified as a Broad-Line Radio Galaxy with the “classical double” (Fanaroff-Riley type II) large-scale radio morphology and located at the redshift z=0.035, is one of the most prominent radio galaxies in the sky and the prime target for detailed multiwavelength investigations in the recent decades, from radio to the X-ray ranges. Now, JU astronomers present the detailed analysis of the distinct X-ray emission features present within its Eastern radio lobe utilising the data obtained from the Chandra X-ray Observatory.

The large-scale radio and X-ray jet in Pictor A originates in the galaxy nucleus and extends up to hundreds of kilo parsecs beyond the host galaxy to the West. The so-called counter-jet is not prominent at radio waves, but can be easily spotted in deep X-ray maps by the Chandra Observatory. The hotspots, located at both sides of the core at the lobes’ edges, mark the termination points of the jets to the West and East. The bright Western hotspot is clearly detected and even resolved at radio, infrared, optical and X-ray frequencies. The radio lobes appear in X-rays as a low-surface brightness cocoon surrounding the large-scale structure of the jets.

Illustration 1: The 0.5–7.0 keV merged Chandra image of the entire structure of Pictor A, smoothed with 3σ Gaussian radius, with the 1.45 GHz VLA total and polarized intensity (3σ) contours superimposed (red and white, respectively). The two elongated yellow rectangles denote the areas across the high-polarization regions of the Eastern lobe, for which the team extracted the surface brightness profiles at X-ray and radio frequencies. Image credit: The Authors.

The large-scale radio and X-ray jet in Pictor A originates in the galaxy nucleus and extends up to hundreds of kilo parsecs beyond the host galaxy to the West. The so-called counter-jet is not prominent at radio waves, but can be easily spotted in deep X-ray maps by the Chandra Observatory. The hotspots, located at both sides of the core at the lobes’ edges, mark the termination points of the jets to the West and East. The bright Western hotspot is clearly detected and even resolved at radio, infrared, optical and X-ray frequencies. The radio lobes appear in X-rays as a low-surface brightness cocoon surrounding the large-scale structure of the jets.

Extended lobes in radio galaxies, formed as backflows when the jet plasma passes through the termination shock and is turned away at the contact discontinuity between the shocked outflow and intergalactic medium, are particularly prominent at radio frequencies, due to the synchrotron emission of ultra-relativistic electrons. While the detailed radio studies of the lobes with the arcsecond angular resolution often reveal a complex morphology with filamentary structures, their X-ray observations, carried out with modern instruments such as Chandra, allowed to resolve the lobes and detect the emission consistent with a non-thermal power-law continuum. Lobes are expected to be extremely low-density but high-pressure envelops surrounding (and also confining) the jets, believed to be filled solely by ultra-relativistic electrons and magnetic field, with the total internal energy equal to that of the jet bulk kinetic energy. However, several observational findings have recently been reported on large amounts of a thermal gas also present in the lobes, providing a prominent contribution to their X-ray radiative output and the pressure balance.

In the recent paper, JU scientists analyzed the archival Chandra data for the extended lobes of Pictor A, focusing on the Eastern (E) lobe and the complex E – hotspot region. The X-ray maps of these targets were compared in detail with various radio maps of the regions, obtained with the Very Large Array (VLA) radio interferometer.

Top: A zoomed view of the rotation measure distribution within the E hotspot region in Pictor A, with the polarized intensity L band contours superimposed. Contours start from 3σ confidence level and are scaled by √2. Bottom: A zoomed view of the 0.5–7.0 keV emission of the E hotspot region in Pictor A, with the 1.45 GHz polarized intensity contours (black) superimposed. The Chandra image is smoothed with 3σ Gaussian (radius 5 px). Radio contours start from 3σ confidence level. Regions selected for the Chandra data analysis are labeled and indicated by red contours. Credit: The Authors.Illustration 2: Top: A zoomed view of the rotation measure distribution within the E hotspot region in Pictor A, with the polarized intensity L band contours superimposed. Contours start from 3σ confidence level and are scaled by √2. Bottom: A zoomed view of the 0.5–7.0 keV emission of the E hotspot region in Pictor A, with the 1.45 GHz polarized intensity contours (black) superimposed. The Chandra image is smoothed with 3σ Gaussian (radius 5 px). Radio contours start from 3σ confidence level. Regions selected for the Chandra data analysis are labeled and indicated by red contours. Credit: The Authors.

The obtained images and results reveal some interesting features. First of all, the double structure of the hotspot is prominent in both total radio intensity and polarized radio intensity maps. So-called ‘secondary’ hotspot (the most prominent and outermost radio feature to the East) coincides with some enhancement in the diffuse X-ray emission, but nonetheless appears dramatically weaker at keV photon energies than the Western hotspot, placed on the other side of the nucleus. There are also several bright compact X-ray sources in the closest vicinity of the double E hotspot, but none of which coincides with the peaks of either total or polarized radio intensity. For the spectral analysis, the team selected four such distinct regions. On the polarized radio intensity maps, all of these happen to be located almost exactly at the edges of the hotspot’s double structure. Moreover, one of the bright compact X-ray sources (P5) lies well outside the radio emission on high-resolution maps.

A relation of point-like X-ray features with no optical counterparts to the radio lobes and hotspot regions of radio galaxies and radio quasars is unclear and subjected to speculations. Such features may simply be background AGNs, unrelated to the observed radio lobe, but may also result from various energy dissipation processes taking place within the lobes with complex magnetic field structure. For example, if the lobes’ radio filaments represent indeed tangled magnetic field tubes, then at the places of the filaments’ interactions with density or magnetic enhancements in the surrounding plasma, localized multiple compact sites of violent reconnection may form, loading turbulence and thus enabling efficient particle acceleration as well as plasma heating.

However, the main findings following from this Pictor A analysis regard the elongated X-ray filament A, located upstream of the jet termination region and extending for at least 30 kpc. Its 0.5–7.0 keV radiative output is consistent with a pure power-law emission, or alternatively a combination of a flat power-law component and a thermal plasma. In the former case, the X-ray slope would be consistent (within the errors) with the slope of the radio continuum at the position of the filament. The latter case would be, on the other hand, in accord with recent findings of a larger amount of a thermal gas possibly present within the radio lobes of radio galaxies.

Contact

Dr Rameshan Thimmappa

Astronomical Observatory
Jagiellonian University

R.Thimmappa [at] uj.edu.pl

Original publication

R. Thimmappa, Ł. Stawarz, U. Pajdosz-Śmierciak, K. Balasubramaniam, V. Marchenko, Complex Structure of the Eastern Lobe of the Pictor A Radio Galaxy: Spectral Analysis and X-ray/Radio Correlations, 2021, [astro-ph.HE]

The research was conducted at the Department of High Energy Astrophysics of the Jagiellonian University’s Astronomical Observatory (OAUJ). This research has made use of data obtained from the Chandra Data Archive. The work was supported by the PolishNSC grant 2016/22/E/ST9/00061.

Astronomy Object of the Month: X-ray magnifying glass enhances view of distant black holes

Illustration: Gravitational lensing in MGB 2016+112. Credit: NASA/CXC/M. Weiss; NASA/CXC/SAO/D. Schwartz et al.By taking advantage of a natural lens in space, astronomers have captured an unprecedented look at X-rays from a black hole system in the early Universe. This magnifying glass was used to sharpen X-ray images, for the first time using NASA’s Chandra X-ray Observatory. It captured details about black holes that would normally be too distant to study using existing X-ray telescopes.

Astronomers applied a phenomenon known as gravitational lensing that occurs when the path taken by light from distant objects is bent by a large concentration of mass, such as a galaxy, that lies along the line of sight. This lensing can magnify and amplify the light by large amounts and create duplicate images of the same object. The configuration of these duplicate images can be used to decipher the complexity of the object and sharpen its images.

Illustration: Gravitational lensing in MGB 2016+112. Credit: NASA/CXC/M. Weiss; NASA/CXC/SAO/D. Schwartz et al.

The gravitationally-lensed system used in the new study is called MG B2016+112. The X-rays detected by Chandra were emitted by this system when the Universe was only 2 billion years old, compared to its current age of nearly 14 billion years. Our efforts to see and understand such distant objects in X-rays would be doomed if we didn't have a natural magnifying glass like this.

The latest research builds on earlier work led by co-author Cristiana Spingola (Italian National Institute for Astrophysics (INAF) in Bologna, Italy). Using radio observations of MGB 2016+112, her team found evidence for a pair of rapidly growing supermassive black holes separated by only about 650 light-years. They found that both of the black hole candidates possibly have jets.

Using a gravitational lensing model based on the radio data, Schwartz and his colleagues concluded that the three X-ray sources they detected from the MG B2016+112 system must have resulted from the lensing of two distinct objects. These two X-ray-emitting objects are likely a pair of growing supermassive black holes, or a growing supermassive black hole and its jet. The estimated separation of these two objects is consistent with the earlier "radio" work.

Previous Chandra measurements of pairs or trios of growing supermassive black holes have generally involved objects much closer to Earth, or with much larger separations between the components. An X-ray jet at an even larger distance from Earth has previously been observed, with light emitted when the Universe was only 7% of its current age. However, the emission from the jet is separated from the black hole by about 160,000 light-years.

The present result is important because it provides crucial information about the speed of growth of black holes in the early Universe and the detection of a possible double black hole system. The gravitational lens amplifies the light from these far-flung objects that otherwise would be too faint to detect. The detected X-ray light from one of the objects visible in MG B2016+112 may be up to 300 times brighter than it would have been without the lensing.

Astronomers have discovered black holes with masses billions of times greater than that of our Sun, being formed just hundreds of millions of years after the Big Bang. Now they want to solve the mystery of how these supermassive black holes gained mass so quickly. The boosts from gravitational lensing may also enable researchers to estimate how many systems containing two supermassive black holes have separations small enough to produce gravitational waves observable in the future with space-based detectors.

In many ways, this result is an exciting proof-of-concept of how this ‘magnifying glass’ can help us reveal physics of the distant supermassive black holes in a novel approach. Without this effect, Chandra would have had to observe it a few hundred times longer and even then would not reveal the complex structures, said co-author Anna Barnacka (CfA/Jagiellonian University), who developed the techniques for turning gravitational lenses into high-resolution telescopes to sharpen the images.

The uncertainty in the X-ray position of one of the objects in MG B2016+112 is 130 light-years in one dimension and 2,000 light-years in the other, perpendicular dimension. This means that the size of the area where the source is likely located is more than 100 times smaller than the corresponding area for a typical Chandra source that is not lensed. Such precision in a position determination is unparalleled in X-ray astronomy for a source at this distance.
 

Contact

Dr hab. Anna Barnacka

Astronomical Observatory
Jagiellonian University

A.Barnacka [at] uj.edu.pl

Original publication

Daniel Schwartz, Cristiana Spingola, Anna Barnacka, Resolving Complex Inner X-ray Structure of the Gravitationaly Lensed AGN MGB2016+112, 2021, The Astrophysical Journal, 917, 26.

The research was conducted at the Department of High Energy Astrophysics of the Jagiellonian University’s Astronomical Observatory (OAUJ). NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

Astronomy Object of the Month: J0028+0035 - a fidget spinner like radio galaxy

Cygnus AFidget spinners are toys that became popular in 2017, typically consisting of four bearings connected with durable plastic, resembling a triangle with a central bearing serving as a handle.

Radio astronomers use powerful radio telescopes to map the sky in a similar way to observations made with optical telescopes, such as the Hubble Space Telescope. However, images taken with a radio telescope reveal the sky in a completely different way. In the radio sky, stars and galaxies are not directly visible, but it shows numerous complex structures linked to supermassive black holes at the centers of galaxies. Most of the dust and gas surrounding a supermassive black hole is swallowed by it, but some matter can be ejected with a very high speed into space. Charged particles that move within a weak magnetic field shine as ghostly structures: radio galaxies, which we can observe using radio telescopes.

Illustration: Cygnus A - a typical radio galaxy. The radio core at the centre which resides in a not too distant galaxy (redshift z~0.06) is associated with a supermassive (about 2.5 billion solar masses) black hole. Jets of charged relativistic particles emanate in opposite directions and are topped with hot spots. From the hot spots, particles diffuse towards the centre, creating huge, expanding lobes. The size of the radio galaxy (as measured between hot spots) is approx. 400 thousand light yrs. Source: own composition based on VLA observations presented in the work: Perley, R. A., Dreher, J.W., Cowan, J. J., 1984, ApJ, 285L, 35.

Illustration 2: Left: J0028+0035 radio galaxy with an unusual triple structure in the centre, obtained at 323 MHz with use of the GMRT interferometer. Its size is approximately 3.8 million light yrs (for comparison, the distance between the Galaxy and M31 is about 2.5 million light yrs). Right: Fidget spinner - a popular toy resembling the central structure of J0028+0035. Source: own composition based on the data contained in the team's publication and available on the Internet.

 

The first picture shows a typical radio galaxy. It consists of a central core, thin jets of relativistic matter terminating with hot spots, and huge lobes. The eponymous radio galaxy J0028+0035 has three components in the centre, thus its morphology resembles a fidget spinner. The central component on the left is a distant blazar, not connected physically with the other objects visible on the map. The other two components on the right, which can be seen better in the right-hand side image, constitute a small radio galaxy consisting of a core and two lobes. J0028+0035 belongs to a rare class of restarting radio galaxies with two pairs of lobes, involving components that emerged from two different cycles of activity of the central object.

Moreover, to make yourself better acquainted with radio galaxies, we invite you to get involved with the "Radio Galaxy Zoo: LOFAR", which is a part of the Zooniverse project, the world's largest and most vibrant community-based research platform based on citizen science community. Participating in the "LOFAR Radio Galaxy Zoo" will become an exciting scientific adventure for you, while helping professional radio astronomers in exploration of the Universe.

 

Contact

Prof. Marek Jamrozy

Astronomical Observatory
Jagiellonian University

M.Jamrozy [at] uj.edu.pl

Original publication

Marecki, A., Jamrozy, M., Machalski, J., Pajdosz-Śmierciak, U., Multifrequency study of a double-double radio galaxy J0028+0035, 2021, MNRAS, 501, 853.

The research was conducted at the Department of Stellar and Extragalactic Astronomy and the Department of Radioastronomy and Space Physic Jagiellonian University’s Astronomical Observatory (OAUJ). The work was supported by the Polish National Science Centre through the grant 2018/29/B/ST9/01793.

Astronomy Object of the Month: Kinematics of coronal mass ejections in the LASCO field of view

Deep fields lofarAn accurate understanding of the propagation of coronal mass ejections (CMEs) is crucial in the prediction of space weather. CMEs generate geomagnetic storms causing catastrophic damages to power grids on Earth and are serious radiation threat to satellites on low-Earth orbit and their crew during spacewalks. Basic parameters such as their velocity and acceleration varying with time and heliospheric distance away from the Sun gives researchers the opportunity to predict their arrival time in the vicinity of the Earth. In this paper, we analyze the trend of this parameter in regards to the solar cycles 23 and 24. 

Illustration: Evolution of a Coronal Mass Ejection seen by Large Angle and Spectrometric Coronagraphs (LASCO) on board SOlar and Heliospheric Observatory (SOHO). A clear 3-part structure comprising (1) a bright front or leading edge; (2) a dark cavity; and (3) a bright, compact core is visible. Credit: NASA’s SOHO/LASCO.

Space weather is mostly controlled by coronal mass ejections (CMEs), which are huge expulsions of magnetized plasma from the solar atmosphere. They have been intensively studied for their significant impact on the Earth’s environment. The first CME was recorded by the coronograph on board the 7th Orbiting Solar Observatory (OSO-7) satellite. Since 1995 CMEs have been intensively studied using the sensitive Large Angle and Spectrometric Coronagraph (LASCO) instrument on board the Solar and Heliospheric Observatory (SOHO) spacecraft. SOHO/LASCO recorded about 30,000 CMEs until December 2017. The basic attributes of CMEs, determined manually from LASCO images, are stored in the SOHO/LASCO catalog. The initial velocity of CMEs, obtained by fitting a straight line to the height-time data points, has been the basic parameter used in prediction of geoeffectiveness of CMEs.

The two basic parameters, velocity and acceleration of CMEs, are obtained by fitting a straight and quadratic line to all the height-time data points measured for a given event. The parameters determined in this way, in some sense, reflect the average values in the field of view of the LASCO coronagraphs. Nevertheless, it is evident that both these parameters are continuously changing with distance and time after CME onset from the Sun. Therefore, the average values of velocity and acceleration, used in many studies, do not give a correct description of CME propagation. In this paper we present a statistical study of the kinematic properties of 28894 CMEs recorded by LASCO from 1996 to mid-2017. This research covers a large number of events observed during the 23 and 24 solar cycles. For the study, we employed SOHO/ LASCO catalog data and a new technique to determine the speed of ejections.

The presented statistical analysis reveals that at the beginning of their expansion, in the vicinity of the Sun, CMEs are subject to several factors (Lorentz Force, CME-CME interaction, speed differences between leading and trailing parts of the CME) that determine their propagation. Although their average values of catalog accelerations are always close to zero, a more detailed study shows that their instantaneous accelerations may be quite different depending on the conditions prevailing in the Sun and the environment in which they propagate. These conditions vary depending on the individual eruption and over time as the solar activity changes. The initial acceleration phase is characterized by a rapid increase in CME velocity just after eruption in the inner corona. This phase is followed by a non-significant residual acceleration (deceleration) characterized by an almost constant speed of CMEs. We demonstrate that the initial acceleration is in the range 0.24–2616 ms−2 with median (average) value of 57 ms−2 (ms−2) and it takes place up to a distance of about 28 RSUN with median (average) value of 7.8 RSUN (6 RSUN).

We note that the significant driving force of CME, namely Lorentz force, can operate up to a distance of 6 RSUN from the Sun during the first 2 hours of propagation. We found a significant anti-correlation between the initial acceleration magnitude and the acceleration duration, whereas the residual acceleration covers a range from −1224 to 0 m ms−2 with a median (average) value of −34 ms−2 (−17 ms−2). One intriguing finding is that the residual acceleration is much smaller during the 24 cycle in comparison to the 23 cycle of solar activity. Our study has also revealed that the considered parameters, initial acceleration (ACCINI), residual acceleration (ACCRES), maximum velocity (VMAX), and time at maximum velocity (TimeMAX) mostly follow solar cycles and the intensities of the individual cycle.

Contact

Prof. Grzegorz Michałek

Astronomical Observatory
Jagiellonian University

G.Michalek [at] uj.edu.pl

Anitha Ravishankar

Postdoctoral Associate
University of Calgary, Canada

 

 

Original publication

Kinematics of coronal mass ejections in the LASCO field of view, Ravishankar, A., Michałek, G., Yashiro, S, 2020, A&A, 639, A68.

The research was conducted at the Department of High Energy Astrophysics of the Jagiellonian University’s Astronomical Observatory (OAUJ). The work was supported by the Polish National Science Centre through the grant UMO-2017/25/B/ ST9/00536 and DSC grant N17/MNS/000038. This work was also supported by NASA LWS project led by Dr. N. Gopalswamy.

Astronomy Object of the Month: Nickel atoms detected in the cold gas around interstellar comet 2I/Borisov

Deep fields lofarUnbound nickel atoms and other heavy elements have been observed in very hot cosmic environments, including the atmospheres of ultra-hot exoplanets and evaporating comets that ventured too close to our Sun or other stars. A new study conducted by JU researchers reveals the presence of nickel atoms in the cold gasses surrounding the interstellar comet 2I/Borisov. The team’s finding is being published in Nature on 19 May 2021.

 

Interstellar comets and asteroids are precious to science because, unlike millions of minor bodies that formed in our Solar System, they originate from distant planetary systems. Until very recently, the existence of such cosmic vagabonds has merely been an interesting possibility, based on the fact that our Solar System ejected most of the primordial comets and asteroids into the interstellar space in its early days. The objects came to light in 2017 with the unexpected detection of the asteroidal 1I/‘Oumuamua, followed by the discovery of the only known cometary interloper, 2I/Borisov, in 2019. “The scientific value of these objects is absolutely overwhelming, as they carry a plethora of information about their home planetary systems,” says Piotr Guzik of the Jagiellonian University in Poland, author of the new study on 2I/Borisov.

The gasses around 2I/Borisov enabled astronomers to obtain the first precious insights into the chemical composition of an alien icy world. “We were curious what atoms and molecules make up the gasses around 2I/Borisov,” explains study co-author Michał Drahus of the Jagiellonian University. There was only one way to find out. Over three nights in late January 2020, the Very Large Telescope of the European Southern Observatory in Chile was pointed at comet 2I/Borisov to collect the object’s faint light. The incoming photons were directed to the X-shooter spectrograph, which split the light into its constituent wavelengths, enabling the identification of atoms and molecules through their characteristic spectral signatures.

Guzik and Drahus immediately scrutinized the incoming data and realized the existence of unforeseen spectral features. “At first, these features seemed impossible to identify with standard cometary species,” says Guzik. After months of fruitless research, the team was close to giving up. But unexpectedly, a solution appeared on the horizon. “It was literally a ‘Beautiful Mind’ kind of situation, when the wavelengths of these lines materialized in a tabulated spectrum of comet Ikeya-Seki and pointed at atomic nickel,” says Guzik, who first realized the surprising answer. “It didn’t seem to make any sense,” Drahus adds, “but it really did!”

The problem was that comet Ikeya-Seki passed so close to the Sun that the surrounding dust started evaporating, releasing various metals. The same mechanism could not apply to the cold comet 2I/Borisov, which passed too far from the Sun. “The nickel in 2I/Borisov seems to originate from a short-lived nickel-bearing molecule that is incorporated in the cometary ice and sublimates at low temperatures,” explains Guzik. “This is really cool because heavy elements have not been observed in cold cosmic environments before.” According to the study, nickel is not very abundant, accounting for less than 1 in 100,000 atoms in the gasses around 2I/Borisov.

Contact

Piotr Guzik

Astronomical Observatory
Jagiellonian University

piotr.guzik@doctoral.uj.edu.pl

Michał Drahus

Astronomical Observatory
Jagiellonian University

drahus@oa.uj.edu.pl

 

Original publication

Piotr Guzik, Michał Drahus: Gaseous atomic nickel in the coma of interstellar comet 2I/Borisov, Nature, 2021.

The study was supported by the National Science Centre of Poland through ETIUDA scholarship no. 2020/36/T/ST9/00596 and SONATA BIS grant no. 2016/22/E/ST9/00109, as well as the Polish Ministry of Science and Higher Education through grant no. DIR/WK/2018/12. The project is part of research conducted at the Department of Stellar and Extragalactic Astronomy of the Jagiellonian University’s Astronomical Observatory.

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