Astronomy Object of the Month: Kinematics of coronal mass ejections in the LASCO field of view
An 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.
Prof. Grzegorz Michałek
G.Michalek [at] uj.edu.pl
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/BorisovUnbound 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.
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.
Astronomy Object of the Month: Ultra-sensitive radio images reveal thousands of star-forming galaxies in early Universe
An international team of astronomers including JU scientists has published the most sensitive images of the Universe ever taken at low radio frequencies, using the International Low Frequency Array (LOFAR). By observing the same regions of sky over and over again and combining the data to make a single very-long exposure image, the team has detected the faint radio glow of stars exploding as supernovae, in tens of thousands of galaxies out to the most distant parts of the Universe. A special issue of the scientific journal Astronomy & Astrophysics is dedicated to fourteen research papers describing these images and the first scientific results.
Astronomy Object of the Month: A Multi-wavelength look at a sample of Compact Radio Galaxies
Compact radio galaxies are a particularly interesting class of active galactic nuclei (AGN), with newly born radio structures (jets and lobes) fully confined within their host galaxies. They can provide information on the processes that lead to the production of relativistic jets in AGN, as well as insight into the complex dynamics of feedback between evolving supermassive black holes and interstellar medium. Recently work was published by an international group, led by researchers at the Astronomical Observatory of Jagiellonian University, on the infrared X-ray properties of a sample of 29 of this type of galaxy.
Astronomy Object of the Month: Can we observe that the magnetic field heats the surrounding gas?
Magnetic fields can do a lot of things. They are even believed to govern star formation, by supporting the contraction of gas. Not to mention, that the galactic evolution often depends on them. They are practically everywhere. And the gas is also everywhere. Would it be possible, then, that the magnetic fields can heat the gas that surrounds them? To find out, a study is being performed that combines analyses of both X-ray and radio observations of a sample of quite extraordinary spiral galaxies. One of them is NGC 5236, better known to sky enthusiasts as M83.
Astronomy Object of the Month: Freely falling bodies in standing-wave spacetime
The phenomena of standing waves is well known in mechanical and electromagnetic setting where the wave has the maximum and minimum amplitude at the antinodes and nodes, respectively. In context of exact solution to Einstein Field equations, we analyze a spacetime which represents standing gravitational waves in an expanding Universe.
Astronomy Object of the Month: New Optical Luminosity-Time correlation for more than 100 GRBs
A new correlation has been discovered in optical observations of gamma-ray bursts (GRBs) thatmay be the key to using GRBs as cosmological distance indicators. Under Dr. Dainottimentorship (KIPAC alum, currently Assistant Professor at Jagiellonian University in Poland and Senior Research Scientist at the RIKEN iTHEMs in Japan and affiliated senior research scientistat Space Science Institute), Samantha Livermore (fourth-year physics major at Tufts University) investigated the “plateau emission” in optical GRB observations during Samantha’s summer internship at SLAC National Accelerator Laboratory and Stanford University. The work continued afterwards during Livermore’s thesis research until its publication.
Dainotti and Livermore worked with a large team of international collaborators located in US, Europe, Mexico and Australia to gather a sizable sample and conduct their rigorous statistical analysis. This research, a continuation of Dr. Dainotti’s previous work on the plateau emission of GRBs, features the largest sample of optical plateaus in the literature to date, and has been accepted to be published in the Astrophysical Journal Letters.
Tworząc lepsze jutro - 6: Gwiazdy
A special type of binary stars, i.e. cataclysmic systems, is the main research area of MSc. Sebastian Kurowski, PhD student at the Astronomical Observatory of the Jagiellonian University. In the latest episode of the „Tworząc lepsze jutro” ("Creating a Better Tomorrow") series, our interlocutor reveals what research equipment our astronomers use to study this type of objects and explains the job prospects of an astronomy graduate.