Monday, November 20, 2023

Detection of long-lasting aurora-like radio emission above a sunspot

nature astronomy:

Here we report observations of long-lasting solar radio bursts with high brightness temperature, wide bandwidth and high circular polarization fraction akin to these auroral and exo-auroral radio emissions, albeit two to three orders of magnitude weaker than those on certain low-mass stars. Spatially, spectrally and temporally resolved analysis suggests that the source is located above a sunspot where a strong, converging magnetic field is present. 

Our findings offer new insights into the origin of such intense solar radio bursts and may provide an alternative explanation for aurora-like radio emissions on other flare stars with large starspots.

(Figure 1 caption) a, Example of a VLA snapshot image at 1.0 GHz (orange) of the radio emission from the sunspot with the image of the radio-hosting NOAA 12529 AR observed in EUV wavelengths by the AIA, 171 Å (blue), 94 Å (cyan) and 1,600 Å (red) overlaid on the photospheric image observed by the HMI aboard the SDO. Also shown is a VLA 3.8 GHz image (magenta) of the radio emission from the flare site. b, Closer view of the sunspot region (box in a). The 1.0 GHz and 3.8 GHz are shown as yellow and magenta contours, respectively, at 50%, 70% and 90% of the maximum. The white box in b is discussed further at Fig. 4.


Scientists have spotted a stunning "aurora-like" display of crackling radio waves over the surface of the sun that is strikingly similar to the Northern Lights on Earth. 

"This is quite unlike the typical, transient solar radio bursts typically lasting minutes or hours," lead author Sijie Yu, an astronomer at New Jersey Institute of Technology's Center for Solar-Terrestrial Research (NJIT-CSTR), said in a statement. "It's an exciting discovery that has the potential to alter our comprehension of stellar magnetic processes."

The researchers say their discovery has opened up new ways to study the sun's activity, and they have begun poring through archival data to find hidden evidence of past solar auroras. "We're beginning to piece together the puzzle of how energetic particles and magnetic fields interact in a system with the presence of long-lasting starspots," study co-author Surajit Mondal, a solar physicist at NJIT, said in the statement. "Not just on our own Sun but also on stars far beyond our solar system."

This is a really exciting discovery! The resolution required to do this kind of work is fairly low so it seems completely plausible that past observations of the Sun in radio may have captured these sorts of effects. The duration is also interesting--a week is a long time for solar processes. Something I'm particularly curious about is whether we expect to see more of these now that a long and early solar maximum is just around the corner.


NOAA’s Space Weather Prediction Center (SWPC) issued a revised prediction for solar activity during Solar Cycle 25 that concludes solar activity will increase more quickly and peak at a higher level than that predicted by an expert panel in December 2019. The updated prediction now calls for Solar Cycle 25 to peak between January and October of 2024, with a maximum sunspot number between 137 and 173.

The solar maximum is a period in the solar cycle when the Sun's activity, particularly in terms of sunspots and solar flares, is at its highest. The solar cycle is an approximately 11-year cycle during which the Sun undergoes a regular pattern of changes in solar activity. This cycle is characterized by the waxing and waning of the number of sunspots on the Sun's surface.

During solar maximum, the number of sunspots is at its peak, and solar activity is generally more intense. Sunspots are temporary phenomena on the Sun's photosphere that appear as spots darker than the surrounding areas. They are associated with strong magnetic activity and are often the source of solar flares and coronal mass ejections (CMEs). It therefore seems pretty reasonable to me that we might expect more of these aurora-like transients, which seemed to form above a large sunspot.

Previously on this blog:

ALMA Achieve Unprecedented Resolution to Observe the Universe

ALMA Observatory:

An international team of astronomers and engineers has successfully conducted an observation that achieved an extraordinary resolution of 5 milliarcseconds, using ALMA's highest frequency Band 10 receiver and an array configuration that spans 16 kilometers. 

This groundbreaking observation allowed the team to capture unprecedented details of a maser around an evolved star within the Milky Way. 

Yoshiharu Asaki, the ALMA Astronomer who led this project, highlighted the collaborative effort: "This remarkable achievement in high-resolution imaging through ALMA's advanced capabilities marks a significant milestone in our quest to understand the Universe. The success of the Band 10 high-resolution observation showcases our commitment to innovation and reinforces ALMA's position as a leader in astronomical discovery. We are excited about the new possibilities for the scientific community."

5 milliarcseconds is certainly an impressive resolution. For comparison, the VLBI array that examined SN 1993J at 8 GHz achieved a resolution of ~1 milliarcsecond. For a single station to achieve this is incredible.


The Atacama Large Millimeter/submillimeter Array (ALMA) was used in 2021 to image the carbon-rich evolved star R Lep in Bands 8–10 (397–908 GHz) with baselines up to 16 km. The goal was to validate the calibration...and the imaging procedures required to obtain the maximum angular resolution achievable with ALMA.

It's quite interesting seeing that the paper is very focused on what amounts to a test and validation of the capabilities of ALMA, but still got good coverage in the media. This isn't a bad thing at all--usually buzzwordy science results grab all the attention--and it's nice to see a shift towards interest in some of the technical aspects of the field.


Monday, September 11, 2023

Mysterious Black Hole Twins May Fuel The Brightest Galaxies in Space


We propose that AGN flux variability and changes in jet morphology can both be of deterministic nature, i.e., having a geometric/kinetic origin linked to the time-variable Doppler beaming of the jet emission as its direction changes due to precession (and nutation).

We demonstrate this modulating power of precession for OJ 287. For the first time, we show that the spectral state of the spectral energy distribution (SED) can be directly related to the jet's precession phase.

We show that for OJ 287 precession seems to dominate the long-term variability (≳1 yr) of the AGN flux, SED spectral state, and jet morphology, while stochastic processes affect the variability on short timescales (≲0.2 yr).

OJ 287 is an incredibly interesting object. It's a massive quasar that we've observed periodic outbursts in for >100 years, which are attributed to a ~100 million solar mass black hole orbiting a much larger 18 billion solar mass black hole. (For context, the huge M87 black hole was "only" 6 billion solar masses). This paper specifically attributes the emission to the precessing jet caused by the orbiting black holes.


Led by astronomer Silke Britzen of the Max Planck Institute for Radio Astronomy in Germany, an international team studied 12 blazar galaxies, finding an interpretation of circling black holes could be applied to all of them.

This could be a clue as to how supermassive black holes millions to billions of times the mass of the Sun grow to such tremendous size.

We currently lack instrumentation with the resolution to observe the disk architecture that would reveal these binary black holes, but continued monitoring of the precession, as well as long-term observation of other blazars, could continue to yield information about their existence.

Jets blasted out by feeding supermassive black holes at the hearts of active galaxies could brighten and curve due to a "wobble" caused by a second orbiting supermassive black hole, a new study reports.

"We present evidence and discuss the possibility that it is, in fact, the precession of the jet source, either caused by a supermassive binary black hole at the footpoint of the jet or — less likely — by a warped accretion disk around a single black hole, that is responsible for the observed variability," study leader Silke Britzen, a researcher at the Max Planck Institute for Radio Astronomy in Bonn, Germany, said in a statement.

The team can't fully rule out factors in jet physics, such as shock waves or instabilities in the jet, or even magnetic fields, as the driving force behind the curved jets. However, they argue, the jets in question wouldn't be quite as curvy or as bright if it weren't for their wobble.


Previously on this blog:




Sunday, June 4, 2023

SN 2023ixf early photometry

This supernova just exploded in the galaxy M101, just 6 Mpc away, making it the closest supernova since SN 2011fe. Research groups around the world are scrambling to conduct analyses of this object. Some have already started popping up on arXiv.


We present the early-stage analysis of the low-resolution (R=1000) optical spectra and the near-infrared light curves of the bright Type II supernova (SN II) 2023ixf in the notable nearby face-on spiral galaxy M101, which are obtained since t=1.7 until 8.0 d.

Compared with SNe II showing the flash-ionized features, we suggest that this SN could be categorized into high-luminosity SNe II with a nitrogen/helium-rich circumstellar material (CSM), e.g., SNe 2014G, 2017ahn, and 2020pni. 

These observational facts support that SN 2023ixf is well consistent with a high-luminosity SN II with the dense nitrogen/helium-rich CSM.

It's great to see the comparisons to previous objects. 23ixf doesn't have too many remarkable qualities aside from some very early flash features (and its proximity), but it's difficult to find good comparisons since we really don't get to observe SNe early this often.

Wednesday, May 17, 2023

A radio-detected Type Ia supernova with helium-rich circumstellar material


However, despite extensive efforts, no SN Ia has ever been detected at radio wavelengths, which suggests a clean environment and a companion star that is itself a degenerate WD star. Here we report on the study of SN 2020eyj, a SN Ia showing helium-rich CSM, as revealed by its spectral features, infrared emission and, for the first time in a SN Ia, a radio counterpart. Based on our modeling, we conclude the CSM likely originates from a single-degenerate (SD) binary system where a WD accretes material from a helium donor star, an often hypothesized formation channel for SNe Ia. 


The CSM interaction in SN 2020eyj is also confirmed, for the first time in a SN Ia, through the detection of a radio counterpart, at a frequency of 5.1 GHz at 605 and 741 days after the first detection. Follow-up in the X-rays did not yield a detection. We model the radio synchrotron emission, which results from the shock interaction between the ejecta and the CSM.

For the SD shell model, the radio detections are best explained with a CSM mass of M_csm = 0.36 M⊙ (see ‘CSM shells’ section in Methods), with the expectation that the radio light curve will start to drop off rapidly at around 900 days. 


 Previously on this blog:

Monday, May 8, 2023

Update to: Evidence of near-ambient superconductivity in a N-doped lutetium hydride


Given the questions, several scientists say Dias should make his data public. “I am unhappy that Dias is supposedly not cooperating with researchers who are questioning his data,” says Marvin Cohen, a theoretical physicist at UC Berkeley. Schilling is blunt: “I told Dias to give [Hirsch] the raw data, for heaven’s sake.”

In his email [responding to Hirsch's request for the raw data], Dias wrote, “Given that you have an active comment on our work, we consider such a request would not be reasonable.” Frustrated, Hirsch requested the data from Nature and the National Science Foundation (NSF), which funded the work. On 30 August, Nature appended an editor’s note to Dias’s paper saying: “The editors of Nature have been alerted to undeclared access restrictions relating to the data behind this paper. We are working with the authors to correct the data availability statement.” NSF and the University of Rochester both tell Science they cannot comment on possible investigative matters.

A theoretical analysis on the theoretical feasibility of superconductivity in lutetium hydride was published. The results add an interesting dimension to the controversy.


Recently, room-temperature superconductivity has been reported in a nitrogen-doped lutetium hydride at near-ambient pressure [Dasenbrock-Gammon et al., Nature 615, 244 (2023)]. 

Here, we systematically study the phase diagram of Lu–N–H at 1 GPa using first-principles calculations, and we do not find any thermodynamically stable ternary compounds.

Our theoretical results show that the Tc values of N-doped LuH3 estimated using the Allen–Dynes-modified McMillan equation are much lower than room temperature.

The conclusion seems to be that, based on existing theory, it is not possible to form a stable combination of lutetium, nitrogen, and hydrogen. 

Notably, all predicted potential ternary compounds lie above the convex hull at 1 GPa. Thus, no ternary Lu–N–H compounds can remain thermodynamically stable at this pressure, which is consistent with the main results of Xie et al.26

And even if it were, it seems it would superconduct at far lower than room temperature, in line with existing experiments. 

Our simulations show that the lowest T_c is 4 K for LuH3 without doping. In addition, T_c increases with increasing N-doping concentration; thus, doping N atoms into LuH3 will increase T_c. However, the highest T_c in this VCA calculation is 22 K, obtained with 1% N-doping at 30 GPa, which is much lower than room temperature.

It's worth noting that 30 GPa is about 300 kbar, which is 30 times higher than the pressures reported in Dias et al. (2023). Further investigation is needed, but it seems theoretically unlikely to produce a material like the doped LuNH3 at the reported temperatures and pressures. Certainly even less likely for it to superconduct at room temperatures. This is based on existing theory, so the possibility remains that Dias et al. have discovered an exciting new effect that will require more advanced models to explain.  

Previously on this blog:

Sunday, May 7, 2023

Friends of Pando release 360 degree photographic data

St. George:

Armed with a mission, researchers, volunteers and citizen scientists navigated a trembling giant’s rough terrain, toting high-tech camera equipment and collecting data. Recently, Friends of Pando released the first of many data sets from the survey, allowing individuals from across the globe to study and experience one of the world’s largest organisms — Pando — from the comfort of their living rooms.

The Pando photographic survey is a hugely impressive scientific and artistic accomplishment, cataloging vast swathes of the Pando organism with enough detail and precision to enable rigorous analyses through the exploitation of modern imaging methods. 

Despite its massive size, weighing an estimated 13 million pounds and consisting of over 40,000 trees, Pando is a single organism, according to the Forest Service. The tree, the largest known aspen clone, was germinated from a single seed. It regenerates via “suckering,” where it sends up new shoots, or saplings, from its root system. Pando means “I spread” in Latin.

The tree, first observed in 1976, is thousands of years old and boasts an estimated 47,000 branches, the release states. “Little is known about the workings of the tree,” and the survey will mark the first time the organism has been inventoried.


Developed in collaboration with Fishlake National Forest and Snow College Richfield, the record offers immediate and long-term value for field and remote research efforts. Documenting Pando every 7m with high accuracy, Oditt says the plot map itself has already been used for field research planning. Long-term, the maps and image data sets can be replicated to monitor Pando for generations to come. For remote research, the system offers a flexible model that allows scientists to use the data sets as provided or, mix-and-match recorded locations to design areas of interest. This work, which explores the use of advanced imaging models and statistical techniques, can provide insights on topics such as disease, regeneration and ground cover.

Detection of long-lasting aurora-like radio emission above a sunspot

nature astronomy : Here we report observations of long-lasting solar radio bursts with high brightness temperature, wide bandwidth and high ...