Periodic Reporting for period 2 - M2FINDERS (Mapping Magnetic Fields with INterferometry Down to Event hoRizon Scales)
Berichtszeitraum: 2023-05-01 bis 2024-10-31
Cosmic black holes, first predicted by Einstein's general relativity, represent the universe's most extreme environments, where matter, space, and time are stretched to their limits. The area around a black hole’s event horizon - the boundary beyond which nothing can escape - conceals the mysterious interior from outside observers. This region is crucial for understanding the fundamental laws of physics that govern the universe.
Studying black holes is a key focus in modern astrophysics, and recent years have seen groundbreaking achievements. Scientists have detected gravitational waves from colliding black holes and captured the first images of black hole "shadows," created by the intense bending of light near their event horizons.
However, it's possible that other compact objects, which lack event horizons, might mimic black holes. These objects could produce similar gravitational waves and shadows, making it challenging to differentiate them from traditional black holes. To distinguish between these possibilities, we need significant improvements in the sensitivity and accuracy of gravitational wave detectors and black hole imaging. These upgrades, though complex and expensive, are in progress and should be completed over the next decade.
Given this context, it might be worth exploring some additional indicators to distinguish black holes from their horizonless counterparts. One promising factor is the properties of the magnetic field near the event horizon. For horizonless objects, the magnetic field strength is expected to be four or more magnitudes higher. This difference is significant enough to be detectable from about 10,000 gravitational radii away - that's about 10,000 times the event horizon's scale. These measurements can be made using current technology, specifically radio interferometric imaging of polarized light from the area surrounding these compact objects.
The M2FINDERS project is taking advantage of this opportunity by using Very Long Baseline Interferometry (VLBI) to conduct detailed measurements of the magnetic field's total strength and three-dimensional distribution near supermassive black holes in active galaxies. These measurements are among the most efficient and reliable methods to investigate the presence of event horizons in black holes. The approach chosen by M2FINDERS will help us distinguish traditional black holes from alternative models, including exotic horizonless objects like boson stars, gravastars, and wormholes.
The impact of the activities of the M2FINDERS project is manifold. Black hole research continues to capture the public imagination, and we regularly share research news with the general public, such as last year's first image of a jet and black hole shadow together in Messier 87. We also engage the academic community through the four M2FINDERS training schools we have organised, covering astronomical imaging, polarisation calibration and magnetohydrodynamical simulations. In addition, the astronomical community benefits from our efforts through presentations at national and international conferences, with dozens of talks and posters so far, and regular publications in scientific journals. As of the end of June, there are fifty peer-reviewed papers from the programme, including twenty in the European open access journal Astronomy & Astrophysics, fifteen in the US open access journal The Astrophysical Journal, and others in prestigious journals such as Nature and Nature Astronomy.
As well as pushing the boundaries of our understanding of the Universe, the M2FINDERS project is inspiring a global audience and training the next generation of astrophysicists, making a lasting impact on both science and society.
Studying black holes is a key focus in modern astrophysics, and recent years have seen groundbreaking achievements. Scientists have detected gravitational waves from colliding black holes and captured the first images of black hole "shadows," created by the intense bending of light near their event horizons.
However, it's possible that other compact objects, which lack event horizons, might mimic black holes. These objects could produce similar gravitational waves and shadows, making it challenging to differentiate them from traditional black holes. To distinguish between these possibilities, we need significant improvements in the sensitivity and accuracy of gravitational wave detectors and black hole imaging. These upgrades, though complex and expensive, are in progress and should be completed over the next decade.
Given this context, it might be worth exploring some additional indicators to distinguish black holes from their horizonless counterparts. One promising factor is the properties of the magnetic field near the event horizon. For horizonless objects, the magnetic field strength is expected to be four or more magnitudes higher. This difference is significant enough to be detectable from about 10,000 gravitational radii away - that's about 10,000 times the event horizon's scale. These measurements can be made using current technology, specifically radio interferometric imaging of polarized light from the area surrounding these compact objects.
The M2FINDERS project is taking advantage of this opportunity by using Very Long Baseline Interferometry (VLBI) to conduct detailed measurements of the magnetic field's total strength and three-dimensional distribution near supermassive black holes in active galaxies. These measurements are among the most efficient and reliable methods to investigate the presence of event horizons in black holes. The approach chosen by M2FINDERS will help us distinguish traditional black holes from alternative models, including exotic horizonless objects like boson stars, gravastars, and wormholes.
The impact of the activities of the M2FINDERS project is manifold. Black hole research continues to capture the public imagination, and we regularly share research news with the general public, such as last year's first image of a jet and black hole shadow together in Messier 87. We also engage the academic community through the four M2FINDERS training schools we have organised, covering astronomical imaging, polarisation calibration and magnetohydrodynamical simulations. In addition, the astronomical community benefits from our efforts through presentations at national and international conferences, with dozens of talks and posters so far, and regular publications in scientific journals. As of the end of June, there are fifty peer-reviewed papers from the programme, including twenty in the European open access journal Astronomy & Astrophysics, fifteen in the US open access journal The Astrophysical Journal, and others in prestigious journals such as Nature and Nature Astronomy.
As well as pushing the boundaries of our understanding of the Universe, the M2FINDERS project is inspiring a global audience and training the next generation of astrophysicists, making a lasting impact on both science and society.
The project is organised along three main areas of work dealing with Magnetic field measurements, Interferometric techniques, and Physical modelling.
The first area focuses on conducting polarimetric multifrequency VLBI observations of a sample of seven Active Galactic Nuclei (AGN) and using these observations for estimating the strength and morphology of magnetic fields in these objects on scales up to 10,000 gravitational radii. The observations have been performed with the Very Long Baseline Array (VLBA) at frequencies 15, 22, and 43 GHz and with the Global Millimetre VLBI Array (GMVA) at 86 GHz. The correlation and calibration of the VLBA data have been completed, and the data are now being imaged in the total and polarised intensity. The correlation of GMVA data is now underway. In addition to these observations, VLBI data at 230 GHz from the Event Horizon Telescope (EHT) have been analysed, yielding measurements of brightness temperatures in seven bright AGN. These measurements have been used to obtain robust estimates of magnetic field on the horizon scale, showing strong evidence for field strength of about 100,000 Gauss.
The second area of work addresses calibration and imaging of the VLBI data and introduction of the novel frequency phase transfer (FPT) technique for observations at 22/43/86 GHz with the Effelsberg 100-m telescope. In parallel, tests of the FPT technique have been performed between the Korean VLBI Network (KVN) and the telescope in Yebes (Spain). Data from these tests are being analysed now, demonstrating that the FPT technique can be successfully applied for telescopes separated by intercontinental distances. Further tests with Effelsberg, the East Asian VLBI Network (EAVN), and Yebes are being planned now. The FPT-capable receivers for Effelsberg (at 22/43/86 GHz) and APEX (86/230 and 86/345 GHz) have been designed and are now under construction. M2FINDERS project has developed two new imaging algorithms (DoG-HiT and DoB-CLEAN) for VLBI analysis, and extended the Bayesian imaging framework RESOLVE to include self-calibration and polarisation calibration. These imaging algorithms have been applied to the M2FINDERS observed data.
The third working area is dedicated to developing methods for describing fundamental properties of the magnetic field in AGN on scales up to 10,000 gravitational radii and applying them for modelling and interpretation of the polarimetric multifrequency VLBI M2FINDERS observations. Methods for using multifrequency VLBI images to map the distribution of peak frequency in the synchrotron spectrum are being developed. A semi-analytical model has been developed for describing the properties of polarised emission in the vicinity of the black hole event horizon. The model has been applied to explaining the polarised intensity image of M87 obtained with the EHT, showing that the observed structure is consistent with the radial magnetic field expected to be found in traversable wormholes.
The first area focuses on conducting polarimetric multifrequency VLBI observations of a sample of seven Active Galactic Nuclei (AGN) and using these observations for estimating the strength and morphology of magnetic fields in these objects on scales up to 10,000 gravitational radii. The observations have been performed with the Very Long Baseline Array (VLBA) at frequencies 15, 22, and 43 GHz and with the Global Millimetre VLBI Array (GMVA) at 86 GHz. The correlation and calibration of the VLBA data have been completed, and the data are now being imaged in the total and polarised intensity. The correlation of GMVA data is now underway. In addition to these observations, VLBI data at 230 GHz from the Event Horizon Telescope (EHT) have been analysed, yielding measurements of brightness temperatures in seven bright AGN. These measurements have been used to obtain robust estimates of magnetic field on the horizon scale, showing strong evidence for field strength of about 100,000 Gauss.
The second area of work addresses calibration and imaging of the VLBI data and introduction of the novel frequency phase transfer (FPT) technique for observations at 22/43/86 GHz with the Effelsberg 100-m telescope. In parallel, tests of the FPT technique have been performed between the Korean VLBI Network (KVN) and the telescope in Yebes (Spain). Data from these tests are being analysed now, demonstrating that the FPT technique can be successfully applied for telescopes separated by intercontinental distances. Further tests with Effelsberg, the East Asian VLBI Network (EAVN), and Yebes are being planned now. The FPT-capable receivers for Effelsberg (at 22/43/86 GHz) and APEX (86/230 and 86/345 GHz) have been designed and are now under construction. M2FINDERS project has developed two new imaging algorithms (DoG-HiT and DoB-CLEAN) for VLBI analysis, and extended the Bayesian imaging framework RESOLVE to include self-calibration and polarisation calibration. These imaging algorithms have been applied to the M2FINDERS observed data.
The third working area is dedicated to developing methods for describing fundamental properties of the magnetic field in AGN on scales up to 10,000 gravitational radii and applying them for modelling and interpretation of the polarimetric multifrequency VLBI M2FINDERS observations. Methods for using multifrequency VLBI images to map the distribution of peak frequency in the synchrotron spectrum are being developed. A semi-analytical model has been developed for describing the properties of polarised emission in the vicinity of the black hole event horizon. The model has been applied to explaining the polarised intensity image of M87 obtained with the EHT, showing that the observed structure is consistent with the radial magnetic field expected to be found in traversable wormholes.
Frontier results obtained so far with M2FINDERS include: 1) first robust estimates of magnetic field strength on the event horizon scale, obtained from brightness temperature measurements made from VLBI data; 2) introduction of new imaging methods pioneering the use of wavelet deconvolution and Bayesian imaging for application to VLBI data; 3) demonstrating the feasibility of application of the frequency phase transfer technique to interferometric measurements made on intercontinental baselines; and 4) describing the properties of the magnetic field in the vicinity of the event horizon with semi-analytic models.
In the remaining project timeline, these results will be applied and combined with the information gained from the completed analysis of the VLBI M2FINDERS data. This combination will be used for making a dedicated analysis of the strength, radial dependence, and three-dimensional structure of the magnetic field in each of the individual objects studied. Results from this analysis will be used for answering the ultimate question of whether the observed magnetic field properties are consistent with the canonical black holes.
In the remaining project timeline, these results will be applied and combined with the information gained from the completed analysis of the VLBI M2FINDERS data. This combination will be used for making a dedicated analysis of the strength, radial dependence, and three-dimensional structure of the magnetic field in each of the individual objects studied. Results from this analysis will be used for answering the ultimate question of whether the observed magnetic field properties are consistent with the canonical black holes.